Mudfish

As sruglettes diversified, there was an obstacle to their expansion into some habitats, and while others simply waited for standing water or bred elsewhere, a few were more adventurous, and worked with what they had. The mudfish are a descendant of sruglettes with lunged larvae (specifically those of the subgenus protopulmonis) that became increasingly more adapted to laying their eggs in mud (and some similar substrates), as a manner of expanding into environments that did not often have standing water, and eventually back into areas to exploit the niche they’ve carved out for themselves.

Mudfish are a fairly diverse bunch, but in many ways quite similar to their ancestors, being flighted surge gilltails with a distinct and flightless larval stage. It is in this larval stage, however, where they primarily differ, not only do all mudfish have lungs as larvae (as do some sruglettes), but they usually live in mud instead of water. Whether it’s borderline muddy water after a rainforest flood, or whole flats of it out in the salt marsh, you can generally expect there to be some mudfish breeding there, this has necessitated a very special adaptation: actual ground mobility. Mudfish have modified their two ventral fins into strange structures consisting usually of just a row of bifurcated fin rays, as well as extended rays on their wing fins, allowing them to ‘crawl’ with a sort of swimming motion aided by the pectorals; their larvae also primarily use this, though also sometimes burrow into the mud, either to hide from predators or eat more of the mud, many mudfish species have larvae or even adults that can ‘hop’ along the ground with their wings for a burst of speed.

Adult mudfish tend to be more terrestrial than their ancestors, being better adapted to walk on the ground, and often having retracted fin membranes in favor of robust, spiny fin rays. Mudfish are still very capable fliers however, and some species will even use their pectoral spines to hang off of branches or rough surfaces, they are not quite so good at swimming however, and most mudfish can only manage a sort of wiggle through the water, it is not uncommon for mudfish to drown if they find themselves unable to get out of the water, as they also cannot flip over as easily to take a breath. Some mudfish do have better developed fins and can swim far better, but the majority are restricted to habitats with some sort of ‘land’. That is, apart from species that have specialized for a surprising habitat: puffgrass rafts, initially evolving from species that laid their eggs in moist rotting vegetation (and those still exist, to be clear), their larvae (seen in the middle left, just below A166) are fairly salt tolerant and capable of some limited swimming. Like most moist rotting vegetation specialists, albeit most extreme in the raft-dwelling ones, these larvae are elongated to worm their way through their much more tangled habitat, and their beaks are often a good bit stronger to slice through tough fibrous food (albeit, they cannot eat wood, lacking both gut microbes specialized enough for this and any reasonable way to evolve strong enough jaws). Raft-dwelling mudfish are the reason this genus group is global, as when their rafts wash ashore, adults can take fairly easily to laying their eggs in other stranded vegetation, which eventually moves to the mud, and then up the river to follow that mud, leading to freshwater, mud-dwelling species once more.

Mudfish often live a good bit longer than their ancestors, as they spend a lot more time resting rather than constantly exerting themselves with flight, and the average lifespan of the genus, rather than a few months, is roughly a year.

One more notable group are the paedomorphic mudfish (such as the purple one in the upper left corner), though once again they aren’t monophyletic (much to the agony of the subgeneric taxonomists), they do share some unique traits, their fin rays are often much more delicate due to their smaller size not requiring robust spiny ones, these are perhaps the shortest lived mudfish, akin to some diminutive terran reef gobies (though not as extreme). These mudfish tend to be specialized toward perching on vegetation and lunging at prey rather than skittering around chasing it (though this ambush predation lifestyle isn’t unique to them), the individual shown, belonging to the subgenus Diversoculus, also shows how some species have evolved eyes on turrets to allow them to look around better.

Marine species (defined as those that nest on puffgrass rafts (with the exception of the driftwood islands) are interestingly rather good at swimming, in contrast to most species; this was a necessary adaptation because it was not uncommon for them to metamorphose and find themselves somewhere with no land or land-dwelling prey for miles, because most mudfish need to eat they had to solve this issue somehow. Marine mudfish do not tend to go for prey latching onto solid surfaces or at the benthos, but nekton and plankton are both fair game. It would seem surprising then, with how avid at swimming these marine mudfish are, that no freshwater mudfish exist, why is this? Simply put, mudfish can’t put up with competitors in these much more cramped environments, and with plenty of prey to hunt on land, they almost always adapt to hunting there instead.