Effects of temperature on early life stages of Atlantic cod Gadus morhua: A descriptive study

Temperature is an important parameter during the early life stages of fish and has been a topic of interest for marine species for a long time. Atlantic cod Gadus morhua is an economically important species and a great candidate for aquaculture diversification despite the present bottlenecks of high production costs and low market prices. The aim of this study was to describe the effects of temperature on early life stages of Atlantic cod, G. morhua. Secondary data was obtained from laboratory studies done on various Atlantic cod stocks and inductive reasoning research strategy was used applying the systematic literature review approach. Numerous studies showed that temperature has a large effect on the timing of important developmental stages like time to hatching. A synthesis of five case studies showed that time to hatching in days (Tdays) was inversely related to temperature in an exponential way (T days= 28.904e-0.125x ). Development rates were faster for higher temperatures than lower temperatures although structural changes slowed and accelerated at different developmental stages. Results also confirmed that temperature has significant effects on fertilization success and egg quality whereas effects on egg mortality show a high degree of variability. Temperature altered the number and size of embryonic muscle fibres in different ways for different stocks, while respiration rate and otolith growth generally increased with temperature. Prevalence of particular vertebral malformations was also found to be temperature dependent. Finally, a 32 hour stepwise increase from ambient temperature (4.5˚C) to optimal temperature (9.5 ˚C) was found as the best option of increasing temperatures whilst avoiding a reduction in the quality and quantity of viable larvae. Temperature changes may cause a mismatch between the occurrence of first feeding cod larvae and their prey organisms, and in a changing climate, variable and changing environmental conditions may affect growth and mortality and generate recruitment variability. In conclusion, temperature is an important factor in both the aquaculture of cod and for recruitment of wild cod stocks.