The effect of different plant diets on the growth performance, gastric evacuation rate and carcass composition of Tilapia rendalli

Abstract

The culture of macrophagous fish that naturally feed on plant diets may be the solution to reduce the current dependence on fishmeal. Fishmeal is not only expensive but its supply is not always guaranteed. This study focuses on the growth performance, gastric evacuation rate, gastric transit time and carcass composition of Tilapia rendalli fed fresh plants, to determine the extent to which T. rendalli can utilise fresh plants. Kikuyu grass (Pennisetum clandestinum), cabbage (Brassica oleracea), duckweed (Lemna minor), vallisneria (Vallisneria aethiopica) and fishmeal pellets (control) were offered ad libitum to duplicate groups of T. rendalli for 224 days. Specific Grow Rate (SGR), Protein Efficiency Ratio (PER) and Food Conversion Ratio (FCR) were used to determine the growth performance. Fish fed kikuyu grass attained a significantly (p<0.05) higher SGR and a better FCR than those fed the other plant diets. Fish fed vallisneria lost weight. The serial slaughter method showed that vallisneria was evacuated significantly (p<0.05, ANCOVA) faster and was eaten in significantly (p<0.05) higher quantities than the other diets. Kikuyu grass was evacuated much more slowly and eaten in lesser amounts. The low energy content (14.74 MJ kg -1) of vallisneria may explain its faster evacuation and high consumption levels. Fish fed kikuyu grass had higher protein levels, higher omega-3 fatty acids (25.13%) and higher mineral content than those fed the other experimental diets. Fishmeal fed fish had the lowest content of the omega-3 fatty acids (2.52%). T. rendalli performed better when fed plant diets with higher protein and energy contents. © 2011 Academic Journals Inc.