BODY SHAPE, DIET AND ONTOGENIC DIET SHIFTS IN YOUNG FISH OF THE SINNAMARY RIVER, FRENCH-GUIANA, SOUTH-AMERICA

A total of 1468 young fish representing 66 taxa from the Sinnamary Riv er, French Guiana was classified by complete cluster analysis of mean relative body width and mean relative body height into four groups. Th ese had anguilliform, disciform, flat or intermediate body shapes and belonged chiefly to Gymnotiformes, Perciformes, Siluriformes and Chara ciformes, respectively. Several of the taxa shifted from one to anothe r body shape during ontogenesis. Seven diet groups were defined by com plete cluster analysis. Among these, six groups were represented by ca rnivorous fish. The three most frequent groups had diets of (1) mainly insect larvae and small crustaceans, (2) insect larvae, and (3) predo minantly terrestrial insects. The majority of the fish taxa showed ont ogenetic diet shifts. Carnivorous fish usually switched from small-siz e prey, such as small crustaceans, to intermediate-size prey, such as insect larvae and/or to large-size prey, such as insects and/or fish. However, taxa differed in their capacities to switch from small pray t o intermediate and/or to large prey. Taxa of different body shapes had significantly different diets. Disciform fish fed mainly on aquatic i nsect larvae and terrestrial insects but also. in small amounts, on sm all curstaceans. Most anguilliform taxa ate insect larvae. Individuals belonging to the depressiform or intermediate morphotype had varied d iets ranging from plant debris and substratum to fish. (C) 1998 The Fi sheries Society of the British Isles.