Temporal variations in hematological, immunological and serum biochemical parameters of rainbow trout (Oncorhynchus mykiss) acclimated to high-saline water in the Northern Aegean Sea

The present study evaluated the health status of rainbow trout (30.24 +/- 5.34 g) acclimated to high-saline water (28 parts per thousand). Among adaptation procedures, gradually-acclimated (for 48 h) fish showed best performance, which were then introduced to the offshore cage-farm for further monitoring of fish health in marine environment over a long-term period of 100 days, until harvest weight of 319.9 +/- 48.51 g. Fish health and welfare was evaluated by means of biochemical parameters (viscerasomatic index, hepatosomatic index, mesenteric fat index, and spleen somatic index), hematological parameters (serum glucose, triglyceride, cholesterol, total protein, albumin, globulin), and immune parameters (lysozyme, myeloperoxidase, respiratory burst and potential killing values). Gradual acclimation to high-saline water did not show any adverse effects on health parameters. No significant differences were found in biometric measures (P>0.05). However, a time-dependent increase was recorded in hematology markers (P<0.05) after seawater transfer, and the health status improved over long-term from March 7 to June 14, 2018. All serum biochemical markers, except the total protein showed significant alterations (P<0.05) in long-term but without detrimental influence by day-100. Therefore, it seems possible to expand trout farms from brackish water sites to higher saline environments up to 28 parts per thousand salinity, with no detrimental impacts on fish health, that in turns may significantly contribute to the extension of potential aquaculture sites to wider areas.

Automated summary

The present study evaluated the health status of rainbow trout acclimated to high-saline water and found that gradual acclimation did not have adverse effects on fish health. Hematology markers showed a time-dependent increase after seawater transfer, but the health status improved over the long-term. Therefore, trout farms can potentially be expanded to higher saline environments without detrimental impacts on fish health.