Piscators: The Fishermen Fish

Though most swordsharks that have persisted this long and diversified in the early Thermocene, 100 million years hence, are the large and remarkable swordwhales, there are a few outliers. Smaller, still sporting more resemblance to their colonist ancestors, are the piscators, or fishermen fish, the most basal living swordsharks.

Piscators descend from a small fish-hunting ancestor that threshed through the shallow seas and used its elongated tail lobe to stun baitfish. They are a clade which evolved more complex food-sourcing behaviors involving their tails and which have colonized several new niches in Serina's seas. In all species the tail is extremely exaggerated, and these fish are no longer fast-swimmers in the open sea. Instead they evolved to use their snaking tails to poke around the sea floor, into the burrows of other fishes and crustaceans, and to function either to flush them out where the hunter could snatch them or to lure them out by imitating prey such as a worm.

The noodler is a generalized piscator which does just this. Swimming leisurely in weed-choked shallow seas, this fish eyes the sandy sea floor for patches of disturbed sediment that might indicate a hidden burrow. The sly hunter pokes at them with its tail sword, and probes deep down into the tunnels, no matter how they twist and turn as a result of its highly flexible fin. Eventually it reaches the end of the tunnel and corners its inhabitant, often a crayfish, which is likely to respond aggressively and defensively and pinch the intruder. The noodler has been waiting for this moment, however, and now flings its tail to the side, almost instantly pulling its tail from the tunnel and frequently bringing with it the crustacean, too bewildered by the sudden jerk to the surface to have even unclenched his claws. With a brief burst of speed, the noodler turns and grabs its prey, crushing it in powerful teeth, and then goes on its way to angle down another burrow.

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Some piscators have modified their tails into full-time lures. These species are relatively sedentary ambush predators. Some are flattened, shallow-water hunters that dangle their tails, worm-like, out of the sand and wait for passers-by to nibble. But one group are even stranger; they have become open-water hunters that live in Serina's deepest, murkiest depths and hunt by night, using bioluminescence to draw in their prey right into their waiting teeth.

The worm-on-a-string is one such denizen of the dark depths. It is named for its tail lure, which is stiff and rod like most of its length but becomes very flexible at its brilliantly illuminated tip, where light-producing cells produce a blue illumination that draws in curious fish from all around. The worm-on-a-string floats motionless in the water column, save for flicks of its tail, for many hours until something approaches. This sly hunter then thrashes its tail closer and closer toward its teeth, imitating an injured invertebrate prey. When the smaller fish is within range, it engulfs it in some two hundred viciously sharp and needle-like teeth. Worm-on-a-string are notable for their widely extensible jaws and even more expandable guts which let them consume prey nearly their own length - an adaptation to potential shortages of food in these deeper, darker waters which also allows the predator to retire deeper and into cover for long periods and so limit the time it spends in the open, potentially advertising itself as a meal for a larger hunter in the shadows.