Active osmoregulation in the Australian Bass, Macquaria novemaculeata (Steindachner), and the golden perch, Macquaria ambigua (Richardson) (Percichthyidae)

Abstract

The Australian bass, M. novemaculeata, and the golden perch, M. ambigua, differed in the osmoregulatory response of the gills to salinity change. Bass displayed lower gill Na⁺/K⁺-transporting ATPase and succinate dehydrogenase activities in salt water than in fresh water, whereas golden perch displayed the opposite pattern. This difference may indicate that the golden perch has evolved further toward a fresh- water life cycle than the bass, with reduced osmoregulatory effort, particularly in the critical juvenile phase, in fresh water. The spawning and initial juvenile residence of bass in hypertonic conditions may similarly represent preference for, or adaptation to, a habitat that requires reduced osmoregulatory effort by the juveniles. It is suggested that artificial rearing conditions known to compromise the development of Na⁺/K⁺-transporting ATPase-dependent osmoregulation in other species should be avoided, particularly in bass reared in high salinities for stocking into fresh water.