Optimal stocking density for beluga, Huso huso, and ship sturgeon, Acipenser nudiventris during the grow‐out phase

The influence of three different initial stocking densities (SD) in flowthrough systems was evaluated on growth performance and feed utilizaition in beluga, Huso huso, and ship sturgeon, Acipenser nudiventris, juveniles in three different grow‐out phases for 228 days. In each grow‐out phase, fish were randomly distributed in 18 concrete square tanks (2.0 × 1.0 × 1.2 m3; 2 m3 of volume) according to the experimental SD. At the first phase, both fish species were subjected to three SD including 1.5, 3 and 6 kg/m2 for 60 days. In the second phase, fish were submitted to three SD including 3, 6 and 9 kg/m2, whereas in the third phase, beluga were stocked at 6, 9 and 12 kg/m2 and ship sturgeon were stocked at 6, 8 and 10 kg/m2 and each phase lasted for 12 weeks. In both species, the growth performance and feed intake (FI) significantly decreased with increasing SD at the end of the first phase (p < 0.05). In the second phase, growth performance and FI in beluga decreased with increasing SD, whereas in ship sturgeon neither growth nor FI were affected by SD. Interestingly, the growth performance and feed utilization in both species were not decreased with increasing SD in the third phase indicating adaptability of these species to high stocking density during grow‐out period. According to the result of this study, the appropriate initial SD for beluga within the range of 100–500, 500–2,000 and 1,500–3,000 g were at 1.5, 6 and 12 kg/m2, respectively in an open flow‐throw system. Regarding to ship sturgeon, initial SD at 1.5 and 10 kg/m2recommended for fish within the range of 100–300 and 300–1,200 g, respectively in an open flow‐throw system.