14 June 2010 be ascribed to better digestibility and mineralization in fish fed diets with DCM. Also there was a general increase in the gross energy of the diets as a result of inclusion of DCM. The growth performance of the fish (Table 3) showed that DCM can replace up to 75 percent of yellow corn in the diets of African catfish. However, replacement at 25 percent produced significantly better performance than other treatments including the fish fed the control diet. Replacement at 100 percent led to very poor growth performance. Carcass proximate composition (Table 4) showed a decreasing trend in the moisture content of the fish as a result of inclusion of DCM in the diets. There was also a general increase in carcass protein, lipid and ash content attributable to the effect of DCM in the diets. However, while the carcass ash was improved significantly, protein and lipid content of the fish were improved marginally. Table 5 shows that the effect of the DCM on the diets was mostly reflected in the mineral composition of the fish, because the fish that received diets of DCM had significantly higher Ca, P, Mg and Fe than the fish fed the control diet. However, the K content showed a decreasing trend with increasing levels of DCM in the diets. Hence, fish fed the control diet contained significantly higher K than the fish fed other diets. Also, the Ca, Mg and Fe contents of the fish showed an increasing trend with increasing levels of DCM in the diets. The hematological profile of the fish (Table 6) showed no noticeable change related to treatment. There were no significant differences among the treatments for any of the measured parameters. Table 3. Growth performance of African catfish fed on varied levels of discarded cocoa bean meal. Mean values1 Diets 1 2 3 4 5 Initial weight (g) 11.4±0.4 12.3±0.8 11.1±0.6 11.7±0.9 12.5±0.8 Final weight (g) 27.9b±4.8 43.7c±2.1 33.3b±5.0 32.5b 16.7a±0.6 Weight gain (g) 16.4b±4.6 31.5c±2.1 22.2b±5.2 20.7b±4.7 4.16a±0.3 Percent weight gain 143.1b 255.7c 201.7bc 177.1b 33.4a Specific growth rate 1.25b±0.2 1.80c±0.1 1.56bc±0.3 1.44b±0.2 0.41a±0.0 Feed conversion ratio 1.70b±1.1 1.01a±0.1 1.43ab±0.4 1.34ab±0.2 3.27c±0.6 1Means in each row with the same superscript letters are not significantly different (P>0.05) Table 4. Proximate composition of the fish after experiment (g/100 g dry matter) Mean Values1 Diets 1 2 3 4 5 Moisture 9.00b±1.9 4.88a±0.7 4.83a±0.9 4.82a±0.9 4.81a±1.1 Crude protein 64.9a±0.6 65.6a±1.6 65.7a±0.6 65.9a±1.2 65.9a±0.8 Crude lipid 13.2a±0.8 13.4a±1.9 13.5a±1.2 13.4a±2.0 13.7a±0.2 Ash 12.7a±0.8 16.6bc±1.1 17.2c±0.3 15.8b±0.5 16.5bc±0.2 1Means in each row with the same superscript letters are not significantly different (P>0.05) Table 5. Mineral composition of the fish after experiment. Mean Values1 Diets 1 2 3 4 5 Ca (mg g-1) 28.5a±1.9 32.8b±0.7 32.9b±0.9 32.9b±0.6 35.2c±0.2 P (mg g-1) 18.6a±0.0 20.3b±0.0 21.2c±0.0 20.6b±0.1 20.1b±0.0 Mg (mg g-1) 3.01a±0.0 3.88b±0.0 3.88b±0.0 3.89b±2.0 4.02c±0.0 K (mg g-1) 32.0c±0.2 31.6bc±0.1 24.8b±0.1 19.1a±0.5 19.5a±0.1 Fe (µ g-1) 37.0a±0.3 49.5b±1.0 59.3c±0.8 59.4c±1.4 59.5c±1.4 1Means in each row with the same superscript letters are not significantly different (P>0.05) 5 percent level of significance to detect differences among treatment means. Economic estimation A simple economic model of Vincke (1969) was used to estimate the costs of production, the incidence of cost (IC) and benefits and the profit index (PI). The model is based on the relationships between fish weight gain and the cost of feed, and the value of total fish produced and the cost of feed. Hence IC is given as cost of feed/weight gain while PI is defined as value of fish/cost feed. During costing, 50 percent of the cost of yellow corn was assumed for the cost of the DCM to cover expected costs of processing the discarded cocoa bean meal. Results The proximate composition of the experimental diets (Table 2) showed uniformity in all the parameters. The parameters were so closely related that the effect of replacement of yellow corn with DCM was not noticeable. Therefore, the effect reflected on the growth parameters, and especially the mineral composition of the fish could
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