The Stoutling

Despite all the interesting developments on Apterra's land, the planet is, even more so than Earth, a water world. Over four-fifths of its area is covered by a global ocean, which is roughly divided into two unequal sections by the loop-like structure of the planet's primary landmass. The section in the middle of the supercontinent is known as the Medithalassic Ocean, while the larger sea surrounding Panapterra is called the Perithalassic. This massive ocean, which by itself covers most of the planet's surface, is connected in a surprising way to an ecosystem more than 100 kilometers inland. Here, in the cool rain-pseudoforests of a land we haven't seen yet, is a lake. It sits in the middle of the world's largest island continent, one referred to as Unciolis because it was originally intended for the preservation of snow leopards This is also Apterra's only major landmass entirely devoid of tropical regions; its mid-latitude position has resulted in it being completely temperate, save for a few scattered (but growing) glaciers on its highest peaks. 

In the placid shallows swims a fish known as the Iris Minnow (Iridichthys fulgeolanx). Shining with bright blue, green, and silver-colored scales, these swarm in shoals of millions across the cool lake. There are few predators here, for only a small handful of species have migrated up from the sea after so recently evolving to tolerate the briny waters. On the banks, there are no large rats or kiwis looking to snag a fish to snack on, nor are there any large neotenic mosquitoes that might make a meal of these small fry. And indeed, the Iris Minnows are young; none currently measure over a centimeter, but they put on weight quickly. Over their first three months, they double in mass every week, feasting on a generalistic diet of algae, detritus, plankton, and - once they've grown large enough - smaller fish, including unfortunate members of their own species. They soon cross a size threshold; upon reaching several kilograms in mass, they instinctually exit their childhood home through the fast-moving river at its northern tip.

These descendants of Gambusia bifurcauda have inherited their predecessor's powerful swimming abilities, moving in explosive bursts when they need to evade predators or rapids. Darting from one calm eddy to another, they gradually make their way to the sea over the course of a few weeks, packing on another 50% of their pre-migration body weight along the way. Once they reach the Perithalassic Ocean, they disperse far and wide across the subpolar seas. While they lived in extreme densities in the lake, they now keep a wide berth, roving across thousands of miles of fertile waters for about six months. Before their first birthday, they weigh over fifteen kilograms. These are no longer iris minnows; mature members of this species are known as Rainbow Stoutlings. Such coloration is not apparent at this stage, for they have become a duller grey since entering the ocean. At the end of winter, though, something changes. 

As they approach one full year of age, male stoutlings take on a spectrum of colors. These are unique to every individual, as females prefer to mate with whoever has the brightest and most varied array of patterns. Mating takes place in the open water around this time, with males briefly foregoing food and spending all their time scouring the vast sea for potential partners. After a few weeks, males return to their non-breeding appearance and females begin the journey back up the river. They must race against time, for their developing young will vacate their mothers' bodies after 40 days, regardless of whether they've made it to the lake yet. If this happens, the fry will inevitably perish due to the strong currents, so females must devote all of their efforts into climbing the rapids. This, unfortunately, will be their first and last trip back to where they were born; they die from exhaustion within hours of giving birth.

Males, on the other hand, can live up to five years, growing ever-larger with each passing season. Females are limited both by their short lifespans and by the often-shallow river they must traverse. For this reason, mature males may outweigh their mates by a factor of four, rivaling the largest ocean-going Apterran fish.