Reversibility of deleterious effects of the pisciculture byproduct nitrite on cultured nile tilapia (Oreochromis niloticus)

• Autor(a) principal: Azevedo, Maristela
• Data de Publicação: 2004
• Outros Autores: Souza, Marta Marques de, Freire, Carolina Arruda
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da FURG (RI FURG)
• Texto Completo: http://repositorio.furg.br/handle/1/794
• topic: Aquaculture; Methaemoglobin; Nile tilapia; Nitrite; Oreochromis; Osmoregulation

The effects of nitrite (NO2 –) on the Nile tilapia (Oreochromis niloticus) were investigated, due to their relevance to worldwide aquaculture. Hematological parameters – functional haemoglobin (oxy+deoxy-Hb, %), methaemoglobin (MetHb%), and hematocrit (Hct) – and – plasma osmolality, plasma chloride ([Cl−]) and magnesium ([Mg2+]) concentrations – were analysed. Two experiments were conducted, each with its own non-contaminated control, 8 tilapias for each group. In experiment 1 (48 hours), and the first 48 hours of experiment 2, fish were contaminated with 0.4 mM NO2 – (added as NaNO2). In experiment 2, ambient NaNO2 – was removed for the second 48 hours. NaNO2 – exposure increased plasma [NO2 –] to 0.4 mM, which increased MetHb from 10.8 ± 2.5% to 46.8 ± 8.0%, and consequently decreased functional Hb from 89.2 ± 2.5% to 53.2 ± 8.0%. NaNO2 removal led to recovery of both parameters. Both Hct and plasma Mg2+ were lowest in fish recovering from nitrite exposure. Thus, these parameters did not show recovery. Plasma osmolality and [Cl−] were not affected by NaNO2 –, probably due to the moderate rise in plasma [NO2 –]. O. niloticus was thus sensitive to 48 hours of exposure to 0.4 mM NaNO2, and partially recovered from its effects after 48 hours in sodium nitrite-free water. Cultivators of Nile tilapia should thus consider the toxicity of nitrite, especially in aquaculture systems using recirculating water.