World Aquaculture 13 Table 1. Ingredient composition of experimental diets (g/100 g). Ingredient Diets 1 2 3 4 5 Fish meal (65 %CP)1 35.8 35.8 35.8 35.8 35.8 Soy bean meal (45%CP) 17.0 17.0 17.0 17.0 17.0 Ground nut cake (48%CP) 19.0 19.0 19.0 19.0 19.0 Yellow corn 19.2 14.4 9.60 4.80 0.00 Discarded cocoa bean meal 0.00 4.80 9.60 14.4 19.2 Cod liver oil 5.00 5.00 5.00 5.00 5.00 Vitamin-mineral premix2 3.00 3.00 3.00 3.00 3.00 Methionine 0.30 0.30 0.30 0.30 0.30 Carboxymethylcellulose 0.70 0.7 0.70 0.70 0.70 Chromic oxide 0.50 0.50 0.50 0.50 0.50 1Values in bracket (crude protein) 2Per Kg of diet: Vit. A 1,000,000 IU; Vit. D3 600,000 IU; Vit. E 12,000 IU, Vit. K315mg; Vit. C 12,500mg; Vit. B1 250mg; Vit. B2 1,750mg; Vit. B6 875; Vit. B12 2,500mg; Ca-Dpantothenate 5000mg, Nicotinic acid 3,750mg; Folic acid 250mg; Co. 24,999mg; Cu 1,999mg; Fe 11, 249mg; Se (Na2SeO3.5H2O) 75mg; I (KI) 106mg; antioxidant 250mg. Table 2. Proximate composition of experimental diets (percent dry matter). Parameter Diets 1 2 3 4 5 Moisture 12.5 11.7 11.3 11.5 11.1 Crude protein 40.2 40.4 40.6 40.4 40.8 Crude lipid 12.2 12.5 12.5 12.3 12.6 Crude fibre 7.50 6.40 6.20 6.20 7.20 Ash 15.8 14.3 14.6 14.4 14.7 NFE1 11.8 14.4 14.8 14.6 13.6 Gross energy (KJ/g) 18.1 18.5 18.6 18.5 18.4 1NFE (nitrogen free extract) = 100- percent crude protein + percent crude Lipid + crude fiber + percent ash) Experimental tanks and feeding trial Fifteen glass tanks filled with 40 L of water were used for the study. The five dietary treatments were replicated three times. The tanks were aerated to maintain the level of dissolved oxygen at 7.5-8.3 throughout the experimental period. The pH and dissolved oxygen levels in the experimental tanks ranged frin 6-8 and 27-30ºC. Healthy juvenile African catfish (11.8±0.68g) purchased from Esabol Fish Farm, Oba-Ile Estate Akure were acclimated for two weeks and stocked at 12 fish per tank. The fish were fed to satiation twice daily between 0800-0900 and 1600-1700 for 70 days. Weight measurements were taken biweekly for assessment of fish performance. Each day before feeding, the fecal matter in the tanks was siphoned and 30 percent of the tank water was replaced every three days to maintain the water quality. Growth performance was calculated after Castell and Tiews (1980) as follows: mean weight gain = final mean weight – initial mean weight; specific growth rate =100 x (loge final weight-Loge initial weight/ culture period in days; feed conversion ratio = weight of feed fed/fish weight gain. Analytical Methods Proximate and mineral analysis of fish samples At the end of the experiment the fish were not fed for 24 h. The catfish were weighed and four fish from each tank were sacrificed for proximate analysis (three replicate analyses per treatment) according to the methods of AOAC (1990). About 2.0 g of the samples were ashed for 48 h at 480ºC. After the ash had cooled to room temperature, 6 mL of HCl was added and the mixture was brought to the boiling point. After cooling to room temperature, another 2.5 mL of 6N HCl was added and the mixture was warmed to dissolve all the solutes. The solution was then cooled and diluted to 25 mL with distilled deionized water. Then the minerals (Mg, Ca, K and Fe) were measured by Atomic Absorption Spectrophotomry (AAS). Phosphorus content was analysed using the Vanadomolybophosphoric acid colorimetric method 4500p with slight modifications. To 3 mL of the diluted solution of the sample, 3 ml of vanadatemolydate reagent was added and the phosphorus concentration was measured spectrophotometrically at 430 nm. Blood analyses After the feeding trial, the fish were starved for 24 h and blood samples were collected by cardiac puncture and put into tubes containing 15 IU of heparin/ml of blood. The blood was centrifuged at 4,000 g for 5 min and the plasma was extracted and stored at -20ºC. Hematological examinations of the red blood cells (RBC), haematocrit (PCV), haemoglobin (Hb), erythrocyte sedimentation rate and the white blood cell counts were carried out using the methods of Svobodova et al. (2006). Statistical analyses Growth, carcass, minerals data and blood parameters were analysed using one-way analysis of variance (ANOVA), followed by Duncan’s new multiple range test (Duncan 1955) at the
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