Family : Muraenidae
Text © Giuseppe Mazza
English translation by Mario Beltramini
The Spotted moray (Gymnothorax moringa) lives along the tropical coasts of west Atlantic up to St. Helena and Ascension Islands © Kevin Bryant
The Spotted moray, Gymnothorax moringa (Cuvier, 1829), belongs to the class of the Actinopterygii, the ray-finned fishes, to the order of Anguilliformes and to the family of Muraenidae that counts 16 genera and 211 species present in the temperate and tropical seas of the whole world.
The name of the genus Gymnothorax originates from the Greek “gymnos”, naked and from the Latin “thorax”, thorax, with reference to the fact that unlike the eels, as in all morays, their thorax is bare because the pectoral fins are absent.
The specific name moringa is the diminutive given locally to the morays of modest size.
After Gymnothorax funebris, it’s the biggest Caribbean moray, even 2 m long with a scary mouth armed with sharp teeth © Allison & Carlos Estape
Zoogeography
The Spotted moray is present in the tropical and subtropical waters along the Atlantic American coasts from North Carolina and the Bermudas up to the Gulf of Mexico and then in all Central America and the Antilles up to Guyana and Brazil.
Carried by the currents the larvae have then reached the Trindade and Martim Vaz, 1200 km far from the continent and, finally, in the middle of the Atlantic Ocean, the islands of St. Helena and Ascension.
Ecology-Habitat
A second inner mobile jaw, called pharyngeal, hooks, positions and carries then towards belly also the largest preys that then are swallowed whole © Allison & Carlos Estape
Gymnothorax moringa is a benthic species often present in the ravines of the reefs and in rocky zones where it lives, solitary, mainly in shallow waters, not deeper than 35 m, even if it has been sighted at 200 m and some talk of 300 m.
It frequents the phanerogams beds but avoids the unclear waters of the harbours and of the bays.
Morphophysiology
After Gymnothorax funebris, Gymnothorax moringa is the largest moray in the Caribbean.
Swimming is undulating with fins merged in a high skin crest. Here it’s about to bite an Azurina multilineata found in the night darkness thanks to its very fine smell © Karine Marangon
As a matter of fact, it may exceed the 2 m in length with a published maximum weight of 2,5 kg, although the current size, much inferior, is of about 60-75 cm.
Like all Anguilliformes, it has lost the pelvic fins. The dorsal, the caudal and the anal have merged to form a unique long cutaneous crest, here particularly high, used for a wavy swim.
The gill orifice are simple dark fissures located at the end of the head on the prolongation of the jaws, practically invisible among the spots of the livery.
By day the Spotted moray often looks around from the den. Opportunist as it is, could even seize these young passing by Haemulon plumierii © Kevin Bryant
From these goes out the air that has oxygenated the gills, pushed by the rhythmic movement of the mouth that opens and closes often for breathing, and not for threatening as one might think at first glance.
On the head we note two tubular nostrils and just above two more, less showy. In fact, the morays are fishes hunting usually in the darkness based mainly on the sense of smell.
The eye, located just before the middle of the mouth, has a yellowish iris and the snout elongated and sharp, seen in profile with closed jaws, displays an unusually long fissure between the two.
Conversely here it looks at two Brachygenys chrysargyreum, easy prey much diffused in the Caribbean © Kevin Bryant
The mouth, white inside with brown spots and double rows of teeth, has strong and sharp canines on the outer side of the jaws and up, in the middle, 3 long impressive tusks for seizing the preys.
This assault structure is then followed by a second inner mobile jaw, called pharyngeal, typical of the bigger morays, that projects forward with pharyngeal and vomerian teeth to hook the victim and position it for swallowing it whole.
The skin, scaleless, is soaked in a slippery mucus that protects it from bacteria and parasites and allows these fishes to slip in everywhere without scratches.
Instead this flaming Apogon maculatus risks nothing because the moray is getting removed by two Stenopus hispidus the skin parasites and the flesh left between its teeth © Kevin Bryant
The background colour, white or pale yellow, is dotted with dense irregular spots, violaceous or brown, more or less big and often overlapping for a perfect mimicry.
Initially the juveniles are wholly black with a pale cutaneous crest and lower jaw. Then, growing, they lighten and progressively appear the dark dotting while the long cutaneous crest rises.
Ethology-Reproductive Biology
In the belly of Gymnothorax moringa there is always room and a female may lay 10.000 eggs several times a year © Allison & Carlos Estape
Gymnothorax moringa nourishes of modest-sized fishes: among which many species of Haemulidae like, for instance Haemulon plumierii, Haemulon aurolineatum, or Brachygenys chrysargyreum, of Labridae like often Halichoeres bivittatus, or of Pomacentridae like Azurina multilineata.
It hunts mostly at night also preying on octopuses and small crabs, in particular Mithrax sculptus and Pitho anisodon, but stands out above all for the fight to the ill-famed Pterois volitans, fishes carelessly introduced by man that have become invasive to the detrimento of various Caribbean species.
The Spotted moray may reach the age of 23 years, according to the growth rings of the otoliths.
There is a slight sexual dimorphism with males longer than the females and the head more massive and muscular starting from 1 m of size.
The modalities of the reproduction are still partly to be discovered.
It is known that this is an oviparous species with females that in the reproductive period, usually between April and autumn but also often longer, may lay as many as ten thousand eggs per month.
It seems that they disperse them with a particular scent that attracts the males for the fecundation.
They are planktonic and hatch after 30-45 days.
The larvae then go wandering for about one year carried by the currents while they assume the typical shape of the Anguilliformes, called leptocephalus, similar in appearance to a transparent willow leaf, with very small head and protruding needle-shaped teeth.
The leptocephali do not catch zooplankton, like the normal larvae of the fishes, but they grasp tiny food particles carried by the currents. They can also swim backwards with rapid undulating movements or even curl getting the look of a little wandering cylinder that renders them similar to a gelatinous unappetizing zooplankton like the jellyfishes.
The larvae move for about one year carried by currents while assuming a nastriform shape like this, called leptocephalus, typical of Anguilliformes © Mickey Charteris
Just after larval phase juveniles are wholly black, but the white long skin crest and the chin. Then, growing, they fade and we note the first spots © Allison & Carlos Estape
The adults are preyed upon by big groupers and barracudas, not to forget the divers, who sometimes eat their trophies careless of the fact that the flesh of Gymnothorax moringa might be at risk of ciguatera, a serious food poisoning always possible when a species fed itself for years of fishes storing in their diet the toxin produced by the dinoflagellate Gambierdiscus toxicus.
The resilience of the Spotted moray is low with a minimal time of 4,5-14 years for doubling the populations and the fishing vulnerability index, very high, marks even 90 on a scale of 100.
On top, a juvenile with the skin crest growing while below the livery is now the adult one. Gymnothorax moringa can live 23 years and is not an endangered species © Allison & Carlos Estape
However, it stands as “LC, Least Concern” in the evaluation of the IUCN Red List on the endangered species, given its ample distribution and the fact that it is locally abundant.
Synonyms
Muraena moringa Cuvier, 1829; Sidera moringa (Cuvier, 1829); Gymnothorax rostratus Agassiz, 1831; Murenophis caramuru Castelnau, 1855; Murenophis curvilineata Castelnau, 1855; Thyrsoidea concolor Abbott, 1860; Gymnothorax flavoscriptus Poey, 1876; Gymnothorax picturatus Poey, 1880; Lycodontis albimentis Evermann & Marsh, 1900; Gymnothorax albimentis (Evermann & Marsh, 1900).