Interactive effects of incubation temperature and salinity on the early life stages of pacific cod Gadus macrocephalus

Abstract

The combined effects of incubation temperature and salinity on the early life stages of Pacific cod Gadus macrocephalus were examined under controlled laboratory conditions. Data were collected from two synchronized experiments. Experiment 1 was designed to evaluate the interactive effects of incubation temperature and salinity on the hatchability of fertilized G. macrocephalus eggs. Experiment 2 was set up to evaluate the interactive effects of incubation temperature and salinity on the time from hatching to 50% mortality of the non-fed yolk-sac larvae (M50). The results show that temperature could significantly influence the development and hatchability of the larvae, as well as the hatching characteristics of G. macrocephalus. Viable hatch was significantly influenced by salinity when the upper and lower thermal limits were approached and shows the synergism of low salinity on egg development at low-temperatures and conversely inhibitory effects of low-salinity at high-temperatures. Data on developmental rates as influenced by temperature were presented at each tested salinity level. No influence of salinity was found at the temperature levels tested. Dome-shaped quadratic curves were fitted to the relationship between temperature and the incidence of larval size and yolk storage at hatch for most of the tested salinity levels. The effect of salinity across all temperatures, however, had a much smaller influence on larval size and no effect on yolk storage at hatch. The influence of temperature on larval duration (time from hatching to M50) could be described in all cases by an exponential power function. Evidence on the synergism of low salinity at low-temperatures and conversely inhibitory effects of low-salinity at high-temperatures was also observed. The results were discussed in reference to salinity modified temperature effects on the early life stages of G. macrocephalus. Maximum hatchability and larval size at hatch, and moderate salinity tolerance and larval duration suggest an optimal temperature range of 4°C to 6°C for the survival and development of the early life stages of G. macrocephalus in the field.