Morphological Variation in Feeding Traits of Native Hawaiian Stream Fishes

Abstract

The five native species of amphidromous gobioid fishes inhabiting Hawaiian streams were compared for dentition, gut length to body length ratios, intestinal convolution, gill raker morphology, position of mouth, and diet. Based on morphological comparisons, three manipulative modes of feeding are indicated, as follows: picking-biting, rock scraping, and sediment foraging. Comparisons indicated a surprising predominance of algae in the diet of all species despite various degrees of morphological specialization for their use. Avoidance of competition for algae was therefore suggested as a potential factor influencing species interactions and community organization. Differential preference among native gobioids for stream invertebrates may also provide mitigation for competitive interactions. Variation in food availability in the benthic landscape of Hawaiian streams, possibly regulated by stream flow and periodic disturbance, is hypothesized as being an important determinant of fish community structure. Human-induced alteration of factors that regulate food availability could therefore influence stability of native fish populations through disturbance of their food base.