2 Million Years Henceforth
World Oceans
Summary
Trout:
Trout and peruvian anchoveta were the only two fish to survive from the first seeding to the time of the second seeding. The trout colonised both rivers and lakes, and saltwater habitats due to their ability to transition between such habitats during migrations. They cover a range of ecological roles and include many a widespread generalist fish by 2 Myh. Peruvian anchoveta on the other hand are specialised for filter feeding and rotate between a few specific habitats as the need arises. They haven't changed much, except that a few large varieties (around 1 m length) have evolved in seas with reliably high production of krill. Some smaller varieties have become general detritus filterers, occupying coasts where waves disturb the sediment, or deep sea where there isn't much competition.
A mature torpout attacks a shoal of juvenile Southern anchoveta in the South Ocean, not far from some islands. They are capable of hunting much larger prey, but in the open waters prey can be scarce and they need to be fast enough to catch anything.
Like on Earth, shallow coastal areas tend to harbour the greatest number of species. Coastal animals tend to be smaller than their ocean-going counterparts. There are exceptions such as cowtrouts (shown as the yellow and black spotted fish below). Also shown below is a typical shallow coastal algae reef with some sponges. All fish below are descendants of trouts, and there are other animals too such as a small squad of scavenger squid, a freshwater snail turned marine snail, and glasslet prawn, very tiny transparent prawn that live amongst and eat algae such as sea lettuce.
In addition the smaller fish usually live in and around the algae and sponges. The striped ones, "blush fish" also make sponge tissue part of it's diet. They flush red on the gills with extra blood flow when under stress or showing aggression, and it can be a signal for others around to hide. There are many other fish in the ocean with the ability to blush like them, their genus has become quite large and diverse. The two green ones sampling the floating sea lettuce particles are also cowtrouts, but they are much younger, faster and twitchier than their more conspicuous adult counterpart.
Deep Ocean Filter Feeders:
Krill make up a large portion of the ocean animal biomass. They eat smaller planktonic animals and micro algae, multiplying into great numbers. They can form large reddish clouds or swarms that can be visible from high in the air. After 2 million years of evolution there are countless species suited for all pelagic habitats, from cold oceans to warm tropical waters, and from the dark depths up to the bright sunlit coastal and epipelagic waters. They are greatest concentrated around nutrient rich locations where their planktonic prey multiply. Some enlarged species live under in darkness under detritus snow, accompanying some species of prawn as detritus feeders with a slow metabolic rate, using their antennae to feel for falling particles.
All this krill provides for other animals. They are hunted individually by some smaller trout descendants, or other crustaceans, but the majority of krill is eaten in bulk. When this planet was first seeded, peruvian anchoveta were the only surviving oceanic filter feeder after the stabilization process of the ecosystem. These fish have taken top role as the krill's main consumer. When some krill evolved a larger body size to make themselves inedible to smaller filter-feeding fish, the fish also increased in size. A larger body size also allows the fish to last for longer without food, and consume more food in one go, allowing them to survive crossings of the ocean "desert" where food can be scarce.
What's more, a larger size cuts down the number of squid that are potential predators to the adult fish. But larger squid continue to be trouble for metre-long anchovies, and now some squid are in competition with the fish for the krill, with broad tentacle protrusions that curl around and grab krill on contact.
