Ionic regulation of four species of penaeid prawn

Abstract

The regulation of sodium, potassium, calcium, magnesium, chloride, and sulphate in adults of the Australian penaeid prawns, Penaeus plebejus Hesse (king prawn), P. esculentus Haswell (tiger prawn), P. merguiensis de Man (banana prawn), and Metapenaeus bennettae Racek & Dall (greasyback prawn) was investigated over the salinity range ( S) 10–50‰. Results for chloride, sodium, total anions, and total cations showed that the king prawn was overall a poor regulator; the tiger prawn was a poor regulator at lower salinities but showed evidence of ability to regulate above S 45‰; the banana prawn regulated well between S 15–40‰; the greasyback prawn regulated efficiently throughout the range tested. This order of regulatory ability was reflected in the other ions. Potassium levels were regulated to some extent in all species, with a tendency towards accumulation. Calcium was accumulated in all species, while magnesium levels were strongly reduced at low salinities, but in the tiger and banana prawn there was a sharp peak at ≈ S 40‰ which returned to previous levels at higher salinities. In the banana prawn there was a depression in sodium levels of almost the same magnitude as this peak. It is suggested that ≈ S 40‰ represents a zone of ionic instability, corresponding to the transition from high rainfall coastlines, where inshore salinities rarely exceed normal, to arid coastlines where inshore salinities rarely fall below S 36‰. The complex nature of the penaeid antennal gland bladder is briefly discussed in relation to these changes. Sulphate was maintained at very low levels at lower salinities, but paralleled the iso-ionic line at higher salinities.