Ontogenetic shift in the diets and foraging behaviour of the Schlegel's Goby, Porogobius schlegelii (Gobiidae) in the qua Iboe Estuary, south eastern Nigeria

Abstract

Gut analysis revealed that 23 food objects re-grouped into 9 major groups (algae, crustaceans, detritus, fish prey, insects, macrophyte materials,  molluscs, nematodes and sand grains) were eaten by schlegel's goby,  Porogobius sclzlegelii in the Qua Iboe estuary, South Eastern Nigeria. The ingestion of the dietaries varied considerably, Crustaceans were the only
food objects eaten by all the length classes (3-11 cm TL). Diet breadth and food richness correlated with fish length class and each other. The  small-sized group (SSG) increased in the consumption of relative  importance of Sesarma remains, Porogobius schlegelii, unidentified fish, Neritina glabrata and nematodes whereas shift in dietaries of Spirogyra, Sesarma alberti, coarse detritus, fish remains, macrophyte materials, and sand grains were in favour of the big-sized group (BSG). Diet breadth and food richness were higher in the BSG than in the SSG. Despite the  significant similarity in the rank-order of the food objects between the size-groups, the proportions of some of them were different. The BSG was significantly higher in the ingestion of the food objects. Analysis of indices of gut fullness: gut repletion index (GRI) and mean gut fullness (MGF) indicated that feeding behaviour of P. schlegelii increased with increasing length class. The higher GRI and MGF in the BSG buttressed the idea of a shift in diets and foraging behaviour by adults vis-a-vis juveniles of P. sclzlegelii.

Keywords: Porogobius schlegelii; ontogenetic shift; foraging behaviour; Qua Thoe estuary; Nigeria.