Ruptured intestine syndrome of unknown etiology in young African catfish, Clarias gariepinus (Burchell 1822), and its relation to the feeding level

Abstract Clinical signs and morphopathology of the ruptured intestine syndrome of unknown etiology (RISue) in growing African catfish ( Clarias gariepinus Burchell 1822) are described. The disease occurs within a short period of ca. 30 days and affects young fish with a weight of 3–5 g, at an age of 5–9 weeks when fed at a high feeding level. It can be classified in five stages: a local inflammation in the hind gut (1) resulting in a rupture of the gut (2), peritonitis producing a haemorrhagic smelling fluid in the abdominal cavity (3), followed by an ulcer, of internal origin, of the ventral abdominal wall (4) and a disappearance of a great part of the gut and ventral abdominal wall (5). In an experiment with 15 groups of 300 fish each, the influence of feeding level, water supply and bacteriological quality of the water on the incidence of RISue of young African catfish was investigated. The results showed a significant influence of feeding level whereas flow rate and number of bacteria and parasites did not influence the incidence of RISue. High feeding levels resulted in a higher percentage of RISue-affected fish.