INITIAL SWIM BLADDER INFLATION IN INTENSIVELY REARED AUSTRALIAN BASS LARVAE, MACQUARIA-NOVEMACULEATA (STEINDACHNER) (PERCIFORMES, PERCICHTHYIDAE)

Laboratory experiments conducted on newly hatched Australian bass (Macquaria novemaculeata) larvae in 60-l aquaria demonstrated that initial swim bladder inflation took place 6-11 days after hatch at a temparature of 19±1°C. While inflation occurred at the time when exogenous feeding normally started, feeding was not a requirement for inflation. Larvae were small (4.4-4.6 mm), negatively phototactic and lightly pigmented at the time of inflation. The mean number of larvae with dilated (liquid filled) swim bladders increased from 0.3% on day 7 to 23.0% on day 10. Survival was not significantly affected by continuous light (100-200 lux), salinity (10 and 30‰) or aeration (0-3000 ml/min). Under conditions of darkness, salinities above 25‰ and low to zero aeration, 66.8-72.0% of larvae inflated their swim bladders by day 11. Continuous exposure to fluorescent light (100-200 lux) almost totally inhibited inflation with only 0.1±0.4% (mean±SD) of larvae inflating their swim bladders. Exposure to light on a 12:12 light:dark photoperiod at intensities of 0.3-50 lux reduced inflation to 18.3-11.0%. Inflation was also reduced at a salinity of 10‰ (32.3±23.0%) and under high aeration, 1000-3000 ml/min (18.4±9.2%). © 1990.