Abstract:
Feed constitutes more than 60% of operational cost in fish farming. Increasing cost of conventional feedstuff due to competition between livestock and human necessitates research into cheaper and readily available unconventional feedstuffs for profitable fish farming. Kenaf (Hibiscus cannabinus) Seed Meal (KSM) has been reported to be a nutrient-rich feedstuff for aquaculture. However, there is limited information on the utilisation of KSM in the diet of important cultured fish species such as Clarias gariepinus. Therefore, effect of differently processed KSM as a replacement for conventional soyabean meal on growth and body physiology of Clarias gariepinus was investigated.
The chemical components: Crude Protein, Tannin and Saponin of differently processed KSM; Roasted (RoKSM), Soaked (SoKSM), Sprouted (SpKSM), Cooked (CoKSM) and Raw (RaKSM) were determined using standard methods. Crude protein Apparent Digestibility Coefficient (ADC) of the meals were calculated for C. gariepinus (n=180, 8.19±0.17g) using standard procedures. Sixteen isonitrogenous diets (40% crude protein) were made from each of the five processed meals, replacing soyabeans meal at 0, 10, 20 and 30%. Clarias gariepinus (n=480; 2.3±0.12 g; 10 fish tank-1) were randomly allotted in triplicate to treatments in a 4 x 5 factorial arrangement. The fish were fed twice daily to satiation for 112 days. Mean Weight Gain (MWG), Specific Growth Rate (SGR) and Net Protein Utilisation (NPU) were calculated. Packed Cell Volume (PCV), Alanine Aminotransferase (ALT), Total Plasma Protein (TPP) and Blood Urea Nitrogen (BUN) were measured using standard procedures. Data were analysed using descriptive statistics, ANOVA and Polynomial Regression at α0.05.
Crude protein significantly varied from 21.17±0.10 % in RaKSM to 30.45±0.22 % in CoKSM. Tannin ranged from 0.02±0.00 % (CoKSM) to 0.11±0.00 % (SoKSM) while saponin was 1.99±0.01 % and 2.37±0.01 % in SpKSM and RaKSM, respectively. The least (51.45±10.83 %) and highest (98.29±0.59 %) crude protein ADC were obtained in RaKSM and SoKSM, respectively. The RoKSM gave significantly highest MWG (9.10±0.84 g), SGR (0.54±0.04 %/fish/day) and NPU (66.72±6.50 %) while CoKSM had the least MWG (5.16±0.84 g), SGR (0.33±0.04 %/fish/day) and NPU (38.63±6.50 %). The MWG (13.04±3.07 g), SGR (0.66±0.06 %/fish/day) and NPU (89.91±27.85 %) were highest in 10% RoKSM and the least MWG (1.38±1.38 g), SGR (0.12±0.12 %/fish/day) and NPU (5.22±5.22 %) was in 20% CoKSM, 20% SoKSM and 30% SoKSM, respectively. Optimum dietary inclusion level of RoKSM relative to MWG was 10.8% (R2=0.49). The PCV ranged from 16.75±3.07 % (RaKSM) to 24.67±3.06 % (RoKSM). Highest PCV (31.73±2.74 %) and ALT (25.40±1.93 IU/l) were recorded in 10% RoKSM, while the least was obtained in 30% RaKSM (PVC: 3.33±2.73 %; ALT: 3.33±1.92 IU/l). Highest TPP (4.97±0.82 g/dl) and BUN (11.20±1.56 mg/dl) was recorded in 0% KSM while 20% RaKSM and 20% CoKSM gave the least TPP (1.03±0.82 g/dl) and BUN (3.27±1.56 mg/dl), respectively.
Roasting was the best processing method for kenaf seed meal and could replace soyabean meal up to 10% in the diet of Clarias gariepinus. Inclusion level of roasted kenaf seed meal beyond 10.8% could negatively affect the growth and blood profile of Clarias gariepinus.
