Effect of environmental temperature on survival, growth and population structure in the mass rearing of the gilthead seabream, Sparus aurata

This study reports the effect of temperature regime in terms of degree-days, during a period of 32 days from hatching, on growth, survival and population size structure of gilthead seabream (Sparus aurata). We hypothesized that larger postlarvae with a higher survival potential at the nursery stage may result from an increase in the duration of exposure of larvae to higher temperatures within the tolerable range. Three culture regimes, differing in degree-day exposure, were chosen consisting of the following temperatures in four consecutive periods, 19, 20.5, 22.5 and 24.5°C. These were applied from the day of hatching for the following periods: (1) 13, 5, 5, 9 days; 682.5 degree-days; (2) 8, 5, 5, 14 days; 710 degree-days and (3) 3, 5, 5, 19 days; 737.5 degree-days. Survival of 32-day-old larvae decreased from 8.7 to 2.8% as number of degree-days increased from 682.5 to 737.5. Wet weights at 32 days increased from 14.0 to 16.3 mg under the same conditions. Size variation of 32-day-old larvae was positively correlated with degree-days. The presence of larger (39.1±1.36 mg; mean±95% CI), more aggressive larvae increased sharply from 2.8 to 18.1% as number of degree-days increased. The inverse relationship between the presence of larger larvae in the population and survival suggests that early size grading of bream larvae contributes to higher survival. The direct relationship between degree-days, growth, and size variation of 32-day-old gilthead seabream larvae and the inverse relationship with survival are discussed.