UTTAR PRADESH JOURNAL OF ZOOLOGY

The historical and cultural significance of fish as a staple food has driven advancements in fish farming technologies, aiming to enhance yield and sustainability. Understanding the immunological aspects of fish is crucial for enhancing aquaculture practices and ensuring the health of fish populations in natural ecosystems. This study explores the immune response of Catla catla, a freshwater fish species of Narmada river of Madhya Pradesh, by examining the expression of the β-defensin 3 gene following exposure to the bacterial pathogen Staphylococcus aureus at laboratory setup. This study provided a comprehensive framework to analyse the gene expression pattern of β-defensin 3, shedding light on the immunological response of Catla catla fish species under bacterial infection. Live specimens of Catla catla were carefully collected from the Narmada River near Bhopal, Madhya Pradesh to investigate the expression of the β-defensin 3 gene. Total RNA was extracted from the tissue samples using TRIZOL reagent. For reverse transcription, 1000 ng of RNA was used to synthesise complementary DNA (cDNA) using the iScript™ cDNA Synthesis Kit.  The expression of β-defensin 3 was analysed using quantitative PCR (qPCR) on the AriaMx Real-time PCR System. Specific primers were designed to amplify the target gene and the housekeeping gene. This methodological approach ensured the precise evaluation of β-defensin 3 gene expression under controlled laboratory conditions, providing valuable insights into the immune responses of Catla catla to bacterial infection. The findings demonstrate a significant increase in the expression of the β-defensin 3 gene in infected Catla catla compared to uninfected control fish. This was quantitatively analysed using polymerase chain reaction (qPCR), revealing a pronounced response to the bacterial challenge. Statistical analysis through an unpaired t-test yielded a p-value of 0.0108, indicating that the elevation of β-defensin 3 expression is a vital immune response mechanism to bacterial infection. The increased levels of β-defensins, known for their antimicrobial properties, underscore their importance in the innate immune system of fish, functioning as a first line of defence against a variety of pathogens. These peptides exhibit the capabilities to disrupt bacterial membranes, which is critical for inhibiting pathogen growth and protecting the host. Additionally, our results highlight the broader implications of environmental factors, particularly water quality, on the immune health of Catla catla. Frequent exposure to harmful bacteria due to pollution necessitates robust immune responses, indicating the need for effective water management strategies in habitats supporting these fish.  This study not only sheds light on the immunological mechanisms at play within Catla catla but also emphasises the importance of maintaining healthy aquatic environments to support fish health and resilience. Such insights are vital for promoting sustainable aquaculture practices, ensuring the health of fish populations, and sustaining biodiversity in freshwater ecosystems.