Some biological aspects of cod larvae (Gadus morhua L.)

The development of functional larval stages is described in relation to different yolk sac stages. Morphological and histological work has been done concomitantly with the observation on the larval feeding behaviour. Larvae were fed different sizes of phytoplankters and nauplii of Artemia salina. Cod larvae proved to avoid small flaggelates but were active feeders on bigger sized phytoplankters. The problem concerning the influence of phytoplankters on the first feeding cod larvae is discussed. Cod larvae were shown to be a visual feeder on nauplii and the light intensity threshold was between 0.1-0.4 lux. The point of no return (PNR) is tentatively determined, and the cod larval condition at that stage is compared to larval groups from the enclosure experiment (ELLERTSEN et al., 1979b) which had experienced different feeding conditions. The following characters were found suitable for determining the condition of first feeding cod larvae: the size of the yolk sac, larval standard length, dry weight, height of the myotome, the differentiation of the swim bladder and the alimentary tract