Performance of Nile Tilapia (Oreochromis Niloticus) Fed on Oilseed meals with Crude Papain Enzyme

Abstract

The greatest challenge to increased aquaculture production in Kenya is the high cost of fish feed. The objective of this study was to determine the effect of replacing fish meal with oilseed meals and improving the availability of nutrients using crude papain enzyme in Nile tilapia diets. A control diet (D1) of 30% crude protein and 2900Kcal DE/kg was formulated using fishmeal (FM), soybean meal (SBM), canola meal (CM) and sunflower meal (SFM). The test diets were formulated by replacing 10% CP of FM by SBM (D2), CM (D3) and SFM (D4), respectively. The diets were analysed for proximate, fatty acid and amino acid composition. The level of inclusion of crude papain enzyme was tested at 0.02%, 0.04%, 0.06% and 0.08% by the in vitro enzyme assay using pH drop method. One hundred and one days feeding trial was conducted in a 4x2 factorial design on 4 diets (D1, D2, D3 & D4) with (0.06%) and without (0%) the enzyme using seven hundred and twenty Nile tilapia fingerlings (7±3g). The fingerlings were randomly distributed into eight groups of three replicates of 30 fingerlings per net hapa (2x1x1m). Fish were fed twice daily at 5% of their biomass at 10am and 4pm in two equal meals. They were weighed fortnightly and slaughtered at the end of feeding trial for carcass quality analysis and sensory evaluation. Apparent nutrient digestibility was done at the end of feeding trial using chromic oxide as an external marker. Substituting FM with SBM, CM and SFM significantly increased the levels of crude fibre (P<0.05) but reduced ash level. The diet based on SFM recorded highest (16.03%) crude fibre content (P<0.05), while CM based diet recorded highest ether extract content (10.75%). Substituting 10% CP of FM with SBM, CM and SFM, reduced the levels of isoleucine, leucine, arginine, lysine, phenylalanine, histidine and threonine (P<0.05) and increased levels of methionine in diet with SBM. In all the diets, methionine was the 1st limiting amino acid and isoleucine 2nd limiting. Though the diet containing FM exhibited higher (P<0.05) essential amino acid index (EAAI) (0.97), it was not satisfactory because it was limiting in methionine. EAAI reduced (P<0.05) with replacement of fishmeal; SBM (0.78), CM (0.77) and SFM (0.76). Crude papain extract contained (crude protein 66.61%, ash 6.89%, crude fat 7.69%, crude fiber 1.56%, dry matter 93.55% and nitrogen free extract 16.98%). Addition of crude papain at 0.06% had highest (P<0.05) protein digestibility (39.16%). Apparent Digestibility Coefficients (ADC‟s) increased (P<0.05) for all the nutrients tested upon crude papain enzyme supplementation. Growth performance showed that there was no significant different (P>0.05) on final body weight (47.32g) on 0.06% enzyme and (46.17g) on 0% papain enzyme. However, fish fed FM based diet were larger (56.89g) (P<0.05) than those fed SBM (45.59g) CM (43.89g) and SFM (40.59g). The profit index was highest (2.41) in 0% enzyme and lower in 0.06% enzyme (2.19) (P<0.05). Although 10% CP replacement of FM with SBM, CM and SFM was associated with reduced growth, the economic returns were higher. Final carcass proximate composition increased on enzyme supplementation. Crude papain enzyme supplementation led to increase in saturated and mono saturated fatty acid and decrease in polyunsaturated fatty acid. The overall acceptability of fish decreased (3.87) with 0.06% enzyme. The present results indicates that enzyme supplementation led to increased digestibility and growth of fish but carcass fatty acid, sensory attributes and profit index reduced. Based on this, more research is needed on crude papain enzyme supplementation in Nile tilapia diets.