Submitted to: Aquaculture Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/15/2015
Publication Date: 2/22/2016
Citation: Green, B.W. 2016. Stocking rate effects in a tilapia biofloc production system [abstract]. Aquaculture Conference Proceedings. p.313.
Technical Abstract: Production efficiency is improved when the culture organism can grow rapidly to the desired target weight. Stocking rate is known to affect fish growth, but little information is available for 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 50 – 250 fish/m2 in 50-fish/m2 increments to grow stocker-size (100-150-g) fish in outdoor BFT tanks. Fingerlings (6.6 g/fish) were stocked into each of nine continuously aerated HDPE-lined tanks (18.6 m2, 15.5 m3) at their randomly assigned stocking rate for this 142-day study. Each tank was equipped with a 117-L conical bottom settling chamber to remove solids. Fish were fed to apparent satiation twice daily with a commercially formulated diet (45% protein, 12% lipid decreasing to 40% protein, 10% lipid). Fish in each tank were sampled to monitor growth at approximately 35-d intervals. Water quality measurements were made weekly. Each tank at the 175 fish/m2 stocking rate and higher experienced an unexplained mortality event during the early August-early September period; mortality ranged from 7-84% of the tank’s population. At harvest, tilapia survival was high (mean = 94.5%) for tanks stocked with 50-150 fish/m2, but decreased linearly at higher stocking rates (P < 0.025, R2 = 0.853). As a resu2 = 0.880, respectively), and ranged from 8.2-38.3 kg/m3 and 6.4-37.3 kg/m3, respectively. The largest gross (38.3 kg/m3) and net (37.3 kg/m3) fish yields were obtained at the 150 fish/m2 stocking rate. Mean individual weight at harvest ranged from 163-390 g/fish and decreased linearly (P = 0.003, R2 = 0.850) from 50-200 fish/m2. Mean daily feed ration and total feed fed ranged from 135-197 g/m3/d and 28.5-41.6 kg/m3, respectively, and varied quadratically with stocking rate (P = 0.003, R2 = 0.863 and P = 0.003, R2 = 0.863, respectively). Feed conversion ratio (feed dry weight basis and including weight of mortalities) ranged from 1.05-1.25 and decreased linearly with increased stocking rate (P = 0.041, R2 = 0.473). Nitrite-nitrogen, nitrate-nitrogen, and soluble reactive phosphorus were the only water quality variables affected by total feed input and all increased linearly with feed input. Results suggest that hybrid tilapia grow rapidly over a wide range of stocking rates, but that a shorter production cycle likely is needed to produce 100-150-g stockers, and survival may be affected negatively when stocking rate exceeds 150 fish/m2.