Synopsis
Examination of 681 individuals of electric knife-fishes, Eigenmannia macrops, from the Orinoco River, Venezuela, revealed a pattern of morphological diversity which covaried with habitat. Fishes from the caños (small stream tributaries) are on average smaller than those from offshore habitats and lagoons. Even at the same body size the tails of caño fishes are relatively shorter, their bodies are deeper, and their heads are relatively wider than those from other habitats. Caño fishes are more different from fishes of the deep channels than from those of the shallow channels, beaches, or lagoons. Several factors are examined for their possible relationship to the origin of the observed diversity including electrophysiology, locomotory adaptation, growth rate and ecology. The problems of genetic versus physiological bases of morphological variation are addressed.
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Lundberg, J.G., Stager, J.C. Microgeographic diversity in the neotropical knife-fish Eigenmannia macrops (Gymnotiformes, Sternopygidae). Environ Biol Fish 13, 173–181 (1985). https://doi.org/10.1007/BF00000928
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DOI: https://doi.org/10.1007/BF00000928