Histological Changes in Calcium Regulating Endocrine Gland (Ultimobranchial) After Dimethoate Exposure in Freshwater Catfish <i>Heteropneustes Fossilis</i>

Abstract

Ultimobranchial gland in fishes is associated primarily with calcium regulation. The study was aimed to find effect of an organophosphate pesticide dimethoate on serum Ca2+ and ultimobranchial gland in freshwater catfish Heteropneustes fossilis. Fish were exposed to dimethoate at 2.24 mg/l (75% of 96 h LC50) for short-term (24, 48, 72 and 96 h), and 25% of 96 h LC50 (1.00 mg/l) for long-term (6, 12, 24 and 36 d). The blood samples collected at assigned durations from the anaesthetized fish were used to measure serum Ca2+ levels. At the same time UBG were also extricated from the fish by removing the tissues adjoining esophagus, liver and sinus venosus of the heart for subsequent histological examination. A significant (P<0.05) increase in serum Ca2+ levels of fish following 24 h and 6d dimethoate exposure was observed. However, after 48 h and 12 d the Ca2+ level gradually begins to decline exhibiting significant (P<0.0001) hypocalcaemia after 96 h and 36 d in the exposed fishes. The histological examination of exposed fish glands exhibit significant changes in their cellular activity, staining property, nuclear diameter and nuclear volume, vacuolization and degeneration. It is concluded that dimethoate severely hampers the calcium homeostasis in Heteropneustes fossilis; therefore the pesticide should be cautiously used near aquatic bodies.