Effects of salinity on the growth, survival, haematological parameters and osmoregulation of tambaqui Colossoma macropomum juveniles

The effect of salinity on survival, growth, haematological parameters and osmoregulation was evaluated in tambaqui. This study addressed two questions. Firstly, tambaqui (33.9 +/- 3.4g) reared in freshwater were subjected to gradual increases in salinity until 100% mortality. Two daily increments of salinity were tested with three replicates: 1 and 2gL(-1)day(-1), while control group was kept in freshwater. For 1gL(-1)day(-1), the first mortality appeared from a salinity of 11gL(-1) and the last dead fish was observed at a salinity of 20gL(-1), whereas for 2gL(-1) day(-1), the mortalities occurred only between 20 and 22gL(-1). The main sub-lethal effects observed were food intake stopped, erratic swimming behaviour, increased mucus production and the dark pattern of pigmentation that appeared at 13 and 16gL(-1) for both treatments. Secondly, juveniles (57.4 +/- 6.3g) were reared at 0, 5, 10 and 15gL(-1), in triplicate, for 84days. At the end of the experiment, the results indicated that the survival, growth, haematological parameters and osmoregulatory of fish were significantly affected by salinity. Survival was unaffected by 10gL(-1), whereas higher salinity (15gL(-1)) had a detrimental effect. Differences in final weight, specific growth rates (SGR) and mean daily feed intake (MDFI) among treatments were significant. There were no significant trends in feed conversion rate (FCR) at salinities of 0, 5 and 10 ppt. In these salinities, FCR ranged between 1.2 +/- 0.1 and 1.3 +/- 0.1, whereas FCR at salinity of 15gL(-1) increased to 5.8 +/- 4.4. At the end of the experiments, analysis of blood revealed that all haematological parameters were affected by increase in salinity. From the present investigation, it can be concluded that exposure to salinity significantly affects the survival, growth and physiological response of tambaqui.