Three (un)usual suspects as the identity of the Shatt-al-Arab's venomous mystery fish – the Asian stinging catfish (top); the long-tailed moray eel (centre), and the bull shark (bottom) (public domain)
Yesterday, here on ShukerNature, I offered a blenny for your thoughts (click here). So today, I'm offering another one! You can thank me later.
The Shatt-al-Arab is a 120-mile-long river formed by the confluence of the Tigris and Euphrates rivers in the southern Iraq town of Al-Qurnah. Flowing southwards, it constitutes the physical border of Iraq with Iran, and empties into the Persian Gulf. Many species of fish inhabit its waters, but one of them may be a notable species still unknown to science.
I first learnt of this small but potentially significant unidentified freshwater fish many years ago, when reading Dangerous To Man (1975), Roger Caras's definitive book on creatures hostile to humans, but its mystery remains unsolved to this day. In his book, Caras included the following brief but very intriguing paragraph:
From Tehran comes a report of a diminutive black fish found in the Shatt al Arab River. It reputedly has killed twenty-eight people with a venomous bite. Death is said to be swift. No other information is presently available. (No other fish is known to have a venomous bite, and this report is at least suspect.)
What makes the above snippet so interesting (apart from the fact that except for my own researches into it and documentation of it in various of my books and articles, I have never encountered anything more about this creature anywhere) is Caras's claim that it is its bite that is venomous and that no other fish is known to have a venomous bite. In contrast, a wide range of piscean species possess venomous spines, for instance, or toxin-secreting skin.
My copy of Dangerous To Man by Roger Caras (© Roger Caras; reproduced here on a strictly non-commercial, Fair Use basis only)
But if we assume that such a fish does indeed exist, what could it be, and how can its reputedly venomous nature be explained? Various candidates can be selected from the many thousands of fish species already known to science, but none can offer a comprehensively satisfying solution.
When I originally read Caras's report, the first candidate that came to mind, for several reasons, was the Asian stinging catfish Heteropneustes [formerly Saccobranchus] fossilis. This species does indeed inhabit the Shatt-al-Arab (though it is an imported rather than a native fish here, originating from Indochina). Moreover, it is often only around 4 in long (though it can grow up to 1 ft), it is definitely black in colour, and, of particular significance, it is known to be venomous. So far, so good.
However, unlike the Shatt-al-Arab mystery fish, the Asian stinging catfish is venomous due not to a toxic bite but instead to a poison gland at the base of a spine on each of its two pectoral fins. This can yield an extremely painful but not fatal sting. Consequently, even if victims (or onlookers) were mistaken in assuming that this catfish had bitten them (unless perhaps it had done so in self-defence if they had been molesting it, but this would not have been a source of venom), they would not have died from its fin spines' sting. Exit H. fossilis from further consideration.
A second candidate is the long-tailed or slender giant moray eel Strophidon sathete (aka Thyrsoidea macrura). Although typically marine, and distributed widely in the tropical Indo-Pacific Ocean, it is well known for entering estuaries and travelling considerable distances up rivers, including the Shatt-al-Arab. What is particularly interesting about this species in relation to the latter river's mystery fish is that in a sense it can be said to have a toxic bite, albeit not in the usual convention.
True, its teeth do not actually secrete a toxin, via poison sacs, like those of venomous reptiles do. However, as a voracious carnivore the long-tailed moray eel will certainly have pieces of rotting flesh left over from previous meals and packed with pathogenic bacteria sticking to its teeth, just like crocodiles and carnivorous mammals like lions and tigers do. Consequently, a bite from this fish might well transfer some of those bacteria into the wound caused by its teeth, which in turn may lead to septicaemia developing, especially in someone with a less than robust immune system, such as a child, an elderly person, or someone recovering from a major illness. Even so, no known human fatalities resulting from a bite by this moray eel species are on record, and there is also the not-inconsiderable problem of size difference to reconcile, because it can attain a maximum length of up to 12 ft when fully grown (even its average length is over 2 ft). So this species can hardly be deemed 'diminutive', like the Shatt-al-Arab mystery fish. Don't call us, S. sathete.
Nor can the bull shark Carcharhinus leucas be termed diminutive, bearing in mind that it averages 7.5 ft long. Unlike most sharks, this notably aggressive species is frequently found in freshwater habitats, including the Shatt-al-Arab River, and like those of moray eels its teeth are brimming with pathogenic bacteria from rotting meat still attached from earlier meals. So again, a bite from this fish, although not intrinsically venomous, might well lead to blood poisoning. And several human deaths caused by this fish attacking them have been confirmed here. But as even a new-born specimen is normally around 2.5 ft long, this species clearly has no bearing upon the identity of the Shatt-al-Arab mystery fish.
As I researched further into this ichthyological puzzle, however, I made an unexpected breakthrough, by discovering that one crucial aspect of Caras's account was fundamentally incorrect. Contrary to his statement, some fishes do possess a genuinely venomous bite.
And one of these is the blackline fang blenny Meiacanthus nigrolineatus. Its lower jaw bears sizeable canine teeth that have grooved sides and venom-producing tissue at their base. These teeth enable it to produce a sufficiently unpleasant bite to deter all predatory fishes, large and small. In general appearance, it is relatively nondescript – no more than 3.75 in long, with a blue-grey head and foreparts, and the remainder of its body pale yellow. There is also a thin black stripe running lengthwise just beneath its dorsal fin, which earns it its common name.
Blackline fang blenny (© Akvariumugamyba at http://akvariumugamyba.lt/ - reproduced here on a strictly non-commercial Fair Use basis only)
Over 830 species of true blenny or blennioid are currently known to science, generally small in size and scaleless but many-toothed, and are of worldwide distribution. Most are marine fishes, as indeed is the blackline fang blenny, which is native to the Red Sea and the Gulf of Suez and Aqaba. However, there are freshwater species too (such as the well-known Salaria fluviatilis, which is native to rivers in several European countries as well as in Morocco, Algeria, Israel, and Turkey).
No human fatalities have been recorded with the blackline fang blenny, but what if the Shatt-al-Arab River is harbouring a still-undescribed, darker-coloured, but otherwise comparable freshwater relative that is capable of producing a more potent venom? If such a creature, known locally but attracting little notice from the outside, scientific world, is one day captured and formally identified, then our mystery fish will surely have been unmasked at last - turning up like the bad blenny that it is.
My special thanks to French ichthyologist Dr François de Sarre for very kindly sharing his own thoughts and comments with me regarding this fishy affair.
This ShukerNature blog article is adapted and expanded from my book Karl Shuker's Alien Zoo: From the Pages of Fortean Times.