GAWLICKA, A.*; HORN, M.H; FREEMAN, C.T.; KIM, K.H.: Comparative ultrastructure of the intestinal epithelium in three species of atherinopsid fishes with different diets

We explored possible diet-related specializations of the gut epithelium in stomachless fishes by comparing the surface area of the brush border and qualitative features of the absorptive cells in three closely related species of New World silversides (Atherinopsidae) using electron microscopy. Proximal, middle and distal regions of the intestinal surface of Atherinops affinis from both kelp forest and bay-estuarine habitats, and Atherinopsis californiensis and Leuresthes tenuis, both from open coastal habitats, were compared within and among species. A. affinis is generally a carnivore in kelp-forests and a herbivore in at least some estuaries, whereas A. californiensis is mainly carnivorous and L. tenuis more strictly carnivorous. Relative gut length in these species generally follows the expectations that carnivores have shorter guts than herbivores and omnivores have guts of intermediate length. Comparisons completed to date indicate that overall absorptive surface area of the microvilli is largest in estuarine A. affinis, intermediate in kelp-forest A. affinis and L. tenuis and smallest in A. californiensis. Both A. affinis populations and A. californiensis showed a general pattern of decrease in epithelial surface area from proximal to distal regions, whereas L. tenuis showed the opposite pattern. Our results suggest that a larger absorptive surface is associated with herbivory in these fishes but that trade-offs also occur between gut length and microvillar structure to effect total absorptive surface area of the gut.