Effects of ammonia on the survival and physiology of juveniles and adults of Macrobrachium acanthurus (Caridea: Palaemonidae)

Abstract

Water quality is a key factor influencing the survival and health of aquatic organisms. This study aims to assess the effects of ammonia exposure on Macrobrachium acanthurus, including juveniles, adult males, and ovigerous females. Macrobrachium acanthurus were exposed to total ammonia nitrogen (TAN) concentrations of 0, 20, 40, 60, and 80 mg L⁻¹ for 96 h to assess survival, total hemocyte count (THC), gill damage, and recovery capacity. The median lethal concentration (LC₅₀) of TAN after 96 h of exposure was 54.5 mg L⁻¹ (3.1 mg L⁻¹ NH₃) for juveniles, 50.4 mg L⁻¹ (2.9 mg L⁻¹ NH₃) for adult males, and 59.2 mg L⁻¹ (3.4 mg L⁻¹ NH₃) for ovigerous females. To avoid sub-lethal effects, TAN levels should remain below 5.0 mg L⁻¹ (0.3 mg L⁻¹ NH₃) at 26 °C and pH 8.0, ensuring animal welfare from the nursery stage onward. Reversible and moderate gill lesions occurred at 20 and 40 mg L⁻¹ of TAN, while 60 and 80 mg L⁻¹ resulted in irreversible damage. However, gill recovery was observed after exposure to 20 mg L⁻¹ of TAN. Concentrations above LC₅₀ affected innate immune response, regardless of sex, with changes in THC. These findings demonstrate the sensitivity of M. acanthurus to ammonia exposure and provide results of safe concentrations. Those results will contribute to species conservation and inform sustainable aquaculture practices for native freshwater species in Brazil.