Trophic ecology of four species of emperor fish (Lethrinus) in the Gulf of Mannar along the Indian southeast coast

Abstract

This study presents the trophic ecology and resource partitioning among four species of emperor fishes (Lethrinus lentjan, L.microdon, L. nebulosus and L.olivaceus) in the Gulf of Mannar, based on a year-round study conducted in 2019. All of them are demersal feeders with strong jaws, having certain differences in their body shape and dentition. The diet content analyses revealed that slow-moving benthic invertebrates such as molluscs, crustaceans, and echinoderms were the major diet components of L.lentjan and L. nebulosus, whereas, L.microdon and L.olivaceus predominantly consumed fast-moving prey that included nektons and other invertebrate taxa. The dominant prey components in the diet of smaller fishes are highly contrary to the adults, as larger fishes cover wider feeding grounds and choose among a broader category of prey, which is significant for greater nutritional input. The slender body shape, jaw structure, and foraging behaviour enable larger fish to consume a far greater proportion of nekton. The index of relative importance (IRI %) showed that bivalves, brachyurans, and carideans were the most prevalent food items in the diets of all size classes. TROPH values estimated by species and size groups indicate that L.microdon (3.71) occupies the highest trophic position, followed by L.olivaceus (3.68), L.lentjan (3.45), and L. nebulosus (3.37). The variety and frequency of prey components in L.microdon and L.olivaceus substantiate the distinctive feeding nature of piscivory with an ontogenic diet shift. The observed trophic partitioning among the four Lethrinus species in the Gulf of Mannar can be attributed to vertical habitat partitioning and their distinctive morphological characteristics.