M. Pryor, J.A. Brown
Abstract:
Atlantic cod (Gadus morhua), eggs and yolksac larvae were incubated at three different temperatures to determine temperature effects on incubation time and development. Incubation time (days) was much shorter for both the high (7.0-8.0C) temperatures with developmental time being, on average, 40% longer for the low (0.0-1.0%) temperature. No significant difference was observed between egg dry weights (±0.0001 mg) at the tree temperatures over time. However, egg diameters were significantly different between the temperature treatments with egg diameter increasing proportionately with temperature. Larval development was much slower at 0.0-1.0°C with yolksac absorption taking nearly twice as long as the other two treatments. Larval growth was found to be significantly different between treatments as total larval length was greatest at the lowest temperature both at 50% hatch and at the end of the yolksac stage, while yolksac with at 50% hatch was significantly greater at 3.0-4.0 C. However, larval dry weights at both 50% hatch and at the end of the yolksac stage were not found to be significantly different between the three treatments over time. Based on these results, it appears that while incubation time is decreased with increasing temperature smaller larvae will result at higher temperatures which may be of poorer quality or less able to survive mass rearing conditions. Further study is needed to determine viability of larvae reared at these temperatures so that proper rearing conditions may be developed for future cod hatchery facilities in Newfoundland.
(Marine Institute of Memorial University, P.O. Box 4920, St. John's, NF A1C 5R3, Canada)