Composition of gastrointestinal content, protease and lipase activities in summer and winter of four freshwater siluriforms (Teleostei: Actinopterygii) with two different feeding habits

ABSTRACT The aim of this study was to determine the composition of gastrointestinal content and protease and lipase activities in summer and winter as well as to evaluate the relationship between digestive enzyme activity and centesimal composition of gastrointestinal content and feeding habits of two omnivorous species, Rhamdia quelen (Quoy & Gaimard, 1824) and Pimelodus maculatus (LaCèpede, 1803), and of two detritivorous species, Loricariichthys anus (Valenciennes, 1835) and Hypostomus commersoni (Valenciennes, 1836). The activities of pepsin, trypsin, chymotrypsin, and lipase, and the levels of proteins and lipids in the gastrointestinal tract, were evaluated. The enzyme activities were not related to the centesimal composition of gastrointestinal content or feeding habits. This finding could be associated with the variations of nutrient availability over time in the environment, as was observed in the centesimal composition of food ingested by the fish in summer and winter. The analyzed enzymes exhibited a constitutive character in these species; that is, the digestive enzymes are always available in the gastrointestinal tract to digest any food that the fish may find as an adaptation to better utilize the nutrients available in the environment in winter and summer.

摘要 本研究旨在明确夏冬两季两种杂食性鱼类——银身短尾鲶（Rhamdia quelen, Quoy & Gaimard, 1824）与斑翼胸鲶（Pimelodus maculatus, LaCèpede, 1803），以及两种食腐性鱼类——肛护胸鲶（Loricariichthys anus, Valenciennes, 1835）和康氏下口鲶（Hypostomus commersoni, Valenciennes, 1836）的胃肠道内容物组成、蛋白酶与脂肪酶活性，并探究消化酶活性与胃肠道内容物百分组成、两类鱼类摄食习性之间的关联。本研究检测了胃蛋白酶（pepsin）、胰蛋白酶（trypsin）、胰凝乳蛋白酶（chymotrypsin）及脂肪酶（lipase）的活性，同时测定了胃肠道内蛋白质与脂质的含量。结果表明，消化酶活性与胃肠道内容物的百分组成及鱼类摄食习性并无关联。该发现或与环境中养分可利用性随时间的波动相关，这一点可从夏冬两季鱼类摄食食物的百分组成中得到印证。本次分析所涉消化酶在上述物种中表现出组成型表达特征，即胃肠道内始终存在可消化任意食物的消化酶，这是鱼类为适配冬夏两季环境中可利用养分而演化出的适应性策略。