In my high fantasy medieval world, the ocean is populated by underwater fish people and land dominated by your good old human. Different type of fish people (shark, whale, turtle, shellfish, etc.) live at different depths, and forming their own kingdoms. Several kings would sometimes band together, forming a massive alliance that spanned across the ocean.

What I'm curious about is how would trading look like, both the trade with other underwater kingdoms, and trading with humans. How would the age of sail different now that there are multiple powerful kingdoms under the ocean? Note that neither human nor fish people are capable of fully engage each other, as there is currently no means for human to push their forces deep enough underwater, and the fish people are unable to leave water for too long. Piracy, however, is very much possible, and I envision fish people are going to be doing most of the raiding. The trade routes between underwater kingdoms are too deep undersea for human to raid.

The fish people could leave the water, but only for a short period of time through the use of magic. So I imagine there'd be trading ports that are partly submerged, sort of kind of like Venice, and trading between human and fish people can be conducted there.

Now I know there are a lot of stuff people want from under the ocean, pearls and what not. But what would the fish people need from people up above? What kind of quality goods would they be looking for?

And how would trade looks like between human kingdoms oversea? Would they stay pretty much the same, with the only difference that now there are fish pirates?

I imagine the underwater currents might serve as the trade routes between underwater kingdoms, as a mean of quickly getting goods from one place to another. They'd probably be using muscle beasts, sort of like the counterpart of human trade caravan. How would their ships look like?

To sum up my question:

  1. How would trade look like (methods, trade-route locations, ships, etc.) between:
    • humans and other humans oversea
    • humans and fish people
    • fish people and other fish people undersea
  2. What would the fish people seek to gain from trading with humans?
  3. Other interactions you can think of that related somewhat to trade? Piracy, mercenary, slave-trade, fish people eating humans and humans eating them back as a delicacy, etc.
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    $\begingroup$ Do we know how they communicate? $\endgroup$ – zzz Dec 6 '16 at 23:11
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    $\begingroup$ What sort of level of intelligence / sentience do the fish people have? Are all of the species even on roughly equal ground with each other? More importantly, what motivates the fish? What are their goals/values/desires? Your "summary" point #2 strongly relates to my questions, and I don't think we have enough information to really answer that without getting into idea generation. $\endgroup$ – type_outcast Dec 6 '16 at 23:46
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    $\begingroup$ +1, this is an interesting scenario and I'd love to hear how it turns out. To clarify, where exactly are the kingdoms? Are they all necessarily on the seafloor? Are some suspended in the water due to buoyancy or magic, but anchored down? Since plenty of fish don't spend their lives on the seafloor, and you describe different species based on different fish, I would imagine not all kingdoms are anchored. $\endgroup$ – Zxyrra Dec 7 '16 at 1:00
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    $\begingroup$ @JulietteEvans: Why would the kingdoms be defined by depth and not geographic location like for humans? The vast majority of the sea life lives in a pretty narrow range of depths, and even then the open ocean is largely devoid of life. Most of the ocean is more barren than most terrestrial deserts. So I would think you would have kingdoms centered around consistently productive areas, with most of the open ocean dominated by nomadic tribes that move between various seasonal areas. $\endgroup$ – TheBlackCat Dec 8 '16 at 4:57
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    $\begingroup$ @TheBlackCat They are defined by both. I originally want to use the word "clan" or "tribe", but that feels a little odd given the size I'm envisioning them. But essentially, each kingdom is like a really oversized tribe of (more likely but not necessarily) one or a few similar species, at least that's what my draft vision looks like. But your comment gave me some ideas and I'm thinking I'll modify my vision. That point about civilizations around consistently productive areas is great and totally can be use by my story. $\endgroup$ – Juliette Evans Dec 8 '16 at 14:45

In order to figure it all out, let's go back to First Contact between humans and fish people and play it forward to see how it would work. If you don't mind, I'll name the fish people 'pisces' to make it easier.

They first meet, and they're both unknowns to each other. Humanity has a history of not dealing with unknown Others too well, so things would probably be tense at first, until everyone realizes that neither poses an existential threat to the other - the humans can't destroy the pisces, and the pisces can't destroy the humans. A peace is drawn up and trade is able to begin.

Interspecies trade begins primarily in the major coastal human cities - the pisces are able to surface for a short time there, while humans can't descend to the depths of the pisces cities - and stays there. The humans will have to get pisces trade goods to interior cities on their own.

Intraspecies trade is a bit more difficult, but not drastically. Your idea of the pisces utilizing oceanic currents is a great one. Add in the idea that they've, say, semi-domesticated whales and are able to utilize their migration patterns to move wares and you've got yourself a pretty good system. (Off topic, but I'm actually kinda reminded of interplanetary trade within a star system - you'd have a base on Earth, a base on the moon, on Mars, on various asteroids, and you'd have essentially set paths between them based on orbital mechanics. This system is the same idea, just using oceanic currents instead of orbits.)

The issue becomes human-human trade. Trade within one 'country' or even continent isn't a huge problem, you can just do it overland. We've been doing that for millennia. But how do we get ships across the oceans safely?

Basic economic sense says that it's better to trade with wealthy nations than with poor nations. A wealthy nation is able to produce more, so you can have more options to trade for, and they're able to buy more of your items as well. As such, it is in the interest of the pisces for the human nations to become as wealthy as they can. I can easily imagine that there would be agreements made permitting trading ships to traverse the oceans (relatively) free from harm. There will quite obviously be bandits, pirates, etc, but a simple agreement that there won't be any governmental action taken to prevent human-human trade will make it much more feasible.

As far as what the humans trade with the pisces, I can imagine that metal would be a big part of it, especially tempered metal. It's rather tricky to get fire underwater, so the pisces would likely have little to no concept of metalworking. Knives, buckles/clasps, sturdy fishhooks (okay, that may be too insensitive).... All sorts of things that are drastically improved by being solid metal.

The only major interaction I can think of is shipwrecks. Humans and pisces can make all the agreements they want, but ships will occasionally get caught in storms and sink. What happens to the cargo? The humans can't get at it, so (in our world) they could just call it a loss... But the pisces could get to it, recover some of the cargo.... Does that mean they get these trade goods for free? Are they obligated to return what they can to the humans? Would they skim some off the top before they did return it? I could almost imagine groups of pisces going around the coral reefs, the shoals, the Bermuda Triangles of the world where shipwrecks are common, and scavenging whatever they can get their hands (fins?) on before anyone reports the loss. Get several of those groups going around the world and you could easily have a black market of human trade goods. But this is starting to get into idea generation.

TLDR, it would honestly look a lot like international trade in our world today. Trade what you have, that the other party doesn't, and make sure that you're both able to prosper as a result.


lets start with the basics What would an aquatic race want: remember it needs to survive underwater or they won't want it. They won't have much use for clothing water is not an insulator like air so clothing does not help much in maintaining warmth and there is no rain to keep off.

Glass especially mirrors, bottles, and lenses no way to make glass under water. glass floats will also be popular.

Brass, copper, and steel: steel is actually alright underwater as long as it stays underwater, it will rust faster than on land but will stay usable for decades. . tools and weapons will be especially popular, even brass nails will be valuable.

Lumber especially poles: very little wood underwater and again as long as it stays underwater it will not rot any faster than on land.

Gold: again no way to smelt metal underwater, they can work gold but have no way to smelt it. silver will become quite ugly very quickly however.

Pottery plates are useless but jars are easier to make on by shaping and firing than carving as aquatic races would have to do.

Surface foods food has always been a popular part of trade, this will run both ways and will be most common where both civilizations are close to each other. Cooked food will be popular, every animal ever tested shows a preference for cooked food sue to the higher nutrient availability.

Now for the aquatic races What can they offer.

Sponges sponges have always been valuable enough for trade and they are far easier for them to collect than fishermen.

Ore there are ore deposits underwater just as on land. Many are actually easier to collect.

Fishboth as direct trade and as indirect by selling information about movements

Pearls this one should be self explanatory

Maps seafloor navigation maps take a lot of time to make, an aquatic race can make them much faster and cheaper, they will need a human agent to copy them to air friendly materials.

sunken ships the location and recovery of sunken ships and their cargo will be profitable and fairly easy. This of course could create pirates.

Art coral carvings, shells, and similar art will always have a market.

Ship maintenance certain aspects of ship, bridge, and dock maintenance will be much easier for an aquatic race this could easily be worth trading for.

Travel rights and guards through territories/kingdoms will be a big deal, for those aquatic races that are amphibious this will run both ways. Remember they can sink ship with ease if they want to. I could easily see a negotiation for guards for ships. who better to stop merfolk pirate than other merfolk.

There will be other things they can offer all depending on how they live and what their technology is like. maybe they make a seaweed extract that is really savory or collect a snail venom that is useful for treating cholera.

I can picture trade houses built out of stone that have a waist/chest high wall with water on one side and dry land on the other. trade partnership between merchants should be common. Math and standardized measurements will be important, a pound of iron on land is not a pound underwater.

writing will probably be exchanged each way just for the novelty value.

I imagine their written language will be runic relying on carving rather than ink, I could also see a knot based language like Quipu. Both can be read like braille which will be useful for fishfolk that live in deeper waters. Although I could easily see them farming bioluminescence coral or sponges for light. Pencils work just fine underwater provided you write one slate and not paper, ceramic slates may be popular since they can be made for a much cheaper cost.


What would the fish folk want? Anything you make with fire. Anything that you can't easily craft in water.

Textiles There's a question on here about writing and an underwater civilization. In the answers you'll see that textiles are difficult to make in water--the process of drying and weaving, and because land-based things, like wool, cotton, silk, etcetera are just better materials to make clothing. Your fish people would want textiles specifically made to hold up underwater, but you can bet that some merchant will find a way to market them.

Books/Writing Not the standard kind. But printing underwater is problematic. Out of the water, it's easier to make "books" that hold up underwater. They might be made of fabric and the letters sewn, they might be made of thin pieces of bone or ceramic, the words painted on and preserved with a sealant. Ink and paint doesn't do well underwater, and it's difficult to make fabrics underwater, so this is likely something that would be produced topside.

Leather Degrades quickly underwater and it definitely needs land and fire to dry and cure it. However, during Medieval times there were a great many fabrics used that didn't last in regular air for long--these were used by the nobles and were seen as luxe items that would be replaced regularly. (Not everything they wore was like this--there was a lot that would hold up to use, but there were wearable items crafted NOT to last). A crafty merchant might treat this leather differently so that it would last a little longer under water, but I see this as something that high-status fish folk might wear.

Ceramics They can carve things but don't have a kiln. This would be a luxury-type item. They eventually degrade under water, but I can guess that if there's a trade, land folk will be willing to make things that last longer

Tools and Weaponry Crafting and tempering metal underwater is not an easy task, and the hardness of tempered metal is better than most materials you could find underwater.

Glass This is amongst the things you can make with fire. It would be a luxury item, of course.

What would land lubbers want?

Pearls, coral, food, recovery of lost ships (as John Robinson said in his answer), farmed seaweeds, fish, and whales. And, since this is rare, Byssal (Byssus) Threads

Slave Trade?

I am not sure how this can work, at least, BETWEEN the two, because they exist in completely different environs. And getting slaves to work when you can't spend much time topside (or "downside") is problematic.


The fish people have the advantage here. It absolutely will happen. In and out, fading back into the ocean. Or, just sink the ship. Everyone will drown and you can take it all. I would think that if they want merchants to continue USING a route, that they would just take some.

Eating Each other

If it's culturally acceptable, sure. But do keep in mind that most things living in the sea find land creatures, well--yucky. We probably just don't taste right. That's why, unless there's a gathering of sharks and they get their blood-lust on, they mainly spit us back out. That's my theory anyway. But, your world your rules.

  • $\begingroup$ what makes you think they would use a printed/written language? there are plenty of other ways to "write". And they can make their own leather, fish and other marine life have skin, and their leather will hold up better underwater. $\endgroup$ – John Dec 7 '16 at 17:08
  • $\begingroup$ @John You can't make leather exclusively underwater. Sorry. This is a process that takes curing and a lime bath. There is no process that I know of as far as leather is concerned that could be accomplished in water. Marine animals might have skin, but that's not the same as making leather. $\endgroup$ – Erin Thursby Dec 8 '16 at 4:33
  • $\begingroup$ @John They can write by carving. I already linked to a whole answer on all the ways to "write" underwater in my answer. They may or may not want to use a printed language. They may or may not think metal is the devil's work. $\endgroup$ – Erin Thursby Dec 8 '16 at 4:36
  • $\begingroup$ Why can’t the chemical soaking be done in closed containers that keeps the nasty stuff in? I can certainly take a sealed bag of lye-solution under water. $\endgroup$ – JDługosz Dec 8 '16 at 5:46
  • $\begingroup$ @JDługosz You could. But you could not continue the process completely underwater. You can take a sealed bag, but what happens if you open it underwater to take things out, for the next part in the process? Curing can't happen underwater either. Leather could not be made exclusively underwater. You have lye or whatever is used--but how do you contain it? In air you can move stuff from one vat to another, but how can you move the unfinished goods from one part of the process to the other, underwater, and keep it from being contaminated by seawater? $\endgroup$ – Erin Thursby Dec 8 '16 at 14:45
  1. "Humans and other humans oversea" 50/50 chance the merpeople leave sailing ships alone ("Oh look, another cargo ship. Better leave it alone, or the humans might restrict their trade with us or raise their tariffs") or attack them ("Oh look, a cargo ship! Let's sink it and claim its treasures!")

"Humans and fish people" I agree it'll be in coastal areas, mostly because it'll be easiest for the two to interact there. If merchants tried to negotiate from their boat, they'd have to drop anchor and probably have to shout to overcome the distance between them, unless some sort of platform is lowered down.

Humans would want: seafood, coral, pearls, shells, treasure from shipwrecks

Merpeople would want (credit to Erin, who realized these first, thought the last is my addition): Glass, ceramics, metal, textiles, jewelry

"Fish people and other fish people" They'd have merchants with extensive delivery networks, much like freight companies back in the day. Mounted sharks, whales, or just well-trained dolphins could carry goods from here to there quite effectively.

As for what they trade: Anything from the humans is fair game, I assume they'd trade things like shells or walrus ivory between themselves as well

  1. What would the merpeople seek to gain?

As stated above by me and others, anything that can't be made effectively underwater (metal, ceramics, textiles, glass). Mermaids would probably love mirrors and human jewelry, whereas mermen would be more into weapons. Also, trade relations are a pretty effective conflict buffer; you don't try to tick off your trading partners, do you?

  1. Piracy and mercenaries? Absolutely. Piracy for obvious reasons, mercenaries less so: the two sides (human and Mer) will want to influence each other, the Mer by sinking ships, either to support their allies or as acts of vengeance for CAM (Crimes Against Merpeople); the humans by hiring mer-mercenaries to escort their ships, to attack those responsible for their sunk ships, and to attack those mer-kingdoms who won't negotiate as they desire.

As for the slave trade, there are actually some options for humans here. Number one, seeing mermaids perform or hearing a siren sing could be an exotic form of entertainment.

Eating each other, though, seems poorly thought out. Why on Earth would they do that to each other? Curiosity? Something is clearly wrong if this is actually a thing, as this would severely curb friendly relations.


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