The present study was carried out to evaluate the immunomodulatory effects of vitamin
A and astaxanthin in rainbow trout in order to assess their value as immunostimulants in
aquaculture. To this end, groups of rainbow trout (Oncorhynchus mykiss) were maintained
on practical diets with or without additional vitamin A and/or astaxanthin for 4 months
prior to the measurement of a range of innate and specific defence mechanisms.