Effects of constant Ca2+ concentration in salinity fluctuations on growth and energy budget of juvenile Litopenaeus vannamei

A 50-day experiment was conducted to investigate the effects of constant Ca²⁺ concentration in salinity fluctuations on growth and energy budget of juvenile Litopenaeus vannamei. The salinity and Ca²⁺ concentration of control group S0 were kept 30‰ and 385 mg l⁻¹, respectively throughout the experiment while the ranges of salinity fluctuations of the treatment groups S5 and S5C, S10 and S10C, S15 and S15C, S20 and S20C were 5, 10, 15, and 20‰, respectively. The Ca²⁺ concentration of the treatment groups S5, S10, S15, and S20 (salinity fluctuation groups) changed with salinities, while the Ca²⁺ concentration of the treatment groups S5C, S10C, S15C, and S20C (constant Ca²⁺ concentration groups) was kept 385 mg l⁻¹ during the experiment. The results were as follows: (1) There were no significant differences in SGR of shrimp in salinity fluctuation groups (P > 0.05); But shrimp in the groups S15C and S20C had significantly higher SGR than those in the groups S5C and S0 in constant Ca²⁺ concentration groups (P < 0.05); (2) Results of the t test showed that significant differences in SGR were also found between S15 and S15C (P = 0.012), and between S20 and S20C (P = 0.013); (3) The shrimp in groups S15C and S20C deposited significantly more energy for growth and spent significantly less energy in respiration than those in groups S15 and S20 (P < 0.05), respectively. These results showed that compared with constant salinity and fluctuating salinities, the growth performance of shrimp under constant Ca²⁺ concentration in large ranges of salinity fluctuations could be better.