Genetic identity, allometric traits, and gastro-somatic index of Chromis viridis in Agatti Island, Lakshadweep: Implications for conservation

Abstract

Chromis viridis, a key live bait fish, being used for the pole-and-line tuna fishery of Lakshadweep, plays a vital role in the sustainability of the said traditional fishing practice. Given its ecological and economic importance, understanding the speciesˈ biological and genetic characteristics is essential for effective management and conservation. This study presents the first gender-specific analysis of Length-Weight Relationship (LWR), condition factors, and Gastro-Somatic Index (GaSI) of C. viridis, alongside genetic characterisation using mitochondrial cytochrome c oxidase subunit 1 (CO1) and 16S rRNA gene markers. Specimens were sampled monthly from March 2022 to February 2023. Results revealed distinct seasonal and sex-specific growth patterns. Males exhibited isometric growth (b ≈ 3) in February, April, October, November, and December, while females showed similar growth in March, April, September, and November. Negative allometric growth (b < 3) observed for both sexes indicate fluctuations in energy allocation potentially linked to spawning cycles and environmental variability. The condition factors: Fulton condition factor (K), allometric condition factor (K_A), and relative condition factor (K_R) varied seasonally in both sexes. GaSI values fluctuated throughout the year, reflecting seasonal changes in feeding intensity. Both sexes showed peak GaSI in April, May, and October. Notably, females consistently exhibited higher GaSI values than males, suggesting more energy investment in feeding, which is likely to support oogenesis. These findings provide critical insights into the growth dynamics and physiological responses of C. viridis, contributing valuable data for species-specific, sex-oriented conservation and fisheries management strategies.