Use of energetic substrates after feeding in two Amazon Characidae fish: Colossoma macropomum and Brycon amazonicus

Abstract

Specific dynamic action (SDA) can be defined as the accumulated energy expended in the process of ingestion, digestion, absorption and the assimilation of the food, and there is substantial evidence that protein synthesis is responsible for most of the SDA in fish. A technique developed by Lauff and Wood (Journal of Comparative Physiology B, 1996, 165, 542; Journal of Comparative Physiology B, 1996, 166, 501), called instant quantification of energetic substrate usage, allows quantifying the utilization of lipids, carbohydrates and proteins as energy fuel in a given time, including the SDA period, based only on measurements of oxygen consumption and carbon dioxide and nitrogen excretion. Matrinxã and tambaqui are two important Amazonian fish farmed and marketed worldwide. Despite being considered omnivorous fish, they present specificities in growing, converting food and behaving, suggesting some differences in their digestive system. In the present work, we used specimens of tambaqui and matrinxã to measure metabolic rate, excretion of nitrogen and carbon dioxide and to calculate the relative and absolute use of proteins as an energy source in experimental animals. Our results suggest that small matrinxãs quickly start the anabolic process in the postprandial period and, in larger tambaqui, it occurs late, but present a longer duration. Matrinxã also shows a higher basal nitrogen excretion, which increases faster after feeding. The substrate usage calculations support the hypothesis that in small matrinxã, in initial stages of the postprandial period, the fish use mainly endogenous carbohydrates as fuel, changing into proteins in further stages.