| Summary: | The growth and important structures development in different temperature regime histories were studied during mid-metamorphosis stage of Atlantic cod (Gadus morhua) larvae. In order to see the growth and the organ development differentiation due to different temperatures at a given stage, we exposed the larvae into 4 different temperature regimes; L-L (low temperature at incubation, low temperature after hatching), L-H (low temperature at incubation, high temperature after hatching), H-L (high temperature at incubation, low temperature after hatching) and H-H (high temperature at incubation, high temperature after hatching) (low 4±0.2°C and high 9±0.2°C). The sampling was done according to the expected stage at a given sampling stage. Samples were fixed and studied under light microscope. Standard length and myotome height were measured for growth, swim bladder size, alimentary tract and fin differentiation were studied for organ development. The L-H group fish showed the best growth but had the highest variation in myotome heights. There was a lot of variation in organ developments at the given stages among the temperature groups, yet the groups with high temperatures after hatching period showed better organ development, postulating that besides the age is the key factor for fish to reach a given stage, also temperature is an extrinsic factor in organ development.
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