Interpopulation differences in growth, food conversion efficiency and swimming performance of (0+) juvenile Atlantic cod (Gadus morhua)

Wijekoon, Manjusri Pandula Atapattu (2004) Interpopulation differences in growth, food conversion efficiency and swimming performance of (0+) juvenile Atlantic cod (Gadus morhua). Masters thesis, Memorial University of Newfoundland.

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Abstract

Studies have shown that geographically separated fish populations can exhibit life history variations in growth, and that environmental variability and /or genetic differences are responsible for such variations. It has been suggested that common garden experiments could be used to disassemble the environmental and genetic effects on growth in such latitudinally separated populations. The Counter-gradient variation (CnGV) hypothesis originated from such experiments, and predicts that northern populations will grow faster than their southern counterparts. The Atlantic cod (Gadus morhua) has a wide distribution over the North Atlantic Ocean and growth varies significantly among stocks. Understanding such differences in growth could be beneficial for both fisheries management practices and aquaculture of Atlantic cod. -- In my thesis, I first examined the growth of cod from different populations, using common garden experiments. I compared the specific growth rate, food conversion efficiency, hepatosomatic index and survival of juveniles from two cod stocks (NAFO Division 3Ps- Placentia Bay, NF. 48°N; 54° Wand 4T- Northumberland Strait, P.E.I. 46° N; 64° W) at two temperatures (7°C & 11°C) and rations (2% and 0.67% per day). I found no significant difference in growth, food conversion efficiency or hepatosomatic index; however, 3Ps juveniles had significantly higher survival rate (97%) than 4T juveniles (90%) with 2% ration at 11°C. In addition, reaction norm analysis suggested that genetic differences did exist in certain traits (specific growth rate, hepatosomatic index etc.) between these two cod stocks. -- The CnGV hypothesis also suggests that variations in growth among life-history stages of latitudinally separated populations may lead to trade-offs with other biologically important characteristics such as swimming performance. Thus, in my second experiment, I compared the swimming performance (Ucrit), metabolism (resting, active and scope) and cost of transport (COT) between these two populations. Juveniles from both populations spent more energy on swimming at higher temperature (11°C). There was no significant difference in metabolic scope for activity between 4T and 3Ps juveniles; however, 4T juveniles had a 20% higher metabolic scope for activity over 3Ps at high temperature suggesting a greater availability of energy for activity. I found no other significant differences in metabolic rate, Ucrit, metabolic scope or COT between 3Ps and 4T juveniles.

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