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,Rhamdiaquelen(Quoy & Gaimard, 1824) andPimelodusmaculatus(LaCèpede, 1803), and of two detritivorous species,Loricariichthysanus(Valenciennes, 1835) andHypostomuscommersoni(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.
Highlights
The digestive enzymes in vertebrates are synthetized and secreted throughout the gastrointestinal tract
The highest pepsin activity rate per mg protein was detected in the stomach of the omnivorous species (R. quelen and P. maculatus) in both seasons, and for both species, the higher activity of this enzyme occurred in the winter (Fig. 5)
The highest trypsin activity rate per mg protein in both seasons was detected in L. anus, H. commersoni and P. maculatus (Fig. 7)
Summary
The digestive enzymes in vertebrates are synthetized and secreted throughout the gastrointestinal tract. The appropriate synthesis and levels of digestive enzymes may be affected by environmental factors that vary over time (Garcia Carreño et al 2002, LópezVásquez et al 2009). Fish are usually classified according to feeding habits, and it is expected that digestive enzyme activities reflect the feeding habits and the diet of the fish (Fernández et al 2001, Langeland et al 2013). Most studies dealing with digestive enzyme activities were performed with species raised in fish culture conditions and fed the same diet for at least one month (García Carreño et al 2002, Ren et al 2011, Aguilera et al 2012, Azarm et al 2012, Leef et al 2012)
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