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Determination of acute toxicity of unionized ammonia in juvenile longfin yellowtail (Seriola rivoliana)

Abstract:

The median lethal concentration (LC50) of unionized ammonia (NH3-N) in longfin yellowtail, Seriola rivoliana juveniles was assessed after 96 h of exposure using a semistatic water system. Experimental fish were exposed in triplicate to different ammonia concentrations: 0.55 ± 0.00; 0.94 ± 0.02; 1.18 ± 0.00; 1.72 ± 0.02, and 1.97 ± 0.09 NH3-N mg/L. Additionally, a control group (0.00 ± 0.00 NH3-N mg/L) was included. The 96 h LC50 of unionized ammonia in S. rivoliana was 0.58 mg/L. Fish exposed to different ammonia concentrations for 96 h displayed several lesions on gill tissues, that is, hyperplasia, epithelial lifting, fusion of the secondary lamellae, and some irreversible damage. Erratic behavior, such as swimming in circles and hyperventilation was observed before the fish died. The safe concentration of unionized ammonia in this study was estimated at 0.06 and 1.68 mg/L of total ammonia nitrogen (TAN). The outcomes observed in this study provide valuable insights into unionized ammonia effects for better water quality management in semi-intensive and intensive systems for S. rivoliana culture.