Dual isotope study of food sources of a fish assemblage in the Red River mangrove ecosystem, Vietnam

The food source utilization and trophic relationship of the fish assemblage in the Red River mangrove ecosystem, Vietnam were examined using dual isotope analysis. The carbon and nitrogen stable isotope signatures of 23 fish species ranged from -24.0 to -15.7‰ and from 8.8 to 15.5‰, respectively. Cluster analysis based on the δ¹³C and δ¹⁵N signatures clearly separated the mangrove fish into five feeding groups, representing detritivores, omnivores, piscivores, zoobenthivores, and zooplanktivores, which concurred with the dietary information. The results suggested that mangrove carbon contributed a small proportion in the diets of the mangrove fish, with dominant food sources coming from benthic invertebrates, including ocypodid and grapsid crabs, penaeid shrimps, bivalves, gastropods, and polychaetes. The δ¹⁵N values showed that the food web structure may be divided into different trophic levels (TLs). The lowest TLs associated with Liza macrolepis, Mugil cephalus, and Periophthalmus modestus; 18 fish species had TLs between 3.0 and 3.8; and Pennahia argentata had the highest TL (c. 4.0).