Use of Enzyme Supplementation in Practical Diets for Nile Tilapia Oreochromis niloticus
Type of DegreePhD Dissertation
Fisheries and Allied Aquacultures
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Aquaculture industry is moving towards the use of plant based ingredients in tilapia diets, this due to decreased availability of fish meal worldwide. However, the replacement of fish meal by plant based ingredients can increase the fiber content of the diets thus impairing productivity, this mainly due to anti nutritional factors present. Among these antinutrients are the non starch polysaccharides which are part of the structural components of plant based feedstuffs. In the digestive system of fish, the enzymes necessary to digest non starch polysaccharides are scarce or even absent, reducing the ability of fish to obtain the nutrients from plant based diets. The addition of exogenous enzymes that can break down non starch polysaccharides can be an alternative to increase the digestibility of practical diets and improved performance in Nile tilapia Oreochromis niloticus. A series of experiments were conducted to evaluate commercially available enzyme addition to practical tilapia diets to study growth performance and digestibility. The first study was conducted to evaluate the performance and nutrient digestibility of Nile tilapia Oreochromis niloticus, when supplemented with a commercial beta mannanase enzyme. A basal diet was designed to contain 32% protein and 6% lipid using primarily plant based protein sources allowing high levels of “low” digestibility ingredients. Four levels of enzyme were evaluated (0, 0.05, 0.10, 0.20%). At the conclusion of the growth trial, performance parameters or apparent energy and net protein retention were not improved by beta mannanase addition. However, the inclusion of beta mannanase to the diet resulted in a linear increase in dry matter digestibility (P= 0.0004; R2 =0.75), energy digestibility (P=0.0003; R2 =0.74) and protein digestibility (P=0.0247; R2 =0.41). As compared to the diet without the enzyme; the supplementation of 0.1 and 0.2% of the diet significantly improved digestibility. The second study was designed to evaluate the production performance and digestibility of Nile tilapia Oreochromis niloticus when supplemented with commercial protease and carbohydrases. Ten practical tilapia diets were formulated to contain 32% protein and 6% lipids. Six diets were formulated to contain low levels of fiber (LF) and included free protease (LF-FP), protected protease (LF-PP), free carbohydrase (LF-FC), protected carbohydrase (LF-PC), and a mix of free protease and carbohydrases (LF-MFPFC). Four diets were formulated to contained high levels of fiber (HF) and included a basal diet (HF) and a basal diet supplemented with free protease (HF-FP), free carbohydrase (HF-FC), and a mix of free protease and free carbohydrases (HF-MFPFC), distillers dried grains with solubles (DDGS) was used as a source of fiber in high fiber diets. The level in the diet of free protease (FP) and protected (PP) was 175 g per metric ton, the level of free carbohydrase (FC), protected carbohydrase (PC) and the mix of free protease and carbohydrase (MFPFC) was 125 g per metric ton. Under the conditions of this study, fish maintained on the high fiber diet performed slightly poorer than those on the lower fiber diet. Concerning enzyme supplements, apparent net energy retention was significantly different (P= 0.0001) in low fiber diets when free and protected proteases were added. However, for low and high fiber diets there were no significant differences (P > 0.05) in animal performance and apparent net protein retention. Overall, there were no clear advantages detected to the protected enzymes. Dry matter and energy digestibility were significantly improved by the addition of free carbohydrase and a mixture of free protease and free carbohydrase when supplemented in low and high fiber diets. The third study investigated the production performance of Nile tilapia Oreaochromis niloticus when supplemented with a commercial beta xylanase and beta glucanase enzyme. Two practical basal tilapia diets formulated to contain a low level of fiber (LF) based on soybean meal were modified by top coating liquid enzymes to produce five levels of enzyme inclusion (0.00, 0.015, 0.030, 0.045, and 0.060 g/100g). A second basal diet was formulated to contain a high level of fiber (HF), to increase the fiber content 30% distillers dried grains with solubles were used as a replacement for soybean meal, this basal diet was modified by top coating of liquid enzymes to produce five levels of enzyme inclusion (0.00, 0.015, 0.030, 0.045, and 0.060 g/100g). The inclusion of beta xylanase and beta glucanase resulted in significantly improved growth parameters, final mean weight (P = 0.0029), percent weight gain (P = 0.0128), thermal unit growth coefficients (P = 0.0046) with no change (P > 0.05) in feed conversion ratio (P= 0.2153), apparent net protein retention, apparent net energy retention, hepatosomatic index and intraperitoneal fat index. In general, fish maintained on the high fiber diet performed better with the addition of the enzyme. Based on the results of these studies, exogenous enzymes such as beta mannase, protease, xylanase and betaglucanase can be used to increase digestibility of practical tilapia diets and improve performance of Nile tilapia when plant - based ingredients are the major components of the diets. However, the increase in performance is not always consistent and depends on the type of the enzyme and substrate make up of the diet.