Strategies for enhanced adaptive immune responses of Pterophyllum scalare larvae against Aeromonas hydrophila

Abstract

The present study examines host pathogen response in developmental stage of Pterophyllum scalare (angelfish) infected with Aeromonas hydrophila. The study conducted had two different experiments in which the fish were subjected to formalin-killed Aeromonas hydrophila (FKA) and immunostimulant (β-glucan) by immersion method. The first experiment had three treatment groups viz., immunized, non-immunized and control groups and the exposure time ranged between 12 and 32 dph (days posthatch) of larval rearing. The immunized group exhibited a higher fold expression of RAG-1, RAG-2 and IgM genes compared with non-immunized group. The results demonstrated that the vaccination of 12 dph developmental stage prior to bacterial challenge of angelfish makes it more immunocompetent against the pathogens. Moreover, another experiment using β-glucan was conducted to further examine the development of immune responses in angelfish larvae. The study consisted four treatments containing graded levels of β-glucan dosages such as 100, 200 and 300 mg/L including a control (0 mg/L) for 20 days from 12 to 32 dph. The higher fold change in mRNA expression of RAG-1, RAG-2 and IgM genes was observed in β-glucan (200 mg/L) treated group as compared to non-treated and control group. The highest survivability was observed in the immunized group and immunostimulant treated group in the survival analysis. Hence, the present study suggested that either immunization with FKA or β-glucan (200 mg/L) could be used as a strategy to mitigate the mortality rate and combat infection during the early larval rearing of P. scalare.