Chordate Zoology - textbook - Y. V. Tsaryk - 2013

Chapter 4. DIVISION GNATHOSTOMATA, or ECTOBRANCHIATA. SUPERCLASS PISCES

4.2. CLASS BONY FISHES OSTEICHTHYES

4.2.2. Behavior of Bony Fishes

The behavior of bony Fishes is driven by innate and acquired instincts that facilitate foraging, reproduction (spawning signals, Selection of optimal spawning sites, Various Forms of parental care), migration, territory defense, schooling Organization, and more. Bony fishes are capable of developing conditioned Reflexes to colors, shapes, and sizes of objects, as well as to sounds and other stimuli. Behavioral characteristics determine the existence of distinct population structures in different species. Complex forms of fish behavior are associated not only with the Medulla Oblongata and Midbrain but also with the corpora striata of the Forebrain. For example, after the removal of the forebrain, cichlids (belonging to Perciformes) can still recognize individuals of the opposite sex and explore new territory, but they are unable to spawn, fertilize eggs, or form schools. At the same time, damage to the corpora striata leads to a loss of The ability to guard the eggs.

Territorial behavior is accompanied by The formation of various intra-population groups. Their initial form is likely a "brood"—juveniles hatched from a single clutch. Early larvae pay no attention to one another, but within 2-3 days they usually cluster together and mimic the movements of their neighbors, forming a school with coordinated behavior. This is facilitated by the mimicking instinct, which is based on a specific signaling "schooling" coloration characteristic of the young of many species—the presence of a distinct pattern or a contrasting color spot that serves as an identification landmark. Broods of fry usually soon merge into large schools (elementary populations) consisting of fish that developed together and share a similar physiological state and size. Such groups often persist until sexual maturity. When moving in a school, fish adjust to one another, ensuring a hydrodynamically favorable arrangement. The ORGANIZATION OF THE school is sometimes maintained even during rest.

The advantages of schooling life for so-called non-predatory fish are indisputable: a school finds food concentrations faster, detects an approaching enemy more easily, and makes it difficult for an attacker to orient itself and select a target. Raiding predators form "dispersed schools" or stay solitary, yet remain within "sight" (visual or acoustic range). Such a "formation" facilitates searching for active prey, attacking, and capturing it. Many fish species live in schools throughout their lives (clupeids, gadids, cyprinids, percids, etc.). Others gather during feeding and spawning Migrations but disperse into smaller groups on feeding grounds and spawning sites. Females often occupy separate spawning territories and may stay near the clutch to guard the eggs (Pacific salmon), or this task is performed by males (some tropical catfishes, etc.). Freshwater predators such as catfish and pike, as well as benthic marine fishes (anglerfishes, moray eels from Anguilliformes, gobies from Scorpaeniformes, etc.), live solitarily.

In the event of food scarcity in a Water body, cannibalism—the consumption of one's own eggs and offspring—may occur. In some cases, it can even become the norm. In certain lakes of Western Siberia, large individuals of the European perch feed mainly on small perch, which, in turn, subsist on plankton—a food source inaccessible to large perch. This allows the population to survive in water bodies where no other food is available for adult individuals.

Particularly complex intra- and interspecific relationships are characteristic of fishes inhabiting tropical waters and coral reefs. They exhibit an immense variety of colors and patterns, developed acoustic signaling and display behavior, complex courtship rituals, intricate Hermaphroditism, and parental care (nest building, guarding of eggs and young). Such intraspecific (population) organization structures The Use of space and its vital resources. An example of the Increasing complexity of relationships in the species-rich biocenoses of tropical seas is the existence of small "cleaner" fish that remove parasites from the Skin, Pharynx, and gills of larger "client" fish, which sometimes gather near the cleaners' stations in large groups and "patiently wait for the doctor in the waiting room." The cleaners themselves are usually brightly colored, which prevents attacks on them. One such cleaner, the bluestreak cleaner wrasse (Labroides dimidiatus), which lives in the tropical Pacific, is a protogynous hermaphrodite capable of changing sex within minutes. They live in groups consisting of a dominant male and a harem of females, where larger individuals dominate smaller ones. The male actively prevents females from changing sex; upon his death, the dominant female immediately transforms into a male, taking his place. The relationship between cleaners and large client fish has led to a peculiar form of mimicry: some small predators, resembling cleaners in shape and coloration, penetrate the gill cavities of deceived clients and tear off pieces of their gills.

Species leading a solitary lifestyle are often characterized by protective coloration and formidable defenses (spines, sharp fin rays, which sometimes have venom glands at their base, etc.). Such fish are often capable of generating specific acoustic signals associated with mate searching and territory defense.

Migration is an important element of The life cycle of many fish species. Migrations can be active or passive. In the former case, fish move in a chosen direction, sometimes overcoming strong currents and rapids (e.g., salmonids). In passive migrations, they utilize the force of the current. Both forms of migration usually Complement each other: active in adults, and passive in larvae and juveniles (e.g., migrations of herring and eel larvae). Passive migration is also observed in some slow-moving pelagic fishes living in areas of circular warm currents (ocean sunfish, etc.).

During active migrations, fish orient themselves using all their Senses. Chemical and thermal perceptions are believed to be particularly important. Although fish

are capable of distinguishing even small Temperature differences of a fraction of a degree, the chemical sense likely serves as the primary guide when choosing a direction. Adult eels orient toward increasing salinity, whereas salmon, conversely, orient toward decreasing salinity.

When entering a river, fish orient themselves using chemical memory, which has retained the scent of their "home" river since the larval period. Observations of the behavior of Pacific salmon schools migrating at sea suggest that the choice of the general direction toward their home shore may also occur due to solar orientation or celestial navigation.

In the lives of many fishes, Different types of migrations alternate. After spawning, during feeding migrations, fish move to food-rich "feeding grounds." Some species remain relatively sedentary in these feeding areas until the next reproductive cycle, while others constantly wander in search of food. With the onset of the next breeding season, spawning migrations begin. In many freshwater and some marine fishes of northern and temperate latitudes, wintering migrations occur after feeding. In wintering areas, fish survive the winter period in a state of minimal activity. In freshwater bodies, wintering sites are usually the deepest areas—"deep holes." In our rivers, bream, crucian carp, common carp, and pike-perch winter in these deep holes. The fish move very little, standing close to one another, sometimes in several layers. The Azov anchovy migrates to the deeper Black Sea for wintering.

The onset of wintering migrations is determined by the physiological state of the fish (The amount of accumulated fat, the appearance of "cold" Enzymes, etc.) and changes in environmental conditions (temperature, salinity, oxygen content). Without sufficient fat reserves, the wintering migration may not occur. For example, anchovies with a fat content of up to 14% do not migrate from the Sea of Azov even during a sharp drop in water temperature; if the fat content is 14-17%, they begin migration when the temperature drops to 9-14°C; and with a fat content of around 22%, they migrate en masse even with a slight temperature decrease. Sometimes, sexually mature populations migrate for wintering, while immature individuals continue to feed throughout the winter (bream, pike-perch, etc.).

The population dynamics of fish reflect the interaction of their populations with the environment. Its nature is determined by many factors: the lifespan of individuals, reproduction characteristics and rates, food availability, mortality, and the Variability of environmental factors (fluctuations in water level, temperature, and oxygen content, Changes in the strength and direction of ocean currents, etc.). In semelparous (monocyclic) species that reproduce only once at the end of their lives, population size is less stable and exhibits greater fluctuations than in long-lived iteroparous (polycyclic) species. Population stability depends on food supply; predators and food competitors also exert a significant influence. Due to the greater stability of physicochemical conditions in the aquatic environment, especially in seas, compared to land, fluctuations in fish populations have a smaller amplitude than those of many terrestrial animals.

Recently, the international community has paid significantly more attention to The impact of human economic activity on fish population dynamics: fisheries regulation is being established, control over water pollution by industrial and other wastes is improving, and costly programs for the restoration of water bodies are being implemented.