Spottail moray

Gymnothorax equatorialis is an eastern Pacific moray eel that Hildebrand described in 1946, under the name Priodonophis equatorialis, from two specimens taken near Cabo Blanco, in northern Peru ^[1]. His specimens were dark brown, with pale dots that grow larger toward the tail ^[1]. Unlike the other morays of Costa Rica, which live almost always on rocky bottoms close to shore, this one is caught in trawls over soft bottoms ^[2]; a Mexican study places it over sand and mud and also among rocks ^[3].

It is caught in bottom trawls. Of the works we reviewed, the only one centred on its biology is a study on the coast of Jalisco and Colima, in Mexico, where 707 fish indicated two spawning periods a year ^[3]. The IUCN assesses it as Least Concern ^[4].

Hildebrand described a compressed body, with a strongly compressed tail tapering to a rather narrow point, and a moderately compressed head with a robust snout and a large mouth that opens far beyond the eye ^[1]. The teeth sit in a single row in each jaw (the lower jaw may carry a few depressible teeth in an inner row), are compressed and are serrated on both margins, and there are none on the vomer or the palatines ^[1].

His preserved specimens were dark brown, with the fins darker than the body. The pale dots were minute on the head and grew larger toward the rear, especially on the distal part of the slender tail, and they did not extend onto the underside of the head or trunk ^[1]. The two specimens measured 625 and 795 mm ^[1].

The species it is most easily mistaken for in the eastern Pacific is Gymnothorax phalarus, which Bussing described in 1998 and which turns up almost always in the same trawl hauls ^[2]. Gymnothorax equatorialis has three infraorbital pores, whereas Gymnothorax phalarus has four; it often bears a median intermaxillary tooth; and its tail is narrower and ends in very elongate spots, longer than the eye diameter and widely spaced ^[2]. It also has more vertebrae: by his table of counts, the mean total was 145.6 against 140.1 in Gymnothorax phalarus ^[2].

Similar species

• Gymnothorax phalarus: It has four infraorbital pores, not three, and the spots at the end of the tail are round or oval, smaller than the eye and more closely spaced ^[2].

The Mexican study, relying on field guides, places it from the Gulf of California to Peru and describes it as benthic, living among rocks and over sand and mud bottoms, down to about 125 m depth ^[3]. In Costa Rica, Bussing found that, of the 21 moray species on that coast, only this one and Gymnothorax phalarus enter the trawl fishery, because the others live almost always on rocky bottoms close to shore ^[2].

When Hildebrand described it in 1946, he knew only the two type specimens, taken in the Gulf of Guayaquil near Cabo Blanco, in Peru ^[1]. WoRMS now accepts it as Gymnothorax equatorialis and treats its original name, Priodonophis equatorialis, as a synonym ^[5].

The study from Jalisco and Colima, with 707 fish collected in night trawls between December 1995 and December 1998 and between August and November 1999, is the main source on its reproduction ^[3]. Nearly all the fish measured between 44 and 68 cm total length (98 %), and females were longer, averaging 54.7 cm against 52.1 cm in males ^[3]. The maximum length found was 79.0 cm ^[3]. Females outnumbered males, at a ratio of 1 to 1.4 ^[3].

Half the individuals had mature gonads at 43.7 cm total length in females and at 42.7 cm in males; the smallest mature female measured 36 cm and the smallest mature male 38 cm ^[3]. Total fecundity averaged 32,029 eggs and reached 99,992 in a 67 cm female ^[3].

The ovaries held two main types of oocytes, one of small immature cells of about 85.1 µm and one of large cells in secondary vitellogenesis of about 701.6 µm ^[3]. From the females' gonadosomatic index, the authors conclude that there are two short spawning periods a year, one in the middle and one at the end of the year; in males the index showed no clear trend ^[3]. In both sexes the gonads extend a few centimetres past the anal pore ^[3], and the left one is 30 to 40 % shorter than the right ^[3].

What little is known of its ecology comes from where it is caught. Bussing found it almost always alongside Gymnothorax phalarus in trawl samples over soft bottoms on the Pacific coast of Costa Rica, and compared 63 specimens from that country with 3 from Mexico ^[2]. In Jalisco and Colima, the sample of 707 fish came from trawl nets set at night ^[3].

The works reviewed do not describe its diet or its predators, and this account does not invent them. All they indicate about its role in the ecosystem is that it turns up in trawl catches over soft bottoms ^[2].

We found no Peruvian national assessment and no population estimates, and so say nothing more about its status. The IUCN places it in the global category of Least Concern (LC) ^[4].

The oldest Peruvian data are from 1941: the fishery Mission that worked in Peru took the two type specimens on 15 August of that year with a line trawl, in about 12 fathoms, in the Gulf of Guayaquil near Cabo Blanco ^[1]. The sources reviewed describe it as a species taken in nets over soft bottoms ^[2]; they document no sightings while diving and say nothing about access to the place or restrictions ^[1].