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Abstract
Growth and osmoregulation in fishes are under control of external (environmental) and internal (hormonal) factors. Among the external factors, environmental salinity is considered one of the main contributors that affect fish growth and homeostasis. On the other hand, Growth hormone (GH) / Insulin like growth factor I (IGF-I) axis and Prolactin (PRL) are the major hormones involved in these processes.
Due to the wide diversity of fishes, the exact role of GH/IGF-I axis and PRL in regulating growth and osmoregulation is still unclear and very little information are available on the early stages of development. This study was undertaken to clarify the exact role of GH/IGF-I and PRL on both growth and osmoregulatory processes.
The present study was carried out in Sado Marine Biological station, Niigata University during the period from April through November 2006. Juvenile Oreochromis mossambicus were used in this study. They were segregated into 2 experiments as follows:
Experiment I (FW and 100% SW adaptation experiment):
Eighty fish were divided into 2 groups; freshwater (FW) and full strength (100%) seawater (SW) group. Fish were acclimated for 2 weeks in FW (for FW group) or gradual SW until reached 100% SW (for SW group), then kept for another 3 weeks in FW or 100% SW environments. Samples were collected at day 0 and at the end of the experiment (day 21).