Hypoxia, low salinity and lowered temperature reduce embryo survival and hatch rates in black bream Acanthopagrus butcheri (Munro, 1949)

Embryo survival and hatch rates were measured in black bream Acanthopagrus butcheri exposed to different treatments of dissolved oxygen: hypoxic and normoxic, three salinities: 15, 23 and 35 and two temperatures: 16 and 20 degrees C. Hypoxic conditions (50% saturation) reduced 1 day embryo survival by up to 15% (P < 0.05) compared to embryos held in normoxic (> 80% saturation) conditions. Temperature had no effect on the survival of embryos in these treatments, however, lowered salinity significantly reduced embryo survival at 20 degrees C, but not at 16 degrees C. Mean hatch rates were reduced by 10-28% in hypoxic treatments (P < 0.05) and lowered salinity treatments (P < 0.05). Hatching was delayed by up to 24 h at 16 degrees C and very low (or zero) hatching occurred in hypoxic treatments at salinities of 15 and 23. These results confirm that environmental conditions in estuaries are important factors in determining spawning success of black bream and are discussed in relation to global warming and climate change that are likely to alter the physical conditions in southern Australian estuaries.