Effects of Salinity, Temperature, and Dissolved Oxygen on Early Development of the Pacific Cod (Gadus macrocephalus)

Abstract

Effects of various combinations of levels of salinity, temperature, and dissolved oxygen on incubation of Pacific cod (Gadus macrocephalus) eggs were investigated in the laboratory. Quantitative relations were determined, by response surface analysis, between the environmental variables and four criteria used to estimate success of egg development. Larval size at mean hatching time, and percentages of total hatch, viable hatch, and postmature eggs that failed to hatch were optimized at intermediate salinities (about 15‰), low temperatures (3–5 C), and over a wide range of dissolved oxygen concentrations. Pacific cod eggs are judged to be euryhaline, euryoxic, and stenothermal. As long as temperatures are within the range of about 3–5 C, the developing egg is tolerant of a wide range of salinities, and of dissolved oxygen levels to a minimum of about 2 or 3 ppm. Below 3 C developmental success decreases precipitously; above 5 C it attenuates more slowly.Distribution and abundance of Pacific cod are reviewed in light of the experimental results. Temperature is suggested to be of major importance to successful egg development in the natural environment; the temperature range associated with reasonable egg viability and incubation success is estimated to extend from about 2.5 to 8.5 C.The distribution of cod in the spawning season appears associated with water temperatures between 2.5 and 8.5 C in Asian waters. Near the southern limit of cod distribution on the North American coast the following associations are suggested in relation to temperatures of the upper mixed layer of coastal waters in the spawning period: limit of commercial abundance, 9 C; extent of limited commercial landings, 10 C; limit of occurrence, 13.5 C.