Characteristics and tendencies of fish

Tentaxis refers to the directional action response of animals under unidirectional environmental stimulation. For example, fish move towards light (called positive phototaxis) or backlight action (called negative phototaxis). Taxis is a stereotypic reaction and is the simplest type of instinctive behavior. Although the foraging behavior of fish is also a directional action response, the complex foraging behavior is mixed with a large number of learned components, so it is not considered a taxis behavior.

Taxis requires that the animal concerned has sensitivity and responsiveness, so taxis must rely on the animal's nervous system and muscles to complete.

Tropical behavior is a genetic trait that is retained by natural selection because of its adaptive significance. For example, each type of fish can only live within a certain range of temperature and humidity, and accordingly there are positive and negative thermotaxis and hygrotaxis. Here are just a few common tropisms of fish.

1. Fish phototaxis

Phototaxis is a characteristic that enables fish to produce directional behavioral responses to light stimulation. The directional behavior toward the light source is called positive phototaxis, and the behavior away from the light source is called negative phototaxis. Many fish species have positive phototaxis, such as saury, sardines, fat-eyed herring, squid, mackerel, horse mackerel, spotted sunflower, silverfish, needlefish, squid, etc.

There are various hypotheses on how fish respond to light stimulation, such as curiosity, suitable illumination, bait gathering, conditioned reflex, forced movement, confusion and instinct. The phototaxis process of fish can be roughly divided into two stages: the first stage is when the fish is stimulated by light and swims close to the light source; the second stage is when the fish stays and swims under the light source. However, after a period of time, phototactic fish will leave the light source and swim away due to adaptation to light, fatigue, and changes in the environment. Some adult fish without phototaxis also have phototaxis reactions in their juveniles, such as juvenile fish such as sweetfish and eels. The phototaxis of the same kind of fish varies with the development stage, male and female gender, food intake and swim bladder structure. For example, the juvenile stage is more phototaxis than the adult stage. When the food intake is small, it is easy to be attracted by light. Some fish such as The phototaxis of saury is weakened during the egg-pregnancy period. In addition, the degree of floating of fish after being trapped is related to the structure of the swim bladder.

There are three types of phototaxis: stimulus proportionality, target retention, and retention. Stimulus symmetry is the stimulation caused by the difference in the amount of light on the light-receiving surfaces of the two eyes. Targeting and retention are the stimulation caused by the difference in the amount of light received by the light-receiving surface of the fish eye. Fish develop phototaxis in order to maintain the same amount of light received. The sensitivity curves of fish eyes to different wavelengths of light are different. Bottom fish experience a very narrow spectral range, about 410-650 nanometers, while upper-layer fish have a wider spectral range, about 400-750 nanometers. .

Fish have a certain range of suitable illumination, and they cluster in the water layer with this illumination. The suitable swarming illumination of fish changes with changes in environmental conditions. For example, under the illumination of water lights, saury fish swarm about 2 meters below the light source and stay there for a long time. Under the illumination of underwater lights, although the amount of light is less than that of water lights, fish can surround and swim towards the light source, but they will leave the light source soon after staying. Fish with strong phototaxis are also fish species that are highly gregarious, such as sardines, turtles, mackerel, saury, jade fish, etc. At night, fish stay under the light source for a long time in order to defend themselves, search for bait or find companions, resulting in a swarming reaction.

The phototaxis of fish is related to water temperature and moonlight. Generally speaking, the higher the water temperature, the weaker the phototaxis; conversely, the phototaxis is enhanced. The moonlight is bright and the phototactic clustering effect is poor. If the illumination of the light is enhanced, the clustering effect can be improved.

2. Fish electrotaxis

The directional behavioral response characteristics of fish to electric field stimulation in water. There are three behavioral responses of fish to electric field stimulation: electrosensitivity response, paralysis response and sun-taxis response. Among these three reactions, only the yangtaxis reaction belongs to fish electrotaxis. That is, in a DC electric field, when the voltage increases to a certain value, the fish's head turns to the anode or swims towards the anode. The voltage at this time is called the positive voltage. According to data, when the fish's snout points toward the anode, its induced voltage is 1.5-2.0 times that of the cathode. If the middle value of these two voltages is used to stimulate fish, the fish will be inductive toward the cathode, but not inductive toward the anode.

The current density threshold (amps/square meter), electric field strength threshold (volts/cm2) or behavioral state voltage of the fish body (volts) required for the fish's sun-motility reaction vary depending on the species of fish. Even in fish of the same species, as the body length increases, the current density threshold and electric field intensity threshold during the electrotactic reaction also decrease, but the behavioral state voltage of the fish does not change. In addition, fish with high metabolic intensity are more sensitive to electric current and have stronger ability to resist electric current.

3. Fish thigtaxis

The positioning response of fish to external solid stimuli is also called solidification. The thigmotaxis of fish is achieved by relying on the fish's sense of touch. In addition to nerve endings, taste buds located on the skin and tentacles of fish play a very important role in touch. For example, eels pass through slits, and bottom fish have the characteristics of making parts of their bodies close to the seabed or rocks.

4. Chemotaxis of fish

Fish use the concentration difference of chemical substances in the environmental medium as a stimulus, causing fish to develop directional movement characteristics. This is because the foraging behavior of all animals either mainly depends on or includes responses to the chemical components of food. Soluble or volatile components in food diffuse in the water, causing the chemotactic behavior of fish. Fish sense the spatial and temporal changes in the concentration of chemical stimulus sources through their olfactory organs, move along the direction indicated by the concentration gradient of the stimulus source, and swim toward the stimulus source is called positive chemotaxis; those that are free of the stimulus source are called negative chemotaxis. Not all fish have chemotactic behavior, depending on the sensitivity of the fish's sense of smell. Generally speaking, when fish are near a stimulus source and the concentration gradient of the taste trace is large, chemotactic behavior occurs; with a high concentration of stimulus source, the action range is small and the swimming speed is fast; with a low concentration stimulus source, the action range is large and the swimming speed is slow .

When fish find bait, many fish do not show chemotaxis at the beginning. When they are far away from the bait, they often change directions and swim back and forth or zigzag, gradually narrowing the scope of exploration. When swimming close to the low concentration side, When the concentration is high, turn to the high concentration side. The taste traces of bait in running water are distributed in a narrow range, making it easier for fish to approach the bait. Some scholars believe that the chemotaxis behavior of fish from changing direction to linear motion is caused by the concentration difference of odor sensed by the two nostrils.

When fish obtain bait, it is sometimes difficult to distinguish between the effects of smell or vision, and it is often a combination of both.

5. Flow tendency of fish

Refers to the behavioral response characteristics of fish to the flow direction and velocity in flowing water. Fish adjust their swimming direction and speed according to the direction and speed of the water flow, so that they swim against the current or stay in a certain position in the countercurrent for a long time. This characteristic of fish is caused by water pressure, visual and tactile factors, and is closely related to the natural water environment in which they live. Generally speaking, oceanic migratory fish and fish in river rapids have strong flow tendencies, such as sardines, mackerel, tuna, yearlings, ayu, trout, salmon, etc.

To analyze and study the flow tendency of fish, the perceived flow speed, favorite flow speed and limit flow speed are used as indicators. Perceived flow rate refers to the minimum flow rate value at which fish may respond to the flow rate. The preferred flow speed refers to the most suitable flow speed range among the various flow speed values that fish can adapt to. The ultimate flow speed refers to the maximum flow speed that fish can adapt to, also known as critical flow speed. The perceived flow speeds of various fish are roughly the same, and it can also be considered that the sensitivity of fish to water flow is roughly the same. Due to the different swimming abilities of various fish species, the ultimate flow speeds among them vary greatly. Even fish of the same species have different flow tendencies due to different body lengths. In general, both the ultimate flow rate and the preferred flow rate increase with body length.

Table of ability of fish to adapt to flow speed

animal tags：