Snake eels (family Ophichthidae) are a widespread and highly diverse, but poorly understood group of fishes known worldwide in tropical to temperate waters from inshore to at least 1,300 m depth.
During the dissections of a commercially harvested large marine sciaenid, the Black Jewfish Protonibea diacanthus (Lacépède, 1802), collected from coastal waters off northern Australia, ophichthids were found encased in the mesenteries in the body cavity. Subsequently, specimens of ophichthids were also collected from the stomach contents of P. diacanthus, suggesting this as the potential source of the ophichthids in the body cavity.
Genetic analysis confirmed 4 species of ophichthids were collected from the body cavity of 19 P. diacanthus specimens. Further investigation has revealed the occurrence of at least 3 additional ophichthid species from the body cavities of 10 Australian teleost species classified in 8 different families. Teleost species with ophichthid eels present in their guts were medium to large, opportunistic carnivores suggesting that prey items were targeted rather than incidentally ingested.
Preliminary identification of the eels suggests that some may be new Australian records, highlighting an important, but little used source of ophichthid specimens for scientific studies.
This paper presents the first published report of eels in the body cavity of fishes in Australian waters and is a good example of collaboration and co-operation on collections-based research between various stakeholders in the fisheries industry and of citizen science.
[Keywords: Pisces, Teleostei, Anguilliformes, Ophichthidae, pseudoparasitic, eel, marine biodiversity, northern Australia]
Snake eels, a group of slender, sinuous fish, can perform a gruesome escape after they are swallowed by a bigger fish: They burst out of their predators’ stomachs. But that desperate and grisly bid for freedom may leave them worse off than before, new research reveals.
Most snake eel species’ tails end in a sharp, bony tip that they use for swiftly burrowing into the sandy sea bottom. When a predatory fish swallows a live snake eel, that tip can punch an escape hole in the predator’s stomach wall, which the eel then wriggles through tail-first.
However, this stomach-perforating maneuver doesn’t exactly land the snake eel in a better place. While the eel is not digested alive, it’s still trapped inside the predator’s body, and it soon dies in the gut cavity where it is eventually mummified, researchers reported in a new study describing this bizarre process.
…As early as 1934, scientific studies have described mummified corpses of individual dead snake eels preserved inside the body cavities of carnivorous fishes. For the new study, scientists conducted the first analysis of how widespread this peculiar outcome is, in waters around Australia…Previously, researchers exploring parasites in a type of coastal fish called the black jewfish (Protonibea diacanthus), also found snake eels inside the fishes’ bodies, so the new study’s authors started there. They examined 335 P. diacanthus specimens collected from northern Australia, and found 4 species of preserved snake eels inside the body cavities of 19 P. diacanthus fish. “Presence of these eels was high in comparison to previous reports”, the study authors reported…Some of these predatory fish also had partly-digested snake eels in their bellies that had not managed to escape, which told the scientists that the eels were a part of the fishes’ normal diet.
Snake eels are burrowing fish that frequently hide in seafloor sediments, so they likely have a higher tolerance for low-oxygen environments than some fish do. They therefore “could feasibly stay alive for longer inside the gut cavities of species that predate upon them, once ingested”, the scientists wrote in the study, though they did not specify how much longer a snake eel could survive such conditions. Regardless, that ability doesn’t give snake eels much of an advantage, considering that the eels still slowly suffocate to death after their so-called escape, the study authors reported.