Short Communication: Haematological and immunological responses of sea bass (Dicentrarchus labrax) to a short-term exposure to increased water levels of nitrate

Fish reared under intensive culture conditions very often face stressful adverse conditions which either do not exist in nature, for example living in extremely high stocking densities, or they are quite unlikely, for example increased water ammonia levels (Huntingford et al. 2006). Nitrate (NO3−) which is the ionized form of nitric acid (Cheng and Chen, 2002) and salts, like sodium nitrate, are readily soluble in water and completely dissociated. It is produced by a two-step process called ‘nitrification’ (Hargreaves and Tucker, 2004). During this process, ammonia, which is either excreted from fish or produced by the decomposition of the organic matter in the water, is first oxidized to nitrite (NO2–) and subsequently to nitrate (NO3–). The nitrification rate can be affected by many factors such as water temperature and available diluted oxygen (Hargreaves and Tucker, 2004).