| Popis: |
The effects of nitrite (NO − ) 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 ((Mg 2+ )) concentrations - were analysed. Two experiments were conducted, each with its own non-contaminated con- trol, 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 NO − (added as NaNO2). In experiment 2, ambient NaNO − was removed for the second 48 hours. NaNO − exposure increased plasma (NO − ) to 0.4 mM, which increased MetHb from 10.8 ± 2.5% to 46.8 ± 8.0%, and conse- quently 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 Mg 2+ were lowest in fish recovering from nitrite exposure. Thus, these parameters did not show recovery. Plasma osmolality and (Cl − ) were not affected by NaNO − , probably due to the moderate rise in plasma (NO − ). 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. |
