Abstract
Improving protein digestibility in nutrient poor fish feeds through incorporation of dietary enzymes is expected to be achieved with protease. Understanding the role of other dietary enzymes was therefore evaluated to guide appropriate use for optimal fish growth. Protein digestibility of 30, 35, 50 and 55% crude protein (CP) diets was determined with catfish gut enzyme extract, sprouted sorghum, protease and phytase both singly and in a mixture of 500 units of protease and phytase using the pH drop method in vitro. Significant (p<0.05) digestibilities were recorded in 30 and 35% CP diets incorporated with phytase and in 50 and 55% CP diets incorporated with protease singly. These results showed that protein digestibility was more efficient with protease enzyme in high protein diets while phytase was efficient in low protein diets. This implied that the use of protease was more beneficial in catfish starter feeds and phytase in grower/finisher diets and provided a basis for enzyme selection for production of cost-effective catfish diets. Key words: In-vitro protein digestion, catfish gut enzyme extract, phytase, protease, sprouted sorghum.
Highlights
Feed account for 60 to 70% of operating costs in farming of high value fed species like Clarias gariepinus, and without it stock productivity and profitability will remain a cherished desire (World Bank, 2007).Fish feed quality is compromised by limited use of fishmeal, the most nutritive and digestible protein ingredient traditionally used in fish diets, due to its high cost (US$2/Kg) (World Bank, 2013), associated food insecurity and aquatic degradation (FAO, 2009)
Protein digestibility was significantly higher for Phytase incorporated legume based diets (30 and 35% crude protein) and protease incorporated fish meal based diets (50 and 55% crude protein) than in catfish gut enzyme extract
Protein digestibility in diets incorporated with sprouted sorghum and a mixture of protease and phytase combined was not significantly different from that of catfish gut enzyme extract (Table 7)
Summary
Fish feed quality is compromised by limited use of fishmeal, the most nutritive and digestible protein ingredient traditionally used in fish diets, due to its high cost (US$2/Kg) (World Bank, 2013), associated food insecurity and aquatic degradation (FAO, 2009). This has intensified use of plant protein instead (Gabriel et al, 2007) as they are more accessible and fairly priced (Hecht, 2006). It forms indigestible complexes with nutrients including protein, reducing their utilisation by fish for growth (Gabriel et al, 2007; GarcõÂa-Estepa et al, 1999; Gilani et al, 2005; Hidvegi and Lasztity, 2002; Kumar et al, 2012b).
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