The ecology of Sphyraena barracuda (Osteichthyes: Perciformes) in the Kosi system with notes on the Sphyraenidae of other Natal estuaries

The ecology of Sphyraena barracuda was studied in the Kosi estuary system of Natal. Fry enter from the sea at a length of 20 mm and live in shallow marginal weed-beds until a length of 80 mm when they move to fringing Phragmites reed-beds. After reaching 300 mm they move to open water areas. No specimens longer than 500 mm were recorded and none were mature. Growth is rapid, they attain 180 mm in the first six months and after two years measure 400-500 mm. They leave the estuary after about two years. Their significance in the estuarine fish community is due to their predation, at all sizes, on a variety of estuarine-dependent juvenile fishes (e.g. Rhabdosargus spp., Mugilidae) and adults of estuarine species (e.g. Ambassis spp.). S. barracuda was recorded at salinities between 4°/oo and 35°/oo, only in very clear water and at temperatures from 14,4 °C to 37 °C. Sphyraena bleekeri and S. qenie, which are also clear-water species, were found at Kosi in salinities from 0,5 to 35%o. They are also piscivorous on a range of small teleosts. Sphyraena iello is the most widespread barracuda in Natal estuaries, but only juveniles were recorded. This species is tolerant of a wide range of turbidities and salinities which enables it to live under most estuarine conditions. The distribution, ecology and interspecific interactions among Sphyraenidae in Natal estuaries are discussed in relation to their feeding biology, habitat preferenda and physical tolerances.