Growth performance and proximate composition of Penaeus vannamei reared in low-salinity water with different ionic compositions in a synbiotic system

The aim of the present study was to evaluate the effect of different ionic compositions in low-salinity water on the growth and proximate composition of Penaeus vannamei reared in the synbiotic system. A 56-day trial (300 shrimp m -3 ) was conducted in 60-L units with a completely randomized experimental design involving three treatments (each with three repetitions): Control — seawater diluted to salinity ~ 2.7 g L −1 ; T1 — seawater diluted to salinity ~ 2.7 g L −1 with Ca:Mg:K ratio adjustment (1:3:1); and T2 — seawater diluted to salinity ~ 2.7 g L −1 with Mg 2+ adjustment. The shrimp survival rate varied from 53.7 to 81.48%, shrimp (initial weight = 0.42 ± 0.1 g) reached a final weight ranging from 3.70 ± 0.07 to 4.72 ± 0.09 g and an average yield ranging from 0.61 ± 0.14 to 1.22 ± 0.06 kg m −3 , with significant differences among the treatments. The best overall growth was found in the T2 treatment. The T1 treatment had the significantly lowest results, which may have been due to reduction in the Na:K ratio (Control = 27.39; T2 = 29.03; T1 = 19.55) due to K + corrections. Low concentrations of nitrogen compounds were found due to the synbiotic fertilization and substrate composed of Anomalocardia brasiliana shells that work as substrate for bacteria and a source of calcium carbonate. No significant differences in proximate composition were found among the treatments. A difference in the ash content of the microbial flocs was found among treatments, with a higher percentage in the T1 treatment compared to the Control and T2 treatments. The present results indicate that total alkalinity close to 90 mg CaCO 3 L −1 and the Na:K ratio close to 28:1 produced conditions that did not limit the growth of P. vannamei in low-salinity water with a synbiotic system.