In vitro protein digestibility of different grow-out stages of spotted rose snapper (Lutjanus guttatus, Steindachner, 1869)

Abstract

The aim of this study was to compare in vitro protein digestibility between two groups of fish, at early (21 g) and late stages (400 g) of spotted rose snapper Lutjanus guttatus, to evaluate the degree of hydrolysis (DH) and total amino acid release (TAAR) using crude extracts from stomach, pyloric caeca and intestine of 13 protein ingredients including marine, animal and plant meals. Degree of hydrolysis and TAAR were measured by a pH-Stat method, and the PAGE-Zymogram was also used as complementary technique. Differences in DH were found between both grow-out stages mainly in the alkaline hydrolysis phase. Fish and squid meals (marine sources) had the highest DH and TAAR, followed by porcine meat and poultry meal by-products from recycling sources, and soybean and canola meals (plant sources), which represent better protein sources for use in practical diets. Stomach zymograms showed two pepsin isoforms in both grow-out stages. Pyloric caeca and intestine zymograms showed five bands with proteolytic activity in the early grow-out stage, whereas four additional bands were found in late grow-out stage. Alkaline proteases were identified as serine and metalloproteases. Thus, L. guttatus presents an ontogenetically differentiated digestive enzyme pattern that modifies the DH and TAAR of different protein sources.