Abstract
Metamorphosis is an important growth and developmental process in fish. But a portion of cultivated grouper (Epinephelus lanceolatus) larvae was found to have died without having gone through metamorphosis. Histological studies comparing the thyroid and digestive glands of cultured grouper which underwent (1) spontaneous metamorphosis, (2) artificially-induced metamorphosis by adding 1 ppm triiodothyronine (T3), and (3) non-metamorphosis showed that larvae which underwent spontaneous and artificially-induced metamorphosis persistently had a greater number of follicular cells in the thyroid, thicker muscularis externa, and more gastric folds in the digestive glands. Those larvae that did not metamorphose contained very few follicular cells in the thyroid, and had thinner muscularis externa and less gastric folding in the digestive glands. Obviously, owing to the undeveloped follicular cells in the thyroids, the cultivated grouper larvae did not metamorphose to develop a more-advanced digestive gland and died.
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