Rações para otimizar o crescimento e eficiência alimentar do Robalo-Flecha, Centropomus undecimalis (BLOCH, 1792)

Abstract

The common snook, Centropomus undecimalis, is eurihaline species, with high economic value and potential for aquaculture. This study evaluated the growth performance and the osmoregulatory ability of the common snook reared under different dietary sources of protein and amino acids, and water salinity, respectively. The work consisted of three studies conducted consecutively. The 1st study investigated the effect of dietary amino acid composition of proteins alternate to fishmeal on fish growth performance. Fish of 10.79 ± 0.71 g (n = 150) were stocked in 15 circular tanks of 1 m3 kept sheltered outdoors. A basal diet was formulated to contain 64.34% (as fed basis) of fishmeal and 20.00% of soy protein concentrate (SPC). Two other diets replaced 25% of fishmeal for poultry by-product meal (17.01%) and soy protein concentrate (SPC, 33.49%). Fish were fed twice a day for 84 days. The 2nd study evaluated the growth performance of the common snook fed during 104 days in response to the dietary crude protein (CP) and amino acid content. A total of 750 fish of 21.91 ± 6.97 g were stocked in 25 circular tanks of 5.84 m3 under 5.1 fish/m3. Four diets were formulated to contain 48.70, 52.18, 57.00 and 60.00% CP (on a dry matter basis), with a total content of sulfur amino acids between 1.55 and 1.89% (dry basis) and minimum and maximum levels of methionine and lysine of 1.05% and 1.35 and 2.82 and 3.66%, respectively. The 3rd study determined the iso-osmotic point of common snook exposed to acute (24 h) and chronic (168 h) water salinities of 0, 5, 10, 15, 20 25, 30, 35, 40 and 45. Fish 33.27 ± 10.2 g were transferred without acclimation, from a water salinity of 32, into 30 tanks of 1 m3, with the corresponding salinities and stocked under 8 fish per tank. Osmolarity of fish blood and cultured water were immediately analyzed after 24 and 168 h from fish stocking with a freezing point osmometer. In the 1st study, the common snook grew more slowly (0.24 ± 0.03 and 0.27 ± 0.04 versus 0.35 ± 0.06 g/d), reached a lower body weight (31.1 ± 6.62 and 33.3 ± 10.20 versus 13.18 ± 40.4 g) and a higher FCA (3.69 ± 0.29 and 3.11 ± 0.51 versus 2.33 ± 0.34) when fed with SPC and the basal diet compared to diet with poultry by-product meal, respectively. In the 2nd study, there was no statistically significant difference for the daily growth (0.38 ± 0.10 g), specific growth rate (0.99 ± 0.19%/day), productivity gains (202 ± 58 g/m3), feed intake (132 g of feed/fish) and FCR (3.87 ± 2.48) for the common snook fed with the different protein levels. At harvest, fish body weight ranged from 55.70 ± 2.15 to 66.70 ± 2.18 g. %. Under acute exposure, osmolarity of fish blood increased gradually with water salinity from a minimum of 0.346 ± 0.011 mOsm/kg (freshwater) to a maximum of 0.380 ± 0.021 mOsm/kg (45 salinity). This study indicated that juveniles of the common snook has a greater ability to gain weight and to increase the retention

of nutrients when the dietary protein is of terrestrial animal. Juveniles of the species can survive and grow successfully in captivity with diets with a minimum of 48.70% crude protein (on dry basis) and 1.05% methionine. A water salinity between 0 and 45 the iso-osmotic equilibrium for juvenile common snook is achieved between 10.46 and 11.39 salinity (0.360 to 0.368 mOsm/kg osmolarity).