The aim of this project was to farm, on a pilot commercial scale, two indigenous species of marine fish: snapper, Pagrus auratus; and mulloway, Argyrosomus hololepidotus.

The project involved:

• development of hatchery techniques;
• intensive rearing of larvae;
• transport of live fish;
• design, construction and testing of seacages for research;
• grow-out of juvenile fish in tanks and seacages;
• identifying and treating disease outbreaks in seacages;
• obtaining production data; and
• obtaining preliminary marketing information.

The project sought to provide information on the possibility of enhancing wild stocks of mulloway by the release of fish originating from a hatchery.

This is a report on the second stage of a two part program investigating hatchery production, farming and seeding of the commercial scallop, Pecten fumatus. A total of more than four million scallop spat were produced for farming trials and over 250 000 scallops ranging in size from 20-60 mm were released into Jervis Bay.

Hatchery techniques were broadened to include procedures for the production of triploid P. fumatus. In general, the survival of triploid scallops was considerably lower than that of normal (diploid) scallops, particularly, immediately after treatment and during early larval rearing. No differences were observed between triploid and diploid spat, however, juvenile triploid scallops tended to be larger and heavier with significantly larger muscle tissues. The significant reduction in embryo development percentages (>80%), the relatively low percentage triploidy achieved initially (41%) followed by consistent reductions in percentage triploidy, mean that further research is required before it would be applied to the commercial sector.  

Although our previous research had, for the first time, demonstrated reliable large scale rearing of P. fumatus larvae was possible, several major constraints to hatchery production were noted. Previously, larvae were either retained in the hatchery until they were large enough to be transferred to land based upweller systems, or larvae were settled on mesh in collector bags and transferred directly to the field. A new technique was developed in which larvae were settled on mesh screens held in the hatchery for about a fortnight before being placed in mesh bags at known densities and moved to the field for culture. This technique allows control of spat stocking density, and has produced threefold increases in spat yields over previous bag settlement techniques while significantly reducing maintenance costs.

KEYWORDS: Commercial scallop, hatchery production, farming, reseeding.