Freshwater hatchetfish
Carnegiella marthae
Hatchetfishes ( Gasteropelecidae ) are a family of the order Characins with currently nine species in three genera, the South and Central America are located in. The eye-catching body shape, reminiscent of an ax, motivated the scientific naming (Greek gaster = belly, big pelekis = ax ) and the German popular name. Some of the species are popular aquarium fish.
Dissemination
The distribution of Hatchetfishes includes all states of the South American continent (except Chile ) and Panama. In Panama, the northern limit of the range, only the spotted Beilbauchfisch occurs ( Gasteropelecus maculatus ). All other types of Hatchetfishes exclusively inhabit waters of the northern and central South America to the Río de la Plata in Argentina.
Features
The unique body shape of the Hatchetfishes is a specialization of life on the water surface Represents the back profile is almost horizontal, curved breast and belly line, however, strongly curved, and the mouth upper constant. In relation to their body size, they have an enlarged shoulder girdle with a strong musculature of the wing-like pectoral fins which accounts for up to 25 % of body weight. Species of the genus Carnegiella have no adipose fin, unlike the species of the other two genera. Depending on the nature Hatchetfishes reach a length of between about 30 and 90 mm.
Hatchetfishes are able to overshoot the water surface and several meters "fly" straight through the air. You create it a buzzing sound. Since the movement through the air is the active propulsion attributed by hitting the pectoral fins, they are often seen as the only true flying fish called, in contrast to the marine, flying fish of Exocoetidae family who with the help of its wing-like pectoral fins only in gliding moving through the air. The meter -wide jump out of the water is probably not hunting or grasping the prey, but is only an escape dealing with security threats from the water, such as the attacks. Predatory fish by
Whether Hatchetfishes really have an active flight ability is controversial among experts. While SH Weitzman could observe only indirectly in their own words the flight and back led the whirring noise as a plausible explanation for the beating of the pectoral fins, high-speed imaging and motion analysis in the laboratory could not confirm this. Rather, the pectoral fins were beaten against the water surface, while the caudal fin propulsion made until the fish could leave the water only in the starting phase. In the actual flight phase, the pectoral fins were not used, but only the tail fin, which produced the whirring noise. The observed in the laboratory movement but do not seem to explain the longer distances that can be achieved in nature.
Way of life
Hatchetfishes live both in water streams such as streams, rivers and streams as well as in still waters such as ponds, lakes and temporarily flooded floodplains. Keep preferably just below the water surface, in areas where this is largely free of plants. To escape predators such as Pike Characin they remain almost without exception in the immediate vicinity of protection offered water zones that are dominated depending on the type of water and shading degree of dense water plant canopies, the water reaching marsh or terrestrial plants or highly branched woody debris accumulations.
The waters are where live Hatchetfishes predominantly very soft, low mineral and sour. Often, the total is - and carbonate under the Nachweißgrenze at pH values below 5 to be rare populations found in medium to hard and slightly alkaline water. The Glasbeilbauchfisch ( Carnegiella myersi ) was captured, for example, both in very soft, acidic waters and in waters with total hardness and carbonate hardness of 15 ° dH and a pH value to 7.7. Depending on the species, habitat and season the water temperature can be below 20 ° C to about 30 ° C.
Hatchetfishes live socially in large groups, at times in flocks. They hunt mainly small, fallen on the water surface insects and spiders but also living in water surface near insect larvae.
System
After the revision of Stanley H. Weitzman and Lisa Palmer 2003 are currently nine types described in three genera.
- Carnegiella Eigenmann, 1909 Black Swing Beilbauchfisch ( Carnegiella marthae ) Myers, 1927
- Glasbeilbauchfisch ( Carnegiella myersi ) Fernández- Yépez, 1950
- Carnegiella schereri Fernández- Yépez, 1950
- Marbled Beilbauchfisch ( Carnegiella strigata ) ( Günther, 1864)
- Gasteropelecus levis ( Eigenmann, 1909)
- Spotted Beilbauchfisch ( Gasteropelecus maculatus ) Steindachner, 1879
- Silberbeilbauchfisch ( Gasteropelecus sternicla ) (Linnaeus, 1758)
- Platinbeilbauchfisch ( Thoracocharax securis ) De Fillipi, 1853
- Thoracocharax stellatus ( Kner, 1858)
Since significant differences in the coloration of different populations of the same species occur, is not excluded from Weitzman and Palmer, that there are still undescribed species. So in mid-2013, it was found that there is a swarm of very closely related and externally hardly or not distinguishable ways in which marbled Beilbauchfisch. The smaller Black Swing Beilbauchfisch is phylogenetically within the C. strigata - species flock and is more closely related to the occurring in the northwestern Brazil in Barcelos C. strigata population as this example with the occurring in the western state of Acre C. strigata population. C. strigata is thereby paraphyletic a group to be split in the future, more types. The genus is paraphyletic with Gasteropelecus Gasteropelecus maculatus as basal sister species of all other Beilbauchfische and Gasteropelecus sternicla as a sister group to the genus Carnegiella. Sister group of the Hatchetfishes total is the Bryconidae family with two subfamilies Bryconinae and Salmi Ninae, relatively large fish with trout -like exterior.