THE EFFECT OF SALINITY IN THE EXTENSIVE REARING OF AUSTRALIAN BASS MACQUA RIA NOVEMACULEATA

The Australian bass is a euryhaline catadromous fish requiring salinities of at least 14gl- ' for successful spawning (Llewellyn and Macdonald 1980; van de Wal1985). Adult fish undertake a downstreammigration inearly winter with adults and juveniles returning upstream in winter and early summer. Langdon(l987) postulated that juvenile bass need to remain in estuarine waters until they develop the ability to osmoregulate in fresh water because energy losses due to osmoregulation are minimised within the con-fines of the estuarine habitat where isosmotic conditions are most likely to be found. Thus the timing of this ability to osmoregulate is critical in the transfer to fresh water of artificially reared juvenile bass. Commercial production of Australian bass in Queensland (Qld) commenced in 1988, almost ten years later than inNew South Wales (NSW), where some excellent research had been conducted into the larval biology of these animals by a number of workers. However, two commercial hatcheries in Qld claimed significant larval survival when pansferred to fresh water within a few days of hatching. This was in direct contrast to the findings of Battaglene et al. (1989), who found that larvae could not survive in fresh water before the age of three weeks. Subsequently, a research programme was initiated to compareNSW and Qld stocksreared under identical conditions in a cooperative effor