Comparing Na/K-ATPase activity of Macrobrachium rosenbergii (de Man) larvae at specific developmental stages, using different sodium vs potassium and calcium vs magnesium concentrations, and sodium potassium adsorption ratio (SPAR) mediums

Abstract

The present study analyzed the Na/K-ATPase activity (μmolADP/mgprotein/h) of Macrobrachium rosenbergii larvae at specific developmental stages using different environmental concentrations of sodium vs potassium and calcium vs magnesium, for pairwise comparison. In addition, we also compared the effect of various sodium potassium adsorption ratio (SPAR) mediums to Na/K-ATPase activity. The first experiment compared the effect of sodium concentrations (4000 and 5000ppm) vs potassium concentrations (150 and 200ppm), while the second experiment compared the effect of calcium concentrations (180 and 240ppm) vs magnesium concentrations (300 and 400ppm), as in pairwise combination on the Na/K-ATPase activity. The third experiment compared Na/K-ATPase activity for various SPAR mediums (20, 30, 40 and 50). Larval condition index (LCI), larval dry weight and percent survival were determined at the 1st, 4th, 7th and 11th stages for each experiment. For each experimental treatment, triplicate 80-l closed-loop RAS systems were used. Initial larvae stocking density was 300 larvae l−1. For each container, a 40mg batch of larvae was collected at each of the 4 larval stages to analyze Na/K-ATPase activity and LCI. These results revealed that at the 1st and 4th larval stages both sodium and potassium independently and in combination, affected (P<0.05) Na/K-ATPase activity. However, at the 7th stage, enzyme activity was confirmed only among the treatments, independently. At the 11th stage, enzyme activity was demonstrated among the combined treatments, in addition to potassium, alone. Calcium and magnesium only showed larval Na/K-ATPase activity independently at the 1st and 4th larval stages. Results also showed that at the 1st and 4th larval stages, Na/K-ATPase activity was significantly higher for SPAR 20 but, at the 7th and 11th stages the enzyme activity was significantly higher at both SPAR 20 and 30. Accordingly, our findings have demonstrated that, Na/K-ATPase activity is highly variable during M. rosenbergii larval development and that it is mainly affected by interactions of common environmental macro-elements involved in larval osmoregulation. As such, we recommend M. rosenbergii hatcheries to operate as close as possible to SPAR 30 for early larval development and SPAR 40 for later larval development.