Species diversity and genetic variation of caligids (Copepoda: Siphonostomatoida) infecting the marine fishes of Kerala coast, India

Abstract

This study reports population structure, host preference, species diversity, seasonality, and genetic variability of caligids infecting the marine food fishes of Kerala coast, India. The survey included 22,629 fishes belonging to 85 species, 65 genera, and 34 families sampled from 6 different stations. Of which 24 species of fish from 24 genera and 14 families were found infected with caligids revealing 5% susceptibility. The recovered caligids included 26 species comprising eight genera and genus Caligus was the dominant one with 18 species (69.23%; 18 out of 26). The prevalence was highly varied irrespective of the host fish family. Sampling stations from the northern Kerala showed higher values of abundance, species number, richness and diversity indices compared to the southern stations. k-dominance plot showed the highest dominance and low diversity of caligids in Azhikkal (Northern station) and lower dominance and high diversity in Kalamukku and Thoppumpadi (Southern stations). Seasonal prevalence revealed the highest infection of caligids during post-monsoon and the lowest during monsoon season. Molecular level identification of recovered caligids using mCOI gene revealed 80 to 93% sequence identity with other parasitic copepods based on BLAST results. Phylogenetically, species of Caligus displayed intra-genus variation of 13-27% (k2p genetic distance). The species of the family Caligidae formed distinct clades from that of the families Lernaeopodidae and Lernanthropidae. Present study also documented host preference, site of infection, seasonality, and genetic divergence of the recovered caligids, all of which are relevant for further exploration of the species diversity and genetic variation of caligids along the Indian coasts and Indo-pacific region as well.