Archer fish

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Archer fish
Archerfish (Toxotes jaculatrix)

Archerfish ( Toxotes jaculatrix )

Systematics
Perch relatives (Percomorphaceae)
Carangaria
Order : Carangiformes
Family : Toxotidae
Genre : Archer fish ( Toxotes )
Type : Archer fish
Scientific name
Toxotes jaculatrix
( Pallas , 1767)

The archer fish or spray fish ( Toxotes jaculatrix ) belongs to the family of the archer fish (Toxotidae). The perch-related fish is about 20 cm long and up to twelve years old. It stands out due to its almost straight forehead and back line and an upper mouth. His name comes from his unique hunting technique, in which he shoots insects from surrounding bank plants with a jet of water.

Occurrence

The archer fish is native to the tropical brackish water areas near the coast from the Red Sea via India , China , Thailand , the Philippines to Australia . It is most commonly found in the estuaries and lagoons of mangrove forests . Since the brackish waters are very shallow there, they are subject to strong fluctuations in temperature (23 to 28 ° C) and salinity during the tides . This requires a particularly high ecological tolerance (Euryökie) and has presumably led to the fact that only a few species of archerfish have formed. In addition to Toxotes jaculatrix , six other species of the archerfish genus ( Toxotes ) are known. External gender differences as well as subspecies do not occur in archer fish.

Social behavior

Species poverty corresponds to a relatively high number of individuals. This explains the noticeably conflict-ready behavior towards its conspecifics. The competition is also fueled by the scarce food supply in the shallow waters. However, it is peaceful towards alien fish. Toxotes jaculatrix is always in brackish water.

Special hunting technique

Acquisition of prey from archer fish

Like many fish that live close to the surface, the archer fish feeds primarily on insects that are still alive and that have fallen into the water. In order to increase the range of flies , grasshoppers , ants, etc., he has developed an impressive and effective hunting technique. He shoots his prey with a sharp, targeted jet of water from the leaves or stalks of surrounding shore plants. (Even Colisa species can do that.) To do this, he stands up steeply with his whole body, forms a launching "pipe" by pressing the tongue against the upper palatal groove and presses the water out of the slightly open mouth by squeezing the gill cover is right on the surface. This “shooting” is the result of the spitting reflex (“coughing”) present in all fish, which serves to remove what cannot be eaten from the gill trap and from the oral cavity (see also the spitting of the Balistidae ).

On the one hand, the steep angle of launch makes it easier to calculate the trajectory, on the other hand, the insects fall relatively close into the water and can quickly be secured as “their own prey”. Since the eyes remain under water, the calculated refraction angle between water and air can also be kept small. The jet pressure and target accuracy have been developed surprisingly well. Some specimens only hit objects a few centimeters at a distance of four meters.

The archerfish also adjusts the strength of the water jet to the size of the target by varying the amount of water while maintaining the same jet speed. If the first "shot" was unsuccessful, the fish tries again (even several times).

Aquarium keeping

Archer fish can be kept in very small groups (competition!) In fresh water , brackish water or sea water. A brackish water aquarium , however, best meets the requirements.

The water should have a temperature between 25 and 30 ° C. The aquarium should be around 2 meters long and only be filled up to a third in order to be able to imitate the natural habitat well. At the top of the aquarium you can let insects fly and watch the acquisition of prey. If the imitation of the natural conditions does not succeed, the fish quickly lose interest in their spectacular hunting technique.

For a long time it was considered difficult to rear archer fish in aquariums, as little is known about their reproductive behavior in their natural range. Even today, practically all archerfish available in the trade are not offspring, but wild-caught. Probably the world's first successful rearing of archer fish in human care was achieved in 2011 by Wilhelma in Stuttgart .

Scientific research

The researchers have not yet fully unraveled the peculiar and physically very interesting hunting technique. In experiments with operant conditioning it could be shown that the archer fish can not only differentiate between real prey and dummy after a short time, but also learns the relationship between size and distance of its prey very quickly. He adjusts the amount of water fired to the size of his prey in order to save energy.

Individual evidence

  1. ↑ a b Thomas Schlegel, Christine J. Schmid, Stefan Schuster: Archerfish shots are evolutionarily matched to prey adhesion . In: Current Biology . tape 16 , no. 19 , October 10, 2006, p. R836-R837 .
  2. ↑ Archer fish offspring in the Wilhelma. Retrieved March 15, 2015 .

Web links

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