Effect of temperature on incubation period and hatching success of obscure puffer Takifugu obscurus (Abe) eggs

Artificially fertilized eggs of obscure puffer Takifugu obscurus were obtained by induced spawning of cultured broodstock and incubated at temperatures of 15, 19, 23, and 27 °C. The results showed that the optimal temperature for obscure puffer embryonic development ranged from 19 to 23 °C, based on total hatch rate, viability of newly hatched larvae 24 h post-hatch, and total mortality rate of eggs. At the given temperature range, the times taken for 50% embryos to hatch were 11.3, 6.6, 5.0, and 4.2 days, respectively. There was significant difference in time to 50% hatch among the temperatures used in this experiment. The power law model, quadratic equation, exponential equation, and effective degree-day model all provided good fits for the relationship between incubation temperature and time to 50% hatch, with r2 values greater than 0.90. The formulae for these were y=1031.7T−1.6885, y=44.721−3.1574T+0.0615T2, y=34.663e−0.0813T and y=78.905/(T−7.6033), respectively, where y is time to 50% hatch in days, and T is incubation temperature in degrees Celsius. The effective degree-day model was determined to be the best model because of efficient computation, good fit to the experimental data, and most importantly, the derived parameters, k (the sum of effective degree-days) and t0 (the temperature of biological zero), have important biological meaning. Based on the effective degree-day model, the t0 and k values were calculated as 7.6033 °C and 78.905 degree-days, respectively.