World Aquaculture 15 Table 6. Hematological profile of the fish after experiment. Means Values1 Diets 1 2 3 4 5 ESR (mm)2 1.83±0.3 2.17±0.3 2.33±0.1 2.17±0.2 2.17±0.3 PCV ( %)3 37.3±0.6 36.3±1.2 35.3±0.6 35.4±1.0 36.1±0.0 RBC (mm3) 569.6±23 568.6±17 569.6±10 567.6±16 568.6±23 Haemoglobin (g 100ml-1) 12.4±0.2 12.1±0.0 11.9±0.0 11.6±2.0 11.9±0.3 Lymphocyte ( %) 59.0±0.0 61.0±4.6 60.0±3.6 57.6±3.1 58.6±3.5 Neutrophils ( %) 24.0±2.0 24.0±1.0 24.0±2.0 24.3±2.6 25.0±1.0 Monocyte (%) 14.0±2.0 12.3±3.1 13.3±0.8 14.1±1.0 13.6±1.4 Basophils (%) 2.00±0.0 2.00±0.0 1.67±0.1 2.00±0.0 1.72±0.0 Eosinophils (%) 1.00±0.0 0.95±0.1 1.00±0.0 1.00±0.0 1.00±0.0 1Means in each row with the same superscript letters are not significantly different (P>0.05) 2Erythrocyte sedimentation rate 3Packed cell volume Table 7. Economic estimate. Parameters Diets 1 2 3 4 5 Cost per kg diet 111.8 110.8 109.8 108.9 107.9 Kg of fish produced 1.004 1.57 1.199 1.17 0.601 Value of fish per Kg 351.5 550.6 419.6 409.5 210.4 Incidence of cost 111.3 70.4 91.6 93.0 179.5 Profit index 1.26 1.98 1.53 1.50 0.78 Economic estimation that showed how replacement of yellow corn with DCM affected the incidence of cost and profits of fish production is presented in Table 7. The table shows that the average price of producing 1 Kg of diet as 109.8 units and that the cost of producing a 1 Kg diet decreased consistently with increase in the replacement levels of discarded cocoa bean meal. This is because of the cheaper price of the DCM, which was fixed at 50 percent of the cost of yellow corn to cover the cost of processing. The Kg of fish produced was a reflection of the growth performance of the fish, which also affected the price value of fish per Kg. The incidence of cost (IC) that explains the relationships between the cost of feed and fish weight gain was also affected by the growth performance as high growth would result in low IC. Also, the profit index (PI) that describes the relationships between the price value of fish and feed cost is a function of growth, inasmuch as higher growth performance would result in a higher priced value of the fish and higher profit. The table further showed that, contrary to expectations, the highest IC was recorded by using 100 percent DCM. This was because of the poor growth rate of fish in that treatment. Also, the highest PI was recorded in the fish fed 25 percent DCM. This also confirmed the growth data, which indicated a replacement level of 25 percent DCM as the best. Discussion Corn is a dietary energy that can reduce the oxidation of dietary protein for energy (protein-sparing) which minimizes the quantity/costs of dietary protein (Hanley 1993, Nwanna et al. 2003). The present study revealed a general increase in the gross energy of the diets as a result of inclusion of DCM in the diets. This may support the use of cocoa beverages as energy drinks. There is also evidence that DCM can adequately replace corn as an energy source in fish diets. Adegbola and Omole (1973) and Nwanna et al. (2008) reported higher protein levels in DCM than in yellow corn. A complementary effect of the higher energy and protein in DCM than in corn could have resulted in better growth performance of the fish in the treatments that contained DCM. However, it is disadvantageous to include more than 75 percent of DCM in the diet. For maximum growth, a replacement level of 25 percent DCM is recommended. The efficacy of other non-conventional products as energy feed ingredients in fish diets has been described. Fagbenro et al. (2000) showed favorable comparison of Acha (Digitaria exilix) meal with corn and sorghum meal as a dietary carbohydrate source for Nile tilapia (Oreochromis niloticus). Nwanna et al. (2003) discussed the effectiveness of replacing corn with Acha in the diets of Nile tilapia. Nwanna et al. (2004) also verified that replacing corn with a non-conventional carbohydrate source tamarind (Tamarindus indica) resulted in better growth of Nile tilapia and higher economic returns. The significant increase in the carcass ash as a result of DCM supplementation resulted in a corresponding increase in the carcass minerals. As mineral supplementation in fish feeds constitutes a major cost in aquaculture, the use of DCM in fish diets could reduce the quantity of mineral supplementation, which will invariably reduce the unit cost of feed and fish production. This observation was also made by Nwanna et al. (2007) through the use of phytase to improve mineralization in common carp, thereby reducing the quantity of mineral supplement in the fish diets.
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