Thyroid status alters gill ionic metabolism and chloride cell morphology as evidenced by scanning electron microscopy in a teleost <i style="">Anabas testudineus</i> (Bloch): Short and long term <i style="">in vivo</i> study

Abstract

Gill is the main organ of osmotic regulation in teleosts and chloride cells are the sites of ion transport across gill epithelium. Thyroid hormones are implicated in the regulation of osmotic balance in teleosts also. Treatment with 6-propyl thiouracil (6-PTU) inhibited the membrane bound enzyme Na⁺K⁺ATPase in the gill while triiodothyronine (T₃) injection stimulated it in a short-term <i style="">in vivo</i> study in the teleost <i style="">Anabas testudineus</i>. Na⁺, K⁺ and Ca²⁺ ions were also decreased in the 6-PTU treated fish and the T₃ treatment increased their concentrations in the gill lamellae. The gill morphology also changed according to the thyroid status in the long term study. 6-PTU treatment altered the typical serrated morphology of the gill lamellae, while the T₃ treatment reversed it. T₃ injection increased the density of pavement and chloride cells as evidenced by scanning electron microscopy. The results demonstrate that physiological status of the thyroid influences gill Na⁺ pump activity and chloride cell morphological changes. Further, the study suggests a regulatory role of T₃ on gill ions (Na⁺, K⁺ and Ca²⁺), Na⁺K⁺and Ca²⁺ ATPase activity and the different gill cell types in <i style="">A</i>. <i style="">testudineus</i>.