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

4. THEORETICAL FOUNDATIONS OF FISH REARING UNDER VARIOUS CONDITIONS

4.2. Theoretical foundations of cold-water fish farming

Poikilothermic animals, which include fish inhabiting temperate and high latitudes, have adapted during a long phylogenetic process to regular Changes in the thermal regime that follow a seasonal pattern. Alongside this, the ethological characteristics of various ecological groups of fish regarding Water Temperature changes are quite specific. Unlike warm-water fish species, cold-water species begin their pre-spawning migration, which gradually transitions into spawning, as the water temperature drops. For such species in their natural habitat, autumn-winter spawning is characteristic, along with a relatively prolonged Embryogenesis taking place in a low-temperature range; however, the hatching of free embryos or pre-larvae occurs in spring, with the rise in water temperature serving as the signaling factor for this phenomenon.

Considering the THEORETICAL FOUNDATIONS OF cold-water fish farming, it must be emphasized that technological processes for reproduction, rearing of stocking material, market-size fish, replacement stock, and broodstock are built in cold-water aquaculture upon a profound understanding of the biological CHARACTERISTICS OF THE cultivated fish species. The main objects of modern cold-water fish farming are salmonids, among which trout predominate.

Based on the foregoing, it becomes clear that a prerequisite for the efficient cultivation of cold-water fish species is an adequate water supply with an appropriate temperature range. At the same time, relatively low water temperatures must be combined with a high content of dissolved oxygen, which is a typical requirement for all oxyphils, a category that includes salmonids.

By feeding habits, salmonids are carnivorous fish, among which predators are widely represented—a factor that must be taken into account when feeding.

The biological requirements of cultivated cold-water fish species dictate the feasibility of achieving high fish productivity based on meeting water quality demands at the level of industry standards and appropriate feeding, which serve as objective grounds for determining stocking density, yield from rearing, and average individual weight.

The fish productivity of trout-farming water bodies used in specialized farms is closely related to and requires an appropriate area combined with high-quality preparation. A substantial concentration of fish per unit of area or water volume, against the Background of intensive feeding, requires ensuring adequate water exchange and constant removal of Metabolic waste products and feed residues.

Touching upon The impact of breeding and Selection Methods on trout productivity indicators, it must be emphasized that this depends on the objective formulated for the breeding program, in accordance with which the working methodology is shaped using appropriate techniques.

Breeding and selection methods have a long history; the vast majority of methods used today in fish farming were developed in animal husbandry and adapted to aquaculture. In generalized terms, these primarily include mass selection, individual selection or pedigree selection, combined selection, Inbreeding combined with crossbreeding, and breeding systems. In recent years, there has been a rapid increase in the application of genetic selection methods. Naturally, the improvement of breeding work is adequately reflected in the Qualitative and quantitative parameters that characterize modern cold-water fish farming. Over a long period of selection work, relevant corrective components have been developed to account for the Specific features of fish farming and cold-water fish species in particular.

The initial stage of breeding and selection work, regardless of the specific selection methods employed, is the evaluation of broodstock and replacement broodstock based on weight-size and reproductive indicators. The evaluation of females and males of each breed and age group is carried out during the spawning campaign. When the broodstock population is large, a subset of individuals is evaluated, and the volume of the random sample must be at least 10% of the total breeding herd.

The age of sexual maturity and the duration of spawning in females depend on age, breed group, and external factors, the main ones being temperature and photoperiod duration. Due to the fact that the timing of female spawning is characterized by relatively high repeatability, this indicator can be directionally shifted in time. Consequently, annual data on the dynamics of female spawning must be recorded, compared with one another, and accumulated into a database.

Males typically mature 1.5–2 months earlier than females and produce sperm for 3–5 months, which makes it possible to use

males several times per season. It is advisable to evaluate males before the females begin spawning in order to rationally distribute work over time, making it possible to pre-select males with high fish-breeding qualities for subsequent crossbreeding.

Evaluation (bonitation) of males. Breeding and selection work necessarily includes the bonitation of sexually mature individuals of both sexes. The evaluation of broodstock and the selection of the best individuals to obtain the breeding generation is carried out depending on the form of rainbow trout—in spring or autumn, 2–3 weeks before the expected spawning, in accordance with generally accepted methods in fish selection, and includes the following operations:

- visual inspection of broodstock, involving age determination (using age marks, or in their absence, annual rings on scales), culling of insufficiently well-fed individuals with visible body defects and a prolonged barren maturation period;

- determination of fish mass and basic metric indicators: body length according to Smith, standard length (excluding caudal fin), trunk length, maximum and greatest body girth, and HEAD length.

For breeding purposes, the best-phenotype broodstock individuals are selected, taking into account the selection criterion. As a rule, these include indicators of mass accumulation, high-backed body shape, fecundity, shortening of the maturation period, Disease resistance, The ability to maximize The conversion of artificial feed, and stress tolerance during technological operations.

Following visual selection, individual evaluation of each fish begins, involving weighing and measuring. Fish can be weighed on scales of various designs (infant, commercial, etc.), but electronic scales in a special sling are best. To avoid trauma and damage to the scale cover, each individual is separately wrapped in a moistened gauze or cotton towel, weighed with an accuracy of 10 g, after which the mass of the wet fabric is subtracted. Metric indicators are determined on a standard measuring board or with a tailor's tape measure. Body length (with the Mouth closed) is measured from the tip of the snout to the middle rays of the caudal fin. Maximum body depth and girth are measured at the level of the first ray of the dorsal fin, and minimum depth and girth are measured at the narrowest part of the caudal peduncle. Head length is measured from the tip of the snout to the edge of the operculum. During morphometric Procedures, each specimen is held securely to prevent thrashing, which can cause injury.

Following visual inspection and measurements, sexual products are collected from sexually mature individuals—eggs from females and sperm from males—while determining their qualitative reproductive indicators.

Fish-breeding manipulations with males are carried out first. To do this, the male is wrapped in dry gauze or a cotton towel, and its belly and genital opening are carefully wiped. Using massage movements from the head toward the tail with light pressure near the genital opening, the milt is stripped into a separate graduated, clean, and dry test tube. The sperm should have a cream-like consistency without Blood clots, clumps, or feces. Water, mucus, and other foreign impurities must be prevented from entering the sperm test tubes, as they significantly reduce the fertilizing capacity of spermatozoa and shorten the duration of their functional activity.

After obtaining the ejaculate, its volume is determined, and its quality and sperm motility are visually evaluated, since the duration of motility is directly related to fertilizing capacity.

For rainbow trout males, the normative duration of spermatozoon movement is considered to be within 20–30 seconds. A Microscope and a stopwatch are used to determine sperm motility. Technically, such tests are performed as follows: using a dry Glass rod, a drop of milt is taken from each test tube separately and placed on a glass microscope slide, alongside a drop of water. The prepared slide is placed under the microscope eyepiece, and a preparation needle is used to merge the drops of milt and water while simultaneously starting the stopwatch. The water activates the spermatozoa, and their directed movement can be observed. To evaluate ejaculate quality, the conventional five-point Konradt-Sakharov scale adopted in carp farming is used.

According to leading scientists, sperm rated 4 and 5 points is considered best for Fertilization. The Use of sperm rated 3 points significantly reduces the fertilization rate and is unsuitable for reproduction aimed at forming a breeding stock. Sperm rated 1 or 2 points is entirely unsuitable for reproductive purposes.

Sperm concentration is determined using a Goryayev chamber under a microscope at 20x20 magnification (the standard method used for erythrocyte counts). Semen is drawn from the test tube into a melanger capillary up to the 0,5 mark, excess semen is wiped off, and a 2% sodium chloride solution is immediately drawn up to the 101 mark. The semen is thus diluted at a ratio of 1:200. Shake the melanger for 1-2 minutes to evenly distribute the sperm Cells in the solution, then release a few drops, after which a drop from the melanger is placed into the Goryayev chamber. Each side of the small squares measures 1/20 mm, with an area of 1/400 mm and a volume of 1/400 mm . Sperm count is evaluated in 80 small squares (for large workloads, 10 squares are sufficient), yielding the average value per small square, which is then multiplied by the dilution factor and divided by the volume of the small square. Calculations are performed using the formula:

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where: K — sperm concentration, million/mm ; P — number of sperm cells in a single small square; 200 — dilution factor; V=1/400 — volume of the

small square, mm.

The volume of the ejaculate can vary significantly—from 2 to 20 cm (though single portions exceeding 30 cm are not uncommon)—depending on the age of the fish, keeping conditions, feed quality, and the physiological state of the male at the time of collection.

After stripping the semen from a group of males, the test tubes are left in a dark, dry, and cool place while weighing, biometric measurements, and egg collection from females are carried out. The biotechnology of fish-farming procedures for females is similar to that for males. Eggs from each female are collected into separate, clean, dry enameled bowls, food-grade plastic containers, or glass Laboratory glassware. Water, mucus, blood traces, or feces must not come into contact with the eggs, as foreign impurities negatively affect the fertilization capacity of the eggs. Following stripping, egg quality is evaluated visually. For reproductive purposes, eggs of uniform size without an excessive amount of coelomic fluid or bloody exudate are used. The eggs should have a clear, transparent yellow or orange-pink color, free from fatty inclusions, which indicate overripeness and the onset of egg resorption. After egg selection, the working fecundity of the female is determined as follows: the eggs are weighed, a 10 g sample is taken from the total portion to count the number of eggs it contains, and the total egg count is subsequently calculated.

Working fecundity can also be determined volumetrically. In this case, the total volume of eggs collected individually from each female is measured, after which a 10 cm sample is taken to count the number of eggs and determine fecundity. In breeding programs, It is important to calculate not only the working fecundity but also the relative fecundity, meaning the number of eggs per unit of body mass.

The evaluation of females concludes with the determination of egg size and mass. These indicators serve as baseline parameters for characterizing the offspring. They are closely correlated with the size of future larvae and The amount of nutrients in the yolk sac, which in turn influences the timing of the transition of pre-larvae to active feeding and their survival rate. Egg measurements are performed on fixed material. For this purpose, a sample of 25-50 eggs is placed in a 4% formalin solution. After 7-10 days, once full fixation has occurred and the egg mass has stabilized, the weight of an individual egg is determined using torsion balances. Egg diameter is measured using a caliper or an ocular micrometer. The measurement data are statistically processed to determine mean values of mass and diameter, as well as their coefficient of variation. As a rule, eggs with a high coefficient of variation (greater than 20%) in mass and size exhibit reduced viability during early ontogenesis.

All external measurement values and qualitative characteristics of each individual are recorded in a special logbook, which must include the following parameters:

general indicators — breed group (or a group of specific geographical origin), tag, age, mass, body length, specific external metric parameters, and condition factor;

indicators for males — ejaculate volume, duration of active sperm motility, sperm concentration;

indicators for females — working fecundity, relative fecundity, egg mass and diameter, fertilization rate (%), egg survival rate (%), percentage of abnormally developed embryos and pre-larvae, and duration of hatching of free embryos.

After qualitative evaluation of the broodstock, high-quality eggs from a family or group are placed into a suitable container, and semen from the test tubes is added, ensuring that the eggs are evenly coated with milt. To ensure this, the eggs are immediately and gently stirred with a bird feather, covered with a lid, and left undisturbed for 3-5 minutes. Afterward, a small amount of water is added to the eggs and semen so that it covers the eggs with a 1-2 cm layer; this mixture is gently stirred again, covered, and left for 10 minutes. Following fertilization, the eggs are thoroughly and carefully rinsed with the water in which they will be incubated, and left to swell for 1.5-2 hours under minimal water exchange. The fertilization rate is then determined, and the eggs are transferred to incubation apparatuses in accordance with standard guidelines.

The fertilization rate of the eggs is determined by the flotation method. For this, after the Swelling process is complete, the eggs are placed in a 10.7% sodium chloride solution (1200 g of salt per 10 l of water), in which fertilized eggs sink immediately, while unfertilized ones remain On the surface. They are collected using a gauze landing net and counted, after which the fertilization percentage is calculated.

Taking into account the Variability in egg quality among different females and the groups formed from them, fertilized eggs from each broodstock group (pair, family) are incubated in separate apparatuses.

Egg incubation, the duration of which is 320-340 degree-days for certain salmonid species, is carried out in accordance with universally accepted technology. Specifically, water exchange and water clarity in the incubation apparatuses are closely monitored, and if suspended solids settle on the eggs, they are carefully rinsed. However, taking into account the Specifics of the species, fish-farming manipulations with eggs are avoided during sensitive developmental stages, which include the onset of Gastrulation, blastopore closure, the beginning of eye pigmentation, and immediately before hatching. Egg survival rates and the duration of pre-larval hatching are recorded, mortality at all stages of embryogenesis is accounted for, free embryos are carefully tended to during the resting stage, and timely support is provided for their gradual transition to mixed and active exogenous feeding. During incubation, a daily logbook is maintained to record hydrochemical parameters—water temperature and dissolved oxygen content; stages of embryogenesis and early post-embryogenesis are noted, namely the onset of eye pigmentation (160 degree-days), the start and end of free embryo hatching (320-360 degree-days), the duration of the resting stage of free embryos (80-100 degree-days), and the transition to mixed feeding.

From a biological standpoint, the transition of larvae to mixed feeding is one of the most crucial technological stages. It begins at the moment when

the yolk sac of the free embryos is 50% resorbed and they begin to make isolated vertical ascents from the bottom of the incubation apparatus toward the water surface. For feeding free embryos and larvae, specialized starter feeds of the appropriate fraction are used throughout daylight hours at a frequency of 10-12 times in small portions, in accordance with norms established by feeding methods. At the same time, it is essential to closely monitor the cleanliness of the containers housing the trout juveniles, preventing the accumulation of silt, feed residues, dead eggs, and free embryos. Compliance with Sanitary and hygienic measures during egg incubation and larval rearing will prevent The Development of saprolegniasis.

Once the yolk sac is fully resorbed, the larvae have risen into the water Column, and they have acquired the reflex for active consumption of artificial feeds, the larvae are transferred to rearing tanks. For this purpose, larvae from all broodstock groups are reared separately, with the exception of the group that showed an egg survival rate of less than 70% during incubation and larval rearing. Stocking density for individuals suitable for breeding work should be twice as low as that used for standard stocking material. Larval counting during transfer is performed individually or by conventional volumetric or gravimetric methods. During the rearing of breeding fingerlings, the rearing technology, feeding methods, and daily feed rations are strictly followed, and environmental conditions—hydrochemical and temperature regimes—are closely monitored. Growth rates are controlled by conducting sample catches twice a month, measuring and weighing at least 100 individuals; similarly, during complete harvests, 100 specimens are also measured and weighed. All research results are recorded in a special logbook for breeding progeny. Based on the obtained data, the growth rate of the breeding material is analyzed, and feeding rations and water exchange intensity in the ponds are adjusted.

The Challenge of selection in rainbow trout breeding is complicated by the fact that it is conducted against the backdrop of intensive feeding. During selection work with rainbow trout, they must be kept under conditions close to production standards, but slightly superior. When rearing at stocking densities close to production levels, feeding is conducted using a ration increased by 5-10%. It is very important to monitor the amount of feed distributed, because if feed is excessive, individuals that exhibit good growth rates only under improved conditions—namely, enhanced feeding—may inadvertently be selected into the replacement group. Conversely, under insufficient feeding, individuals that achieve growth at the expense of aggressiveness, and at early stages through cannibalism, may be selected.

The best results in rainbow trout selection are achieved by maintaining fish on specialized diets adapted to the physiological needs of each age group. Feeds from leading foreign companies, such as the Danish "Aller Aqua", "Biomar", and the Finnish "Raisio", are designed for fish from the larval period (starter feeds such as "Brilliant", "Crystal" - "Aller Aqua", "Ecostart 15, 17, 2" - "Biomar" with a protein content of up to 56%), as well as feeds formulated for broodstock feeding—"Ecogen 13" ("Biomar"), "Euval REP 497" with a 53% protein content, and "Euval REP 497 HELSE" ("Aller Aqua") featuring an expanded and enhanced vitamin profile recommended for use during short cultivation periods, while also designed to restore the immune status of fish before and after spawning. Feeding with the aforementioned products is carried out in accordance with ration tables that take into account the weight, age parameters of the fish, and ambient water temperature at the time of feeding. These tables are scientifically and experimentally substantiated and are provided along with a quality certificate upon feed purchase. Modern Perspectives on this issue indicate that diets specialized to the physiological needs of trout broodstock from the aforementioned leading foreign manufacturers positively influence Spermatogenesis and oogenesis in fish, significantly enhancing the quality of their Gametes.

One month prior to spawning, the diet of rainbow trout broodstock is reduced by half, and the fish are fed twice a week; 10 days before spawning, feeding is completely ceased. On the second day after egg collection, the fish are returned to a daily full feeding regimen. Males used for ejaculate collection are fed multiple times throughout the entire spawning campaign, except for the two days prior to gamete collection.

Broodstock and replacement fish must be provided with optimal conditions under which they will achieve peak condition and good growth. Stocking densities for replacement and broodstock in ponds are standard for trout farming and should be as follows, spec./m:

Females and males are kept together throughout the vegetative season and are separated by sex only prior to spawning, being housed in separate tanks. It is desirable that the tanks containing males be located upstream. Water carrying male pheromones stimulates ovulation in females.

Test catches of the replacement and brood stock are conducted twice a month, and the results are recorded in a logbook to adjust the feeding regimen accordingly.

Mortality among broodfish and older replacement groups is not considered normal; however, should it occur, the underlying cause must be identified to prevent and avoid future losses. The loss of broodstock during spawning should be avoided, but if it happens, the contributing factors and causes must be investigated, recorded in a special logbook, and documented in official reports.

Cawed broodfish are also documented with a detailed Description of the reasons for their culling. Co-housing broodfish of different age categories and sizes is unacceptable, as larger individuals are stronger and tend to suppress younger and lighter ones, leading to intraspecific food competition that prevents The production of high-quality broodstock.

As part of the preparation for spawning, annual stock indexing (bonitation) of the broodfish and older replacement groups is carried out exactly one month before the spawning season. This process involves a visual inspection of each individual. During bonitation, the broodfish are sorted by sex, with females divided into three groups based on their readiness to participate in spawning:

Group I — ripe females with oval-shaped, soft bellies, in which egg ovulation has occurred and eggs flow freely from the genital opening;

Group II — ripe females with a well-defined, reasonably soft belly, though ovulation is incomplete, and eggs emerge stuck together in clusters of two or three;

Group III — females with an oval belly that feels firm to the Touch, and manual Palpation indicates that ovulation has not yet taken place.

Females in the first group are used immediately or within the next two days. Overholding ripe females is irrational and poses a real risk of egg over-ripening and loss of fertilizing capacity. The second group of females is checked every three days, and quality eggs are collected progressively as they ripen. The third group is inspected every 10 days and re-sorted into three categories. This operational approach, rooted in the biological traits of the species, prevents over-ripening and spares the fish from excessive handling stress that often leads to injury.

For pre-spawning maintenance of broodstock, the farm must have specialized ponds, hapas, cages, tanks, or other containers numbering at least 6-8, strategically located for sorting operations. These can be earthen or concrete tanks up to 100 m² in size, divided into two or three sections, equipped with an intensive water exchange system and the capability for rapid filling and draining within 30 minutes.

In trout farming, it is common practice to install net cages within ponds; however, under high-density stocking and prolonged holding (up to 1 month), fish in such cages often sustain injuries to their pectoral and pelvic fins, which negatively affects their physiological state and reproductive capacity. It is preferable to use permanent metal-mesh frames (with a neutral anticorrosive coating) divided into sections (2x2 m) with wooden bottoms and hinged covers over each section. The platform created by these covered sections can serve as a convenient workspace for inspection and sorting.

When working with broodstock and replacements, it is necessary to have a sufficient supply of stretchers made of soft, waterproof material, landing nets, and knotless mesh sleeves for minor fish transfers. For stripping sexual products, sufficient quantities of gauze wipes or towels made of soft, absorbent fabric—preferably cotton, measuring 50 cm x 80 cm—must be prepared. The number of towels should match the number of fish undergoing handling. The incubation laboratory should be equipped with a corner table for instruments, accommodating a microscope, a test-tube rack, glass slides, a microscope illuminator, Petri dishes, and scales. A proper supply of enamelled bowls of varying volumes from 1 L to 5 L is mandatory, though food-grade plastic containers are also acceptable.

Bonitation of three-year-old replacement females is carried out 15-20 days later than that of the main stock. Females that prove sterile, despite conforming to breeding standards in exterior, are culled. Eggs are stripped from ripe three-year-old females and used for reproduction.

It is well known that the primary challenge of pond and cage farms utilizing river and lake water supplies lies in significant fluctuations of abiotic environmental parameters, driven by relatively small water volumes and shifting weather conditions. These circumstances are critical when selecting specific breeding and selection methods. Given the reality of unstable rearing conditions, heterozygous individuals hold a selective advantage, allowing for The formation of broodstocks with a sufficiently broad adaptive range. In this case, methods applicable to individual or family selection—which inevitably reduce genetic diversity—are unacceptable. To achieve high heterozygosity in broodstocks, mass selection of broodfish is employed, along with outbred crossings of at least 30 pairs of breeders. Females and males are selected based on appropriate weight-size and reproductive parameters; furthermore, females should ideally be selected according to their maturation timing in a specific spawning season.

To enhance the overall productivity of the reared stock, it is advisable to use a two- or three-line breeding scheme to harness hybrid vigor (heterosis) through crossbreeding between lines.

Based on the analysis of spawning dynamics, the predicted maturation timeframe for females in the current season—most favorable for subsequent progeny rearing—is determined, and the target group of fish for further work is isolated.

Special attention should be paid to justifying the selection interval. Numerous studies and breeders' experience show that selecting breeding individuals whose traits deviate significantly from the herd average leads to reduced genetic diversity, the loss of valuable Gene combinations, and a consequent decline in the overall productivity and viability of the resulting generation. In particular, choosing "record-holders," which are typically few in number, narrows breeding opportunities on a scale necessary for practical commercial farming, yielding negative consequences.

Accordingly, selecting fish with traits close to the population average preserves high genetic diversity while retaining the largest and thus best-adapted group of fish for breeding. At the same time, restricting reproduction solely to the modal group limits the potential for breed or strain improvement, highlighting the need to select females and males whose performance exceeds the herd average. Since female evaluation involves multiple criteria, the initial body weight selection threshold must be set to retain a sufficient number of fish for subsequent multi-criteria selection.

Body weight selection is best carried out within the interval of 0.5σ - X - 1.5σ. This retains a sufficiently large group of fish with an average weight slightly above the herd average, and this stage should be conducted immediately before spawning.

The Second Stage of selection takes place during spawning, allowing for the selection of females based on working fecundity and egg weight exceeding the population averages. The selection intensity for reproductive traits is determined by the number of broodfish required to build the broodstock.

When forming an elite group of males, individuals with lower body weight but high working fecundity are chosen. First, body weight selection is performed within the interval 0.5·σ = X = 1.5σ, followed by selection based on reproductive traits exceeding herd averages. Crossing is performed according to standard methodology, fertilizing eggs from several females with sperm from multiple males.

A comparative analysis of two mass selection schemes based on body weight (single-stage at the fry stage and two-stage at the fingerling and two-year-old stages) showed that they have an identical impact on the fish-farming, biological, and genetic heterozygosity of replacement groups. From an economic

perspective, single-stage selection offers significant advantages. The process involves taking a representative sample of at least 100 individuals once the young reach an average weight of about 2 g, followed by individual weighing with an accuracy of 0.1 g. This allows for the Construction of a variation series or a frequency distribution curve by weight to determine the threshold mass of fish comprising 10-15% of the sample. Within the entire juvenile population, individuals whose individual mass falls within the previously defined interval are selected for breeding. Based on these components, the replacement stock is formed, which will soon transition into the broodstock.

As established by dedicated research, to maximize marketable output, it is most expedient to utilize a breeding scheme involving crosses between two or three lines to maximize heterosis in selected fish. These lines can originate from different trout strains (Kamloops trout, Donaldson trout, steelhead salmon) or genetically distinct groups.

Under cage and pond aquaculture conditions, each intra-herd line must maintain high heterozygosity, which serves as the foundation for the future improvement of the broodstock.

Today, broodfish in such farming operations often exhibit a narrow spectrum of genetic diversity while simultaneously displaying high productive traits.

The methods of broodstock formation can be based on individual selection forms, in particular sib selection. The main traits used for selection are growth rate and survival. To obtain high-quality commercial products, it is advisable to use the above-mentioned methods of crossing between two and three lines, while crossing directly within the lines is carried out According to the 1♀ x 1♂ scheme, which makes it possible to individually evaluate male and female individuals.

The First stage of creating a breed or breed group of rainbow trout using sib selection methods involves evaluating the spawners of the initial broodstock. After analyzing the appraisal data, the selection of spawner founders of the line begins. The selection criteria are body weight and size, as well as the working fecundity of females and males. The selection limits for these indicators remain the same as in mass selection, specifically for female and male body weight 0.58σ = О = 1.58σ. At the same time, working fecundity must be higher than the average value in the stock.

The required number of females and males for paired crossings is selected from a random sample. The sample volume must be at least 10% of the broodstock population. The initial number of paired crosses must be at least 30. The main indicators for evaluating families are survival at various stages of ontogenesis and growth rate.

Family selection for survival is carried out consistently based on the results of egg incubation, free embryo rearing, and larva nursing. Families with survival rates below standard are culled. During subsequent rearing, a continuous record of dead individuals in each family is maintained.

Selection for body weight is carried out when the fish reach one year of age. Families with the highest growth and survival rates over the observation period are retained. Within the selected families, about 30% of the fish lagging in growth rate are culled. Further rearing of sibs can be carried out jointly, provided that the representatives of each family are marked with a serial tag prior to this.

Among mature individuals, broodstock appraisal and corrective selection are performed. Fish with developmental defects, stunted growth, and weakened individuals are culled. The selection of spawners and line successors is carried out in families characterized by a high growth rate, survival, and the greatest fecundity of females and males. The average size of eggs must not be lower than that of the initial stock.

Subsequent work on the reproduction of new breeding generations follows a similar scheme.

To obtain commercial products, spawners of different lines are crossed, which ensures the presence of heterosis, significantly increasing cultivation efficiency.

The specific conditions of warm-water farms indicate the need to select a breeding trait such as Organism heat tolerance. Selection aimed at increasing heat tolerance for cold-water fish species promotes an increase in fish growth rate due to a better match between their individual thermal requirements and maintenance conditions, as well as a reduction in fish mortality during periods of maximum water warming. Thermoresistance (heat tolerance) is used as a breeding indicator when applying the main selection methods—mass and individual. Direct selection for thermoresistance cannot be recommended due to the mortality of a significant amount of stocking material. Indirect selection for heat tolerance must be applied. The methodology is based on the interaction between rheotaxis, inherent in trout, and the avoidance reaction to high temperatures. This concept is based on the fact that fish are placed in thermal gradient conditions with a rapidly increasing temperature background, which allows for tracking the corresponding ethological reaction.

Practically, selection is carried out as follows: fish with an average weight of 0.5–0.7 g are placed in a flow-through trough where, after 2–3 hours of adaptation, the water temperature is increased. The rate of water temperature increase should be 0.05–0.15 °C/min. Water flow rates are set at 20–60 L/min, depending on the size of the trough. The number of fish in the trough must comply with the standard for the given flow-through rate. A mandatory condition of the experiment for this selection is the presence of a water temperature drop of at least 3–5 °C from the inflow to the outflow. To achieve this, it is necessary to lower the air temperature in the room and lengthen the water flow path in the trough using baffles installed in a staggered pattern covering 2/3 of the trough width. Initially, the bulk of the fish gathers near the water inflow; however, when the water temperature gradually rises to 23–26 °C, some of the fish move to the outflow, where the water is cooler. If visual observation during trout movement determines that 5–10% of the fish remain at the inflow, they are separated by a net screen. After that, the water heating is stopped, and the water temperature is gradually brought back to the initial level at a rate of no more than 0.05 °C/min.

As a result of this selection, fish in which positive rheotaxis dominates over the high-temperature avoidance reaction are retained for breeding. At a selection intensity of 5%, these fish possess a heat tolerance 15% higher than individuals from a random sample. The selected fish are reared in accordance with the standards established for maintaining the breeding group of replacement stock. Their reproduction is carried out using the mass selection methods outlined above.

The first stage of individual selection for heat tolerance is based on the evaluation of the initial stock according to piscicultural and biological indicators. Taking the obtained results into account, spawner line founders are selected and paired crosses are performed.

The second stage of developing a thermophilic breed involves selecting the superior families. During egg incubation, free-embryo rearing, and sibling fry nursing, their quality is assessed based on survival rates. Families where free-embryo mortality exceeds standard thresholds are culled. Immediately after the transition to exogenous feeding, sibling fry are evaluated for heat tolerance using mean values from a random sample.

Conducting experiments to determine thermoresistance requires strict adherence to specific methodological conditions. A mandatory two-day preliminary acclimation of the fish to an initial water temperature of 5–10°C is required, with the temperature increase rate maintained at approximately 0.1 °C/min. Meanwhile, the target test water temperature should be set at 28–30°C, while dissolved oxygen concentration must reach 100%. The consistency of experimental conditions—specifically the initial and final temperatures, the rate of temperature increase, and the dissolved oxygen level—must be rigorously ensured and monitored.

Setting up these experiments requires a diverse range of equipment: a water preparation facility equipped with heaters, a degasser, and an oxygenerator, as well as standard fish-farming tanks. If such infrastructure is unavailable, conducting the tests in aquaria is a viable alternative, provided they are equipped with thermoregulation and oxygenation systems.

The survival timeframe starts the moment the test temperature is reached, and dead specimens must be removed from the aquarium every five minutes. This yields a frequency distribution of the fish based on individual survival, which is then used to calculate the mean, standard error, and variability. For further rearing, the 3–4 families exhibiting the highest heat tolerance are selected. The selection differential increases with the number of paired crosses performed; when choosing 4 families out of 20, their heat tolerance should exceed the average by 15–20%.

The Third Stage involves growing the fish to sexual maturity, during which families are evaluated for survival and growth rate. At the fingerling stage, mass selection based on body weight is carried out with a 50% selection intensity. Mature females are assessed based on reproductive performance and offspring quality. The best families are selected, and mass crossing is performed within each family. Based on the results of egg incubation and larval rearing, the specific family designated for producing broodstock and line continuers is identified, and subsequent breeding work follows the aforementioned protocol.

In combined selection, direct selection for heat tolerance is additionally performed among the offspring of the most resistant families. The selection methodology is analogous to the Procedure used for determining average heat tolerance, with the exception of the final water temperature, which at this stage should be set to 27°C. The experimental fish are kept at this temperature until mortality reaches 25% (determined visually), after which heating is stopped. Within 10 minutes, the water temperature is lowered to 20°C and then gradually brought back to the initial baseline. Under these conditions, the intensity of mass selection for heat tolerance is approximately 50%.

The first twice-spawning breed, "Tayakama", was registered in Japan at the Nikko trout farm, which benefits from a year-round constant water temperature from its supply source. It was obtained through prolonged selective breeding utilizing combined selection and artificial photoperiod manipulation. The foundational stock originated from spring-spawning rainbow trout imported as eggs from Colorado. Initially, the spawning season was successfully shifted by four months—from April to early January—followed by a second round of egg collection from females in summer. Widely known studies have demonstrated that twice-spawning females exhibit notably high fecundity, although the eggs produced during the second spawning are smaller and show a lower fertilization rate.

Modern research conducted at the Adler breeding center in Krasnodar Krai has shown that among rainbow trout females of various origins cultivated under stable temperature conditions, 2–15% spawn twice a year. The repeat spawning occurs six-month later. Selective breeding of these fish demonstrated that within the first generation of selection, the proportion of twice-spawning females doubles, which convincingly highlights the high potential of this work. Developing a breed with these traits facilitates the maximum realization of the biological potential of rainbow trout.

According to leading experts, stocking material from this breed can be utilized across various farm types, potentially increasing commercial caviar production 1.5-fold.

The primary goal of aquaculture breeding programs is to develop fish strains characterized by specific morphometric, biological, and other valuable commercial traits. As a stock is established and managed, its population and genetic Structure undergo gradual shifts. A distinctive feature of these genetic-level changes is their rapid pace—they typically manifest in the very first generation, whereas phenotypic changes may take several generations to appear. Given these dynamics, Genetic monitoring of broodstocks becomes essential. Its core methodologies involve analyzing population structures as Key Components of comprehensive studies, with a primary focus on parameters such as karyology, DNA polymorphism, and protein polymorphism.

The Analysis of the conducted research allows for certain Conclusions regarding methodological approaches to genetic monitoring of rainbow trout broodstocks. To obtain a comprehensive profile of a broodstock's genetic structure, at least 100 breeders must be examined, with the sample evenly distributed between males and females. Consequently, 200 alleles will be analyzed for each studied locus, which is sufficient for subsequent statistical Processing. If direct analysis of the broodstock is unfeasible, its evaluation is carried out by assessing the genetic STRUCTURE OF THE offspring. In this case, the sample must be representative, meaning it is recommended to analyze progeny from as many families as possible.

Methodological collection of material is performed in a specific sequence. After taking measurements, weighing, and determining the sex of each fish, tissue samples—including blood serum, Muscle tissue, and Liver—are harvested.

Electrophoretic Separation is carried out using standard protocols. Optimal resolution and band clarity are achieved using starch gel (for isocitrate dehydrogenase) and polyacrylamide gel (for other loci). Among the analyzed polymorphic protein loci in rainbow trout, the most informative are muscle aspartate aminotransferase (AAT-3), blood serum transferrin (Tf-1), and hepatic superoxide dismutase (SOD-1), isocitrate dehydrogenase (IDH-3, and IDH-4).

Analysis of allele frequencies of the listed polymorphic protein loci allows obtaining various indicators that characterize the Features of the genetic structure of the herd, namely the proportion of polymorphic loci, the number of alleles per locus, the average level of heterozygosity, etc. Changes in allele frequencies of polymorphic protein loci most informatively and comprehensively reflect genetic alterations. The instability of protein marker frequencies serves as the primary indicator of changes in the genetic structure (whether desirable or undesirable) occurring within the broodstock. The polymorphic protein loci proposed for trout belong to various enzyme classes, and changes in their allele frequencies demonstrate alterations that have taken place across the entire genome of the broodstock.

The frequency of genetic monitoring depends on the objectives set by the breeder and the methods of breeding and selection work. When applying mass selection with minor culling of breeders and maintaining a sufficiently large broodstock, data collection and analysis for genetic monitoring are carried out once every two to four years. The use of individual selection requires annual genetic monitoring of the broodstock status. The Organization and Execution of broodstock genetic monitoring should be tailored individually for each specific farm, involving highly qualified specialists from relevant research institutions.

As a working framework, it is advisable to consider the calculation of the required number of broodfish and replacement stock based on the specified standards of mass

selection to ensure an annual yield of 20 tons of marketable trout in pond aquaculture conditions. Within 20 tons of trout with an average individual weight of 200g, there are 100 thousand specimens. Given that, according to generally accepted standards, fish mortality during commercial rearing is 5%, 105 thousand yearlings are required. Considering harsh wintering conditions, survival rates in mountain pond farms reach 90%, meaning 115.5 thousand fingerlings are needed. Meanwhile, since the survival rate from larvae to fingerlings under these conditions is 70%, 150.5 thousand larvae are necessary. The amount of eggs that must be laid for incubation, accounting for mortality during incubation, free embryo maintenance, and larval rearing at 30%, requires having 200 thousand eggs. If the average working fecundity of a female is 3,000 eggs, the number of females should total 67 specimens; assuming a 1:1 sex ratio in the herd, an additional 67 males are added. With a 100% reserve of broodstock, the total herd will number 268 individuals. Annually, 25% of the livestock is replaced, which equals 67 specimens. Thus, to replenish the broodstock, the following number of replacement stock must be raised: 70–75 three-year-olds, 80–100 two-year-olds, 1,000–1,500 yearlings, and 10 thousand fingerlings.

With proper organization and professional execution of breeding and selection work, the number of replacement stock being raised can be reduced by increasing the productivity of the broodstock. The experience of trout farms indicates that it is advisable to retain fish for breeding at the following weights: yearlings — 0.02–0.05 kg, two-year-olds — 0.2–0.4 kg, three-year-olds — 0.7–1.0 kg, and four-year-olds — 1.2–1.7 kg. These standards cannot be considered definitive. Depending on climatic conditions, growth rates, level of domestication, and breed group, the fish weight may vary somewhat.

One of the components of breeding and selection work is the tagging of broodfish and replacement stock. When working with rainbow trout, tagging is performed to address various essential tasks during breeding operations. The core requirements for tagging are clear visibility of the tags, their durability, minimal trauma to the fish, as well as simplicity and speed of application. The following methods may be used for tagging rainbow trout on farms:

- Clipping the pectoral, pelvic, and adipose fins in various combinations. The primary requirement for this method is meticulousness during tagging. When clipping the pectoral or pelvic fins, they must be removed entirely along with the basic bone structures; otherwise, regeneration will occur, making tagged fish difficult to distinguish from those with acquired or natural fin defects. This method is suitable for fish weighing over 1 g.

- Tagging with Dyes via subcutaneous injection of dichlorotriazine (M-procion-5SX) dyes. The dye solution, prepared at a rate of 200 mg of dry substance per 10–15 cm of water, is injected subcutaneously into the abdominal area using a syringe. This volume of solution is sufficient for 200–250 fish, and such tags persist for 6–7 years. The use of dyes in various colors makes it possible to expand the number of age and breeding groups of trout. Dye marking is also utilized for individual identification of broodfish and can be applied to fish that have reached a weight of 15 g.

- Combined tagging — a combination of fin clipping and dye marking. In this approach, each breed group is assigned a permanent mark (a specific fin is clipped), while the dye indicates the fish's age across all groups.

- Pendant tags can be used for both mass and individual trout tagging, as each tag features a unique serial number. When applying this method, it must be taken into account that fish often lose or tear off tags from one another, mistaking them for food particles. Therefore, the tag should match the color of the fish's body and be attached beneath the pelvic fins. This ensures high retention rates of the tags. Pendant tags can be applied to fish that have reached a weight of 15 g.

The most modern and reliable tags today are electronic PIT tags or microchips. These individual tags with a designated unique number are indispensable for individual and family crossing of fish. Microchips take the form of plastic or glass capsules measuring 12x2.1 mm, which are injected into the Muscles or Abdominal cavity of the fish using a pneumatic syringe-like device. The tags are read by a special detector. Modern equipment allows integrating the reading detector with a computer containing all information about the tagged fish, making it possible to track the broodfish's complete dynamic history throughout its entire period of use. Electronic tags are applied starting from the fingerling stage, as emphasized in numerous studies. The foundation of modern cold-water aquaculture is a rather limited number of species, among which trouts dominate. Trout farming is one of the most promising areas of aquaculture, yielding delicacy products of high nutritional and dietary qualities. Consequently, trout are farmed in many countries worldwide. The objects of cultivation include rainbow trout (Salmo gairdneri irideus Kich.), steelhead salmon (S. gairdneri gairdneri Rich.), and brown trout (S. trutta m. fario L.).

The main object of trout farming in our country is the rainbow trout. This species easily adapts to environmental conditions. It can withstand water temperatures ranging from near-zero to 27 °C, though the preferred temperature is 15–18 °C. At an oxygen concentration of 9–11 mg/L, rainbow trout actively utilize natural food resources and grow rapidly due to efficient feed utilization.

In recent years, an intensive process of breed formation has been underway in trout farming, accompanied by an increase in the number of cultivated species. In line with this concept, one of the pressing directions for the further development of trout farming is the Introduction of promising new species. One such species is the Kamloops trout (Salmo gairdneri kamloops Lord). This subspecies of rainbow trout spawns in autumn and grows rapidly, making it possible to obtain additional production.

This trout has also been cultivated in the CIS since 1982, and the obtained results indicate that this fish spawns 1.5–2 months earlier than the rainbow trout, the fecundity of females is 25–30% higher, though the egg size is smaller. Of particular note is the rapid growth and high viability of fingerlings, yearlings, and other age groups of these fish. The growth rate of Kamloops trout fry and fingerlings is 2 times higher, and that of yearlings and two-year-olds is 2–2.5 times higher. Through the combined rearing of two trout species, marketable Kamloops trout can be produced in 12–14 months, which is 5–6 months faster than raising rainbow trout in monoculture. This enhances the operational rhythm of farms, reduces production costs for commercial products, and improves equipment utilization. The reproduction and rearing technology for Kamloops trout is similar to that of rainbow trout. Also of interest and high potential is the Donaldson trout, which is characterized by rapid growth rates and increased fecundity, opening up a promising new direction in domestic salmon farming.

The issue of economic efficiency in cold-water aquaculture remains quite problematic to this day, with performance parameters tied directly to current market demand for cold-water aquaculture products. Modern, theoretically grounded technologies in cold-water aquaculture make it possible to rapidly scale up commercial production volumes, which is currently constrained largely by the pricing policy for cold-water aquaculture components, the market realization prices of the finished product, and the low purchasing power of the population.