EFFECTS OF SUBSTITUTING COTTONSEED MEAL PROTEIN WITH Pro sopis juliflora SEED MEAL ON NILE TILAPIA GROWTH

Abstract

By the year 2020 there will be need for an additional 37 million tonnes of farmed fish per year, globally. However, limited availability and high cost of high quality feed stuffs hinders aquaculture development in Sub-Saharan Africa. Therefore, replacing highly demanded and costly ingredients, such as cottonseed meal (CSM), with cheaper, nutritious and locally available ingredients, like Prosopis juliflora seed meal (PJSM), is inevitable. This study evaluated the effects of substituting CSM protein with PJSM in fish diets on growth of Oreochromis niloticus. PJSM was ensiled for 28 days, using 5% formic acid. Ensiled and non-ensiled PJSM was used to replace CSM protein in a control diet of 250 g kg-1 protein, at 25, 50, 75 and 100%. Nine treatment diets were tested in triplicate. The growth performance experiment was conducted for 87 days in a completely randomized design, using 27 aquaria. Each aquarium was stocked with 30 frys of O. niloticus, weighing between 0.32-0.35 g. Fish were fed twice daily, 10 am and 4 pm, at a feeding rate of 10% live body weight in the first month and 5% in subsequent months. Length and weight were measured fortnightly. The bivariate analysis of weight and length was used to estimate growth parameters including maximum growth rate, weight at Critical Standing Crop (CSC), maximum length and maximum weight for each experiment. Analysis of Covariance (ANCOVA) was used to compare performance of the test diets. Ensiling led to a significant (p<0.001) reduction of crude protein in PJSM. Flavonoids, phenols and saponins were destroyed upon ensiling PJSM whereas alkaloids and tannins were not eliminated. Copper, Iron, Zinc, Nitrogen, Phosphorous and potassium were significantly ( p<0.05) reduced in ensiled PJSM. Inclusion of non-ensiled PJSM at 50%, led to a significant (p<0.001) improvement in the growth of O. niloticus, compared to control diet. There was no significant difference on growth performance of O. niloticus upon replacement of CSM with ensiled PJSM, at 0, 25, 50 and 75%, except at 100%, where growth per formance of the fish was significantly (p=0.0102) reduced. Dissolved oxygen, pH and temperature did not influence growth of fish for all the diets. Survival for fish fed diets containing ensiled PJSM ranged between 81.11-85.56% compared to 72.22-81.10% for fish fed diets containing non-ensiled PJSM. Thus, non-ensiled PJSM can be used to substitute CSM up to 50 % whereas ensiled PJSM can be used to replace CSM up to 75% in O. niloticus diets.