Histoarchitectural changes in the vital organs of Oreochromis niloticus fry administered therapeutic, and overdoses of dietary oxytetracycline

Aquaculture is an important source of cheap animal protein for human consumption. The intensive hatchery and aquaculture activities make the seed/fish vulnerable to diseases, which demand the application of drugs. The present study evaluated the impact of in-feed oxytetracycline (OTC) administration ranging from therapeutic (80 mg) to overdoses (240, 400 and 800 mg/kg biomass/day) for 10 days on the histopathology of Oreochromis niloticus fry in comparison with the control. The kidney exhibited degeneration of renal tubules and tubular epithelium, glomerulopathy, nephrocalcinosis, vacuolation, inflammation, and necrosis. The liver had diffusely distributed glycogen-type vacuolation, necrosis, cytoplasmic vacuolation and degeneration, and cellular hypertrophy. The intestine had a loss of absorptive vacuoles, intestinal villi necrosis, mucinous degeneration, and necrotized area. The spleen had splenic necrosis and an increase in sinusoidal space. The impact of OTC was dose-dependent and mild to moderate on the tested organs, which affected the physiological status of the fry and eventually the survival. The withdrawal of therapeutic and overdoses of OTC medication led to the recovery of fry. The observed results suggested that the abuse of in-feed OTC in commercial hatcheries is a cause for concern as it can affect the fry's vitality and harm fish seed production.