Tolerance response to ammonia and nitrite exposure in larvae of two marine fish species (gilthead seabream Sparus aurata L. and Senegal sole Solea senegalensis Kaup)

Abstract

Gilthead seabream Sparus aurata L. and Senegal sole Solea senegalensis Kaup are two species of fish that are of primary importance in Mediterranean aquaculture. In the present study, the larvae of these species were exposed to different concentrations of total ammonia and nitrite for 24 h to examine the toxicity of both nitrogenous compounds to larvae under rearing conditions. The non-ionized ammonia (NH3) and nitrite (NO2–) 24-h LC50 values were 0.24 p.p.m. and 1997 p.p.m., respectively, in 12-day-old S. aurata larvae. According to the criteria of 10% of LC50 value, the rearing water for gilthead seabream larvae has to have levels below 0.024 p.p.m. non-ionized ammonia and 200 p.p.m. nitrite-N to be safe. In 7-day-old S. senegalensis larvae, the non-ionized ammonia (NH3) 24-h LC50 value was 1.32 p.p.m. No deaths occurred when S. senegalensis larvae were exposed to nitrite concentrations of up to 2000 p.p.m. for 24 h. Both species showed different tolerance levels to the two nitrogenous compounds and also showed differences in resistance to toxicity tests. S. senegalensis larvae were more resistant. This is probably associated with the greater amount of mucus in their skin.