Abstract:
Soyabean meal (SBM) could be a suitable replacement for the expensive fishmeal but for its low digestibility in fish. Appropriate dietary supplements of amino acid and protease can improve digestibility of SBM based diets. However, information on supplemental Dietary Amino Acid (DAA) and protease in such diets for optimum growth in cultured fish is limited. Therefore, growth performance and amino acid digestibility in Clarias gariepinus fed SBM based diets supplemented with DAA and protease were investigated.
Soyabean grains processed by roasting and solvent (n-hexane) extraction were assessed for Crude Protein (CP), lysine and methionine content using standard methods. Six diets containing varied combinations of lysine+methionine (g/kg) supplementation were formulated for each of Roasted SBM (RS) and Solvent extracted SBM (SS): RS1, SS1 (Control: without supplementation), RS2, SS2 (0+10), RS3, SS3 (2.5+7.5), RS4, SS4 (5.0+5.0), RS5, SS5 (7.5+2.5) and RS6, SS6 (10+0) respectively. Furthermore, protease (ppm/kg) was supplemented in each of RS and SS: RS0, SS0: (control: without supplementation), RS100, SS100 (100), RS200, SS200 (200), RS300, SS300 (300), RS400, SS400 (400) and RS500, SS500 (500), respectively. Clarias gariepinus (n=1440; 19.70±0.20g) were fed to satiation with the diets for 12 weeks in triplicate in a completely randomised design. Final weight (FW, g) and Feed Conversion Ratio (FCR) were calculated. Blood (5mL) was sampled for Packed Cell Volume (PCV, %) and Alanine Amino Transaminase (ALT, IU/L). True Methionine (TM) and True Lysine (TL) digestibility were determined using standard procedures. Data were analysed using descriptive statistics, polynomial regression and ANOVA at α0.05¬¬¬.
The CP, lysine and methionine were 52.5±2.8%, 58.5±2.5%; 2.3±0.0%, 2.8±0.1% and 0.5±0.0%, 0.6±0.01% in RS and SS, respectively. Least FW 32.60±3.59 and 34.8±1.2 were recorded in RS6 and SS2, respectively while RS5 (36.4±4.6) and SS1 (43.4±4.0) had the highest. The FCR ranged from 3.0±0.7 (RS5), 2.3±0.2 (SS3) to 3.8±0.5 (RS1) and 3.1±0.3 (SS2). The PCV were 21.0±1.7, 27.0±2.7 and ALT 19.3±5.0, in RS1 and RS5, respectively. The PCV and ALT ranged from 22.7±3.8, 23.0±2.0 to 25.7±1.5, 31.0±3.6 in SS1 and SS5, respectively. Significantly least (90.9±0.3) and highest (92.9±0.4) TL were obtained in RS2 and RS4, respectively while it ranged from 86.2±1.0 (SS4) to 95.9±0.2 (SS5). Optimal FW were 35.7 and 35.0g at 0.6+0.4g/100g supplementation in RS (R2=0.8) and SS (R2= 0.7). The FW were least in RS100 (31.2±3.4) and SS0 (32.0±0.7), highest in RS400 (46.9±9.25) and SS400 (44.6±2.9), FCR least in RS400 (1.4±0.3) and SS400 (1.6±0.2), highest in RS100 (2.8±0.6) and SS0 (2.8±0.0). The PCV were 23.5±5.0 (RS500) and 27.0±1.0 (RS0), ALT 20.3±0.6 (RS100), 34.7±13.3 (RS400) TM 77.8±0.2 (RS500), 93.5±0.0 (RS200) and TL 92.7±0.1, (RS300), 96.2±0.0 (RS100). In SS, PCV ranged from 22.7±4.6 (SS500) to 31.3±4.0 (SS0), ALT 20.0±1.0 (SS0) to 26.3±3.1 (SS400), TM 84.3±0.1 (SS100) to 95.8±0.2 (SS0) and TL 87.7±0.1 (SS100) to 95.9±0.1 (SS200). Optimal FW were 42.0 and 41.0g at 400 ppm/kg supplementation in RS (R2=0.6) and SS (R2=0.7), respectively.
Lysine+methionine and protease supplementation at 0.6+0.4g/100g and 400ppm/kg could optimally improve growth and digestibility in Clarias gariepinus fed soyabean meal based diets without negative impact on fish health.
