The effect of eyestalk ablation on haemolymph osmotic and ionic concentrations during acute salinity exposure in the freshwater shrimp Macrobrachium olfersii (Wiegmann)(Crustacea, Decapoda)

The effect of bilateral eyestalk ablation on haemolymph osmotic and Na super(+), Cl super(-), K super(+), Mg super(2+) and Ca super(2+) concentrations was investigated in the freshwater shrimp Macrobrachium olfersii during acute exposure (1, 3, 6, 12 and 24 h) to sea-water of 21 ppt S. Analysis of variance treatment indicated that haemolymph osmotic and Na super(+), Cl super(-), K super(+), Mg super(2+) and Ca super(2+) concentrations were affected by exposure time (P less than or equal to 0.01). However, only (Na super(+)) was affected by eyestalk ablation (P < 0.01), destalked shrimps exhibiting haemolymph Na super(+) concentrations approximately equals 15 to 30% lower than control shrimps. These results are interpreted to indicate that less Na super(+) enters the haemolymph of eyestalkless shrimps on exposure to seawater of 21 ppt S, presumably resulting from the absence of an eyestalk-located neurofactor. A factor causing the influx of Na super(+) into the haemolymph is thus proposed to be present in the eyestalk ganglionic system of intact Macrobrachium olfersii) in freshwater. Reduction in secretion of the factor may act to reduce Na super(+) entry in high salt environments.