Avaliação de densidades de estocagem de alevinos da tilápia Oreochromis niloticus (linhagem Chitralada) cultivado em gaiolas

Abstract

Cage tilapia culture in Northeast region had grown very fast in the last years, where the climate provides adequate culture conditions during all the year. This kind of culture normally is developed in two culture phases: fingerlings or nursery phase and growout phase. Both of them need improvements in the management techniques and in the stocking densities, mainly in the first phase, where the goal is optimize the density to produce fingerlings (about 0.5 g) until adequate transfer size to growout phase (30 g). This work had the objetive to evaluate the stocking densities of tilapia (Oreochromis niloticus), Chitralada strain, in nets inside cages installed in Xingó reservoir, belonging to CHESF (Companhia Hidroelétrica do São Francisco), where the fish culture activity is developed with mean water temperature around 28ºC. Were utilized twelve 5m³ cages revested with 4m³ nets (mesh # 4mm), in which were stocked with 0.85g fingerlings, representing a completely randomized design, with three treatments (800 fingerlings/m³, 950 fingerlings/m³ and 1,100 fingerlings/m³) and four replicates. During the first 15 culture days, the fish were fed eight times per day, with a 55% crude protein powder ration, at a feeding rate of 12.5% of biomass daily. After this period, the ration was change of for another 45% crude protein, pelleted and extruded, at a feeding rate varying from 8 to 6.5% of biomass per day, until the end of culture. The ration quantity wasadjusted every 15 days through population samples (about 5%). During the culture, the following water quality variables: temperature, pH, dissolved oxygen, alkalinity, total hardness, ammonia and nitrite. At the end of the nursery phase, with duration of 54 days, the fingerling were counted, weighed and measured. The survival varied from 90.1 to 95%, without significative difference (P³0.05) among the treatments. The final body weight average was 37.5, 37.2 and 33.0 g, respectively for 800, 950 and 1.100 fingerlings/m³ treatments, without significative difference (P³0.05).The final body length average was 12.3, 12.1 and 11.6cm for the respective treatments, with significative difference (P<0.05) between 800 and 1,100 fingerlings/m³ treatments. The feed conversion ration varied from 1.00 to 1.09 without significative difference (P³0.05) among the treatments. So, it can be conclude that in the cage nursery phase is possible to stock until 1,100 fingerlings/m³ to obtain juveniles of 30 grams, during 54 days culture.