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Variability in condition and growth of Atlantic cod larvae and juveniles reared in mesocosms: environmental and maternal effects

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Standard length, dry mass and RNA : DNA ratio measurements of 3876 Atlantic cod Gadus morhua larvae and juveniles from 26 families of recruit (fish during their first year of spawning) and repeat spawners (fish which were in their subsequent spawning season) reared in two mesocosms (2500 and 4400 m3) under semi-natural conditions were analysed over a period of 10 weeks using microsatellites. Larvae from recruit spawners were significantly longer and heavier at hatch and throughout the 10 weeks. RNA : DNA ratios from recruit spawner offspring were only significantly higher at week 1. The smaller (2500 m3) mesocosm was characterized by low plankton density during the transition from endogenous to exogenous feeding followed by a higher density during the metamorphosis period (weeks 4 and 5), with the reverse pattern evident in the 4400 m3 mesocosm. Patterns of larval growth followed patterns of zooplankton density. Significant differences in RNA : DNA ratios between the mesocosms at all comparable sampling dates were found and within each mesocosm individual fish exhibited a wide range of growth and condition responses under the same environmental conditions. RNA : DNA ratios as a function of size differed in the amount of variability between mesocosms, indicating that the higher food density led to a higher proportion of well-conditioned larvae in the first 3 weeks. Food availability probably has a major role in determining offspring growth and condition, with limited effects due to maternal effects in cases where the broodstock females are approximately of similar size and condition.

Keywords: Atlantic cod; RNA : DNA; growth; maternal effect; microsatellites

Document Type: Regular Paper


Affiliations: 1: Institute für Meereskunde an der Universität Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany, 2: Institute of Marine Research, Flødevigen Research Station, N-4817 His, Norway, 3: The University of Hull, Molecular Ecology & Fisheries Genetics Group, Department of Biological Sciences, Cottingham Road, HU6 7RX Hull, U.K., 4: Fisheries and Oceans, Science Branch, P. O. Box 5667, St. John's, Newfoundland, Canada A1C5X1, 5: Institute of Marine Research, P. O. Box 1870 Nordnes, 5817 Bergen, Norway and 6: Danish Institute for Fisheries Research, P. O. Box 101, 9850 Hirtshals, Denmark

Publication date: March 1, 2003

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