Myo-inositol supplement helps the performance of seawater-acclimated Nile tilapia, Oreochromis niloticus

Seawater (SW)-acclimated Nile tilapia, Oreochromis niloticus, reared under a salinity 30 environment had lower growth and survival than the freshwater (FW)-acclimated fish. It was hypothesized that cells of the SW-acclimated fish had not been able to synthesize an adequate level of a compatible osmolyte, myo-inositol (MI), in adjusting to the salinity 30 environment. In this study, MI supplements, at 250, 500, and 750 mg/kg pellets, were provided to the fish through top-dressing. After the 30-day feeding trial, the following parameters were determined: final body weights; survival; biomass increase; feed conversion ratio (FCR); plasma osmolality and ions; and two transcripts in the gills mips250 and mipa1 encoding enzymes responsible for MI biosynthesis. The SW-acclimated O. niloticus receiving 500-mg MI supplement had significantly higher survival, biomass increase, and lower FCR than those of the SW-acclimated fish receiving no supplement. At 500-mg MI supplemental level, the increasing values of plasma osmolality and Na+ observed in SW-acclimated fish were significantly attenuated. The transcript mipa1, but not mips250, was markedly up-regulated in the SW-acclimated O. niloticus, compared with that of the FW-acclimated fish. Again, MI at 500-mg supplement attenuated the up-regulation significantly. This study suggests that MI supplement at the optimum level enhanced the performance of SW-acclimated O. niloticus, and through yet unknown mechanisms, attenuated some of their physiological responses to the osmotic stress.