Evaluation of the salinity tolerance of Oreochromis mossambicus, O. niloticus and their F1 hybrids

Abstract

The salinity tolerance of freshwater-spawned and reared Oreochromis mossambicus, O. niloticus and their F₁ hybrids of various ages was studied. Several tests were conducted using three indices as practical measures of salinity tolerance: (1) mean survival time (MST); (2) median survival time (ST₅₀); and (3) median lethal salinity-96 hours (MLS-96).

Interspecific and age-specific differences (P<0.01) in salinity tolerance were observed in these species and their F₁ hybrids on the basis of MST and ST₅₀ indices, with salinity tolerance generally increasing with age of brood. No significant age-specific differences (P > 0.05) in salinity tolerance were observed in all four groups on the basis of MLS-96 index. At the same salinity O. niloticus fry at ages from 15 to 90 days post-hatch exhibited significantly lower (P<0.05) salinity tolerance than O. mossambicus and F₁ hybrids. Changes in salinity tolerance were determined to be more closely related to body size than age.