Gymnothorax eurostus
Gymnothorax eurostus was first described in 1860 by Charles Conrad Abbott. This fish belongs to the Muraenidae family, commonly known as moray eels. There is no specific Dutch name for this species. In English, it is referred to as Abbott’s moray eel, Indo-Pacific stout moray, spotted moray, or white-speckled moray.
The genus name Gymnothorax is derived from Greek, where “gymnos” means “naked”, and “thorax” refers to “chest”, indicating the absence of pectoral fins. The species name “eurostus” comes from the Greek εὔρωστος, meaning “sturdy” or “strong”, referring to its compact body shape.
Synonyms: Lycodontis eurostus, Lycodontis laysanus, Gymnothorax laysanus, Muraena laysana, en Thyrsoidea eurosta.
Description
Gymnothorax eurostus has an elongated, slender body, typical of moray eels. The head and body are predominantly dark purple-brown with small yellow spots, which become less dense toward the tail. The body features a pattern of black and brown spots, with a white edge on the tail. The fins are usually dark-colored, blending with the rest of the body. This species can reach a maximum length of about 60 cm (24 inches).
Differences Between Males, Females, and Juveniles
There are no documented physical or behavioral differences between male and female Gymnothorax eurostus. Similarly, no differences have been noted between juveniles and adults.
Behavior and Temperament
Gymnothorax eurostus is a nocturnal predator, primarily active at night. It is a carnivore that mainly preys on reef fish. These eels are generally solitary and are rarely seen in groups. They exhibit semi-aggressive and territorial behavior, especially in an aquarium setting.
They are typically shy, spending the day hidden in crevices and caves. They are bottom-dwellers and are often found in shallow coral reefs.
Threat Display and Open-Mouth Behavior
Like other moray eels, Gymnothorax eurostus often keeps its mouth open as part of its breathing process. Moray eels have small gill openings, so they must keep their mouths open to pump water over their gills, ensuring proper oxygen intake. While this behavior may appear intimidating, it is a normal respiratory function and not necessarily a sign of aggression.
Biotope
Natural Distribution and Ecosystem
Gymnothorax eurostus is a species found in the Indo-Pacific region and exhibits an intertropical distribution. This term describes a biogeographic pattern in which a species is present in the temperate zones of both hemispheres but absent from the tropical regions in between. In the case of Gymnothorax eurostus, this means that the species can be found in several marine locations across the northern and southern temperate zones, yet it is not present in the tropical waters that connect these areas.
They occur in various marine locations, including the eastern Pacific Ocean from Costa Rica to Easter Island, and have also been reported from areas such as the Seychelles, although some sources dispute this. In Australia, they are found along the central coast of Western Australia, around the tropical north, and south to the northern coast of New South Wales.
Habitat and Environment
Gymnothorax eurostus lives mainly in shallow waters, often associated with coral reefs and rocky areas. They are often found in inshore reef environments, hiding in crevices and caves during the day. Their natural habitat consists of an abundance of coral and rocks, which provides them with ample hiding places. The bottom of their habitat often consists of hard coral and rubble substrates.
Food Chain and Predation
Gymnothorax eurostus is a nocturnal predatory fish that feeds on reef fish and other small marine organisms such as octopuses. They are hunters and have no specific natural predators mentioned in the available documents. Their behavior as predators and their ability to hide well in their habitat contribute to their survival in the wild.
Diet
Diet in het Wild
Gymnothorax eurostus is a nocturnal predatory fish that feeds on various marine organisms. In the wild, their diet consists mainly of reef fish, small fish, octopus, crabs and other crustaceans. They are opportunistic hunters and use their sharp teeth to catch and consume their prey.
Food in the Aquarium
In an aquarium environment, it is crucial to provide a diet that mimics the natural feeding habits of the inhabitants. It is advisable to feed them fresh fish, shrimp, crabs, and other crustaceans. These can be served as pieces of fish meat or crustaceans skewered on a long feeding stick and positioned near their hiding spots. To ensure their nutritional needs are met, feeding should take place twice a week.
Reefsafe?
Gymnothorax eurostus is not completely reef-safe. They do not eat coral or polyps but can consume small shrimp and other invertebrates in the reef. Therefore, it is important to be careful when keeping these morays in a reef tank with small invertebrates that could be considered prey.
The Aquarium
Aquarium size
To keep Gymnothorax eurostus, it is recommended to have an aquarium of at least 1500 liters. This size offers ample space for the fish to swim and hide. If you plan to keep multiple specimens, the aquarium should be significantly larger to avoid territorial conflicts and to provide sufficient hiding places.
The Aquarium
To set up the aquarium for a moray eel, it is essential to include plenty of rocks and hiding spots, such as caves and crevices, where the moray can conceal itself during the day. Using live rock is highly recommended, as it not only offers hiding places but also aids in the aquarium’s biological filtration. The substrate should consist of fine sand, as this more closely mimics the moray’s natural environment and helps stabilize the rock structures.
Water parameters
The ideal water parameters for Gymnothorax eurostus in an aquarium are a temperature between 21°C and 28°C, a specific gravity of 1.020 to 1.026, and a pH between 8.1 and 8.4. These parameters help mimic their natural habitat and promote their health and well-being.
Introduction to the Aquarium
It is important to introduce the moray eel into the aquarium only after it has matured properly. This means that the aquarium must have reached a stable biological balance, which usually takes several weeks to months. This ensures that there are sufficient algae and microorganisms present to support a healthy environment.
Suitable Tank Mates
Gymnothorax eurostus can be kept with other semi-aggressive fish that are large enough not to be considered prey. Suitable tankmates include larger reef fish such as angelfish, triggerfish, and larger wrasses. It is important to avoid small fish and invertebrates such as shrimp, as these may be considered food.
Breeding Gymnothorax eurostus
There is no documented information about successful breeding of Gymnothorax eurostus in an aquarium.
Particularities
The Gymnothorax eurostus, also known as Abbott’s moray eel, has some interesting features and peculiarities that go beyond the basic information about their appearance, behavior and habitat.
Toxicity
One notable aspect of the Gymnothorax eurostus is that this species is considered venomous. Although the exact nature of the toxicity is not detailed in the available information, it is warned that the venom can be fatal under certain conditions. This makes it important for aquarists to take precautions when handling these fish and to be prepared for emergencies.
Behavior as an Escape Artist
Gymnothorax eurostus is known as an escape artist. They can escape through very small openings in the aquarium, meaning that a well-covered aquarium is essential to prevent them from escaping. This behavior emphasizes the need for a safe and well-designed aquarium environment.
Color variations
There are reports of several color variations within this species. In addition to the usual dark brown color with yellow spots, there is also a color form that is predominantly white with dark brown markings. These variations can affect the aesthetic appeal of the fish in an aquarium.
Habitat and Depth Range
The Gymnothorax eurostus is usually found in shallow waters, but they can also be found at depths of up to 74 meters. This wide depth range shows their adaptability to different environments.
Food preferences
Although they are primarily carnivores that feed on small fish and crustaceans, it is worth noting that they also eat octopuses. This diet may affect their role in the ecosystem and their interactions with other species.
Conclusion
Gymnothorax eurostus is a fascinating but challenging species to keep in an aquarium. This fish requires a large aquarium of at least 1500 litres, with plenty of hiding places and stable water quality. They are semi-aggressive and can be territorial, meaning they are best kept alone or with other large, robust fish. Their diet should consist of fresh fish and crustaceans.
These moray eels are not suitable for beginners due to their specific care requirements and potentially toxic nature. They are known to be escape artists, meaning a well-covered aquarium is essential. Despite these challenges, experienced aquarists can enjoy their unique behavior and appearance if given the proper care and attention.
Video
Author
John de Lange
Copyright images
