Avaliação do crescimento de três linhagens de tilápia Oreochromis sp, em sistema semi-intensivo, cultivadas em viveiros

Abstract

Three strains of tilapia, Oreochromis sp, were evaluated in a semi-intensive culture, during 112 days, from December 2002 to March 2003, through the use of twelve 50m2 earthen ponds belonging to Estação de Aqüicultura Continental Prof. Johei Koike of the Universidade Federal Rural de Pernambuco, Recife-PE, Brazil. The experiment was designed to contain three treatments according to the strains (nile, red and chitralada) and four replicates. For the ponds preparation were used lime (100g.m-2) and chicken manure (100g.m-2). After 50% of ponds filling it was used inorganic fertilizers (5g.m-2 of ammonium sulphate and 3g.m-2 of simple superphosphate) in order to stimulate the natural productivity. Tilapia juveniles averaging 50.98, 54.54 and 64.51g, respectively, for each strain (nile, red and chitralada) were stocked in randomly ponds. A extruded commercial ration with 32% crude protein was used during the 60 days and another one with 28% for the last 52 days. Water temperature, pH and dissolved oxygen were measured three times per week in the morning and in the afternoon. Alkalinity, total hardness, ortophosphate, total ammonia nitrogen, nitrate and nitrite were measured every two weeks in order to adjust the fertilization program.Fish growth was followed trough fortnightly measurements with approximately 30% of fish population. The main water quality variables (temperature = 31.45°C, pH = 7.23 and dissolved oxygen = 3.78mg.L-1 in average) maintained adequated to the fishculture, except dissolved oxygen that sometimes reached low levels in the morning. Growth and production data were differents (P≤0.05) among treatments. chitralada strain grew better than Vermelha than nile, with specific growth rate of 2.42, 2.06 and 1.77%.day-1, respectively. The weight gain and feed conversion ratio were higher (P≤0.05) to chitralada (396.42g and 1.17) than for red (225.49g and 1.72) and nile (147.00g and 1.80). In this culture system it was possible to maintain a reasonable biomass in the pond since the final biomass was 681.40, 403.60 and 352.60g.m-2, respectively for nile, red and chitralada strains, with significant difference (P≤0.05). Survival averaged 93% for chitralada and red different (P≤0.05) of nile strain 86%. These results show that the best tilapia strain for semi-intensive systems is chitralada, which can be recommended for culture in a commercial scale.