Biology of fork-tailed catfishes from the Sepik River, Papua New Guinea

Abstract

Ariids accounted for approximately 25% of the weight of catches and landings from rivers and lakes in the floodplain region (= 50% weight of native species). Habitat preferences were:A. solidus, lakes and rivers;A. utarus, rivers and occasionally lakes;A. coatesi andA. velutinus, rivers only;A. nox, lakes and floodplain.A. solidus andA. utarus occasionally entered the floodplain but onlyA. nox exhibited any, albeit modest, affinity for this environment. In general, the fishes showed no marked seasonality relating to the flood cycle: in four species slight increases in feeding, condition, breeding and fat deposition occurred during the dry season whilst onlyA. nox showed modest increases in these parameters during the flood season due to its increased feeding on the floodplain at that time. All species are omnivorous but diets differed according to morphology and habitat preferences. Diet overlap was greatest amongstA. coatesi, A. solidus andA. utarus which fed mainly on prawns and a variety of other plant and animal matter.A. nox is a specialised filter-feeder consuming mainly small crustaceans and small insect larvae.A. velutinus fed mainly on large insect larvae and emergent and terrestrial insects and its diet excluded prawns.A. solidus and, especially,A. utarus also fed on fish scales. Feeding commenced immediately after hatching while free embryos were still in the male parent's mouth. Large amounts of fat were stored prior to brooding during which time males fast. The reproductive style of ariid catfishes limits their colonisation of the floodplain and is a constraint to increased fisheries exploitation of the stocks. The importance of ariids to the local fishery and nutrition (fat) for the local people should be recognised.