Ontogenetic, seasonal, and spatial variation in the diet of Heterotis niloticus (Osteoglossiformes: Osteoglossidae) in the Sô River and Lake Hlan, Benin, West Africa

Abstract

SynopsisThe African bonytongue, Heterotis niloticus (Osteoglossidae), is an important fisheries and aquaculture species in West Africa. This species has frequently been characterized either as an omnivore, insectivore or detritivore, the latter, in part, because of its benthic feeding habitats and possession of a gizzard (thickwalled pyloric stomach). We examined diets of two populations of H. niloticus in the SoˆRiver in southern Benin. A population from the river channel and seasonally flooded marginal plains was dominated by juvenile and subadult size classes. Adults size classes were common in a second population from Lake Hlan, a natural lake in the river floodplain located upstream from the channel study region. Heterotis of all sizes consumed a variety of food resources, ranging from aquatic invertebrates to small seeds. Aquatic invertebrates composed a large proportion of the diets of juveniles, and adults consumed a mixture of aquatic invertebrates, seeds, and detritus. Seasonal dietary variation was observed in both populations, and diet breadth was not significantly different between populations. Aquatic invertebrates remained significant in diets of larger size classes; diets of fish between 100 and 200 mm began to include seeds and detritus, with a marked increase in the volumetric proportion of detritus in diets of fish between 300 and 400 mm in Lake Hlan and between 500-600 mm in the river. Relative gut length was inversely related to body size, which supports the notion that Heterotis is an omnivore and not a specialized detritivore. The thick-walled gizzard of Heterotis, which generally contained sand, probably aids digestion of seed coats. Because Heterotis consume mostly invertebrates and grass seeds in shallow waters of seasonal aquatic habitats and lakes in the river floodplain, foraging success and fishery production should be strongly dependent on the annual flood pulse.

Comparative feeding ecology and habitats use of Crenicichla species (Perciformes: Cichlidae) in a Venezuelan floodplain river

“…Prey items were identified to the lowest feasible taxonomic level using keys for aquatic invertebrates (Pennak, 1978) and fishes (multiple literature sources). Diet items were aggregated into taxonomic orders for use in calculation of dietary breadth and diet similarities (see Adite & Winemiller, 1997 for details). Aquatic insects were grouped as Diptera (e.g.…”

Diet breadth variation and trophic plasticity behavior of the African bonytongue <i>Heterotis niloticus</i> (Cuvier, 1829) in the Sô River-Lake Hlan aquatic system (Benin, West Africa): Implications for species conservation and aquaculture development

“…Because Lake Hlan is a relatively more stable aquatic ecosystem with the presence and the persistence of swamp habitats throughout all the seasons, facilitating permanent colonization and availability of food resources [13], we expect to obtain higher diet breadth in this habitat compared to Sô River. The Sô river, a less stable habitat, although periodically flooded (3 -4 months) should exhibit a relatively low food resource availability during much time of the year (dry season: 8 -9 months) and consequently Heterotis population from the Sô river should exhibit a low diet breadth.…”

“…), and freshwater lakes (Toho-Todougba, Nokoue, Hlan, Toho, lagoon of Porto-Novo, Azilli, Nakava, Cele, Codo etc.) [11][12][13]. The species is intensively exploited by both commercial and subsistence fishermen, and therefore, constitutes an important species for artisanal fisheries.…”

“…The species is intensively exploited by both commercial and subsistence fishermen, and therefore, constitutes an important species for artisanal fisheries. Annual capture of Heterotis reached 742 tons and valued about $1,485,000 [13].…”

“…Recent studies [13] reveal that the African bonytongue is an omnivore foraging mainly on detritus, seeds, microcrustacea and aquatic insects.…”