All About Fish - Part 3

Fish Behavior Behavior is the action of a fish in response to its environment including other animals.  The most interesting and sometimes the most obvious behaviors involve interactions with other individuals. Migration: Many species of fish migrate during their life cycle.  It is well known that salmon make long migrations to spawn.  Other fish migrate in response to changing environmental conditions, such as temperature or abundance of food. Schooling:Many fish congregate in groups called schools.  A school is a group of similarly-sized fish of the same species aligned and swimming in the same direction.   Sight seems to be the primary means of maintaining the school.  The lateral line may also be used. Aggression:Aggressive behavior is an interaction between two fish of the same species (intraspecific) or different species (interspecific).  It is usually associated with reproduction or the defense of feeding territory.  It includes posturing, direct attacks and displays such as fin flaring and changes of color. Resting:Some fish spend a good portion of their day resting.  Resting reduces competition, provides protection from predators and may help in energy conservation. Communication:Senses play an important part in fish communication.  Visual communication is important to most fish.  Body movements, postures, colors and color patterns are the primary means of visual communication.  Sound is also used for communication.   Sounds are produced by grinding teeth, flexing or contracting muscles and vibrating the swim bladder.  Fish also communicate by releasing chemicals called pheromones.  These are chemical signals produced by an animal that, when released, influence the behavior of others of the same species.  The sense of smell is important for this form of communication. Cleaning: Some tropical fish are cleaners.  They pick parasites from other fish.  Cleaning fish, such as wrasses, are brightly colored.  They establish cleaning stations that other fish approach in order to be cleaned.  Body posturing, a form of visual communication, is used to initiate cleaning. Color Red: Red is a common color in fish.  You might think that red fish would be very easy for a predator to find.  However, most fish that have this coloration live in dark or deep water, or are nocturnal (active at night).  In deep water, red light is filtered out quickly so red is a good camouflage.  At night, red-colored objects appear gray. Countershading:Many fish are dark on top and light on the bottom.  When seen from above they "disappear" by blending in with the dark color of the depths of the bottom.   Seen from below, the light belly blends into the sky above.

Disruptive Coloration: This is a form of camouflage.  The patterns and lines break up the outline of the fish and help it to blend into the background.  This confuses predators since the fish shape is not easily identifiable. Eye Spots:Eye spots are a form of mimicry.  They eye spot, usually found near the tail, may be used to draw attention away from the real eye which is a target that a predator might strike. Warning Coloration:Many fish use bright colors to "advertise" the presence of venomous spines or some other defensive mechanism. Camouflage:Many fish have colors or patterns that match their backgrounds.  Some fish can even change color to match different backgrounds either to hide from prey (if an ambush is planned!) or to hide from a predator. Food (Preferences, Resources and Digestion) As a group, bony fishes have a diverse range of food preferences.  They may be herbivores (plant-eaters), carnivores (meat-eaters), omnivores (plant- and meat-eaters) or detritivores (animals that eat decomposing plants and animals).  Some of the animals common in the diets of bony fishes include worms, marine snails, mussels, clams, squids, crustaceans, insects, birds, amphibians, small mammals and other fishes. The amount of food a bony fish eats is directly related to its size, its metabolic rate and the temperature of its environment.  Warmwater fishes, such as tropical fish, generally have higher metabolic rates and require more food than coldwater species of the same size. The esophagus in bony fishes is short, expandable and layered with muscles so that large objects can be swallowed.  Most species of bony fishes have a stomach with gastric glands that release substances that break down the food to prepare it for digestion.  The intestine is where the majority of food absorption takes place and the digestive system terminates at the anus. Reproduction in Fish In most species of bony fishes, sperm and eggs develop in separate male and female individuals.  Fertilization is predominately external and, in some instances, internal.  Males and females may look similar, or they may look very different.  Male/female characteristics may include size, coloration, external reproductive organs, head characteristics and body shape.  While reproduction in bony fishes is generally cyclic, various factors may influence bony fish breeding such as changes in the duration of sunlight, temperature changes, moon stages and presence of spawning areas. Bony fishes show at least three types of embryonic development:  egg layers (oviparous), egg retainers (ovoviviparous) and live bearing (viviparous).  Depending on the species, fish parents (male and/or female) may scatter, hide, guard or brood eggs.  There is great variation in the development stage at which offspring are released from the parent fish.  The number of offspring is inversely related to the chance a single egg has to reach maturity and reproduce; in general, species whose eggs have little chance to reach maturity lay the most eggs.  For the most part, many species give no care to their eggs or young.