Dietary magnesium chelate alleviates oxidative stress and improves growth in white-leg shrimp, Penaeus vannamei (Boone, 1931), reared in inland saline water

Nine semi-purified diets containing either magnesium citrate (MgC) levels of 0.0, 2.24, 4.48, 6.72, 8.96 g Kg-1 or magnesium amino acid complex (MgAA) levels of 2.17, 4.35, 6.52, 8.7 g Kg-1 were fed to P. vannamei juveniles thrice daily and reared for 60 days in sub-optimum inland saline ground water (ISGW) of 10%o. Five hundred sixty-seven healthy juvenile shrimps (3.51 & PLUSMN; 0.03 g) were randomly stocked in triplicate into 350 L tanks at a density of 60 m-3. The weight gain (WG %) and specific growth rate were highest in the shrimps fed with 4.48 g Kg-1 MgC and 2.17 g Kg-1 MgAA. Further increase in the dietary magnesium did not show any additional growth, relatively inhibited it. The positive correlations (p < 0.01) between WG % and magnesium contents of serum, body and hepatopancreas suggests indirect involvement of tissue magnesium in growth performance. Conversely, negative correlations (p < 0.01) of WG % with superoxide dismutase and heat shock protein 70 (HSP 70) in gill and hepatopancreas indicate stress-induced inhibition of growth. Higher inclusion of dietary magnesium altered sodium-potassium ATPase (NKA) mRNA expression in hepatopancreas. The minimum dietary MgC and MgAA supplementations of P. vannamei juveniles for growth improvement were determined to be 4.25 g Kg-1 and 2.38 g Kg-1 feed, respectively, which was equivalent to 2.86 g Kg-1 and 1.64 g Kg-1 feed respectively, using broken-line regression analysis based on the weight gain (%). Overall results reveal that dietary MgAA was better than MgC in alleviating ionic stress and improving growth performance and survival rate in shrimp reared in 10%o ISGW of the sub-optimum magnesium suite.