The effect of hot water extraction of seaweed Sargassum angustifoliom on hematological indices and the resistance against the infection with Yersinia bacteria (Yersinia ruckeri) in rainbow trout Oncorhynchus mykiss (Walbaum, 1792)

The aim of this study was to evaluate the effect of edible hot water extraction seaweed, Sargassum angustifoliom, on haematological parameters and survival rate of rainbow trout (O. mykiss) against Yersinia ruckeri. For this purpose, 300 rainbow trout specimens (5.82±0.22 g mean weight) were purchased from a local fish farm and transferred to the laboratory. After 14 days acclimation to the experimental conditions, the fish were randomly divided into five groups with triplicates. Fish were fed with 0 (control), 50, 100, 200 and 400 mg/kg of S. angustifoliom extraction for 56 days. The fish blood samples were takenfor fish exposed with Y. ruckeri bacteria at the end of the experimental period (56 days).The number of red blood cells (RBC), white blood cells (WBC), the percentage of haematocrit and the concentration of haemoglobin were then measured. Results showed that the fish fed with different concentrations of seaweed extraction possessed higher survivability rate and more suitable haematological parameters compared to the control group 56 days after feeding and being exposed to Yersinia bacteria. Meanwhile, the number of RBCs, WBCs, and the percentage of haematocrit and concentration of haemoglobin for the fish fed with 400mg/kg hot extraction of seaweed significantly increased at the end of experimental period. Furthermore, resistance against to the Yersiniosis for these fish increased by using this concentration of seaweed extraction. Therefore the present study suggested that 400mg/kg of seaweed extraction could improve rainbow trout blood parameters and increase the resistance against Yersiniosis.