Compensatory growth and energy reserves changes in the Pacific white shrimp (Litopenaeus vannamei) reared in different temperatures and under feed restriction in biofloc technology system (BFT)

Abstract

It was evaluated the occurrence of compensatory growth in the Litopenaeus vannamei reared in different temperatures and under feed restriction in Biofloc Technology System (BFT) and its effects in energy reserves and immune system. The experiment lasted 64 days and was divided in two phases: (1) Restriction and (2) Recovery. L. vannamei were stocked with 1.78 ± 0.38 g at a stocking density of 300 shrimps/m3. In the first phase (36 days), the experiment was performed using three temperatures and two feed regimes experimental design, totaling six treatments (in triplicate). Three temperatures were chosen: optimum (28 °C), intermediate (24 °C) and low (20 °C) and two feeding regimes were established for each temperature: the control that received 100% of the calculated feed rate and the feed restriction group, where the feed rate was 40% of the control. In phase 2 (28 days), all the experimental units were exposed to favorable conditions. Total protein, glycogen and triglycerides content were quantified in hepatopancreas and muscle and differential hemocyte count (DHC) was analyzed in hemolymph, in days 0, 36 and 64. At the end of the experiment, previously restricted shrimps held at 24 and 28 °C displayed complete body weight catch-up through compensatory growth following the restriction period with depressed growth. Shrimps maintained at 20 and 24 °C with no feed restriction did not reach 28 °C treatment body mass when favorable temperature (28 °C) was established. Protein levels in hepatopancreas and muscle were not affected in any treatment over the experiment and glycogen was used as a metabolic fuel in all restricted groups during phase 1, but fully recovered when total feed supply was offered in phase 2. Triglycerides were also used in restricted shrimps held at 24 and 28 °C in phase 1, and after the recovery period, only treatment previously maintained at 24 °C presented total recovery. DHC presented differences among treatments, but was maintained in the optimal range for healthy shrimps reared in BFT system over the experimental period. Also, survival was not affected by feed restriction or low and intermediary temperatures. Therefore, it is possible to submit L. vannamei to partial feed restriction with as a trigger for total compensatory growth, in order to improve feed efficiency and decrease feed supply. Also, in regions that low temperatures are a limiting to shrimp growing seasons, it is viable to explore partial compensatory growth to increase annual harvests.