Effects of dietary protein content and stocking density on growth performance, nitrogen excretion, and relevant biochemical parameters of juvenile Takifugu rubripes

Abstract:

The effects of protein content and stocking density on growth performance, nitrogen excretion, and related physiological and biochemical indexes of juvenile fish were studied using juvenile tiger puffers (Takifugu rubripes) with an average initial body weight of 15.60 g. A two-factor, three-level (2×3) design was used, with three different protein levels (38.87%, 45.55%, and 51.00% dry matter) and stocking densities of 1.53 kg/m3 (20 fish in a tank of 0.196 m3 volume), 2.30 kg/m3 (30 fish per tank), and 3.06 kg/m3 (40 fish per tank). The feeding trial was conducted in an indoor flow-through system. Each diet was fed to triplicate tanks for 8 weeks. The results showed that, at a certain stocking density, low dietary protein resulted in lower weight gain compared with the medium and high dietary protein levels (P<0.05). Neither dietary protein content nor stocking density significantly affected body proximate composition of experimental fish. At a certain dietary protein level, high stocking density increased total protein and total cholesterol contents in serum compared with medium stocking density (P<0.05). The total protein in serum was higher in the low-protein group than in the medium-protein group (P<0.05). The activity of alkaline phosphatase in serum was significantly higher in the low-protein group than in the high-protein group (P<0.05). No significant interaction was observed between the effects of dietary protein content and stocking density on growth performance and nitrogen excretion. Ammonia nitrogen excretion in the high-stocking-density group was higher than that in the low-stocking-density group at 3 hours after still-water feeding (P<0.05). Results of this study suggest that 45.55% dietary protein was sufficient to maintain normal growth in tiger puffers. Dietary protein content and stocking density had no significant interaction in the effects on growth performance and ammonia nitrogen excretion.