Iranian Journal of Veterinary Medicine

Iranian Journal of Veterinary Medicine

Cellular and humoral immune responses of rainbow trout (Oncorhynchus mykiss) over a long-time post-vaccination: potency of a commercial vaccine using different routes of immunization under farm conditions

Articles in Press

Document Type : Original Articles

Authors
Sudabeh Ramezani 1
Mahdi Soltani 1
Seyed Saed Mirzargar 2
Homan Rahmati Holasoo 1
Fatemeh Yazarlo 1
1 Department of Aquatic Animal Health, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran
2 Department of Aquatic Animal Health, Faculty of Veterinary Medicine, University of Tehran Tehran, Iran
10.22059/ijvm.2026.420463.1006206
Abstract
Background: Streptococcosis/lactococcosis are critically important infectious diseases in aquaculture. Vaccination is a primary preventive strategy for disease control; however, data on the persistence of immune responses induced by commercial vaccines under farm conditions remain limited.
Objective: This study aimed to evaluate a long-term humoral and cellular immune responses of rainbow trout vaccinated using different vaccination protocols under farming conditions.
Methods: Rainbow trout weighing 70 ± 5 g were vaccinated with: a single immersion dose (IM), a single immersion dose plus a booster immersion (IMB) after 45 days, and a single intraperitoneal injection dose (IP). Blood samples were collected on days 0 and very month up to six months post-vaccination. Antibody titers were measured using indirect ELISA and agglutination assays, and immunocompetent cells were also determined.
Results: ELISA results showed that all immunized fish groups developed significantly higher antibody titers than the control (P<0.05). IMB vaccination induced the strongest and most prolonged antibody response, sustaining significantly higher titers than IM and IP groups during the latter sampling periods, despite a gradual decline over time. Vaccinated fish demonstrated significantly higher lymphocyte and monocyte counts and lower heterophil counts than the control throughout the study (P<0.05). IMB progressively revealed the most positive hematological profile, followed by IM and IP groups.
Conclusion: All vaccination strategies effectively improved humoral and cellular immune responses of trout compared with the control, approving their immunogenicity, and IMB exhibited the strongest and the most persistent immune responses, creating it the most efficacious vaccination strategy over long-time vaccination.
Keywords
Rainbow trout
vaccination
antibody titer
immunocompetent cells
Immunological response
Iranian Journal of Veterinary Medicine

Articles in Press, Accepted Manuscript
Available Online from 19 September 2026