PRODUCTION OF STOCKER-SIZE HYBRID TILAPIA IN AN OUTDOOR BIOFLOC PRODUCTION SYSTEM
Production efficiency per unit volume of water can be improved when stocking rate is adjusted to allow rapid growth of the culture organism to the desired target weight. Fingerlings often are grown to stocker size (ca. 100-150 g/fish) at high stocking rates and then the population is thinned to allow continued rapid growth to market size. Little information is available for production of stocker-size tilapia grown in a biofloc technology (BFT) production system. The objective of this study was to quantify the production function and impacts on water quality of stocking sex-reversed fingerling hybrid tilapia (Oreochromis aureus F X O. niloticus M) at 100 - 300 fish/m2 in 50-fish/m2 increments to grow stocker-size fish in outdoor BFT tanks. Fingerlings (12.9 g/fish) were stocked into each of nine continuously aerated HDPE-lined tanks (4.7 m2, 3.6 m3) at their randomly assigned stocking rate for this 78-day study. Each tank was equipped with a 74-L settling chamber to remove solids. Fish were fed to apparent satiation twice daily with a commercially formulated diet (44% protein, 15% lipid decreasing to 30% protein, 6% lipid). Fish in each tank were sampled to monitor growth at approximately 30-d intervals. Water quality measurements were made weekly. At harvest, tilapia survival among tanks was high (mean = 94.5%). Gross fish yield (y) increased linearly with stocking rate (x) (y = 0.0476x + 16.197, R2 = 0.763), and ranged from 20.1 to 30.5 kg/m3. Mean individual weight (y) at harvest decreased linearly from 155.2 to 81.4 g/fish as stocking rate (x) increased (y = 180.89 - 0.3455x, R2 = 0.929). Mean daily feed ration and total feed fed ranged from 251 to 382 g/m3/d and 19.6 to 29.8 kg/m3, respectively, and increased linearly with stocking rate (P = 0.003, R2 = 0.734 and P = 0.003, R2 = 0.734, respectively). Feed conversion ratio (feed dry weight basis) ranged from 1.00-1.13 and was independent of stocking rate (P = 0.959, R2 = 0.000). Stocking density impacted some of the evaluated blood serum parameters (peroxidase activity, lysozyme activity, and cortisol levels) as well as other blood parameters (hematocrit, hemoglobin, and differential blood cell counts). The overall effect of stocking density on measured blood parameters will be discussed. Results suggest that hybrid tilapia grow rapidly over a wide range of stocking rates, and that high yields of stocker size tilapia can be achieved in 78 days.