Feeding in African arowanas


An international team of scientists has published a new study looking at the feeding behaviour of the African arowana.

Alphonse Adite and Emile Fiogbe of the Universite d\'Abomey-Calavi in Benin and Kirk Winemiller of Texas A and M University looked at the feeding patterns of Heterotis niloticus in two different ecosystems in Benin, West Africa.

Unlike the more commonly seen South American arowanas of the Osteoglossum genus, and the Asian species in Scleropages, the African arowana, of which there is only a single species, has always been said to be a filter-feeder rather than a predator.

Most aquarium texts on this difficult-to-keep species, say that it feeds on small particles, but gut analyses have shown that it feeds as an insectivore, omnivore and detritivore.

Like most fish species, the feeding mode this fish uses varies depending on where it lives and how old it is, and the aim of this study was to assess the differences in different seasonal, spatial and age settings.

Two populations of Heterotis were studied: one was in Lake Hlan, the other was in the So River, Benin. The fish caught in the river were mainly juveniles and subadults, while those caught in the lake were largely adult fish.

The study showed that all of the fish ate a range of different foodstuffs. Juveniles feed predominantly on aquatic invertebrates, while adults feed on seeds, aquatic invertebrates and detritus.

At a size of 10-20cm/4-8\" there is a shift from feeding on aquatic invertebrates to seeds and detritus. In the lake, the fish start consuming much more detritus when they reach 30-40cm, but don\'t switch to detritus in the river until they are 50-60cm in length.

The study also showed that the gut length of the arowana is inversely related to body size, which supports the theory that the species is an omnivore, rather than a specialist detritivore.

In addition, the species has a thick-walled gizzard which it fills with sand which is probably used to help break down the tough coats of the seeds consumed.

For more details see the paper: Adite, A., KO Winemiller and ED Fiogbe (2005) - Ontogenetic, seasonal and spatial variation in the diet of Heterotis niloticus (Osteoglossiformes: Osteoglossidae) in the So River and Lake Hlan, Benin, West Africa. Environmental Biology of Fishes. Vol. 73. No. 4. pp 367-378.