Histopathological alterations in the gills of banded gourami (Trichogaster fasciata) exposed to thiamethoxam

Thiamethoxam (THM) is a widely used agro-pesticide in Bangladesh, though European Union has banned this neonicotinoid insecticide due to its toxic effects on non-target organisms. A 60-day experiment was conducted to study the effect of sub-lethal concentrations of THM on gills of Banded Gourami Trichogaster fasciata. The experiment was conducted in 15 PVC tanks each containing 100L water. The 96-h LC50 value of THM was estimated as 161.06mg/L for Banded Gourami. Based on estimated 96-h LC50 value, the experiment was carried out using a control (0 mg/L of THM) and five sub-lethal concentrations (9.37, 18.75, 37.5, 75 and 150 mg/L of THM in water) with three replications. For collection of gills, fishes were sampled on day-30 and day-60 of exposure to THM. Several histopathological changes were observed in the gill tissues of treated fishes viz. clubbing and reduction of gill filaments, telangiectasis of gill lamellae, haemorrhage and damage of gill raker. Water quality parameters (e.g. DO, pH and temperature) were recorded every 15 days interval. The DO levels were found to decrease significantly with increasing THM concentrations and time of exposure, whereas no noticeable changes were observed for pH and temperature. Therefore, neonicotinoid crop insecticide like THM is capable of damaging gill tissues of an small indigenous fish Banded Gourami.