Abstract:
Decline in fish production from capture fisheries has necessitated the development of intensive aquaculture practices such as Cage Culture (CC). However, the practice of CC is not well established in Nigeria. This is due to the fact that information on operational procedures like Stocking Density (SD) and feed forms (floating and sinking) for important culture fish species such as Clarias gariepinus are limited. Therefore, growth performance and nutrient utilisation of C.gariepinus in net cages under varying stocking densities and feed forms were investigated.
Eighteen (1.0m x 1.0m x1.5m)floatingnet cages were set on Owala Lake, Osun State, Nigeria. In each of the cages, C gariepinus (n=3,600; 70.00±0.03g) were randomly allotted to the cages at different stocking densities of 100 (SD1), 200 (SD2) and 300 (SD3) fish per m3 with 100 (SD1) as control. The fish in each SD were fed diet containing 45% crude protein in form of either Extruded Floating Diet (EFD): (SD1-EFD; SD2-EFD; SD3-EFD) or Pelleted Sinking Diet (PSD): (SD1-PSD; SD2-PSD; SD3-PSD). The fish were fed twice daily at 3% body weight for 150 days. All the treatments were replicated three times using 2×3 factorial arrangement in a completely randomised design. Mean Weight Gain (MWG, g), Specific Growth Rate (SGR, %), Survival Rate (SR, %), Protein Efficiency Ratio (PER) and Feed Conversion Ratio (FCR) were measured. Blood (5 ml) was sampled to determine Packed Cell Volume (PCV, %), Heterophil (HET, 106/µl), Lymphocyte (LYM, 106/µl) and Heterophil: Lymphocyte ratio (H: L) using standard methods. Net Revenue (NR; ₦ /kg of fish) and Benefit Cost Ratio (BCR) were determined. Data were analysed using descriptive statistics and ANOVA at α0.05.
The MWG varied from 669.35±1.92 and 902.97±11.52; SGR 1.6±0.02, 1.8±0.02; SR 98.0±0.6, 99.00±0.56 and PER 1.6±0.01, 1.7±0.05 in SD3−PSD and SD1−PSD, respectively. Least and highest MWG 735.3±5.49, 1108.3±3.19, SGR 1.6±0.02, 1.9±0.02, SR 98.0±0.6, 99.0±0.6 and PER 1.7±0.02, 1.8±0.01 were obtained in SD3-EFD and SD1-EFD, respectively. The FCR increased from 1.2±0.01 (SD1−EFD), 1.3±0.01 (SD2−EPD) to 1.3±0.1 (SD2−EFD); 1.4±0.01 (SD2−PSD). Significantly, least and highest PCV 19.0±6.1, 23.0±8.7 and LYM 4.5±2.3, 5.4±2.3 were obtained in SD3-PSD and SD1-EFD, respectively. The HET varied from 3.7±0.4 (SD1-EFD) to 4.0±0.9 (SD3-EFD) while HET was 4.2±0.6 and 4.3±1.2 in (SD1-PSD) and (SD3-PSD), respectively. Least and highest H: L were recorded in SD1-EFD (0.7±0.2), SD1-PS (0.70±0.09) and SD3-EFD (1.0±1.2), SD3-PSD (1.0±2.1). The NR significantly increased from ₦13,974.50±697.9 (SD1−EFD) to ₦20,653.02±308.3 (SD2−EFD). The NR was ₦17,512.93±216.5 and ₦29,848.1±190.3 in SD1-PSD and SD3-PSD, respectively. Least (1.1±0.02) and highest (1.3±0.03) BCR were recorded in SD3-EFD and SD1−EFD, respectively while BCR ranged from 1.34±0.02 SD3-PSD to 1.43±0.02 SD1-PSD.
Production of Clarias gariepinus could be enhanced in net cages at stocking density of 100 fish/m3 when fed either floating or sinking pellet. However, benefit cost ratio was higher in Clarias gariepinus fed sinking diet at 100 fish/m3.
