Effects of water temperature on bluefin tuna spawning biology in captivity

Effects of water temperature on the periodicity of spawning, egg size, and spawning time were examined for the bluefin tuna Thunnus orientalis in captivity. Spawning of bluefin tuna was observed for the period between May 13 and November 10, which is a longer spawning duration than the previous reports for bluefin. The spawning pattern suggested that the initiation and duration of spawning are affected by a rapid change of water temperature (WT) from 23 deg C before spawning. The quick increase in the WT from 23 deg C induces early spawning and it continues for a longer duration. Mean egg diameter ranged from 0.90- 1.06 mm and the minimum egg size was 0.83 mm. There was a strong inverse relationship between egg diameter and WT. In this study spawning was observed between 17:31-23:36. Spawning of bluefin as late as 23:30 has not been reported in past studies. A strong correlation between WT and spawning time was observed (as WT increased the time of spawning became later). In this study, it was apparent that water temperature strongly influenced the periodicity of spawning, egg size, and spawning time of bluefin. This information could be vital for managing broodstock of bluefin tuna.