Partial and complete replacement of fish meal with gambusia meal in diets for red tilapia 'Oreochromis niloticus x O-mossambicus '

A 12-week experiment was conducted to evaluate the suitability of gambusia (Gambusia affinis ) fish meal (GFM) as a partial and complete substitute for the protein supplied by herring fish meal (HFM) in diets for red tilapia fingerlings (mean weight 0.42 g). Seven isonitrogenous (35% crude protein), isolipidic (9% fat) and isoenergetic (15.9 kJ DE-g(-1) diets were formulated in which GFM replaced 0.0, 10, 25, 50, 75, 90 and 100% of the protein supplied by HFM. In general, GFM exhibited good potential as a substitute for HFM in red tilapia diets with no adverse effects on growth, feed efficiency, body composition, blood parameters or apparent digestibility of dry matter, protein and gross energy compared with the HFM-based control diet. Growth performance (in terms of final weight, weight gain, per cent increase in weight and growth rate) of fish fed diets containing GFM at 25 or 50% level of replacement for HFM-protein (diets 3 and 4) was statistically higher than for fish fed diets containing GFM at replacement levels >50%. Diet 4 had the best economic efficiency of fish weight gain. Partial or complete substitution of GFM for HFM did not affect feed utilization efficiency (in terms of FCR, FER, PER and APU) or digestibility coefficients of dry matter, protein and gross energy compared with those of the HFM-based diet. Apparent protein digestibility varied little between diets, ranging from 84.2 to 87.3% with no significant differences. Survival of fish fed all the experimental diets (except for fish fed GFM at 90 or 100% level of replacement for HFM-protein) was comparable with that of fish fed the control diet and ranged from 91.7 to 98.3%.