Effect of premature transfer to sea water on growth and morphology of the pituitary, thyroid, pancreas, and interrenal in juvenile coho salmon (Oncorhynchus kisutch)

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Abstract
Stunted coho salmon exhibited prominent parr marks and had a lower coefficient of condition than normal coho in sea water. Light and electron microscopic observations of the pituitary gland indicated that the prolactin cells of the runts were less active than in normal seawater coho whereas the growth hormone cells were more numerous and filled with secretory granules. The thyroid and endocrine pancreas had regressed while the interrenal cells showed little difference from the controls.After return to fresh water for 4 months, the runts acquired a silvery appearance and their condition factor increased to the normal level. In fresh water, the pituitary regained a more normal appearance. The prolactin cells became hypertrophied while the growth hormone cells contained less secretory material.
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