Tiny. Yellow. Stripey. Weird faces. Worship large ocean predators as gods. Wherever you find a kraken, say, or a pod of whales, or even just a big shark, you will find some of these guys lurking around nibbling on its parasites. In the case of something intelligent like a kraken this basically just forms a clan of expendable mooks that it uses to do its bidding on land in what would probably be the most standard and boring campaign ever. In the case of something dumber like a sea serpent or a giant three-headed dragon turtle that grants wishes if you steal the right jewel from its forehead but the other two jewels are cursed, the pilotfishmen get to make all the decisions. This means finding places for it to spawn, reliable sources of its favourite food, coming up with clever ways to exterminate particularly insidious parasites. A leviathan will often have a colony of pilotfishmen living in hollowed-out barnacles on its back.
Pilotfishmen also worship ships. You will never convince them that ships are not alive. They will follow in the wake of a trading vessel for miles and are considered good luck by the sailors, who don't generally realize that the pilotfishmen see them as parasites which need to be torn apart and eaten. If a pilotfishman ever actually manages to exterminate all humans aboard a ship then when it starts to sink he will have an existential crisis and become a kind of Pilotfishman Nietzche, dedicated to the eradication of all large ocean predators everywhere.
Tall, slender, genteel and eloquent, fightingfishmen are the elves of the fishman world. They build arcades and palaces in shallow rivers and pools of stagnant water, out of sticky froth they exude from their mouths and that only lasts a couple of weeks. They are renowned watercolourists, excellent cooks (although their cuisine is largely insect-based) and have perfected a highly allusive form of stand-up comedy that's more like beat poetry than anything else. When they laugh it sounds like a polite gurgle. They can breath air for much longer than most fishmen, having a specially adapted labyrinth organ which allows them to survive in the oxygen-poor waters of their native jungles (this is a real thing in the real world go google it right now), and so are often invited to human dinner parties.
Any two male fightingfishmen who meet for the first time must engage in a courteously orchestrated combat ritual until one of them backs down or is seriously injured. They are deeply embarrassed about this and would prefer you didn't talk about it. There's a whole culture around arranging for fishmen (as opposed to fishwomen) to meet in private for the first time where they can try to kill each other with nobody watching. Fightingfishmen prefer not to carry weapons in case they hurt someone. They are intensely proud, however, and even though it means nothing they also really really don't want to back down from the aforementioned fights, so if you ask them why they don't just chicken out at the first opportunity you will only get evasive answers.
Some fightingfishmen actually get off on the fights. This is hugely taboo so of course it's also pretty common. There are places you can go, often oxbow lakes (which have a whole set of dangerous-but-sexy connotations in fightingfishmen culture), to watch fishmen get introduced to each other in pairs and engage in exhibitionistic fight sprees. Fishmen who are into this will talk about the beauty and grace of combat and the way that it's the only place you feel truly alive but of course people still die, like, all the time. They will carry peculiar and exotic weapons, the more peculiar and exotic the better, like glaives and knobkerries and macuahuitls and shit.
Fightingfishmen get a bonus to movement speed and attack when fighting another fishman for the first time, but of course this cancels out and doesn't do anything but look cool.
Frogfishmen are incredibly solitary creatures that do nothing but trudge along the ocean floor, blending in with their environments, eating whatever comes too close and thinking about philosophy. Frogfishmen are all geniuses. They are experts on 1d6 randomly selected schools of philosophy, all of which they have figured out for themselves through a process of pure Cartesian induction. Frogfishmen can't read and wouldn't have access to books if they did, so none of their knowledge is empirical, they just work everything out for themselves over time. They are excellent mathematicians, logicians and metaphysicists but know very little about the sciences and have only the most minimal concept of ethics. About a third of all frogfishmen believe in God, but only a single, unified God - none of them are polytheists.
A frogfishman hunts by luring a philosopher underwater, getting her to come close enough to ask it some troubling question about the universe, then massively expanding the volume of its mouth in a space of under six milliseconds and sucking her in.
When frightened, startled, or disturbed in any way, the first reflex of a pufferfishman is to puff. By sucking in water very quickly it can double in size in under a second and cover itself in brightly-coloured spikes. This is extremely frightening, startling and disturbing. Pufferfishmen are gregarious, pompous, pedantic and uncomfortable with change, like members of the House of Lords. Even a single Act of Puff (as they insist on calling it) can trigger a chain reaction that results in whole townships inflating one by one until there's no more room for anybody to move and everyone's spiking everyone else in an uncomfortably intimate way. Like a village full of people who can't stop yawning because everyone else is. As a result, surprises are illegal in puffer society. Each township has its own incredibly rigid and unchangeable set of bureaucratic mandates designed to make every day exactly the same as every other one. Like in Piffington everyone has to buy a loaf of plankton at exactly 10:00 in the morning, in Poffershaven outsiders must be clean-shaven and always whistling. These are decided on by the Mayor of each township and his appallingly smug and complacent council of advisors, who have never changed their minds about anything, ever.
If a pufferfishman ever has any kind of radical epiphany she might literally explode. Imagine a rich man's monocle popping off so hard he dies. So new ideas are suppressed with brutal force, often by hired mercenaries (makomen, sea orcs, crab princesses, siphonophorcerers, that kind of thing) who can look at it without danger. Puffers might not mean any harm but if they get it into their heads that, e.g., slavery is okay, then you will have to labour thousands of years to get them to reconsider it even the smallest amount. Some of them are incredibly rich.
- Koi boys
For hundreds of years the aristocrats of the Guang Dynasty have been breeding these decorative garden slaves. They plan, build, maintain and spawn in vast networks of terraced pools, artificial waterfalls, bridges, bamboo forests, fern beds and philosophically perfect rock gardens, all of which have been left to spread out indefinitely in every direction since the aristocrats of the Guang Dynasty were all dragged from their beds by peasants and sliced into little tiny pieces. Now vast patches of the countryside have been supplanted by these incredibly complex peace labyrinths, built to coexist in flawless harmony with their natural surroundings and to be totally useless in every other way. If left alone for even a week your average garden would disintegrate into ecological chaos, so the koi boys put a terrifying amount of time and effort into maintaining each individual facet, from the precise number of dragonflies in a given pond to the placement of individual waterlilies. They also run an intensely complex breeding program, choosing from thousands of koi boy babies the ones that are beautiful enough to be allowed to live and grinding the rest into a fine paste, which they use to fertilize the water lilies. Koi boys live up to a hundred years, have an elaborate internal hierarchy, are adorably clumsy and about as intelligent as ten-year-olds. It's like Lord of the Flies in there. The koi boy in charge of food distribution is actually called the Lord of the Flies because, you know, they eat those.
The leaders of the Peasant's Republic resent the koi boys for taking up prime agricultural land which could be used to feed their starving citizens. There's a small bounty out on the whiskers of any individual koi boy and a large reward for the destruction of particular gardens, which of course requires the obliteration of the koi boy tribes residing within. Koi boys aren't fighters but their gardens are of course heavily and ingeniously trapped and they also breed decorative guard animals like lammasu and dragon turtles. The koi boys don't use money but have access to the leftover treasures of the Guang Dynasty, with which they might reward you for e.g. fetching them a particularly nice rock. You'll have to venture into the now-decrepit treasure rooms yourself, though. They're not allowed inside the house.
Hagfishmen live in whalecorpse citadels on the ocean floor. Though sedentary by nature, poorer hagfishman communities are forced into nomadicism by the infrequency of whale deaths and wind up making vast journeys across the deep sea, moving from whalegrave to whalegrave as each one is stripped to the bone, preserving as much as they can for times of drought. Wealthier hagfishman communities trade for meat with the surface world, paying for it with commodities of the deep such as pearls, sulphur, luminescent bacteria and rare metals from their underwater mines. They are vitally important as a point of communication between the world of fishmen and the world of menmen.
Hagfish are all convinced that they are incredibly beautiful. Their sense of aesthetics in general is exactly the reverse of that of a human (or manman). This is how they can stand to live in their hideous lumpy castles of rotting flesh. Hagfishmen will often pay human or dwarven whalers (dwarven whaling is a whole thing) to herd pods of smaller cetaceans to the location of their enclaves before harpooning them, gutting them and letting the carcass and the intestines settle like streamers at a parade. This is always an occasion for celebration among the higher echelons of hagfishman society.
Hagfishmen can exude immense amounts of slime from vents all over their long, sinuous bodies, and will do this all the time for basically no reason. Sometimes it's to escape, sometimes it's to seize a decisive advantage in a negotiation, sometimes it's just to annoy you. The slime has no special qualities except for being incredibly slimy. Hagfishmen also collect curses, to which they are immune and with which they are incredibly fascinated. A hagfishmen will often offer a poor sailor a reasonably large sum of money if she can test out her brand new skin-to-fingernails malediction on what she will promise is only an isolated area of her body. Hagfishmen sometimes use curses as guarantors for an important deal and sometimes just throw them around like douchebags.
Hagfishman slime is a delicacy in certain parts of the world, used in a cuisine in a way similar to egg whites. Hagfishman meringue cures most curses and some diseases. Hagfishmen have no shortage of slime but have a vested interest in controlling the market and will not let you take any for free.
Hagfishman don't have writing. They communicate across long distances by tying bits of whale intestine into complicated coded knots. They can also tie their own bodies into the very same knots, and will use this as a form of sign language, more or less interchangeably with anything spoken. Among hagfishmen the difference between written and spoken language is not as clear as it is with us. The practice of divination by entrails is alive and well among hagfishmen and is often indistinguishable from architecture. Hagfishmen dolphingut sculpture prophecies are the object of many an ancient hagfishmen epic, and are about the only thing they're at all unwilling to sell.
Pilotfishmen hate hagfishmen.