Effect of vegetable based diets on growth, intestinal morphology, activity of intestinal enzymes and haematological stress indicators in meagre (Argyrosomus regius)

Abstract

A performance trial (88days) was undertaken to evaluate the effects of replacing fishmeal (FM) and/or fish oil (FO) in a practical formulation for juvenile meagre with a mixture of plant proteins (PP) and vegetable oils (VO), in terms of growth performance, nutrient utilization, intestinal structure and functionality and several haematological stress indicators. Twelve homogenous groups of 75 meagre (mean initial body weight: 55.4±3.5g) were fed one of four isonitrogenous (51% DM), isolipidic (17% DM) and isoenergetic diets (22.9MJ·kg−1 DM). A FMFO diet was formulated with high levels of marine protein sources (45%) and fish oil as the sole fat source. Based on this formulation, 60% of fish oil was replaced by a blend of vegetable oils (diet FMVO). Two other diets were formulated with a 50% replacement of marine proteins by plant protein sources. One of these plant protein-rich diets contained fish oil as the sole fat source (PPFO), while in the other 60% of fish oil was replaced by a blend of vegetable oils (PPVO). Growth of meagre was not significantly affected (P>0.05) by the replacement of fishmeal and fish oil by ingredients of vegetable origin. Meagre fed the plant-protein rich diets (PPFO and PPVO) showed a significant enhancement (P<0.05) of feed efficiency (FE) and retention of protein (PER), lipids and energy. Dietary lipid source had no effect (P>0.05) on FE, PER and nutrient retention. Dietary treatments had no effect (P>0.05) on the whole-body composition of fish. This good tolerance towards plant protein sources exhibited by meagre was further corroborated by the apparent digestibility data of individual ingredients. As expected, fish fed the blend of vegetable oils showed a reduction of total n-3 series fatty acids and a concomitant increase of total n-6 series fatty acids. Dietary changes on both protein and lipid sources did not affect (P>0.05) intestinal morphology, activity of intestinal brush border enzymes and selected haematological stress indicators in fish. Signs of liver steatosis were found in meagre, but not directly associated to dietary changes of protein and lipid sources. Meagre showed a good ability to cope with vegetable based diets. However, although not statistically significant in this short-term trial, present data also suggests possible detrimental effects on fish performance associated to concomitant high inclusion levels of plant protein and vegetable oils.