Efeito do ajuste iônico em água de baixa salinidade no desempenho zootécnico e composição centesimal do Litopenaeus vannamei cultivado em sistema simbiótico

Abstract

Shrimp farming in inland waters is carried out under different salinity and ionic water profiles worldwide. Despite the contribution of this culture modality, several obstacles are observed to accomplish a complete farming cycle. This study aimed the evaluation of different ionic compositions in oligohaline water on the zootechnical performance and proximal composition of Litopenaeus vannamei reared in synbiotic system. A 56- day trial (300 shrimp/m³) was performed in 60 L experimental units in a completely randomized experimental design, under three treatments: IP – water at a salinity ~2,7 g/L with its Ca:Mg:K ratio adjusted to 1:3:1, C1 (control) - water at a salinity ~2,7 g/L, and C2 - water at a salinity ~2,7 g/L with a magnesium (Mg2+) adjusted seawater equivalent concentration, all in triplicates. The individuals reached a final weight (g) of 3.79 ± 0.07 – 4.72 ± 0.09 and an average yield (kg/m³) of 0.61 ± 0.14 - 1.22 ± 0.06, showing significant differences among treatments, the best overall growth and average yield were observed at C1 and C2, in the other hand PI treatment presented the worst results, this may be influenced due to potassium chloride (KCl) addition to increase potassium (K+) concentration, resulting in a Na:K ratio reduction. Regarding the water quality, an increase of total alkalinity (mg CaCO3/L) was observed in all low salinity treatments during the experiment, also, low concentrations of nitrogenous compounds were observed, this may be accomplished due to the presence of artificial substrates composed by Anomalocardia brasiliana shells, that worked as a substrate for bacteria and a calcium carbonate source. Shrimps’ proximal compositions did not show significant differences among treatments, however, microbial floc composition presented significant differences in ashes (%). Na/K ratio showed a positive relationship to shrimps zootechnical performance in this study. Our results indicate that shrimp juveniles present satisfactory performance in oligohaline water in synbiotic system.