Shoaling and schooling
A swarm of fish is a fish that, swims along with many other fish of the same species, but also with other species. The individual fish swim largely parallel to each other, in approximately the same distance and in the same direction. Schooling fish can form such a swarm all year round, seasonal or only on occasion. Swarm behavior is also known from birds, cuttlefish, krill and many other animals. Corresponding formations of mammals called herds.
In a smooth transition can be distinguished from the schooling fish such animals, the only live together in groups ( schools).
True Gregarious
True schooling fish are characterized by a constant distance Individual, disorientation isolated animals, coordinated movement of the entire swarm, communication between individuals of the swarm, and usually lifelong guidance in the swarm. In a swarm, swim usually animals of the same species and the same age.
The real swarm fish include, for example, the herring, but other species of fish in open sea. In freshwater true schooling fish are rare. Examples are Haibarben, Rummy or the oblique float the genus Thayeria, which still predominantly the criteria for a true shoaling fish are met. Basically, there are animal species that live under high predation pressure. The species have characteristics that promote the cohesion of the swarm, in the case of these freshwater species, there are certain features of the drawing.
Loggerhead schooling fish
Loggerhead schooling fish or group of fish showing in larger groups in existence of external factors threatening tendencies to swarm formation. It also animals of different species and age classes may be grouped. In smaller groups, or in the absence of confounding factors change the behavior, but isolated animals are never disoriented in space or under a high individual stress.
This group includes many freshwater fish from the orders of the tetras and barbs. They meet numerous criteria for schooling fish, yet they differ in some, important points of real schooling fish. So the cardinal tetra is in Artaquarien even in large groups of several hundred individuals rather an easy territorially organized fish, the individuals are distributed throughout the available habitat and especially the males boundaries where small individual areas from which they defend against conspecifics. Only in the presence of external interference factors, such as predators in nature, the animals gather to a swarm and then show the criteria for schooling fish.
Other examples of gregarious group fish among the freshwater fish are the armored catfish of the genera Aspidoras, Brochis and Corydoras or a series of loaches of the genus Botia. These animals live together in nature in schools, which may well include several hundred to a thousand individuals. The joint activities include primarily food intake, for example on open, unprotected feeding grounds ( sand banks ), where the school or large group individuals provides appropriate protection. Otherwise no other criteria for schooling fish apply to these animals.
Advantages of swarm formation
The swarm formation is connected to the fish with advantages and disadvantages. An advantage is the higher in the swarm for the individual animal likely to survive the attack of a predator. Individual fish can be tracked more targeted and therefore have an attack of a predator also at higher risk if they are unable to bring immediately, for example, in a cave or in a sea anemone in safety. The protection of the flock from predators mainly results from the fact that a robber can keep only a limited number of fish in the eye and can only eat a limited number of fish. So the more fish swimming together, the lower the risk for each individual fish in an attack. On the other hand, a swarm also disadvantages: Large swarms could attract more predators than a small flock or a single fish. Therefore, the number of attacks, and thus the risk of a robber to be eaten, increase with the swarm size.
The higher the risk for a fish, he falls victim to a robber, the more attentive he should look out for predators out and the less time remains for him to eat. One of the main reasons why animals come together to swarm is likely to " see many eyes better" and that swarm every single individual has to spend less time to look for predators out, and thus each animal has more time to eat.
A crucial factor in the question of whether a species lives in shoals, is the distribution of food in the room. Is the food of a particular fish species widely distributed in small portions, so this species may not use this economical food when she swims in shoals. No member of the swarm then would find enough to eat. However, if the food distributed in large portions in space ( eg, swarms of crustaceans ) then has swarm behavior for this species hardly disadvantages because there is enough for everyone, and outweigh the benefits.
In coordinated hunting strategy, schools of fish can be very dangerous for swarms of smaller fish. This can be observed good example for Barracuda, Jacks or perch shoals. Another advantage of the swarm is that the probability to find a mate to reproduce, in the swarm is higher than in solitary lifestyle.
In many fish - including popular aquarium fish, such as the Salmlerarten the genera Hyphesso, Hemigrammus and Paracheirodon to swarm behavior can be observed throughout the year or at certain times. During courtship and mating season but also borders otherwise typical schooling fish quite small areas from which they defend against each other. For merger of the swarm occurs, however, when predators appear. Isolated schooling fish often suffer from severe stress, they show up scared and die in extreme cases soon.