The stinging or airsac catfishes comprise a single genus with about three species found naturally from Pakistan through India to Thailand.

The family is characterised by an elongate and compressed body with a flattened head; the mouth is small and transverse with fleshy, papillated lips; villiform teeth present on the jaws and vomer; 4 pairs of barbels present (nasal, maxillary and 2 mandibular); the anterior nostril is tubular and the posterior nostril a slit; gill openings wide and gill membranes free from the isthmus; air sacs are present (see below); swimbladder very small; the dorsal fin is short and spineless; no evident adipose fin; very long anal fin confluent with the caudal or separated from it by a notch; pectoral fin with a strong and venomous spine; skin scaleless; and branchiostegal rays 7.

These fishes can live in stagnant water by breathing air. They are dangerous to man since the pectoral spine harbours a strong venom. Stinging catfishes nonetheless are an important food in the native range.

Genus Heteropneustes
Müller, 1840

The only genus in the family, its characters are given above.

Heteropneustes fossilis
(Bloch, 1794)

Common names

eshlambo or abu shalambo (note variants on this word are used for catfishes and mudskippers); dudeh, doodeh or dood in Khuzestan (= smoke, perhaps because it is blackish); bu shalambo in Khuzestan; گربه ماهي نيش زن (= gorbeh mahi-e nishzan); گربه ماهي هندي (= gorbeh mahi hendi, meaning Indian catfish).

[samaka, abu-al-hukum, abu al-hakim, samma, djirri lasseye or jamhoori (latter at Baghdad in reference to the then new republic or jamhooria (F. Kedairy, in litt., 21 December 2005)) in Arabic; singhi in Pakistan; Indian stinging catfish].

Systematics

Silurus fossilis was originally described from India. A syntype of this species is in the Museum für Naturkunde, Universität Humboldt, Berlin under ZMB 3074 (Eschmeyer et al., 1996).

Key characters

The 4 pairs of barbels, short and spineless dorsal fin, absence of an adipose fin, and the long anal fin are distinctive. The head is small and very flattened and tapers both dorsally and ventrally to a terminal mouth.

Morphology

There are two, tubular air sacs extending from the gill cavity almost to the caudal peduncle, enabling this catfish to breathe air. On capture, air from these sacs may escape and cause a peculiar squawking sound. The anatomy and function of these organs was reviewed by Datta Munshi (1993).

Dorsal fin with 6-8 rays but no spine, anal fin rays 60-79, pectoral fin branched rays 7-8 after a strong spine serrated on its inner margin, and pelvic fin branched rays 5-6. Fin rays are difficult to count without dissection or x-rays because of the fleshy and heavily pigmented nature of the fins. Iranian specimens generally fall within the ranges cited above from literature sources as far as can be determined. Spine serrations are more notch-like than toothed. Al-Hassan et al. (1990) have demonstrated that the level of asymmetry in pectoral fin ray and total gill raker counts increases with fish length. Gill rakers are elongate, reaching adjacent raker 5-7 when appressed and number about 25. Barbels are elongate, the snout barbel being the shortest at about head length, the inner mandibular barbel being head length or longer, and the mouth corner and outer mandibular barbel being much longer than the head. The gut is elongate with several posterior coils.

Zakaria (1964) gives details of the pectoral fin spine anatomy. Singhkohli and Goswami (1987) and Kaul and Rishi (1987) describe abnormalities in this species including an upturned tail, a forked tail and forked barbels.

Sexual dimorphism

Unknown.

Colour

Yellow or leaden to dark green, grey-brown, rust-brown or even black, occasionally with two yellowish stripes. The flanks may also be spotted. The barbels are darker than the adjacent body. The eye is yellow. Young specimens are reddish and have a pale belly with numerous melanophores.

Size

Males reach 24.2 cm, females 34.4 cm in India (Datta Munshi and Choudhary, 1996).

Distribution

First recorded from Iraq for 1960 by Khalaf (1961) and Zakaria (1964) when a strange fish was reported to have inflicted a "painful bite" on several victims. The species spread northward and also eastward into Iran from southern Iraq. One collection from Dezful (see below) is dated February 1960 so the spread into Iran must have been very rapid or the original Iraqi introduction some years earlier than documented. Found from Iraq eastward but not continuously through South Asia to Vietnam. It is common in rivers and marshes of Khuzestan including the Dasht-e Azadegan and the Arvand River (Abdoli, 2000). Berra (2001) omits their Middle Eastern distribution as they are thought to be introduced.

Zoogeography

An Iraqi biologist told me that this species was introduced to Iraq for mosquito control (sic) by local authorities although no one would later admit to it. A more reasonable assumption is that it was introduced to eat the snail Bulinus truncatus, a vector for the human parasite causing schistosomiasis. It was ineffective in this regard (L. A. J. Al-Hassan, in litt., 1995; Jawad, 2003). There has probably been no natural, large scale migration from Pakistan as envisaged by Banister and Clarke (1977) and Banister (1980). Some Sumerian names may refer to this species but this is by no means certain (Sahrhage, 1999).

Habitat

It is common in rivers, marshes, ponds and canals and is found in both fresh and slightly brackish waters. Al-Daham and Bhatti (1977) found this species to suffer a 25% mortality over 72 hours at 10.25‰  sea water. It was most abundant in polluted and stagnant areas in the lower Diyala River where it dominated catches or was the only fish present (Khalaf et al., 1986; Biro et al., 1988). It is common in swamps and can survive temperatures up to 39.8°C (Pethiyagoda, 1991). Specimens survived 3-6 hours in air. It air breathes every 3-5 minutes but the frequency varies with time of day and weather conditions. On hot and calm days it visits the surface more frequently than during a heavy shower. S. Cowton (pers. comm., 23 August 2005) has observed schools of this species gaping at the surface in the artificial lake around Al Faw Palace in Baghdad, presumably in response to high temperatures and low oxygen. Individuals were also seen rapidly swimming straight up to the surface, gulping and diving straight back down again. On especially sultry days it may float or swim near the surface. In the dry season of India it can live in semi-liquid mud or at the bottom of fissures where the mud has cracked (Jayaram, 1980). It makes nest holes in the sides of ponds about 1 foot below the water surface in the form of anastomosing tubes with several exits. Up to 364 fish can be found in one complex of holes (Datta Munshi and Choudhary, 1996). Tekrival and Rao (1999) report its aquarium preferences and habits as 22-25°C, pH 7.5-8.5, alkaline water, predator, not too bright lighting, bottom dwelling with stones, roots and crevices preferred and cave brooding reproduction. Zakaria (1964) noted aquarium specimens producing audible squeaks when excited and preferred the darker side of an aquarium.

Age and growth

Khalaf et al. (1987) gave length-weight relationships for Diyala River, Iraq fish in autumn as W = 9.12 L^2.95 (r = 0.98, n = 58) and in spring W = 0.11 L^2.15 (r = 0.84, n = 66) and condition factor was 0.0012 in autumn and 0.08 in spring. Islam et al. (1982) give the following length-weight relationships for fish from the Ashar Canal, Basrah, Iraq:- log W = -6.35211 + 3.53226 log TL (r = 0.93543), log W = -5.96765 + 3.42353 log SL (r = 0.93687), and log W = -1.35223 + 2.04705 log GL (r = 0.87876) (TL = total length, SL = standard length, GL = girth length). Tabrez Nasar (1993) studied populations in India and gives length-weight relationships, log W = 1.7661 + 3.035 log L for one population and log W = 1.805 + 2.615log L for another. The coefficient of condition varied from 1.582 to 2.151, mean 1.89. A pond population did not grow as well as a natural one. Life span was up to 4 years in Iraq at Qarmat Ali using ocular lens diameter and vertebral rings (Al-Hassan et al., 1992) and may be 4+ years in India (Datta Munshi and Choudhary, 1996).

Food

Al-Daham et al. (1977) studied the diel feeding of this species in the Ashar Canal, Basrah, Iraq. Two feeding peaks were observed - at 0500 hours and 1700 hours, dawn and dusk, but stomachs examined around the clock had food in them. Aquatic plants and detritus are the bulk of the diet, followed by entomostracans and aquatic insect larvae. Also present are fish parts, molluscs and non-aquatic organisms. Cannibalism is reported in India for young fish (Jayaram, 1980). Khalaf et al. (1987) studied this species in the Diyala River, Iraq and found young fish to take chironomids and worms while larger ones ate fish. However all sizes take aquatic insects in spring. There is some competition with Barbus sharpeyi, a commercial species (Jawad, 2003). In a study of the recovering Hawr al Hammar, diet was 47.2% insects, 22.1% shrimps and 20.8% fish, in the Hawr al Hawizah 33.9% shrimps, 25.8% fish, 20.8% insects and 19.2% snails and in the Al Kaba'ish (= Chabaish) Marsh 51.2% shrimps, 26.4% fish, 12.0% insects and 10.4% snails (Hussain et al., 2006).

Chili macaroni, corned beef casserole, mixed vegetables and salad are dietary items at Camp Liberty, a former palace in Baghdad, where American soldiers feed leftovers from a distinguished visitors dining hall to catfishes, apparently this species (www.estripes.com, downloaded 7 September 2006).

Small Iranian specimens contained insects in their guts including Notonectidae and Diptera larvae. Abdoli (2000) lists diatoms, Chlorophyceaae, fish remains, Corixidae, Hemiptera, cyclopoid Copepoda, termites, Isopoda, Chironomidae, Oligochaeta and Rotifera.

Reproduction

Sexual maturity in India is reached when fish are about 1 year old, at 8.5 cm for males and 12.0 cm for females. Fecundity reaches 12,000 eggs (Haniffa et al., 2008). Eggs are laid in a shallow depression excavated by both the male and female in mud or sand. Eggs are light green. They hatch in about 2 days in Sri Lanka. The parents guard the eggs and young until the young fish are about a month old and able to look after themselves. Singh Kohli and Goswami (1987) describe spawning behaviour in aquaria after hypophysation using pituitary glands of Indian major carps. A pair of males circled each other in a figure 8 pattern until one established dominance. The dominant male chased the female, swimming underneath her or obstructing her path, and touching barbels. The male tried to bite the female in the chases and shivered its whole body while making lateral passes. The male arcs its body into a u-shape, the female touches the male's genital papilla and the pair remain motionless for 2-5 seconds. The female jerks and separates from the male releasing the eggs which settle to the bottom. The pair rest before mating agian. About 40-200 eggs are released after each mating. Mating acts number 20-100 and always occur near the surface of the aquarium. Spawning is more complete and egg fertilisation is better when there is one female and two males, the other male acting as a stimulator, with the spawning male quarrelling with the non-spawning male between mating with the female. Datta Munshi and Choudhary (1996) report similar behaviour. The male nudges the genital region of the female with his head, occasionally shaking it from side to side. Eventually the female is aroused and nudges the male genital region. This female action was necessary for mating to occur. Mating did not happen when spawners were of different sizes. Once the female has her snout below the male genitalia, the male twists his body to place his snout below her genitalia. The fish remain motionless for 2 seconds, then the male vibrates his body and the female convulses and releases eggs. This can happen 30-50 times for each couple at 2-3 minute and then later 5-10 minutes or longer intervals. About 100-150 eggs are extruded, the number decreasing over time. If more than one male is present, mating only occurs after one establishes dominance. Males may eat eggs. Spawners mate in the water column or near the surface.

Parasites and predators

Jalali et al. (2005) summarise the occurrence of Gyrodactylus species in Iran and record G. fossilis in fish from the Karun River.

Economic importance

An important food fish in India and Sri Lanka, where its flesh is reported to have invigorating qualities. Some fish are exported from Sri Lanka for the aquarium trade. V. D. Vladykov reported (in litt., 22 July 1963) that he had seen this species in pet shops in Tehran, on sale at about $2.00 each.

The pectoral spine can cause a serious wound because of the toxin content of the epidermal cells covering the spine. The histology of the pectoral spines was described by Bhimachar (1944) based on Indian material and the toxin was found to have both neurotoxic and haemolytic effects. The toxin is fatal to frogs (within 15-20 minutes of subcutaneous injection of glycerinated venom) and to other fishes.

Zakaria (1964) reported severe swelling involving the whole arm from a hand sting in Iraq. The swelling and pain recede after about a day but the puncture wound can take about two weeks to heal and some pain can be felt when applying pressure to the wound site up to six weeks later. Caras (1964) (probably based on a report in Farsi in Game and Nature, Tehran, ca. 1961) recorded a diminutive black fish found in the Shatt al Arab which reputedly killed 28 people with a venomous bite (sic). Death was said to be swift. This was presumably a garbled report on this species. Verbal and newspaper reports from Tehran (V. D. Vladykov, in litt., 26 August 1961) maintain that this species could cause death to cattle and humans although Vladykov (in litt., 30 September 1963) considered fatal cases "not well proved". I was stung in the thumb by this fish in Iran with no effect (although I did devote considerable time and effort into squeezing and sucking blood from the puncture site!). Freshly caught or netted fish swing the head from side to side and thus are active envenomators (despite knowing this I was still stung). Treatment is symptomatic and some relief can be obtained by immersing the sting site in water as hot as can be withstood and applying a meat tenderiser. These treatments serve to coagulate the protein toxin. The wound should be cleaned to avoid secondary infections such as tetanus (Halstead, 1967-1970; Coad, 1979b).

R. Beck (pers. comm., 2000) reports that this fish is now present in the Syrian Euphrates, its tributaries, and in irrigation canals. Incredible numbers occur near town sewage outlets and in weed beds. It is known to consume eggs of Barbus grypus, a preferred food species

Robins et al. (1991) list this species as important to North Americans. Importance is based on its use in aquaculture, as food, in textbooks and because of its venomous nature.

Conservation

This is an exotic species and requires no conservation although it is is listed as Vulnerable in its natural habitats (Haniffa et al., 2008a).

Further work

The distribution of this species should be mapped as it is potentially hazardous to humans.

Sources

Iranian material:- CMNFI 1979-0087, 1, 189.0 mm standard length, Khuzestan, Karun River at Ahvaz (31º19'N, 48º42'E), CMNFI 1979-0359, 5, 96.9-114.2 mm standard length, Khuzestan, Karkheh River at Hamidiyeh (31º29'N, 48º26'E); CMNFI 1980-0909, 4, 113.2-165.0 mm standard length, ? Khuzestan (no other locality data); BM(NH) 1980.8.28:4-5, 2, 91.7-98.0 mm standard length, Khuzestan, Dezful (32º23'N, 48º24'E); ZSM 27369, 3, 111.9-139.0 mm standard length, Khuzestan, Karun River near Ahvaz (ca. 31º19'N, ca. 48º42'E).

Comparative material: BM(NH) 1962.7.26:80-83, 4, 127.8-189.0, Iraq, Baghdad (33º21'N, 44º25'E); BM(NH) 1974.2.22:1785, 1, 89.8 mm standard length, Iraq (no other locality data); BM(NH) 1974.2.22:1786-1788, 3, 102.3-165.3 mm standard length, Iraq (no other locality data); ZSM 19455-56, 2, 123.2-127.7 mm standard length, Iraq, Tigris River near Amara (ca. 31º43'N, ca. 47º06'E).

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