Heteropneustes fossilis (Bloch, 1794)

Freyhof, Jörg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, GmbH, Berlin / Boston: De Gruyter : 595-596

Heteropneustes fossilis

Common name. Stinging catfish.

Diagnosis. Distinguished from other species of catfishes in West Asia by: ○ adipose absent / ○ nasal barbel present, very long / ○ anal long, 60–70 rays / ○ dorsal short, 6–7 rays, without spine. Size up to 280 mm SL.

Distribution . Euphrates and Tigris drainages. In Tigris, from about Diyarbakır and Syrian Euphrates south to southern marshes and Shatt al Arab/Arvand in Iraq. Common in rivers and marshes of Khuzestan prov. in Iran, in Azadegan, and Karkheh. Native from Indus east to Myanmar.

Habitat. Slow-flowing rivers, marshes, reservoirs, and lakes with fresh or slightly brackish water. Can inhabit heavily polluted habitats and waters with very low oxygen levels, survive in semi-liquid mud, move overland, and move to bottom of cracks and crevices formed by mud cracking.

Biology. Usually gregarious. Spawns first time at 1 year and about 50–100 mm SL ( India). Spawns under water surface. Mating position, held in a form of amplexus for several seconds. Several copulations during a spawn. Does not guard eggs or larvae. Two tubular air sacs extending from gill cavity almost to caudal peduncle. Bimodal respirator and may respire aerially by gulping air at different intervals when oxygen content of water is reduced below saturation. Digs burrows in form of anastomosing tubes with multiple exits; up to 364 individuals have been found in one burrow complex. Feeds on a wide variety of invertebrates and plant material.

Conservation status. Non-native; first reported from Iraq and Iran in 1950s. Most likely introduced to control Bulinus truncatus snails, an important schistosomiasis vector. Still expanding its range northwards. Locally threatened by overexploitation for human consumption in its native range.

Remarks. Regarded as a pest in West Asia and not eaten. High market value and demand in India, where the species is used for medicinal purposes. Stinging catfish have the pectoral spine connected to a venom gland. Freshly caught or netted fish swing their heads from side to side and are active venomators. The venom is neurotoxic, hemolytic, and very painful. A sting in hand causes severe swelling, usually over the whole arm. The swelling and pain will subside in about a day, and the sting may take up to two weeks to heal. If the venom is squeezed and sucked out of sting, the effect can be negligible. While Clarias also have some sacs for breathing atmospheric air, in Heteropneustes , this structure is much more developed and resembles lungs. The air chambers begin above the gills and extend back to the tail as long, tubular sacs that emerge from the branchial cavity between the second and third gill arches and lie close to the backbone.

Further reading. Datta et al. 1982; Whitear et al. 1991 (venoum); Coad 2010a (introduction, biology); Ünlü et al. 2011 (range expansion).

Fish physiology: Getting rid of waste without water. Most nitrogenous wastes in fish are produced and excreted as ammonia or urea. Animals that excrete their nitrogenous wastes primarily as ammonia (NH 3) are classified as ammoniotelic, including agnathans and most teleost fish. Approximately 80–90 % of their nitrogenous wastes are excreted as ammonia, with the remainder excreted as urea. In high concentrations, ammonia is highly toxic, as it increases the internal pH of the cells, inhibiting key enzymes required for energy generation. Most air-breathing teleosts are primarily ammoniotelic but appear to have retained the genes for the urea cycle enzymes since a full complement of urea cycle enzymes has been reported for many of them. The capacity to synthesise urea in these fish may be an adaptation to their amphibious nature and their normal habitat of marshes, where the water ammonia level may be quite high, often rendering it uninhabitable to typical freshwater fish. Heteropneustes fossilis is capable of tolerating extremely high levels of total ammonia in its environment (up to 75 mm ammonium chloride vs. 100–200 μM, rarely up to 1000 μM in most fishes, up to 40–80 μM in humans). It can do so for extended periods without any adverse effects. When exposed to stressful conditions, the transition from ammoniotelism to ureotelism occurs in some air-breathing fishes. This happens when they live in semi-dry conditions inside mud during habitat drying. Although the real mechanism(s) of regulation of ureogenesis is unclear, it is hypothesised that the accumulation of ammonia within the body is likely the internal modulator for enhanced ureogenesis. This is mainly to avoid any build-up of ammonia to a level that can be toxic. It is hypothesised that the urea cycle is the predominant source of urea in air-breathing fishes despite the presence of uricolysis. The significant carbamoyl phosphate synthetase (CPS) levels observed in these fishes may play an important physiological role in their tolerance of high ammonia concentrations.

Further reading. Saha & Ratha 1998 (ureogenesis).

Figures

Heteropneustes fossilis

Distribution