Cod larvae, Gadus morhua L., were reared in the laboratory and released to a large marine enclosure4 to Sdaysafter hatching(6-8" C). Thedevelopment ofthedigestive system was studied until day 24 after hatching. Morphological investigations of the jaw apparatus and the digestive tract showed that the larvae are able to absorb ingested food well before exhaustion of the yolk sac. The foregut, and especially the midgut, were particularly active in lipid absorption, and the hindgut was characterized by pinocytotic activity. During the first days of feeding, no distinct prey organisms were observed in the gut. and signs of food absorption in the epithelial cells of the gut were sparse. A distinct red fluorescence, restricted to the hindgut, was observed from day I 1 to day 19. On the basis of changes in absorptive pattern in the gut we suggest that changes in digestive and absorptive abilities, as well as in nutritional needs, take place around days 15-17 after hatching.In starved larvae, signs of degeneration of the gut tissue were first visible in the foregut. By day 9 after hatching, microvilli was degenerated to such an extent that the ability to absorb food must have been severely restricted. Iflarvae are starved longer than this, they will probably not survive.

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In March-April 1983, 2.5 x 106 yolk-sac Atlantic cod larvae were released in a dammed estuarine pond. One month later, more than halfa million metamorphosed. The larvae and metamorphosed juveniles depleted the natural food supply by mid-May, but the fish accepted small pellets containing 30% krill meal dispensed from automatic feeders. From mid-June, young Atlantic cod primarily ate the pellets, supplemented with minor amounts of wild calanoid and harpacticoid copepods. The population declined during summer probably due to cannibalism and predation from birds. No outbreaks of disease were observed, and in•bstation with parasites (nematodes) was less than 20%. Altogether, 75,000 juvenile Atlantic cod were captured alive from late May to October. By October, about 20,000 15-cm-long juveniles were tagged and released in the Austevoll region in a first attempt to augment the fishery for Atlantic cod.

Three different groups of cod larvae Gadus morhua L., feeding on natural plankton in two large enclosures, were analyzed for fatty acid composition through development. Unfed control groups and different size‐fractions of plankton were also analyzed. Consistency in changes of fatty acid composition suggests three developmental periods during early larval development. The periods corresponded with dietary shifts in the larvae, but a metabolic origin for changes in certain fatty acids was also evident. In the first period, relative amounts of n‐9 monounsaturates decreased, while n‐3 polyunsaturates together with certain fatty acids abundant in the small‐sized phytoplankton fraction increased. In the second and third periods, relative amounts of the longer n‐3 PUFA decreased, while fatty acids of calanoid copepod origin occurred in one group. The consistency in changes of larval fatty acid profiles in cod suggests development in both lipid absorption and lipid metabolism during ontogenesis.