A mini-review on cathelicidin in fish: Gene expression, immune function, and evolutionary insights.

Cathelicidins are a family of cationic antimicrobial peptides that play a critical role in innate immune defense. Like other antimicrobial peptides, cathelicidins can effectively kill pathogens while minimizing the risk of promoting antimicrobial resistance, a growing concern in the aquaculture. Although cathelicidins are widely distributed across vertebrates, from basal vertebrate species such as hagfish and lampreys to mammals, the number of identified cathelicidin sequences in fish remains relatively limited. This review aims to provide a comprehensively summary of current knowledge on teleost cathelicidins, focusing on their expression patterns, antimicrobial activity, and immunomodulatory functions, while also outlining future research directions. Additionally, we conducted a genomic analysis to explore the species distribution and evolutionary history of fish cathelicidins. Our results revealed conserved synteny of cathelicidin loci in both cartilaginous and bony fishes, as well as lineage-specific expansions and chromosomal rearrangements that may have contributed to gene loss. Overall, this study serves as valuable resource for understanding cathelicidins in fish, and lays the groundwork for future investigations into their evolution, biological functions, and potential applications in fish health and aquaculture.