The Effect of Temperature on the Development, Growth and Survival of Atlantic Cod (Gadus morhua) During Early Life-Histories

For poikilothennic animals, and in particular those that inhabit aquatic habitats, temperature has a significant effect on all life processes. The purpose of this research was to investigate the contribution of temperature on embryonic development and survival and its effect on vital rates. Of particular interest was what aspect(s) of egg and larval life-histories are most affected by temperature and what consequence temperature effects may have on cumulative mortality. Three batches of Atlantic cod (Gadus morhua) eggs were acquired from a Newfoundland source of adult broodstock held at 4555°C. The eggs were divided andacclimated to four constant temperature regimes at approximately 2,4,8 and 12°C. Observations on development, growth and survival were made approximately every 4 degree days (mean temperature X number of days). Measurements taken included development stage for egg and yolk-sac period larvae, standard length of larvae, yolk-sac area, and the mortality of eggs and larvae. The analysis of size and development stage at hatch shows that the two measures are correlated. During the yolk-sac period, development-based changes in length largely eliminated any early differences in size. There was no relationship between size at hatch and the incidence of first-feeding larvae, but there was a dome-shaped relationship between temperature and the incidence of first-feeding. Relationships between the environmental temperature and rates of mortality, growth, development and yolk-sac absorption were constructed. Data were collected from two synchronized experiments. Experiment 1 was designed to evaluate the effects of temperature on the development of eggs and then on the growth of larvae. While collecting development and growth information, the yolk-sac size, feeding incidence and the condition of larvae were also noted. Experiment 2 was set up to evaluate the effects of temperature on the mortality of eggs and larvae. Temperature affected egg development and mortality, and larval growth, yolk-absorption, feeding and larval mortality, all known as vital rates. Increasing temperature exponentially decreased the time it took to reach the point at which feeding is initiated. The post yolk-sac growth for all temperatures resulted in a log-normal relationship. From the growth-temperature relationship, the maximum slope, where the growth rate per degree is maximized, and a temperature where growth per day was maximized was calculated. The predicted temperature of maximum growth rate was 7.g°C, and the predicted temperature the growth rate per degree was maximized was 4.2"C. A linear regression model best described the rate of yolk reduction across the different temperatures. The mean survival time during the egg stage showed an exponential decrease with temperature. The mean survival time for larvae resulted in a log-normal model, again with decreasing survival times with increasing temperature. The results are discussed in reference to normal temperature effects, which cause increasing vital rates with increasing temperature, and negative temperature effects, which changes the relative metabolic cost at different temperatures. Negative effects begin to dominate outside a optimal range of temperatures between 4-8°C. The temperature of maximum growth rate per degree is suggested as the optimal temperature for growth for larval cod in the field.