Nitrite stress and arginase activity in freshwater aquatic animals: similarities and differences between fish and shrimp

Adult specimens of the three species were acclimated at 27 C and a photoperiod of 14h: 10h L: D in separated tanks (biological filter+ dechlorinated tap water). They were individually treated with NaNO2 for 3h (A. nigrofasciata and C. multidentata, 2 mM and 1 mM, respectively), or 24h (D. rerio, 2 mM). Water samples were collected at intervals to determine the urea excretion; at the end of the treatment blood/haemolymph was collected, animals were euthanized and muscle tissue was dissected and frozen at-80 C. Animal procedures on fish were approved by the Institutional Animal Care and Use Committee (CESA) of the University of Naples Federico II, Naples, Italy. Blood samples were treated according to Dalla Via et al.(1994). Tissue samples were treated according to Dunn et al.(1986). Urea levels were measured with a diacetyl-monoxime method (Uliano et al. 2010). Urea excretion was expressed as mmol h-1 Kg-1. Nitrite was determined with the Griess method (Shechter et al., 1972).