 The genus Gnatholebias, |
Gnatholebias Costa 1998 was erected for Pterolebias zonatus Myers, 1935 and Pterolebias hoignei Thomerson, 1974. These fishes have a shorter body, are more laterally compressed, and are higher, than other Pterolebias spp. This morphological data, plus additional osteological and genetic evidence, made the distinction clearcut. ‘Gnatho-’ is derived from the Greek for jaw, as this genus has elongated jaws
The two members of this genus live (and are often sympatric) in the upper tributaries of the Orinoco, at the foothills of the Andes in northwest Venezuela. Their habitats are isolated pools that have marginal vegetation, and are situated in open landscape, with muddy yellow or grey clay bottoms. Mostly the pools are near the rivers that come from the higher mountain range.
During the rainy season the terrain is often flooded, and the pools become connected to the rivers. In that event, predators including cichlids and prey such as Poeciliids can migrate into the pools. Later, in the dry season, pools often dry up totally. As water levels become lower, vegetation remains only on the edges of the pools. The water becomes milky due to dispersal of sediment. Collecting these annual fishes is extremely easy as waters are at the lowest level, before complete evaporation. However, collecting during the high water period is almost, if not totally, impossible, due to the steep walls and thick vegetation at the edges of the pools.
Together with Gnatholebias we can find Terranatos, Llanolebias and Austrofundulus spp.; and, as stated earlier, after flooding non-annual fishes including Rivulus, Cichlids and Poecilia spp. may also be present.
Behaviour:
As a typical annual, Gnatholebias dives in the bottom layer to bury their eggs. Because of their larger size, a deep soft bottom is required. Females are much smaller than males. The genus is very productive. Eggs need 5-10 months to develop. From the type of terrain they inhabit, we can tell the waters never reach low pH (acidic), because the clay has a potent alkaline buffering capacity. Thus throughout their life these fish are to be kept in neutral or alkaline water.
Breeding is not too problematic, but best results are achieved by experienced breeders with knowledge of the fishes’ habitat and specific demands. Growth is rather quick, and a lot of food must be given to ensure all fry grow equally. Reproduction starts when the fishes are not even half their final length.