Hemato-biochemical responses and histopathological alterations in the gill and kidney tissues of Osteobrama belangeri (Valenciennes, 1844) exposed to different sub-lethal unionized ammonia

Ammonia is a factor restricting production in aquaculture systems, hindering fish production adversely. A detailed study was planned and conducted using a static water system to scrutinize the toxic effects of unionized ammonia (UIA) on patho-physiological responses of O. belangeri, an important aquaculture candidate for diversification of freshwater aquaculture and endangered species, when exposed to different sub-lethal concentrations of UIA. The 96-h LC50 value of UIA on O. belangeri was found to be 1.36 mg l−1. The sub-lethal toxicity test with three UIA concentrations, i.e., 0.27, 0.68, and 0.80 mg l−1 at different exposure period of 24, 48, 72, and 96-h revealed that exposure to UIA induced a significant reduction in hematological parameters, such as total erythrocyte count (TEC), total leukocyte count (TLC), hemoglobin (Hb), and hematocrit (Hct). Mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) also substantially declined due to UIA exposure. Among biochemical parameters, blood glucose, serum glutamate pyruvate transaminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT) and Na+ and K+ ion increased significantly. In contrast, serum protein, alkaline phosphatase (ALP) and serum albumin notably decreased due to ammonia exposure. Fish exposed to different UIA concentrations for 96-h displayed several histopathologic alterations in the gill and kidney tissues. Gill tissues showed several lamellar deformations, while kidney tissues showed significant changes at the level of the glomerulus and tubular epithelium. The NOEL or safe concentration of UIA for this particular fish species was found to be 0.07 mg l−1. The observed patho-physiological alterations in the present study establish the most detail insights of UIA stress in O. belangeri and will enhance the international literature on UIA toxicity. [Display omitted] •The LC50 value of NH3-N to Osteobrama belangeri was found to be 1.36 mg l−1.•Hematological and biochemical parameters revealed organs dysfunction.•Unionized ammonia stress caused severe histological damages to gills and kidney.•The degree of damage increased in correlation with unionized ammonia concentration.