HORMONE INDUCTION AND LARVAL REARING OF MULLOWAY, ARGYROSOMUS-HOLOLEPIDOTUS (PISCES, SCIAENIDAE)

Pond-held mulloway (Argyrosomus hololepidotus) from Port Hacking, New South Wales, were induced to spawn by injecting human chorionic gonadotrophin (hCG) at 1000 IU/kg for females and 250 IU/kg for males. Two pairs of fish were stripped, and fertilised eggs were incubated at 23.5 +/- 1 degrees C. Fecundity was high with an estimated 900 000 and 1 042 000 eggs collected from each female. At hatch, larvae averaged 2.25 +/- 0.09 mm TL (mean +/- s.d.) with a yolk sac of 0.88 +/- 0.08 mm and an oil globule of 0.27 +/- 0.03 mm. Feeding and initial swim bladder inflation started between day 3 and 4 after hatch. Metamorphosis started when larvae reached 12 mm at 23 days of age, and was complete by day 34 when larvae were 15-26 mm. Larvae with functional swim bladders (> 70% by day 11) grew faster than those without swim bladders. Cannibalism of smaller fish, many without swim bladders (4.2 +/- 0.06 mm), occurred from day 18. Fish were offered live food to day 68, supplemented with finely chopped pilchards and pellets from day 38. From day 106 to day 180 fish were feeding solely on pellets. Juveniles grew to a mean weight of 21.0 +/- 0.7 g and a mean length of 121.5 +/- 1.3 mm in 180 days. These results indicate that A. hololepidotus has potential for hatchery production.