The only cooperative, interspecies hunting behaviour recorded between fish occurs in Guinjata Bay! It is a unique behaviour as yet largely unknown to the world of marine biology.
Moray eels, an abundant fish here on our reefs, are ‘recruited’ by Roving Coralgroupers to hunt together. The grouper will ‘invite’ a moray by shaking its head, forming a new partnership. It is unclear the advantage to the eel of doing such, but the eel aids the grouper by flushing prey out of narrow crevices that are otherwise inaccessible to the groupers.
Cooperative and symbiotic relationships are well known and researched, both in the ocean and on land, but this is the first hunting partnership (between fish) recorded.
Moray eel are snake-like fish, often mistake for serpentines, which almost exclusively inhabit marine waters. Although there are over 200 species with an innumerable number of colours and intricate skin patterns, when diving these eels are usually highly distinguishable by their heads just poking out of crevices and holes in an almost ominous way.
Moray eels have their mouths open most of the time in order to provide constant water circulation to their gills; not, as they are widely mistaken to be, because they’re in a continual search for prey. The eels are carnivorous though. They feed mostly on octopus, crabs, squid and cuttlefish while themselves predated by groupers, barracudas, sharks and sea snakes. In comparison to the wide array of prey available, morays are actually hunted by comparatively few species. This allows them to burrow in holes and crevices, a potentially risky residence where fast escape is not easily accessible.
Circumstantial evidence indicates a couple of species may be poisonous, but they generally are no threat to divers. Similarly, in some species the mucus which is secreted over the skin is toxic in a minority of species. All morays (toxic and not) have the ability to produce a considerable amount of mucus in goblet cells in the skin though, which provides protection from abrasion when swimming fast and in crevices (also aids streamlining and lubrication). The mucus also adheres well to sand granules, making the walls of sand burrow residences more permanent.
Interestingly, the eels have two sets of teeth: one set directly in the most and visible to divers, the second inside their throat (‘pharyngeal jaws’). Both sets of jaws are launched open to actively capture prey and transport it; Morays are unique as the only animals known to use the pharyngeal to assist with the capture and restraint (most animals will just use for digestion). The teeth in both set are pointed backwards to stop prey getting away – the rare occasion where eels have struggled to differentiate fingers and food, fingers must be manually prised off the teeth. One interesting theory for having two sets of jaws is that their head is too narrow to create adequate low pressure which most fish use to swallow.
Although most abundant in shallow, tropical reefs, moray eels are found in tropical and temperate climates (even if only extend marginally beyond subtropics). Temperature also dictates mating season; when the temp and food availability are both optimum then the females release up to 10,000 eggs, while wrapping themselves around the male. Simultaneously the males release sperm and externally fertilize the eggs to form leaf-shaped larvae, which swim independently in the water with plankton. After 8 months, the larvae drop to the ocean floor and begin life as fully formed adult moray eels. Their life expectancy is 6-36 years. Although this is the basic life and reproductive cycle of the eels, research has shown morays to be hermaphrodites too. Some are synchronous, with both functional testes and ovaries, whereas others are sequential (changing from male to female). It is then possible for these to mate with either sex, increasing the chances of successful reproduction.
Moray eels are commercially fished, but not extensively. However, eating the fish can cause ciguatera fish poisoning, a food borne illness from reef fish where toxics in plankton accumulate up the food chain to dangerous concentrations. There are also often parasites on the skin – making the eels popular with cleaner shrimps and wrasses but also a greater threat for consumption.