Habitat Specificity and Feeding Ecology of Juvenile Mangrove Red Snapper (Lutjanus argentimaculatus Forsskal, 1775)

Abstract

Mangrove Red Snapper (Lutjanus argentimaculatus) is an important commercial and recreational fish throughout its range and considered to be an excellent food fish. In Vietnam, Mangrove Red Snapper has been a favourite fish species for mariculture, however, the bulk of Vietnam's mariculture of Mangrove Red Snapper relies on the depends on fingerlings recruitment in the two remaining locations where juveniles recruit in sufficient numbers to support harvesting. In this study, I investigated habitat specificity and feeding ecology of juvenile Mangrove Red Snapper in central Vietnam by combining field surveys with confirmatory experimental studies. The results showed that there was only one major recruitment season of juvenile in central Vietnam, from July to August. During the recruitment period, juvenile fish mostly occupied complex rocky habitats within a salinity range of 10-25ppt, and consumed a wide range of planktonic and benthic prey. Fish revealed seasonal and ontogenetic changes in feeding habit, and the intensity of their feeding activity was also governed by tidal rhythm, being maximal on the rising tide. Consumption of prey varied with maturity of the juveniles, with mysid shrimps providing the bulk of prey for the smallest size class. Larger juveniles foraged in different strata of the water column and consumed both benthic and planktonic prey, but relied entirely on sergestid shrimps during the winter months. It was found that hard-complex habitat structure had benefits in term of growth while moderate salinity water improved survival of fish in experiments. My experimental findings also demonstrated that using natural food prey species (Acetes and mysid shrimps) as the diet of cultured juveniles strongly promoted both growth and survival of juvenile fish. Therefore, the findings of this study reveal that a simple way to enhance commercial production is to culture juveniles in moderately saline water (15- 20ppt), in the presence of hard, complex structures such as rocks or snags, and using live shrimp prey as Acetes and mysids to feed fish. It is clear that the presence of complex rocky habitats within mangrove-lined estuaries and the associated food resources play an important role for growth and/or survival of juvenile Mangrove Red Snapper, and represent critical habitat for juvenile recruitment.