PEARSE FISHES OF LAKE VALENCIA, VENEZUELA 13 



there is opportunity for more species to live in it. The lake, 

 being more uniform as to conditions, contains fewer species. 

 This view is supported by the ecological distribution of the 

 fishes in the lake. The habitats have species in direct ratio 

 to the variety of conditions they possess ten species frequent 

 the shores of the islands; seven occur on the rush covered mud 

 bottom about the margin of the lake; only four are found on 

 the soft ooze in deep water. 



Fishes unquestionably choose particular habitats which in 

 general suit their particular needs. The mataguaro, panaque, 

 and a sardina (Hemigrammus marginatus) were found in 

 turbulent water formations (on the sandy and pebbly shores 

 of islands, in the swift flowing streams), never on muddy 

 bottoms or in quiet water. The chusco (Aquidens pulcher) 

 occurred wherever there were muddy bottoms and quiet 

 water and, as both these conditions were lacking in the swift 

 flowing streams draining into Lake Valencia, the species is 

 confined to the lake itself. Two sardinas, Gephyrocharax 

 valenciae and Creagrutus beni, and a top minnow, Lebistes 

 reticulatus, were found only at the mouths of or in streams. 

 The sardina, Gephyrocharax valenciae, was abundant along the 

 shores of islands and along the rushes on the lake's margin, but 

 was never found in streams or in deep water. Another sardina, 

 Creagrutus beni, was common along the shores of Isla del Euro, 

 but was not found on muddy rush-grown shores. 



The fishes invading all habitats are those in general having 

 a wide range geographically. Among the three examined 

 intensively at Lake Valencia, the guabina is a fish-eater (90 

 per cent); the sardina, Astyanax bimaculatus, feeds on plants 

 (51), insects (30), and fish (15); the anguila eats insects (63), 

 bottom deposits (22), and fish; the chusco, common in all lake 

 habitats, partook largely of snails (49), insects (22), and fish 

 (16). Although these four species are more or less specialized 

 in their food habits, they feed on common ubiquitous foods. 

 The two other species (Rhamdia quelen and Plecostomus 

 plecostomus) of wide geographic range which occur in the 

 Valencia region are largely associated with rivers, but feed on 

 ubiquitous mud and insects. Ecologically the ability of a 

 species to extend over a wide range depends upon an abundant 

 food supply and the ability to invade a variety of habitats. 



