Effects of the macroalga Sargassum angustifolium hot water extract on hematological parameters and immune responses in rainbow trout (Oncohrynchus mykiss) infected with Yersinia rukeri

Rainbow trout, Oncorynchus mykiss , specimens ( n = 300, 6.43 ± 0.66 g) were fed with diets containing hot water extract (0.0, 50, 100, 200, and 400 mg kg −1 of a basal diet) of the brown alga Sargassum angustifolium within five triplicate groups (20 fish per group) for 8 weeks. Serum biochemical and hematological parameters, immune responses, and survival rates of the fish were analyzed at the end of growth performance period. The results showed the highest weight gain and specific growth rate in fish fed with dietary algal extract of 400 mg kg −1 after 8 weeks of feeding trial. Hemoglobin, hematocrit, red and white blood cells, total protein, and albumin were also highest in fish fed with 400-mg-kg −1 diet. Lysozyme activity and complement system showed no significant differences between the treatments. Exposure of the fish to the bacterial species, Yersinia rukeri , revealed that fish fed with the algal extracts displayed increased levels of blood and serum biochemical parameters, stronger immunity responses, and greater survival rates than the control group. According to the results, supplementing the diet of rainbow trout with hot water extract of S. angustifolium up to 400 mg kg −1 considerably affects the growth performance, immunity, and resistance to Y. rukeri .