The Turbo Eel

This guest entry was written and illustrated by Troll Man

For hundreds of millions of years, the seas of the canary world have been dominated by ray-finned fish. Ever since the first ones adapted to the saline waters only a few millennia after life was first seeded upon it, they have since proliferated into tens of thousands of species over this vast time scale. Even as numerous avian lineages that descended from the land to make claim of the ocean depths again and again, fish remain as omnipresent here as ever. Many of them are superficially familiar, with the guppies, platies, and mollies having almost inevitably diverged down similar lines to many fish on Earth to fill similar niches.

Of course, there are also some which have developed wholly new and remarkable forms far removed from anything that exists or has existed, offshoots, that are often short-lived, but nonetheless prove extremely fascinating experiments of natural selection. And there are the even rarer few which rise above their peculiar origins to become success stories which last many millions of years. It is often a mere chance of luck which separates the two, to turn a single adaptation into a long-lasting triumph of evolution and not merely a glint in the vast ecological timescale. The mass extinction which occurred at the end of the Thermocene created an evolutionary vacuum, allowing a very small sample of survivors to recolonize the oceans, and some have done so with new and novel bodyplans.

The turbo eel from a glance does not appear too unusual as a moray-like hunter slinking its way through the tropical snail reefs and sea bamboo meadows, a mid-level predator of smaller fish and crustaceans. But it is far removed from its original guppy ancestor in many respects; although evolved from a livebearer ancestor, it is one of many fish lineages which has returned to an oviparous reproductive strategy and subsequently lost the characteristic gonopodium of its ancestor, with little remaining benefit to internal fertilization. The development of an adipose fin is also evident, which has even began to supplant the original dorsal fin’s function, and accompanies the complete loss of the pectoral fins (although it rarely occurs as an atavistic mutation). This is because a new form of locomotion has developed in this species uniquely and independent of fin-powered swimming: jet propulsion.

left: two turbo eels aligning themselves in preparation to mate

right: a turbo eel utilizing its jet propulsion to dart away from a pursuing predator, also newly evolved in the Pangeacene ocean - a dolfinch

As an elongated, bottom-dwelling fish, it is not equipped for fast-paced movement and has high-reduced the size of its scales to an extent that it appears scaleless. Its body is therefore soft and its skin loose to facilitate flexible movement through the winding seabed, between curling and winding colonies of snails and into the rocky crags beneath in search of prey. However, at only about forty to fifty centimetres in length (females are slightly larger, but there’s otherwise little dimorphism), it is far from the largest predator of its environment and must contend with its own share of threats. To escape from hunters it pulls out a secret defence mechanism just as they close in, sucking water into large, elastic gill chambers and rapidly ejecting it through the contraction of rows of ringed muscles to produce sudden thrust. Such explosive and abrupt acceleration is often enough to literally leave any predators in the dust as its escape billows a cloud of sediment to mask its retreat.

It is probable this adaptation originally appeared as the ancestor of the turbo eel dug through low oxygenated tunnels of burrowing fish and crustaceans, its enlarged gill chambers allowing the fish to breathe even as its head and upper body was underground. In a clear example of exaptation (or preadaptation), it would prove suitable in a secondary function providing a slight speed boost in swimming as quantities of water were ejected. This is not unheard of among fish, as some species of anglerfish on Earth have been known to use jet propulsion from modified gills, but the turbo eel has honed it further. Over thousands of generations it became more specialized for this purpose, becoming slightly more effective over millennia at evading predators and chasing prey. As it gulps in water through its mouth, this same water powers its speedy movement as it’s squeezed out of the gill sphincter, oxygenating itself at the same time, making it a streamlined locomotory system. In effect, fin-based locomotion was, and still is, being reduced, with the total loss of its pectoral fins, and the dorsal fin reduced to a vestigial feature in the modern turbo eel. Its pelvic fins retain functional as both sensory organs and display structures, detecting minute vibrations in the water to help the fish identify camouflaged prey, and to signal fellow eels with their bright yellow tips.

On occasion, turbo eels have been known to form congregations which hunt collaboratively, working to systematically flush out prey in a contracting circle to ensure that little can escape. This style of hunting seems to occur mostly during periods of diminished prey availability in order to increase hunting efficiency. Eels take turns flushing small animals from the seabed or hovering close above to catch any that manage to escape from the eels below. There are few capable of outpacing a jetting turbo eel in a short burst and fewer still which can outpace several eels together. The eels have also been known to create numerous burrows, using the natural protective slime coating their bodies to stabilize the walls, and then vacating the burrows to trick small animals into thinking they’re abandoned and allowing them to settle in, then returning several days later to catch and eat them. This trap-making strategy is particularly common in sandier environments where there are fewer naturally occurring holes to hide in, making the burrows it produces desirable (it will also create and use these burrows itself when nesting).

This ability to strategically hunt and adapt its strategies to maximize capturing efficiency is just as important to the success of the turbo eel as its gill-derived propulsion organs, which, so far, are only useful in brief spurts, as it requires more energy than fin-powered swimming and is difficult to control once in motion. The turbo eel occurs widely throughout the shallow, coastal depths and in some environments almost monopolizes its trophic level; with few other predatory fish of its size able to compete in areas where turbo eels have settled (in some cases, the eels will intentionally mob and harass competitors in small shoals to drive them out and reduce interspecific competition). Although a unique oddity in this era of Serinan history, its long future success as an oceanic hunter nonetheless seems assured.