Chronic nitrate toxicity on juvenile clownfish Amphiprion ocellaris
Clownfish Amphiprion ocellaris is one of the most important marine ornamental fish species, both in extractive and production aspects. Nitrate is considered a substance with a low potential for toxicity compared to other nitrogen compounds (ammonia and nitrite), but because it is the final product of nitrification, it can accumulate in production systems with low water exchange, such as water recirculation systems. However, studies on the toxicity of this compound to marine fish are still scarce, and little is known about its effects on clownfish. Therefore, the present study had as objective to analyze the chronic effect of nitrate for juveniles of clownfish A. ocellaris. For this, the experiment had four treatments in triplicate, being three concentrations of nitrate 30, 60 and 90 mg/L, plus a control treatment without addition of nitrate. A total of 180 fish were randomly distributed in 12 tanks with a capacity of 15 L (15 fish / tank), 20 days after hatching (28.68 ± 1.09 mg and 12.09 ± 0.19 mm), constant aeration, photoperiod 12h /12h (light/dark) and controlled temperature (27ºC). The experiment lasted 42 days and at the end the zootechnical performance and the oxidative status of the whole fish were evaluated. There was no difference for parameters of survival and zootechnical performance, except for the condition factor K, however, there was an increase in TBARS (lipoperoxidation) and nonprotein Tiol (NPSH) in nitrate concentrations of 60 and 90 mg/L. This increase in non-protein thiol (NPSH), corroborates with GST (Glutathione S-Tranferase) activity significantly lower at the same concentrations. However, no differences were observed for total capacity against a peroxyl radical (ACAP) and protein thiol (PSH) .Thus this study demonstrates the level of up to 30 mg/L of N-NO3- does not cause damage to the juvenile production of clownfish A. ocellaris.