In the great lake nestled halfway between Ailuropia and Loxodia, a massive radiation of fish species has occurred over the past 500,000 years. In earlier ages, the fish isolated in this ecosystem diversified into dozens of forms, each colonizing its own niche. Today that number has soared to over three hundred, with no signs of stopping. They have gradually displaced nearly all other fish from the lake, dominating all its habitats. In some cases, speciation was the result of niche partitioning, but just as often reproductive barriers have driven diversification. Like the multicolored ocean-going fish of ages past, these fish display an enormous variety of patterns, colors, and textures. These are often adaptive, serving as camouflage against predators or prey, but can also serve display purposes. All Ailoxichthyids are mouth-brooders, keeping their newborn fry safe inside their mouths for the first two weeks or so after giving birth. 

Despite how closely-related all members of this group are, different species already show wildly diverging morphologies. Algae eaters like Scabognathus have flat bellies, allowing them to scrape rock surfaces with their downward-pointing jaws. These fish can reach up to forty centimeters long. Within this genus, there are species specializing in deep waters where algae is scarce but competition is minimal, and others live in shallower, predator-choked waters. All of them are armored, possessing thick scales that deter attacks from above, though they're vulnerable if flipped on their backs. Their dorsal fins have a sharp spine on the front-most ray, and a muscles connecting to the spinal column allows this weapon to be raised in a fraction of a second, further helping to deter would-be attackers. Despite their strength and potential for inflicting injury, they are generally non-aggressive towards each other, swimming in schools of a few dozen as they scour the lakebed.

Joining the ranks of peaceful Ailoxichthyid herbivores is the grazing Mowerfish (Dolorichthys), a half-meter-long, sleek-looking fish common around the lakeshore. There are more than twenty species of mowerfish, each of which displays its own unique combination of reds, greens, blues, and blacks. The fins are especially colorful, as they can be retracted to hide their bright patterns when predators are nearby. Their jaws are powerful, sliding forward and down into the muck to uproot semi-aquatic plants. While normally solitary, they join massive breeding colonies in springtime to protect their tiny fry from predators. Each species has its own designated location where all members return year after year, preventing hybridization.

Appearing not too different from its Gambusia ancestors, the Sunset Minnow (Siccaneichthys) is among the smallest genera in the lake. Found in all shades of red and brown, it blends in well against the clay-rich local soil. It never ventures into open water, preferring the safety of the shallows. It sticks so close to the shore that, during dry spells, groups of them often get stuck in small pools as the lake's water level drops. This genus is uniquely well-adapted to surviving these conditions, though, for they are extremely tolerant of the anoxia, temperature swings, and high ammonia levels common in these puddles. So long as some water remains, they can survive for months like this, waiting patiently until a storm raises the waterline once more, then swim off to return to their normal feeding grounds. They are omnivores, eating a combination of algae, detritus, and small mosquito larvae.

While the larger neotenic forms of the formerly semelparous mosquitoes are off the menu for such tiny fish as Siccaneichthys, its larger cousin the Sunrise Minnow (Procellichthys) specializes on these and similar prey. This five-centimeter-long, orange-yellow-colored livebearer patrols the surface layers of the middle of the lake, where many millions of worm-like "larvae" can be found, along with fast-swimming isopods and aquatic microcrustaceans. The mosquitoes are particularly difficult prey, as many have evolved spines along their bodies Additionally, the tails of some have become shaped for swimming, with the siphon and gills forming the top and bottom lobes of a fish-like fin, permitting impressive bursts of speed. In response, the sunrise minnows are agile and very fast for their size, possessing a deeply forked tail and powerful body muscles to pursue their targets. Sunrise minnows are also devoted partners, with males ensuring their mates remain safe during the brooding period.

These small fish are in turn preyed upon by the lake's apex predator, a massive carnivore called the Jaguarfish (Ailoxichthys). This dark-colored, spotted hunter spends most of its day stationary on the lakebed, remaining hidden in the murky waters until its prey approaches. Small targets like minnows are swallowed with a quick gulp, often without the jaguarfish even needing to move from its resting place. Larger prey are ambushed with a powerful bite, usually being dismembered before they knew what hit them. 

While Ailox lake will remain an insular habitat for many years to come, not all its inhabitants will stay trapped here as the Muricene progresses. Sunset minnows are already beginning to expand their range, spreading into disconnected rivers and streams during floods, as their extreme hardiness and tiny size allow them to wriggle their way across patches of semi-submerged land that no other fish can tolerate. With time, they could make their way into every low-lying waterway of Panapterra.