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Specific growth rates and survival were not significantly different among the pelagic juveniles of three electrophoretically distinguishable stocks of Norwegian cod (Gadus morhua), co-reared in four replicate 5.2 m3 mesocosms, from hatch to day 38 or day 43 post-hatch. Arcto-Norwegian cod (AC, the main commercial cod stock which spawn in Lofoten and are distributed in the Barents Sea, mostly north of 70N), were compared with a nearby coastal stock (Balsfjord cod, BC – from a fjord near Tromsø at 6930N), and a more southern coastal cod stock (CC, from near Bergen at 60N). The increment width series of the lapillus – otolith growth history – and the relative daily growth rate were not significantly different among stocks within any mesocosm. Although AC larvae were larger, being derived from larger brood stock, they did not exhibit consistently greater otolith growth during the experiment. Larger size at harvest was correlated with growth during the latter part of rearing (>fourth week), which is when most differences in size at age are generated. Decreases in daily increment widths occurred in all stocks within 1–2 days, when the zooplankton food supply was changed from nauplii and copepodites to adult copepods, and when th