Induced ovulation and larval rearing of four species of Australian marine fish

This thesis developed techniques for the large-scale breeding of marine fish in New South Wales. It provides the first published account of the hormone induction and larval rearing to metamorphosis of Australian bass Macquarie novemaculeata (Percichthyidae), snapper Pagrus auratus (Sparidae), mulloway Argyrosomus hololepidotus (Sciaenidae) and sand whiting Sillago ciliate (Silliganidae) in Australia. Wild-caught broodstock were induced to spawn using hormones (hCG, LHRHa, Ovaprim) and either spawned naturally or were stripped. Pagrus auratus and S. ciliate were found to be multiple spawners with asynchronous ovaries. Conversely, M. novemaculeata and A. hololepidotus were found to be highly fecund single spawners having group synchronous ovaries. All four species were successfully induced to ovulate after periods in captivity ranging from one to five years. Species specific differences in hormone induction were determined, particularly in relation to the overripening of eggs and the optimum time between treatment and stripping. Commercial scale batches of larvae were reared in 2000 L conical tanks and replicated experiments were conducted in aquaria ranging in size from 2 to 70 L. Larval development for all four species was described and egg size, time to hatch, size at hatch, yolk size, oil globule size, and beginning of exogenous feeding were compared among species. First feeding larvae were reared on rotifers Brachionus plicatilis and then brine shrimp Artemia sp. Survival, growth and weaning of larvae at metamorphosis were compared. Factors affecting larval survival, particularly those influencing initial swim bladder development were tested in replicated laboratory experiments. The timing of swim bladder inflation was found to coincide with the start of exogenous feeding but feeding was not required for initial swim bladder inflation. Larvae that failed to inflate their swim bladder grew poorly and were susceptible to stress induced mortality. Light intensity, was shown to be an important factor influencing swim bladder inflation in cultured larvae. The effect of light intensity on inflation in M. novemaculeata and S. ciliate was quantified. Exposure to continuous light (100-200 Lux) inhibited inflation in M. novemaculeata. In contrast, S. ciliate were shown to have a diel pattern of nocturnal inflation and required higher light intensities to feed (1000 Lux). Manipulative experiments with S. ciliate larvae showed that they responded to darkness by inflating their swim bladders. Other abiotic factors such as surface access, low salinity and high aeration were shown to reduce inflation in larvae. Initial swim bladder inflation strategies are discussed and recommendations made regarding the importance of maximising inflation. The results of the study were used to assess the relative difficulty of intensive commercial production of each species for aquaculture.