Effect of Stocking Density and Rearing Facility on Growth and Profitability of Tilapia rendalli Fry
A study was conducted to compare the growth potential of Tilapia rendalli at three different stocking densities, using different rearing facilities. T. rendalli fry of 0.9±0.1g average weight were stocked in tanks and hapa-in-ponds at the stocking density of 30, 60 and 90 fry/m 3 . Locally made feed (CP-18%) was administered at 5% body weight three times a day for three months. Monthly sampling was conducted to assess growth by measuring weight and length for specific growth rate (SGR), average daily gain (ADG), weight gain (WG), and biomass (BM). The results of the study showed a significantly higher (P 0.05) as well as within the stocking densities (P > 0.05). The results of this study have a significant contribution towards stocking densities as well as rearing facilities used by hatchery operators. It is recommended that hapas mounted in pond fry rearing for T. rendalli fingerling production is most ideal. The results of the present study suggested that production of good quality fingerlings at stocking densities of 30 fry/m 3 must be adopted in the culture of T. rendalli as fish grows faster than the other stocking densities of 60 and 90 fry/m 3 as demonstrated in this study.
Genetic evaluation of four strains of Oreochromis shiranus for harvest body weight in a diallel cross
Abstract Estimates of strain additive genetic, total heterosis and general reciprocal effects were obtained from a complete diallel cross with four strains (Shire, Nkhotakota, Chilwa and Chiuta) of Oreochromis shiranus in Malawi. Growth was recorded at harvest on 367 individually tagged progeny from 16 strain combinations after a grow-out period of 180 days across three test environments that represented different agro-climatic zones of the country. Each of the 16 strain combinations was produced from 3 to 5 five single-pair matings; i.e., 6–10 parents per strain combination. In total, the number of contributing sires per strain ranged from 14 to 16 and the number of contributing dams also from 14 to16. Across the test environments, the mean body weight was 75 g and the males had a significantly higher body weight at harvest than the females (23%; P P  > 0.05) meaning that with respect to the harvest body weight trait, there is no need to develop specific strains for the different agro-climatic conditions of the country. The strain total heterosis effect accounted for 15.3% ( P P P  > 0.05) effects. For the strain additive genetic effect, Shire was the best and Chiuta the poorest strain, performing 16.9% above and 10.3% below the mean of the purebred strains, respectively. Five out of the six strain crosses showed a significant positive total heterosis effect ranging from 12.3% to 17.0% above the mean body weight of the purebred strains. The average heterosis effect was 12.5%. The correlation between the strain additive genetic and the strain additive genetic plus total heterosis performance of the six strain crosses was low ( r  = 0.25). The results show that for harvest body weight there are substantial additive genetic and total heterosis differences among pure and crossbred strains of O. shiranus . The exploitation of these genetic differences in a breeding program is discussed.
Comparative study of growth performance of three strains of Nile tilapia, Oreochromis niloticus, L. at two stocking densities
This study was conducted to investigate the effect of stocking density (125 or 200 fish m−3) on the growth performance of three strains of the Nile tilapia, Oreochromis niloticus: the non-improved strain (NS), the genetically improved farmed tilapia (GIFT) and the Freshwater Aquaculture Center selected tilapia known as the FaST selected line (SL). Each strain and density combination was triplicated in 0.42 m3 fibreglass tanks within a re-circulating water system. Water temperature was maintained at 29.0±1.0°C. Large Nile tilapia having a mean body weight of 100–110 g were stocked in each tank and hand-fed four times daily with commercial tilapia pellets (35% protein) for 104 days. Results showed that at the two stocking densities, the GIFT and SL strains showed a significantly higher (P<0.05) mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), feed conversion ratio (FCR) and gross yield (GY) than the NS. In all three strains, growth performance was negatively affected by stocking density. The lower density (125 fish m−3) treatments had significantly higher MWT, DGR and SGR than the higher density one (200 fish m−3). However, higher FCR and GY were observed at the higher density. Survival rates were high in all treatments and were not affected by strain or density. In general, the SL strain had better growth parameters than the GIFT strain. The findings of this study demonstrated the superior growth performance of the improved strains at both densities compared with the NS. The higher density (200 fish m−3) could be more profitable for the tilapia farms in Kuwait than the lower density of (125 fish m−3) in terms of reduced land cost and facilities, demand on the limited low-salinity underground water and manpower.