The present study had the dual purpose of
comparing the salinity tolerance of sub-adults of O.
bonariensis and O. hatcheri, and obtaining
preliminary information on their osmoregulatory and
compensatory stress responses under different NaCl
concentrations. Sodium chloride instead of seawater
was used in this study because these are the salts most
commonly employed to raise salinity during
husbandry practices of these species. Thus, there was
also an interest in the elucidation of the relation
between NaCl and improved performance. The study
consisted of the ana1ysis of survival and blood
parameters (Na+ and cr ion levels, osmolality,
hematocrit and cortisol) in fish gradually or direct1y
exposed to sa1initiesbetween Oand 3.0 % NaCl.