Ailoxichthyids of Abeli

The loss of Lake Ailox at the height of the Ice Age drove many Ailoxichthyids to extinction, freezing them solid in a tomb that would not thaw for thousands of generations. Though almost 90% of the family was lost, the lucky few that escaped quickly emerged as the dominant large- and medium-sized freshwater fish, a title they hold to this day. Dispersal mechanisms are varied; some species can survive out of water long enough to wriggle overland to new watersheds, while others reproduce in mountainous headwaters - places where rivers that will eventually end up thousands of kilometers apart may begin just a short distance from one another. As erosion shapes the landscape, rivers change their courses, and the boundaries between one freshwater system and another never remain stationary for long. Ailoxichthyid species counts are greatest in Abeli, as this equatorial continent recovered the quickest at the beginning of the Arthrocene. They dominate every aquatic biome that Abeli has to offer, with their species numbering over a thousand - more than the rest of global Ailoxichthyid diversity combined.

Small rivers that run through wooded environments are often inhabited by the Root-Ripper (Rhizovellus). This is a descendant of the mowerfish, whose vegan diet it has inherited. The largest mowerfish are now long gone, as their size prevented them from leaving the lake when the ice advanced. Even the smaller survivors faced difficulty, as the soft, nutritious semi-aquatic grasses of Ailox didn't exist in their new riverine homes. They instead evolved to feed on hybrid tree roots, which often grew up to the very edge of the riverbank. Though this food source was tough, it was rich in sugar, which the trees stored in their roots to prevent them freezing in the permafrost. Over time, the river-mowers' lower teeth evolved to become larger, harder, and shaper, giving the fish a massive underbite. Powerful jaw muscles began to develop, generating immense leverage that allowed them to dislodge heavy roots from the hardened earth. As temperatures rose and taiga gave way to temperate forest, other streamside plants like Lyrus began sprouting, allowing the proto-root-rippers to broaden their diets. The number of teeth in the upper jaw increased, and they took on a flat, leaf-like shape, allowing them to crop these herbaceous morsels, though roots still made up the majority of their diet. Today, root-rippers are commonplace, with every major tract of forest being home to a unique endemic species.

In a similar fashion to the previous genus, large Scabognathus did not survive into the Arthrocene. Instead, the Sucker Eel (Exsugognathus) descends from a smaller offshoot that first ventured out of Ailox as far back as the Middle Muricene. Though they initially had an omnivorous diet, they eventually specialized to eat algae almost exclusively. Their elongated bodies reduce drag against fast-moving water, helping them keep steady as they creep along the riverbed. Their young, born at an early stage of development, have few of their adult features beyond a mouth and a stomach. The fry affix themselves to a rock immediately, remaining attached for up to three weeks as they grow. They are immensely vulnerable to predators at this stage, as they can inch along at no more than half a centimeter per second. They cannot simply detach and swim away because they have no fins yet - being swept away in the current would mean certain death. For this genus, reproduction is a game of pure chance, with thousands of newborns being deposited across dozens of locations in the hope that a few will survive. Once at a length of about three centimeters, the juveniles can then disperse to new locations, with their instincts driving them first to swim downstream, then upstream again into a different branch of their river where they can establish a stable territory. The tiny percentage that reach adulthood have few predators, kept safe by their tough, scaly armor, and they may live into their thirties.

An eel-like form has evolved independently within a different branch of the Ailoxichthyid family. The Muricene sunset minnow was a true survivor, with the ability to survive - and even reproduce - in some of the least hospitable waterways imaginable. These ephemeral pools, cut off from the dangers of the open water and too harsh for most competitors to withstand, served as temporary refuges for the tiny livebearers and their young. Sunset Eels (Xeranguilla), the largest of the sunset minnow clade, are desert-dwellers. They make their permanent homes around watering holes, an environment that mimics the small ephemeral pools on a grander scale. During wet spells, these short-lived oases may swell to many square kilometers, during which the eels feed, grow, and generally go about their lives like any other fish. After a few weeks or months, though, the water level inevitably begins to fall. Once enough water has evaporated that the pond is only a few centimeters deep, the sunset eels pair off, though they don't mate yet. Instead, they construct a burrow where they'll ride out the dry season together. Even when there's no water on the surface, moisture can still be found underground, but they must dig deep to ensure they'll remain below the water table as it continues to drop over the following months and years. Only once they are secure in the sand will they mate, after which they fall into a deep hibernation. They awake to the sensation of rain above them, emerging just as the aboveground pool begins to reform. The young are then born, maturing as the lake grows ever-larger around them. On occasion - perhaps only once or twice per century - the desert rains will be so extreme and long-lasting that they allow for a dispersal event. When this happens, subadult individuals will leave their watering holes and wriggle across the wet sand in search of new homes. Though sunset eels have no air-breathing abilities, the downpour ensures their gills remain wet throughout their journey. By taking advantage of these rare events, sunset eels can colonize new areas and maintain gene flow across different basins.

The sunrise minnow is the ancestor of the most speciose Ailoxichthyid taxon in the present day. The subfamily Procellichtyinae contains about a third of the Abelian Ailoxichthyids, with two genera being especially common. Heliichthys - also known as the Sunshiner - can be found in calm waters across the continent. Though never more than 25 centimeters long, they are highly efficient sight-based hunters. They can't swim very quickly, but they can sneak up on prey, approaching from below while their target is none the wiser. Food is caught with a fast, powerful suction that is all but inescapable for the small fish, isopods, and aquatic mosquitoes the sunshiner feeds on. Algae and detritus also form a modest fraction of this genus's diet, especially when other food is scarce. The sunshiner's cousin the Flamesnapper (Laceridon) inhabits all of Abeli's major river systems, though their numbers are highest in the tropics. These sharp-toothed pack hunters can reach a third of a meter long, and their schools can number into the low triple digits. They primarily target terrestrial animals, striking the weak and injured as they attempt to cross the water. Herd-birds and Muridiungulates often find that young, old, or sick individuals quietly disappear during these crossings, as flamesnappers tend to attack their victim's throat. This prevents a drawn-out struggle that could injure the fish.

This subfamily owes its diversity to its devoted parental care. All Procellichthyines defend their young fiercely, often holding them carefully in their mouth to keep them safe. Even when the fry begin to mature, their parents often continue looking after them until they reach nearly half their full size. As a result, they have a much greater chance of reaching adulthood than other fish, giving them an upper hand against their competition. The process does, however, take a great toll on the parents, who must spend nearly all their time and energy taking care of their offspring. Schooling Procellichthyines like the flamesnapper must partner up and leave the safety of their schools during the breeding season, while the open-water sunshiner is forced to leave its preferred habitat to find a secluded spot hidden from danger. The stress of reproduction means that maternal and paternal mortality is very high in this group, with only 40% of parents surviving to breed a second time.

Perhaps the most surprising member of the family to have survived the Ice Age is the jaguarfish (which now makes up the subfamily Ailoxichthyinae). Even the smallest Muricene-aged Ailoxichthys were too large to navigate the surrounding streams, leaving the genus stranded as the glaciers advanced. They escaped by traveling downriver out of the lake, persisting as apex predators in the downstream watershed until it too began to freeze over. With nowhere else to turn, a single species adapted to tolerate brackish conditions, the only Ailoxichthyid yet to do so. This species spread across coastal regions as the mass extinction progressed, making its way into the mouths of various other rivers. Rapid speciation followed, with different lineages settling in different areas. Those in Post-Abeli evolved for life in the tideslopes, becoming the estuarine jaguarfish, while those that migrated into mainland Abeli secondarily specialized for freshwater ecosystems.

The Jumping Jaguarfish (Respergovenator) is the smallest and most basal of the Abelian Ailoxichthyines, and it's also the only genus on the continent that can still handle slightly salty water. It lives in coastal forests and swamps, waiting patiently beneath overhanging tree branches. About 40 centimeters long, it can leap four times its body length into the air with great accuracy, snatching small tree-dwellers from their perches. While adults are too fast to have any major threats, newborn fry don't stand a chance against oceanic predators that sometimes venture into the estuaries. To combat this threat, jumping jaguarfish travel upriver once a year to breed, depositing the next generation in calm highland streams before returning to their ideal habitat. This is carefully timed so the baby jaguarfish are born just before the arrival of semelparous stoutlings in the early spring. They feast on the dead Iridichthyids, bulking up on the abundant food source. They quickly develop their fins and torpedo-like body shape, appearing like miniature adults. This allows them to tackle moving prey, including the still-helpless young stoutlings. By the time the surviving subadults head to the sea, the jaguarfish will have built up enough muscle mass to perform jumps. They then follow the river back to the coast, rejoining their elders and shifting to land-based food sources.

Abeli's rivers are also home to the Common Jaguarfish (Abeliichthys vulgaris), a stocky and powerful carnivore at the top of the food chain. It's one of the only species capable of holding its own against a shoal of flamesnappers, though it prefers larger game. It hunts by ramming its heavy body into its prey, often with its mouth wide open to tear apart flesh with its serrated, triangular teeth. Root-rippers are ideal prey, as they move slowly and rely on their size for safety. This is ineffective against the forty-kilo jaguarfish, which can rip off chunks of meat with little difficulty. Their only shortcoming is their massive size, which prevents them from chasing the root-rippers into smaller creeks.

The other member of the Abeliichthys genus is A. bimodalis, the Two-Faced Jaguarfish. This species is native to the largest river on the continent, the one that converges on the Founding Plains in the north. With such a huge territory, the local jaguarfish is naturally the largest in its subfamily, at a meter and a half long and over 50 kilograms in mass. Its lifestyle is quite similar to that of its common cousin, though its diet contains more land animals because the savanna supports many megafauna. Life is easy for these giants most years, as they go uncontested as the dominant species in the river. However, the very richness and habitability of their home opens the door for a rare threat: giant stoutlings. These nearly went extinct when the great Unciolan lakes froze over, but like the jaguarfish, one species made it out alive. The Medithalassic Red Stoutling (Rubrichthys maximus) breeds only once every seven years, but during this period life becomes hellish for the jaguarfish. Outclassed in size by a factor of three, the predators become prey. By the time the stoutlings leave two months later, over 90% of the Abeliichthys will be dead. Those that remain reproduce, and their high stress hormone levels trigger a change in the developing eggs. When the fry are born, they grow only half as big as their parents, taking on a mesopredatory niche. Subadult stoutlings will be the new top predators until they finally abandon the river at three years old. The jaguarfish then breed again, and their offspring will once again grow to full size. The cycle repeats itself continuously - the non-stoutling generation lives four years, then the stoutling generation lives for three. This phenotypic plasticity allows the species to survive the changing conditions it faces, a testament to the adaptability of the Ailoxichthyid family as a whole.