THEORETICAL FOUNDATIONS OF FISH FARMING - I.M. Sherman - 2011

2. THEORETICAL FOUNDATIONS OF THE FORMATION AND UTILIZATION OF PRODUCTIVE TRAITS IN FISH

2.2. Prospects for realizing the growth potential of fish in natural and artificial water bodies

Fish growth rate is of paramount importance when selecting objects for domestication, and it is equally critical for determining the species composition of commercial ichthyofauna as The basis of the fishery.

Long-term observations and specialized studies involving various fish species have established that the older an Organism grows, the slower its growth rate becomes. A definite regularity has been determined: the growth rate of an organism is inversely proportional to its age. In other words, an organism's growth rate is a function of its age.

The internal factors that govern the intensity of an organism's growth decrease with age, and these changes lead to a gradual deceleration of growth. The organism's regenerative capacity also declines with age.

The decline in growth intensity, as well as the duration of an organism's growth, depends on those internal factors that emerge during the growth process under the Influence of Environmental conditions. These factors are the primary reason why growth intensity decreases as age and body mass increase. An organism's growth seemingly carries within itself and gradually accumulates the very factors that inhibit its own growth.

An organism's growth depends on numerous external and internal factors, The impact of which can accelerate, retard, or completely halt it. Under unfavorable living conditions, the increase in linear dimensions and body mass may temporarily stop; however, as soon as these conditions improve, the organism rapidly increases in size and mass, catching up with its peers that grew under favorable conditions the entire time. Consequently, under adverse living conditions, an organism does not grow, but rather preserves its capacity for growth, with some animals retaining this ability even beyond the normal growth period.

Under METABOLISM/18.html">The Influence of environmental factors, qualitative changes in cellular content and organ-forming processes (organism differentiation) occur within the fish body, accompanied by alterations in growth intensity. These changes are referred to as internal growth factors. Fish of the same age but of different sizes grow at different rates, indicating that their internal growth factors differ. Conversely, fish of different ages but of the same size grow at almost the same rate, which is presumably because such fish possess nearly identical internal growth factors.

At the same time, growth intensity is not a simple function of the organism's age. The age-related decline in growth rate is caused by more than just the organism's age; the growth intensity of fish systematically decreases in correlation with the increase in body size. It is hypothesized that internal growth-inhibiting factors arise in connection with the increase in body size. Furthermore, fish of the same size that have experienced different growth histories grow at different rates, indicating that their internal growth factors are not identical. Based on the foregoing, it is clear that these circumstances must be taken into account when studying the impact of external factors on an organism's growth—that is, experiments should not rely solely on comparing fish of the same size or the same age.

Organisms of the same species that share the same age, size, and growth history possess identical factors determining growth. Consequently, under identical conditions, such fish grow at the same rate.

Fish of the same age inhabiting different Water bodies with varying developmental conditions mature at different ages. This indicates that fish of the same age are at different Selection/3.html">Stages of development. The duration of the pre-adult period of a fish's life, much like the Embryonic Stage, varies significantly depending on the ecological conditions under which the organism develops. Against one ecological Background, a particular period of life is shortened in time, while under another, it is prolonged. This feature should not be overlooked when identifying specific processes in fish that have lived for the same length of time under different conditions.

Fish of the same age raised in different water bodies may undergo sexual maturation at different body lengths, demonstrating that fish of the same size can be at different stages of individual development.

Therefore, a fish's length and mass, much like its chronological age, cannot serve as a reliable external indicator of its developmental stage. The primary reason why fish of the same species mature at different body lengths across various water bodies lies in external factors, which must be considered when drafting fishing regulations for commercial aquatic areas and when forming broodstock groups under artificial reproduction conditions.

As a rule, male fish mature and spawn for the first time at a smaller body length than females, indicating that males and females of the same size are at different stages of individual development.

The features examined above provide convincing evidence that the ecological component significantly influences dynamic processes.

Building on this, let us examine the ecological patterns governing the age-related and seasonal dynamics of metabolism in fish.

In developing The Theory of management and expanded reproduction of biological resources as a whole, two main directions are distinguished that do not contradict the specifics of our subject—fish.

The first direction involves organizing the protection of natural populations' life cycles, preserving their Structure, and maintaining the functional stability of individual biological communities. Alongside the protection of natural reproduction, some populations may also be sustained through artificial reproduction.

The second direction entails organizing control over The life cycle of populations, relying entirely on artificial reproduction and the management of all ontogenetic stages, population numbers, and the productivity of organism communities maintained in artificial conditions.

The Development of modern Methods for managing fish ontogenesis is based on research into GROWTH AND DEVELOPMENT physiology, as well as The Study of age-related metabolic shifts, since population parameters—such as mortality, reproduction rate, and productivity—are determined precisely by metabolic patterns.

The generalization of numerous research findings on this subject has revealed the existence of general metabolic patterns across species with Different types of embryonic development. The sequence and rate of utilization of CARBOHYDRATES, Proteins, and Lipids during the embryonic development of fish were found to be similar. In representatives of salmonids, sturgeons, and flatfishes, the carbohydrate content from fertilized eggs to the hatching of pre-larvae or free embryos decreased by a factor of 3–5, protein content by 20–40%, and fat content by 10–20%. During Embryogenesis, the Amino Acid Composition of proteins and the fractional and fatty acid composition of lipids change significantly. In particular, the ratio between two groups of Amino Acids—Alanine + Proline + Serine and Glycine + Methionine + Lysine—changes substantially, while the content of Phospholipids and highly Unsaturated Fatty acids increases.

During early fish embryogenesis, a significant metabolic restructuring occurs immediately before and during the hatching of pre-larvae, as well as during the transition of pre-larvae to active external feeding. As is well known, The process of pre-larval hatching and reaching the larval stage requires additional Energy Expenditure. By this time, carbohydrate consumption accelerates, the resorption of Reserve Proteins intensifies, and the level of highly reactive, highly unsaturated fatty acids—especially docosahexaenoic acid, which contains six double bonds—increases. By the time of hatching, The activity of certain Enzymes, notably cholinesterase and various Phosphatases, rises sharply in fish. The intensity of oxygen consumption by the organism also increases immediately before and after hatching.

Even more drastic PHYSIOLOGICAL AND BIOCHEMICAL changes occur when pre-larvae transition to external feeding. During this period, carbohydrate consumption increases significantly (despite, evidently, their intensive synthesis), expenditures of protein and fat grow, oxygen consumption intensity rises, and the synthesis of highly unsaturated fatty acids intensifies.

Overall, considering the period from Fertilization to the transition to external feeding, salmonid roe and embryos lose up to 60% of fat and up to 40% of protein, whereas sturgeons at the same developmental stage lose up to 40% of fat and up to 60% of protein.

Once prelarvae transition to exogenous feeding, their further development and growth rely on natural food sources available in the environment. At this stage, the range of fish environmental tolerance broadens significantly, and The formation of structures essential for vital bodily Functions—such as Respiration, feeding, and excretion—is completed. Concurrently, the direction of metabolism shifts: protein and lipids begin to accumulate within the organism, while relative water content decreases alongside an increase in caloric value.

The onset of sexual maturity is associated with the rapid development and growth of Germ Cells. During this period, the Gonads of both females and males rapidly increase in size. Generative metabolism demands a substantial portion of the organism's reserve substances and exerts an inhibitory effect on somatic growth processes. While metabolic processes during the juvenile period of ontogenesis provide optimal conditions for intensive fish growth, sexual maturity brings about a new metabolic form—generative metabolism—which is sometimes regarded as a specialized type of plastic metabolism. At this stage, the organism primarily prioritizes optimal metabolic conditions for gamete maturation and successful individual reproduction.

It should be noted that the onset of sexual maturity in fish is linked to reaching a specific threshold of body fat content.

Along with the above, It is important to introduce several propositions that stem from and refine these General Principles:

- in younger fish, the size and mass of eggs, as well as their dry matter and fat content, are lower than those of older (though not the oldest) specimens;

- in early-maturing fish that grow rapidly and accumulate fat, the period of protoplasmic oocyte growth is shortened, and vitellogenesis begins at smaller oocyte sizes;

- fish with a higher body fat content show an absolute and relative increase in the number of eggs produced;

- fish that mature at an earlier age differ from late-maturing individuals of the same generation by having a reduced individual reproductive capacity, smaller size and mass of mature eggs, and a lower content of dry matter and fat within them.

There is a distinct correlation between the quality of feed provided to broodstock and the quality of their offspring. Carp achieve the best growth rates when fed diets with an amino acid profile closely matching that of their Muscle protein, and faster-growing broodstock yield higher-quality offspring. An increase in muscle protein is accompanied by a higher protein content in the eggs, which in turn dictates the viability of the larvae. The elevated amino acid content in eggs is attributed to higher protein levels in the feed, while the quality of fish embryos and larvae depends largely on The amino acid profile of the eggs.

In many fish species, the replenishment of the spawning stock is complicated by the asynchronous maturation of individuals within the same generation. Due to significant variations in growth and developmental rates within a single generation, individuals exhibit pronounced differentiation not only in the absolute content of protein, fat, and other organic and mineral components, but also in the ratios of these substances. Shifts in the balance between plastic and energetic components (proteins and lipids) largely trigger the segregation of mature individuals from the rest of the cohort.

Individuals reaching sexual maturity are larger and possess higher fat content than immature fish of the same generation. Mature females differ from their immature age-mates not only by a higher organic matter equivalent, but also by The ratio of the energy equivalents of protein and fat.

Just as the Conclusion of the juvenile period in fish is marked by the accumulation of compounds critical for the upcoming development of generative Tissues, the period of sexual maturity involves The transport of these substances from the Muscles, Liver, and bloodstream into the gonads. Furthermore, The Emergence of this new form of generative metabolism is accompanied by the Synthesis of specific substances (such as phospholipids in the liver) necessary for gamete development.

During the ontogeny of fish, regular changes in metabolism also occur: the intensity of Protein Synthesis AND the efficiency of somatic growth steadily decline. Throughout the sexually mature stage of the organism's life cycle, the proportion of generative metabolism in the total metabolic rate steadily increases, while the efficiency of using assimilated food for somatic Cell growth decreases. At the same time, the scale of Energy Metabolism expands, driven by the enhanced deposition of reserve Energy Sources, specifically fat and Glycogen. Initially, the level of generative metabolism increases and subsequently stabilizes.

In fish with different lifestyles—that is, those inhabiting water bodies with distinct environmental conditions—the ratio of individual metabolic pathways varies. While During the first months of life, young planktivores, benthivores, and predators feeding on zooplankton show no significant differences in the ratio of plastic to energy metabolism, as growth and development continue, these differences become more pronounced. In small planktivores (such as sardines, sprats, and silversides), growth efficiency decreases significantly during ontogeny, coupled with a parallel increase in energy metabolism costs. In fish with high locomotor activity—typically schooling pelagic planktivores—specific energy expenditures are 3 to 4 times higher than those of less active benthic and demersal fish, which are primarily predators and benthivores.

Data on the efficiency with which different age groups utilize food for growth, combined with population Abundance estimates, enable the calculation of food resource consumption by a given fish population. Furthermore, these insights help optimize the rearing of commercially valuable fish species in aquaculture.

The experience of human civilization convincingly demonstrates that the planet's flora and fauna undergo significant changes with age. The foundation of these shifts is rooted in profound physiological transformations throughout the lifespan. Therefore, when examining the metabolism of cultured individuals across time and space, and when working to improve and regulate fisheries management, it is essential to understand metabolic processes during the senescence of fish.

Senescence is defined as a state of the organism in which the normal metabolic flow characteristic of earlier ontogenetic stages is disrupted, and the majority of ingested food is channeled into maintenance rather than production processes. In older individuals, the quality and quantity of produced offspring decline, and reproductive periodicity is frequently disrupted. From a certain age onward, the relative mass of generated reproductive products decreases, the enlargement of mature Gametes halts, and eventually their size begins to diminish. Prior to the onset of these signs, one observes a decline in Lipid Metabolism intensity alongside an increased water content in Organs and tissues. In older individuals, glycogen reserves are significantly depleted; disruptions in its synthesis may stem from a decline in the activity of enzymes that catalyze glucose phosphorylation.

The contradiction between reproductive investment and the maintenance of individual Homeostasis is most acutely manifested during

the spawning and post-spawning periods, when exhaustion reaches its peak. It is well established that while the proportion of generative metabolism in total metabolism remains constant with age in fish, the efficiency with which consumed food is utilized for the repair and growth of somatic tissues declines more rapidly. During this period, generative metabolism and spawning draw upon not only energy reserves but also structural body components. This leads to exhaustion, which, with an increasing number of consecutive spawnings, reaches irreversible levels, resulting in the death of the fish.

Consequently, during senescence, the synthetic Functions of the organism decline sequentially: first the efficiency of protein synthesis, later lipid synthesis, and finally reproductive efficiency.

In conclusion, it should be recognized that fast-growing, early-maturing fish spawn fewer times and drop out of the spawning stock earlier. Conversely, slow-growing, late-maturing fish remain part of the spawning stock for a longer duration. Thus, fast-growing fish age more rapidly and exhaust the physiological and biochemical resources of their organism required for reproduction earlier.

Based on the aforementioned features of age-related changes, it can be asserted that a clear relationship exists between the age and physiological state of spawners and the viability and physiological-biochemical parameters of their offspring.

Many researchers have established that, in most cases, the optimal protein-to-lipid ratio for survival is observed in offspring obtained from middle-aged spawners. The smallest egg sizes and lowest lipid content are found in the youngest females of the spawning stock. In older females, egg size is also smaller, and protein content is reduced, although the lipid content and caloric value of the eggs may remain high.

Obtaining this information, along with other comprehensive research data, makes it possible to evaluate THE CONTRIBUTION OF individual age groups within natural populations to reproduction and to formulate theoretical foundations for selecting spawners for artificial propagation. Overall, scientific research in the field of age-related physiology and biochemistry of fish provides valuable insights for understanding the establishment and realization of individual adaptation mechanisms that ensure an individual's survival, growth, development, and reproduction.

During early ontogeny, the action of individual homeostatic mechanisms is aimed at individual survival and the creation of conditions necessary to contribute to population reproduction. Once sexual maturity is reached, metabolism changes significantly; the organism prioritizes optimal conditions for the growth and development of gametes above all else.

The development of a new form of metabolism—generative metabolism—alters the overall direction of metabolic processes within the organism. From this point onward, the efficiency of food utilization for somatic growth drops sharply, while the relative cost of maintaining vital physiological functions increases significantly. At the same time, the scale of generative synthesis initially increases and then stabilizes; however, within the total cost of maintaining the organism's vital processes, the component associated with ensuring generative synthesis continuously grows, as the efficiency of all synthetic processes declines during ontogeny. As a result, with each successive spawning, the expenditure of matter and energy required to sustain generative metabolism increases. Concurrently, the gradual disruption in the ratios of individual metabolic pathways becomes irreversible, ultimately impairing the mechanisms responsible for maintaining individual homeostasis.

Meanwhile, the ecological significance of age-related metabolic changes lies in ensuring the survival of the individual until it reaches reproductive age and takes part in reproduction.

Age-related physiological changes in fish serve as the foundation for maintaining and refining individual homeostatic mechanisms up to certain Stages of Ontogeny. A continuous increase in both the absolute and relative fat content of the organism—occurring against a backdrop of declining protein growth efficiency—alongside an increase in Blood oxygen capacity, provides the energetic basis for enhanced locomotor activity in fish as they age. This leads to greater swimming speed and range, as well as increased foraging efficiency. Furthermore, the increasing lipid content in fish tissues, particularly in common carp, correlates with a growing resistance to low temperatures during ontogeny. Thus, shifts in the ontogenetic relationship between the individual and its environment are fundamentally driven by regular age-related changes in metabolism.

Given that fish are poikilothermic animals and their metabolism is closely tied to the dynamics of Temperature regimes across time and space, it is appropriate to examine seasonal physiological Changes in the organism.

Seasonal physiological rhythms in fish are inextricably linked with ontogenetic studies. Diel and seasonal variations in physiological and biochemical processes constitute an integral part of individual development. These rhythms have evolved under the direct influence of cyclic changes in abiotic and biotic factors, and the integration of seasonal physiological rhythms forms the annual biological cycle of a population.

It is today beyond doubt that during ontogeny, each successive cyclic process emerges against the backdrop of the aforementioned irreversible age-related metabolic changes. It has also been established that a general trend in physiological processes exists across all classes of vertebrates. Specifically, young animals exhibit a longer growth period and a lower sensitivity to seasonal physiological rhythms. Furthermore, it has been shown that as fish age, the amplitude of seasonal fluctuations in morphophysiological and biochemical traits—namely, the relative mass of The Liver and Muscle tissue, as well as the content of protein, fat, and glycogen—increases. Ontogeny is also marked by an extended period of depletion and subsequent recovery following spawning and wintering, alongside a shortening of the period during which protein, fat, and generative tissue mass accumulate.

Additionally, divergences in the rhythms of certain physiological processes are observed between females and males. In males of many gadid species, the period of protein growth within the annual cycle is shorter than in females. Gonadal maturation has a lesser impact on other physiological processes in their bodies; however, the energetic costs of spawning are much higher for males than for females. During this period, males exhibit an extraordinarily intense depletion of energy reserves.

Common and distinct features in the seasonal dynamics of absolute and relative protein, fat, glycogen, and water content across various organs and tissues have been identified in fish belonging to different ecological groups. The relative protein content in the muscles of clupeids, gadids, and pleuronectids does not change significantly throughout the year; this decline is primarily observed in mature fish during the pre-spawning and spawning periods, and in immature individuals following wintering. Over the course of wintering and spawning, the absolute protein content decreases by 10–20% in planktivores, and by 20–40% in piscivores and benthivores. As the growth period shortens from high- to low-latitude fish species, the annual amplitude of fluctuations in absolute protein content decreases correspondingly.

Several distinct phases can be distinguished in the annual cycle of protein content fluctuations in boreal spring-spawning fish, specifically regarding protein synthesis during the feeding period and its expenditure during wintering and spawning.

At the beginning of the feeding season, a slow Rate of protein accumulation is observed. This period is primarily dedicated to the restoration of blood proteins, sarcoplasmic proteins, and Muscle Proteins that were depleted during wintering and spawning. Once the recovery phase is complete, rapid protein growth occurs within the optimal temperature range. In autumn, protein accumulation in boreal fish slows down until a further drop in temperature halts it altogether. This is followed by a period of stabilization in the body's protein content. During winter, protein is utilized slowly, and its content begins to drop rapidly in spring as generative metabolism intensifies and the fish enter the pre-spawning period.

In autumn-spawning species, seasonal fluctuations in protein content are less pronounced. Gonadal development in these fish occurs concurrently with protein growth, relying primarily on exogenous sources—dietary protein. Moreover, significant fat reserves accumulated in the bodies of these fish prior to spawning ensure the maintenance of vital processes throughout the entire winter period.

It should be noted that seasonal changes in the lipid content of fish differ significantly from changes in protein content. The amplitude of seasonal fat fluctuations within the fish organism is many times greater than that of protein.

Throughout the annual cycle, not only the quantitative content of proteins and lipids changes, but also their qualitative composition. However, variations in the qualitative composition of proteins are less pronounced than those of lipids, primarily affecting the fractional composition of sarcoplasmic and blood proteins, as well as the amino acid profile of developing gonadal proteins. While the qualitative composition of muscle proteins remains stable, Lipid Composition undergoes profound changes over the course of the cycle.

During the first half of the feeding season, gadid fish actively accumulate barely modified dietary fats—primarily triacylglycerols—in their liver, whereas clupeids and certain other species accumulate them in their muscles and body cavity, and pleuronectids in the myosepta of deep musculature. In the second half of the vegetation season, phospholipids and sterol esters accumulate more intensively, serving as a specific "building material" for the formation of gametes.

Throughout wintering and spawning, energy metabolism relies primarily on triacylglycerols, whereas structural lipids are utilized as an energy source only during periods of extreme exhaustion. Nevertheless, these lipids play an active role in generative metabolism.

Much like during early ontogeny and periods of sharply increased locomotor activity, adult individuals exhibit a substantial increase in non-esterified Fatty Acids and sterol esters—comprising polyunsaturated fatty acids along with carbohydrates as direct energy Donors—during spawning migration and the spawning process itself.

The Specificity of Carbohydrate Metabolism in fish and seasonal variations in carbohydrate levels are determined by the high lability and rapid restorability of carbohydrate reserves, as well as their capacity to release large amounts of energy over a relatively short period of time. Furthermore, as is known, a portion of carbohydrates in fish is involved in anaerobic Glycolysis.

Two maxima and two minima in glycogen content have been noted in the muscles and liver of gadid fish: the first occurs at the end of the feeding period, when glycogen accumulates in the liver alongside fat and is subsequently consumed during wintering; the second occurs immediately prior to spawning as a result of Gluconeogenesis from the breakdown products of muscle protein-lipid complexes. It has also been revealed that gluconeogenesis is more pronounced in females than in males.

A close interconnection has been established between water-Mineral Metabolism and protein and lipid metabolism, as well as feeding seasonality in fish. The seasonal dynamics of liver relative mass and chemical composition serve as an indicator of the seasonal changes in the physiological state of fish.

As an object of commercial fisheries and modern aquaculture alike, fish require professionals to possess up-to-date knowledge regarding physiological and biochemical processes within the organism during various periods of the annual cycle. Without this awareness, it is exceedingly difficult to consciously apply modern technologies.

As is well known, the annual biological cycle is divided into periods characterized by a specific metabolic direction, distinctive population-aquatic environment interactions, and a defined amplitude of physiological and biological parameter Variability.

For species with spring and summer spawning, the following periods are distinguished: pre-spawning, spawning, post-spawning, feeding, and wintering. In autumn-spawning fish, a different sequence of periods is observed: the spawning period is followed by wintering, which includes the wintering

migration, followed by the feeding period and a somewhat abbreviated pre-spawning period.

The duration and qualitative Characteristics of Individual periods within the annual cycle are determined by the specific lifestyle of particular fish populations.

Preparation for the transition into each successive period of the annual cycle begins deep within the preceding one. During transitional moments, regulatory systems are readjusted, and significant energy reserves are accumulated in the organism. As a result of compensatory biochemical, physiological, and behavioral reactions, natural mortality in fish is reduced.

In fish populations exposed to severe cold stress during winter, particularly in northern marine species, the post-spawning period is the most critical phase of the annual cycle. Most fish that have spawned exhibit signs of marked exhaustion: edematous organs and tissues, depleted fat reserves and structural proteins, reduced membrane permeability, and lowered resistance to low temperatures, parasitic infestations, and infections. The degree of exhaustion in males during this period is significantly higher than in females.

During the feeding period, the energy and plastic reserves consumed over winter and spawning are replenished. This is followed by an increase in protein growth and fat accumulation.

In species with winter and early spring spawning (such as saithe, navaga, and polar flounder), fat is accumulated first after spawning. As the water temperature rises, the depleted muscle proteins are restored.

During the feeding period in boreal species with spring spawning, the processes of Protein metabolism, fat accumulation, and gonad maturation are temporally separated. During the period of active protein growth within the optimal temperature range—which is fueled by the energy of lipid dissimilation—intensive fat deposition does not occur. Only at the end of the feeding period, when low temperatures halt protein growth, does fat accumulation begin to prevail over protein accretion. At this stage, significant shifts occur in the state of the gonads: yolk deposition begins in the oocytes, and spermatogonia formation commences in the Testes.

Upon completion of protein growth and fat accumulation, as the capacity for nutrient assimilation and transformation declines under low temperatures, the wintering phase begins. In many fish species, this period is preceded by a wintering migration.

The primary metabolic feature of boreal fish during wintering is a sharp decline in The rate of overall metabolism and locomotor activity, the Minimization of energy expenditures, and the suspension of general metabolic processes.

The pre-spawning period is characterized by the activation of generative metabolism, heightened endocrine gland activity, and increased locomotor activity. During this phase, reserve substance expenditure intensifies, and proteins are recruited into energy metabolism. In fish that feed prior to spawning, partially restored energy resources support gonad maturation and the spawning process itself.

All preceding periods of the annual cycle—with their systems of physiological and biochemical adaptations aimed at increasing plastic and energy resource reserves (the feeding period), conserving energy (the wintering period), ensuring individual survival, and creating optimal conditions for gamete growth and development—serve to some extent as preparation for the most critical phase of the annual cycle: spawning. During this period, all biochemical, physiological, and behavioral resources of the organism are mobilized to execute the reproductive process with maximum efficiency. Energy metabolism recruits not only reserve lipid fractions but also structural ones, the concentration of non-esterified fatty acids increases, and glycogen reserves previously accumulated via gluconeogenesis are utilized. In this phase, differences in The chemical composition of organs and tissues between females and males become particularly pronounced. Throughout the spawning act itself, males expend a substantial amount of energy, leaving their bodies much more exhausted immediately post-spawning than those of females. This circumstance accounts for the widely known high post-spawning mortality observed in males of many fish species.

In species and populations with autumn spawning (such as brown trout, notothenioid fish, and autumn Baltic herring), the dynamics of individual substance content throughout the annual cycle vary. Their relatively brief pre-spawning period and spawning occur shortly after the conclusion of the feeding season. Gonads in these fish develop at the expense of exogenous feeding. Consequently, prior to spawning, these fish accumulate significant reserves of protein, fat, and glycogen. Immediately after spawning, wintering begins, during which the substances accumulated during the feeding period are utilized.

The lipid content of organs and tissues in autumn-spawning species is generally higher than that in phylogenetically close spring-spawning fish. Furthermore, these fish rely less on proteins for energy metabolism and exhibit a lower degree of gluconeogenesis.

Thus, regular metabolic shifts occur during the ontogenesis of fish, which to a certain extent govern age-related changes in the interactions between individuals and their environment. The relative content of energy reserves and the caloric value of the organism increase, leading to enhanced locomotor activity and expanded distributional ranges. Resistance to unfavorable environmental factors is enhanced. Up to a certain age, individual homeostasis mechanisms are refined. Gradually, over the course of ontogenesis, a metabolic imbalance emerges in fish, driven by a mismatch between the declining rate of somatic protein synthesis on the one hand, and the escalating energy costs required to sustain vital activity and reproduction on the other. Initially, these phenomena are reversible, but over time irreversible changes may accumulate, ultimately leading to The breakdown of homeostatic mechanisms and the death of the individual.

The complex processes manifested in the integration of individual and seasonal physiological rhythms represent a key expression of population homeostasis: they sustain population resilience under fluctuating ecological conditions.

Given that the common carp is the oldest subject of warm-water pond aquaculture and is simultaneously widespread, it is appropriate to examine the ecophysiological foundations of carp adaptation under high levels of intensification in pond aquaculture. As is well known, the intensification of pond aquaculture is achieved primarily by increasing the stocking density of fish per unit of water surface area, as well as by applying concentrated compound feeds, organic fertilizers, and mineral fertilizers. All of this leads to profound disruptions in the ecological status of water bodies and water quality, necessitating an in-depth study of fish responses to external stressors through the application of diverse methodologies.

It has been proven that an increase in fish abundance per unit volume exerts a negative impact on water quality. The prevailing view is that the stocking density of carp fingerlings in rearing ponds should not exceed 40–50 thousand ind./ha. However, even during the first days of rearing at a stocking density of 80–100 thousand ind./ha, a significant amount of metabolites accumulates in the water, as evidenced by rising ammonia concentrations, which can reach 3 mg/dm³ or more.

Meanwhile, it has been experimentally demonstrated that an ammonia concentration of 3 mg/dm³ in water leads to a decline in feeding intensity and reduces the productive effect of nitrogen on fish biomass gain, whereas an ammonia concentration of 5 mg/dm³ results in the mortality of juvenile fish.

At high stocking densities, the general hydrochemical composition of pond water changes substantially, manifested by increased alkalinity, permanganate oxidizability, and elevated levels of chlorides, sulfates, and nitrogen salts, which serve as indicators of organic water pollution. An increase in fish abundance also affects dissolved oxygen content.

As stocking density increases, chlorophyll content decreases and the yellow-green index rises. Shifts in primary production lead to alterations in the natural food base. The total biomass of zooplankton organisms increases due to a rise in the abundance of all copepods and rotifers—which positively correlate with stocking density—while the numbers of *Daphnia* and *Bosmina* decline. The biomass of zoobenthos also decreases slightly at a density of 80–100 ind./ha, driven by a reduction in the chironomid complex and an increase in oligochetes such as *Tubifex tubifex*, which serve as indicators of severe organic pollution in fishponds. Among chironomids, *Chironomus plumosus* becomes the dominant form.

Stocking densities of up to 40–50 thousand ind./ha intensify all metabolic processes, improving the nutritional status of juvenile fish. A further increase in stocking density leads to the suppression of plastic metabolism and an escalation in the energy costs of organic matter required to maintain vital bodily functions. Elevating the stocking density to 80–100 ind./ha results in a depletion of glycogen in organs and tissues.

The intensification of metabolic processes, driven by heightened oxygen demands under high stocking densities, enhances the organism's Hemoglobin supply. In fish at a stocking density of 50 thousand ind./ha, blood volume increases due to formed elements, whereas at densities of 80 and 100 thousand ind./ha, it increases through circulating Blood Plasma, accompanied by an expansion in the amplitude of erythrocyte osmotic resistance.

The realization of growth potential in fish is closely tied to established and accumulated data regarding the regularities of intrapopulation variability in the physiological and biochemical parameters of fish.

Establishing the links between the variability of physiological and biochemical traits and living conditions enables the identification of the metabolic underpinnings governing fluctuations in survival,

growth, and reproduction across individual generations and populations. Individual and group variability in the rhythms of seasonal physiological processes shapes the characteristic amplitude of population variability during specific periods of the annual cycle. The heterogeneity of individuals in terms of traits such as total metabolic rate, protein growth rate, energy reserve accumulation, and relative gonad mass represents a vital property of every population.

Fish, as representatives of lower vertebrates, exhibit a remarkably high metabolic plasticity. The most prominent adaptive significance of this plasticity is observed in traits such as growth rate or the scale of energy reserve accumulation in individuals belonging to eurybiotic species that inhabit water bodies with fluctuating environmental conditions. The near-absolute positive correlation between fish body mass and individual absolute fecundity, coupled with the relationship between the rates of protein and lipid accumulation in their bodies and lifespan, renders fish exceptionally convenient models for studying the general regularities of variability.

The variability of physiological and biochemical indicators is viewed from an ecological perspective as a group ADAPTATION OF ORGANISMS that ensures relative species stability and enhanced efficiency in the utilization of fluctuating natural factors by populations within the Limits of the species' norm of reaction.

It is known that the degree of size variability in newly hatched pre-larvae of fish is small, but it increases during development because the developmental rates of different individuals vary: moreover, these rates may decelerate in early ontogeny for some individuals and accelerate for others. In many cases, the degree of variability is determined by selective mortality within a generation, with growth-lagging individuals being eliminated in the majority of cases.

At any given time, the variability of a specific trait within a population is the result of a complex interplay of variations across various intrapopulation groups: age groups, their respective sex-age subgroups, and individual generation cohorts comprising specimens that differ in the intensity and rhythms of specific processes, such as protein growth and lipid accumulation.

"Age-related variability" refers to the decrease or increase in the variability of individual traits with age, driven by the impact of selective mortality on different segments of a cohort, changes in metabolic ratios during ontogenesis (which can also manifest as shifts in the mass ratios of specific organs and tissues), and impaired reproductive function in older specimens, where regular correlations between individual absolute fecundity, body mass, and fat content are drastically disrupted.

"Seasonal variability" refers to fluctuations in the variability of a given trait within a generation or an entire population from season to season. These amplitudes of variability are determined by varying degrees of mismatch in the rhythms of seasonal physiological processes during different periods of the annual cycle among distinct generations, females and males, and various groups of specimens within the same generation that differ in metabolic characteristics. Other drivers of seasonal variability include selective mortality—such as the mortality of low-fat carp fingerlings in ponds and marine fish during wintering—as well as compensatory processes.

To identify ecological patterns of variability, researchers must isolate traits that, on the one hand, serve as reliable indicators of changes in population living conditions and, on the other hand, are easily quantified. Such a "universal indicator" is the growth rate of fish, which is closely linked to the rate of development, given that growth is the quantitative dimension of development. After all, fish growth is one of the most vital mechanisms through which an individual specimen and The population as a whole automatically respond to changes in food availability by adjusting their reproductive tempo and feeding intensity.

Based on the preceding information, it is appropriate to examine the factors driving the morphophysiological variability of fish.

The considerable variability in the protein growth of fish is driven by the high dependence of their metabolism on environmental factors, The complexity of the trophodynamic structure of aquatic ecosystems, wide fluctuations in food supply, and repeated shifts in feeding behavior throughout ontogenesis.

As a result of high fish fecundity and the variability of growth-related metrics, significant variance in developmental rates—even among age-mates from the same parents, where some individuals experience accelerated development and others delayed—triggers corresponding shifts in the growth rates of individual organs or body parts that are not always strictly synchronized. As a rule, variability in the mass and linear dimensions of fish pre-larvae upon hatching is low, peaks toward the end of the first year of life, and subsequently declines again as sexual maturity is approached.

The proportion of body size variability determined by the intrinsic genotype of the growing organism generally increases during the growth process. This raises the questions of what accounts for the increasing variability in body size and mass of fish during ontogenesis, and what the ecological aspects of this variability are. G. D. Polyakov (1975) links changes in the degree of differentiation to the living conditions of populations, primarily to the variability of food supply among different age, size, and weight groups both across the entire population and within individual generations. For the growth and development of fish fingerlings, changes in feeding habits are of great importance; these occur repeatedly and over short timeframes throughout the first year of life.

Significant variability in the size and mass of individuals within generations persists in fish during their first years of life. Other metabolic indicators are closely linked to individual growth rates, namely oxygen consumption intensity, as well as the rate and scale of energy resource accumulation and expenditure. A specific protein growth rate, alongside other physiological and biochemical metrics, reflects a distinct metabolic type that persists in the majority of cohort members throughout their lifespan. Growth rate represents the quantitative aspect of development and to a certain extent mirrors developmental tempos. Variability in individual growth rates within a generation thus reflects variability in developmental rates.

As the individual growth rate within a generation increases, the intensity of oxygen consumption decreases. For a given body mass, older slow-growing individuals from two adjacent generations exhibited a higher oxygen consumption intensity than younger fast-growing individuals from the subsequent generation.

Considering a generation as a whole, it can be hypothesized that growth programs vary among individuals. Fast-growing fish reach sexual maturity earlier; at an earlier age, their metabolism shifts toward the predominance of energy resource accumulation over protein growth. Prior to sexual maturity, fish protein growth is more variable, more susceptible to environmental factors, and proceeds with maximum efficiency. Upon reaching sexual maturity, metabolism shifts toward securing optimal internal conditions for the normal course of generative metabolic processes. Consequently, the somatic growth rate of sexually mature specimens becomes relatively less dependent on fluctuating environmental factors.

In addition to endogenous factors associated with metabolic shifts toward energy reserve accumulation and reproductive preparation, age brings an expansion in the tolerance ranges of A number of processes—including protein growth—to abiotic factors.

Significant variability in individual growth rates within separate generations during the first years of life, and the resulting substantial variance in length, body mass, and the absolute amount of energy accumulated as organic matter, determine staggered timings for the attainment of sexual maturity.

It should be noted that the variability of certain morphophysiological and biochemical parameters differs between male and female fish: females exhibit greater variability in traits characterizing plastic metabolism, namely body length and mass, condition factor, and muscle protein content. Conversely, males have been found to exhibit higher variability in parameters associated with energy metabolism, such as fat content, its individual fractions, and hemoglobin levels.

For specific generations and certain fish species (such as navaga, cod, Baltic herring, and European flounder), researchers have compared the variability of a set of metrics among groups of individuals with differing growth rates, tracing The Link Between growth rate, lipid accumulation, and the Qualitative and quantitative parameters of the Reproductive System. As a rule, a positive correlation between fat accumulation and protein growth rate is observed in fish up to a certain threshold. However, at higher growth intensities, the energy costs of protein synthesis become so immense that achieving a high fat content is rendered impossible.

Within individual generations, fast-growing specimens prove to be physiologically older: they exhibit lower oxygen consumption intensity, lower fat content, and a smaller share of generative metabolism. Regarding such integrative metabolic indicators as oxygen consumption intensity and food conversion efficiency for growth, this pattern manifests as early as the embryonic, larval, and juvenile periods; a decline in lipid and generative metabolism intensity is likewise observed in older age groups of the population.

Consequently, the directional shifts in morphophysiological and biochemical parameters within individual generations mirror those observed throughout ontogenesis.

The differentiation of generation members by growth and developmental rates holds profound ecological significance for fish. During early ontogenetic stages, it is associated with a more complete and efficient utilization of the food base by the population. The staggered attainment of sexual maturity among cohort members with varying growth rates acts to stabilize the reproductive process. Numerous fish species have demonstrated a reduced survival rate in offspring originating from spawners that reached sexual maturity at the earliest ages.

Furthermore, the rate at which fish reach sexual maturity is intrinsically linked to their lifespan. Slowed metabolic processes—including a delayed onset of Aging in such fish—help preserve reproductive capacity. Fish characterized by delayed growth and development participate in a greater number of spawning events than specimens with accelerated development. The protracted timeframe for reaching sexual maturity and the varying lifespans among fish with differing growth and developmental rates give rise to Lee's phenomenon, which posits that fish reaching the oldest ages are those that grew slowly during their early years.

Thus, the variability of biochemical parameters in fish organs and tissues changes predictably from season to season: it is minimal at the end of the feeding period, when the mismatch in seasonal physiological rhythms among fish of different ages, developmental rates, and growth speeds is least pronounced, and maximal during the spawning period, when endogenous bodily resources are heavily depleted.

Intrapopulation variability in the morphophysiological and BIOCHEMICAL COMPONENTS OF fish should be viewed as the product of prolonged phylogenesis, while the Current state of quality serves as a core component and theoretical foundation for professional training.

The ecological significance of intrapopulation variability in morphophysiological and biochemical indicators stems from the overarching concept that it is a crucial component for informed technological decision-making.

A vital feature in this regard is the exceptionally high variability of protein growth during early ontogenetic stages up to the attainment of sexual maturity. Under conditions of high juvenile population densities and significant interseasonal and interannual fluctuations in the food supply of natural and artificial water bodies, substantial variability in fish size and mass ensures a more complete utilization of limited food resources.

Fast-growing individuals are logically characterized by high growth tempos, a more rapid decline in integrative metabolic indicators, and an increased intensity of generative metabolism. When food availability deteriorates, disruptions in the balance between plastic and energy metabolism manifest more quickly in these fish. Moreover, as early as their second or third spawning events, such fish begin to show severe discrepancies between the scale of generative metabolism and the organism's capacity to supply it with plastic and energy resources. Such imbalances between metabolic forms, coupled with heightened endocrine activity of the gonads, lead to a breakdown in homeostatic mechanisms and the premature mortality of these fish.

Variability in growth rates and the timing of sexual maturity stabilizes Population structure and ensures greater consistency in reproduction under conditions of high juvenile mortality during early developmental stages. On the other hand, high variability in growth and developmental tempos provides a "playing field" for selective natural mortality; through the elimination of fish with specific metabolic types, we observe the characteristic known as "age-related variability," culminating in the survival of the slowest-growing specimens to their maximum lifespan.

Variability in the growth rate of fish, particularly the age at sexual maturity, is largely determined by fluctuations in the accumulation of energy reserves, primarily fat. It should be noted that while the variability of protein growth is most pronounced during early ontogeny, variability in fat content, conversely, increases with age as the balance between protein synthesis and lipid accumulation shifts in favor of the latter.

Understanding these theoretical foundations provides tangible opportunities to manage metabolic processes in fish, which is crucial for controlling the timing of weight gain and sexual maturation.

Developing approaches to manage individual developmental processes requires deep insight into age-related metabolic shifts, taking into account the organism's ADAPTATION TO ENVIRONMENTAL conditions. It is well established that ontogeny involves the establishment of homeostatic mechanisms that ensure survival, development, growth, and reproduction; the organism's range of resistance to environmental factors broadens, and integrative mechanisms further develop.

Throughout the individual development of fish, the potential efficiency of somatic growth steadily declines against the backdrop of rising energy metabolism, which is supported by the accumulation of reserve energy compounds—carbohydrates and, predominantly, lipids—in organs and tissues. This exact concept was formulated in the works of G.E. Shulman (1972) and M.I. Shatunovsky (1980) as a result of extensive dedicated research.

Substantial changes occur during the ontogeny of fish regarding specific metabolic pathways.

M.I. Shatunovsky (1980) asserts that throughout the juvenile period of ontogeny, the maturation phase, the adult stage, and senescence, the efficiency of utilizing consumed matter (and energy) for somatic growth exhibits a consistent downward trend.

As fish grow older and larger, their food supply changes, accompanied by repeated shifts in feeding habits throughout ontogeny. At the same time, the actual rations consumed by certain age groups of fish are significantly lower than the maximum possible levels. Consequently, despite a physiologically high capacity to convert ingested food into growth, considerably lower K₂ coefficients are recorded. True values of the physiological efficiency of food utilization for growth in various freshwater fish age groups are substantially higher, as established experimentally. Discrepancies between actual and theoretically possible K₂ coefficients reveal distinct opportunities for intensifying and enhancing fish growth efficiency in aquaculture. Under natural conditions, low K₂ values are attributed to inadequate food availability or suboptimal conditions for its assimilation and conversion into growth. Energy metabolism exerts a certain limiting influence on the overall growth efficiency index under natural conditions. In some fish species, it has been demonstrated that during sexual maturation, the efficiency of converting assimilated food into somatic tissue growth drops by nearly half. In carp and rainbow trout, the onset of sexual maturation is associated with a sharp decline in growth rate and efficiency. Therefore, one potential measure to increase fish productivity is to rear juveniles to the largest possible size under conditions that ensure high rates of ingested food conversion into somatic growth.

It is also known that fish age and body size exert less influence on metabolic rate than on somatic growth. However, industrial-type rearing systems offer the possibility of reducing energy (functional) metabolism while enhancing somatic growth efficiency. Approaches to managing energy metabolism and growth stem from a detailed analysis of individual factors and their cumulative impact. The primary controlling factor is temperature, which dictates the rhythm of feeding, Digestion, nutrient assimilation, the incorporation of nutrients into metabolism, and tissue growth.

The development of approaches to manage growth and development processes focuses on modifying specific physiological pathways under human-controlled conditions. The ultimate goal of controlled intervention in early-stage fish rearing is a significant increase in juvenile survival rates in aquaculture compared to nature, yielding robust stocking material. The Second Stage of management involves rearing young individuals to marketable size and body weight with maximum efficiency. Therefore, managing this process must be based on experimentally and theoretically calculated growth potentials by organizing optimal feeding regimens, reducing energy metabolism, and completing the production cycle in the shortest possible time (ideally an annual cycle) against a background of high and gradually declining K₂ values.

In addition to commercial fish farming, an equally important objective in aquaculture is the development of broodstock under artificial conditions. In this case, starting from the Cytology/cytology/16.html">Early stages of ontogeny, it is advisable that rearing conditions be directed not toward achieving maximum body mass in the shortest possible time, but rather toward ensuring optimal

conditions for the development of generative metabolism and the formation of high-quality gametes. The rearing and rational management of broodstock individuals must rely on continuous monitoring of their physiological state, especially in industrial fish farming. By adjusting the thermal regime, illumination, water gas regime, artificial feeding protocols, and diet composition, one can control the maturation timing of spawners to a certain extent and direct the quality of developing sex products as needed. An important element of artificial reproduction is the age-based selection of spawners. One of the foundations of age selection is establishing correlations between the physiological and biochemical status of fish spawners, the quality metrics of mature sex products, and offspring survival. A key management task during broodstock rearing is to extend the optimal reproductive age interval while identifying and excluding first-time spawners and aging fish with diminished gamete quality from the reproduction process.