Hormones and Egg/Larval Quality in Fish

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Abstract
Recent evidence suggests that hormones are passed on to eggs by broodfish. This store of maternal hormones may fill the regulatory needs of fish larvae for growth, development, osmoregulation, stress response and other physiological functions prior to the functional development of their own endocrine glands. Thus the hormonal levels in eggs/larvae may be an important determinant of egg/larval quality.Thyroid hormones have been best studied in this regard. Both thyroxine (T4) and triiodothyronine (T3) are present in fish eggs and in most cases, the levels decrease as development proceeds until the onset of endogenous thyroid hormone production, which usually occurs before or at around yolk‐sac resorption. Enhancement of T4/T3 levels in newly‐hatched larvae through immersion or maternal injection has been shown to promote larval growth, development and/or survival in several fish species, although overdose causes thyrotoxicosis.Other hormones such as corticosteroids, sex steroids, growth hormone and prolactin are also being studied, but to a much lesser extent.The paper reviews the evidence and discusses the practical implications of the various findings for larval rearing in aquaculture.