Reproduction and embryo viability of a range-limited tropical freshwater fish exposed to fluctuating hypoxia

Abstract

Hypoxia can profoundly affect fish reproduction and larval development, but its effects on fish from tropical Australia are not well understood. In the present study, the effects of diel fluctuating hypoxia on reproduction and embryo viability were investigated for a range-limited tropical freshwater fish, namely the Utchee Creek rainbowfish (Melanotaenia utcheensis). The lethal level for adult rainbowfish after gradual oxygen depletion was ~7% dissolved oxygen (DO) saturation. After 28 days, the reproductive success of adult fish exposed to fluctuating hypoxia treatments was measured by fecundity, gonad health, egg incubation time, egg and larval mortality, viability and size of hatching larvae. Reproduction was impaired in the lowest sublethal treatment (minimum 10% DO saturation each day). No ill effects of parental exposure to diel fluctuating hypoxia on embryos were identified, and minor differences in temperature between aquaria had a greater effect on embryos than parental hypoxia treatments. Similarly, no effects of embryonic exposure to diel fluctuating hypoxia were identified. Utchee Creek rainbowfish appear to be more hypoxia tolerant than temperate species, in keeping with their habitat in warm lowland streams, but they are still susceptible to the increasing frequency and intensity of hypoxia possible with increasing temperature and reduced flow as a result of climate change.