Abstract

A study was undertaken to determine the protein requirements of the Patagonian blennie (Eleginops maclovinus) juveniles as well as the metabolic response of intermediary metabolism enzymes. For this, six isoenergetic and isolipidic diets were formulated, containing different protein levels of inclusion (from 9% to 44% dry weight) based on fish meal. Each diet was assigned to triplicate groups of 40 fish, with an initial mean average weight of 40 g, and fed to satiety for 98 days. Fish fed the 9% protein diet rejected feed and lost weight at the end of the trial, while the other experimental groups gain weight, being weight gain directly correlated to dietary protein. feed efficiency (FE) increased with dietary protein while protein efficiency ratio (PER) and nitrogen retention (% N intake) remained constant when dietary protein was above 15%. No significant increase of weight gain or nitrogen retention (g kg ABW(-1) day(-1)) was observed when dietary protein was above 30% of inclusion. Below 30% of dietary protein a significant decrease in digestibility was observed, being the apparent digestibility coefficients (ADCs) of feed, protein and energy compromised at low dietary protein levels. An exponential model of regression best fitted data correlating dietary protein to specific growth rate (SGR) and dietary protein to nitrogen retention (g kg ABW-1 day-1). Based on that model, dietary protein required for maximum growth and nitrogen retention was 34.7% and 35.7% of inclusion, respectively and dietary protein required for maintenance of growth and body nitrogen was 8.9% and 10.8%, respectively. At the end of the trial differences in whole body weight were observed for fish fed protein levels below 30%, increasing fat content with the increase of dietary protein. No variation pattern was seen for HSI or VI in this experiment. Specific activity of hepatic amino-acid catabolism enzyme ALT significantly varied with dietary protein, while AST and GDH enzymes were not changed by dietary protein. The lipogenic malic enzyme (ME) and glucose-6-P-dehydrogenase (G6PDH) were not correlated with dietary protein, unlike fatty acid synthetase (FAS) which increased with dietary protein. The activity of gluconeogenic enzyme fructose-1,6-biphosphatase (FBPase) augmented with dietary protein, while pyruvate kinase (PK) enzyme decreased when dietary protein was higher than 22%. No significant response to dietary protein was observed for GK and HK enzymes. (C) 2014 Elsevier B.V. All rights reserved.