Head-kidney thyroid in some Indian teleosts

Six species of fishes, with different habits and belonging to different habitats and families, have been investigated. Only four, namely Discognathus lamta, Carassius auratus, Glossogobius giuris and Polynemus sexfilis have shown the presence of heterotopic thyroid follicles in their head-kidneys. The heterotopic thyroid follicles of Discognathus lamta appear to be functional while those of the rest of fishes are in non-functional state.