Effect of stock density on growth performance for small size of rainbow trout

The present study investigated the potential production of rainbow trout up to 50 g in 9 concrete ponds (19 × 2.2 × 1.5 m) using different stock density comprising 100, 115 and 130 fish/m2 with initial average weight 5 ± 1 g. This experiment carried out in a completely randomized design with three treatments (triplication for each) for 75 days. Total stock for treatments were 4180, 4807 and 5434, respectively. A well with 30 l/s was used as a source of water that divided for 9 ponds uniformly. Firstly, feeding was started with 4.8 percent of biomass of each pond (with 5 times per day) and then decreased at 2.5 percent (with 3 times per day) at the end of rearing period according to fish size and water temperature. The results showed that treatment with 100 fish/m2 had significantly higher body weight gain (50.83 g) and total length (12 cm), and also lower feed conversion ratio (1.37) than other groups (p < 0.05). In addition, the highest specific growth rate (2.57) and protein efficiency ratio (1.81) were significantly observed for 100 fish/m2 compared to other treatments (p < 0.05). Therefore, the optimum stock density at100 fish/m2 up to 50 g is recommended for present ponds without aeration.