This study investigated the onset of liver function in larval crimson-spotted rainbowfish (Melanotaenia fluviatilis). Mortality was determined for various aged larval fish pulse exposed (PE) for 2 h to two liver metabolized chemicals: cyanazine which is detoxified, and malathion which is activated to a more toxic metabolite. Cyanazine toxicity decreased between day 0 and day 3 post-hatch with no further change up to day 12 post-hatch. No significant difference in malathion toxicity with age was found but a trend of increased toxicity between day 0 and day 3 post-hatch was evident. The results indicated that rainbowfish liver becomes functional between 0 and 3 days post-hatch. Static replacement 96 h LC50s (slope, 95% F.L) for 4-month-old adult rainbowfish continuously exposed to cyanazine and malathion were 24.6 (9.48; 20.6, 28.3) and 2.09 (94.6; 1.6, 2.6) mg/l respectively; 2 h PE NOEC and LOEC values based on larval mortality for cyanazine and malathion were < 1.9 and 1.9 mg/l, and < 15.6 and 15.6 mg/l respectively. These results indicate that rainbowfish are moderately sensitive to cyanazine and malathion toxicity.

Several studies have demonstrated the potential for induction of the cytochrome P450 biotransformation enzymes to interfere with reproduction. The polychlorinated biphenyl (PCB) isomer 3,3{prime},4,4{prime},5 pentachlorobiphenyl, is a major component of the EROD inducing fraction of commercial PCB mixtures which have been shown to have adverse effects on reproductive function. Australian crimson-spotted rainbow fish (Melanotaenia fluviatilis) were exposed for 8 or 21 days to either 3,3{prime},4,4{prime},5-PCB (approx 0.2 ttg/fish/day) contaminated food or carrier control food. EROD and ECOD activities were measured on livers collected at the end of exposure. Reproductive performance was monitored throughout the exposure as rainbow fish produce eggs daily. Female EROD activity (nmol/min/g of liver) was elevated by PCB exposure 2.6 and 2.2 fold at days 8 and 21 respectively. Female ECOD activity was elevated 1.8 fold on day 21 only. There was a trend towards elevated male EROD at both sampling intervals. Male ECOD was not significantly altered. There was no effect of PCB on egg and larvae numbers or hatchability. In summary, these results show that induction of EROD activity was not associated with impairment of reproductive function, but represented a potentially useful biomarker of PCB exposure in female crimson spotted rainbow fish.

This paper describes the early ontogeny of the crimson-spotted rainbowfish Melanotaenia fluviatilis. Eggs ranged in size from 0.98 to 1.07 mm and 35-45 oil droplets were present, as were numerous adhesive filaments which originated from one point. Hatching was predominantly 7-9 days after spawning at 25.5 degrees C. At hatching, larvae (4.2 mm standard length) had a reduced but still present yolk sac and were strong enough swimmers to remain in the upper 1 cm water layer. The swim bladder inflated within 10 h of hatching and the first ingested food was observed after 12 h. At 32 days after hatching, the mean larval length was 13.86 mm and at 72 days was 21 mm. Knowledge of the critical developmental stages described in the paper is important in understanding the impact of the major biotic modifying factors influencing the impact of chemicals and other pollutants on rainbowfish, especially given that they are used by ecotoxicologists as a surrogate species for Australian freshwater fish in general.