This is a world with underwater merfolks and other humanoids. They have opposable thumbs, so they can use tools humans can use. Lets assume there's different subspecies and races of these merfolks, so they have very different dietary needs. They have human level intelligence. They cannot get goods from land themselves.

What would their trade center around? What commodities are important to sustain the population and increase productivity? What services would be important that we don't have on land?

Edit: The technological level would be very medieval and agricultural. Cities, but still a lot of foragers in the rural parts. The species is very multicultural, but most of the societies are aristocratic city states or empires. There's cities with more than 10 000 people, but these are rare power centers in the region.

They can dive to a depth of 500 meters without trouble.

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    $\begingroup$ Trade and economy are not constants in time, laws of nature, things that just are. They developed over we don't even know how long, but longer than history (~ 6k years). We are dealing with a thing that changed constantly from prehistoric times until now. And even at a given time, people trade with different things regionally or even within the same city or company. You need to give us more information. Btw, why not simply "fish" and other ocean related foods? $\endgroup$
    – Raditz_35
    Aug 7, 2017 at 10:48
  • $\begingroup$ How deeply can they dive? This is VERY important. Can they reach geothermal vents? $\endgroup$
    – Maciej
    Aug 7, 2017 at 11:09
  • $\begingroup$ @Empischon About 500 meters without trouble. Maximun 700 meters. $\endgroup$
    – pimmen
    Aug 7, 2017 at 12:08
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    $\begingroup$ Typical mer-sales pitch: "You want thingamabobs? I've got twenty!" $\endgroup$
    – 1006a
    Aug 7, 2017 at 17:41
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    $\begingroup$ The best humans can dive to 250m. I think that 700m is stingy for creatures which are literally half fish. Also, the continental shelf drops off pretty quickly so not much of the sea is 500m deep or less - these merfolk have to give close to the coast. 2 to 4km seems like it would be better if I’m honest. $\endgroup$
    – Tim
    Aug 8, 2017 at 2:47

5 Answers 5


The usual basics are probably still needed. Food, tools and clothing/adornings (I'll assume they don't need clothes to protect them from the element (singular because it's just water) which they should be adapted to, but likely from the point of modesty or fashion).

Grooming services will be needed and basically any activities which comes with the level of technological advancement you desire. A hunter/gatherer tribe does not need much in terms of economy as there is very little degree of specialization.

But as soon as you need to specialize you get the need for services such as childcare and schooling. With medical advancement you need to set aside tribe members for various medical professions. With religion you get a priestly caste and probably also a need for a military/constabulary profession (to keep the flock in line and to enforce the laws of Neptun/Dagon/Old Father Shark). These are no longer producing their own food and as such need to sell their service (collect tax).

And of course you have the old trope about the "oldest profession" though if they procreate like fish that might be moot. (Also you probably need to invent shame and sexual repression for it to be a viable trade, so presumably priests come first. Properly refuted by Perkins, we agree that shame and sexual repression does improve the market though.)

Also, the question (to me at least) is what kind of trade will occur between land and sea. If they are isolated and have no contact with humans, just pick a technological level (pre-civilzation, ancient, medieval, pre-industrial, post-industrial, information age... whatever suits you story) and assume that there will be analogues to whatever land economy you're mirroring. (Herding dolphins instead of cows, harvesting kelp instead of wheat, using lava flows and heat vents to cook food and make tools.) If they have contact with the other element you want to think about what's made where. Perhaps tools are made on land and traded for pearls and corals (or hard to fish from the surface fish and crustaceans).


G0BLiN asked, so I'll see what I can think of. Paper currency is of course out and metal might be unfeasible as well depending on the tech level. (Whether they can use lava flows to forge or not.) But there are a lot of other viable currencies.

  • Commodity money. The Mayans used cocoa beans. The world of Metro 2033 uses pre-collapse ammunition. It's basically assigning a base unit for barter trade. I'm not enough of an economist to say how this affects inflation. Will a bumper crop ruin the economy or will supply and demand automatically adjust price levels? This could be anything (driftwood, tubers, shark eggs) but preferably small enough to carry around in a pouch around your neck for when you go shopping.
  • Shell money. Pieces of coral, pearls polished rocks, sea shells. Anything shiny that sentients like. There are a great number of precedents here.
  • Stone money. This is my favorite, seeing as how it kind of works like our current system. A value is given to a thing, usually a large rock that has been worked in some way. The Rai stone is a large carved stone disc (or wheel) that can weigh up to 4 metric tons (8,800 lb). This is rarely ever moved but ownership is agreed upon by everyone and using it for trade is just transfering the ownership. It is a system which depends a lot on honesty (especially in lieu of solid record keeping) but from a cynical perspective it does not differ that much from having money in the form of a number in a database field somewhere.
  • Domestic animals This is pretty much a form of commodity money but based on livestock. If your merfolk herds some sort of sea animal they can be used as the base for an barter economy (Fish might be tricky, but crustaceans or cephalopods may work). Camels have been known to be used like this on land.
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    $\begingroup$ Excellent answer. Consider also addressing the question of currency - they probably won't use metals for that, and definitely can't use paper - so, what's the equivalent of the 'royal mint'? $\endgroup$
    – G0BLiN
    Aug 7, 2017 at 15:27
  • $\begingroup$ You don't need shame and repression for it to be a viable trade. There are recorded instances of the behaviour occurring between monkeys even. All you need is disparity in the drives and motivations of the two sexes. $\endgroup$
    – Perkins
    Aug 7, 2017 at 22:58
  • $\begingroup$ @G0BLiN There are a lot of options. I'll edit in those I can think of. $\endgroup$
    – Doomfrost
    Aug 8, 2017 at 6:11
  • $\begingroup$ @Perkins Fair enough, didn't think about the apes. Trying to find verification for my theory in writings about sexuality in hunter gatherer tribes as I recall reading about how sexuality is viewed (and used) differently in those. But I don't find any useful source so I'll withdraw that notion. $\endgroup$
    – Doomfrost
    Aug 8, 2017 at 7:02
  • $\begingroup$ @Doomfrost Shame and repression can make it a much more lucrative trade though by drying up supply. Black-market anything tends to be more expensive. :) $\endgroup$
    – Perkins
    Aug 8, 2017 at 18:57


This one goes both ways. In medieval times iron was valuable. People often don't realise how valuable. A few ounces of good iron could buy a cow and cows were valuable back then.

Merfolks are going to have great difficulty forging metals if they need to stay underwater.

However they may have access to metal nodules from the sea floor.

metal nodules

This gives us at least one pair of trade goods such that both sides benefit from the arrangement. The merfolk sell metal ore nuggets, the humans sell metal tools.

  • $\begingroup$ As a side note, the iron nodels on the sea floor have nicke in them (and magnesium if I recall). Humans trading for merfolk iorn would actualy have stainless steal (rust proof swords). They could also potentialy extract the magnesium to use for explosives. $\endgroup$
    – PCSgtL
    Aug 30, 2017 at 16:45

"The technological level would be very medieval and agricultural."

No, it wouldn't be; don't just try to transpose terrestrial societies into the water and expect it to be plausible. Agriculture is a function of sedentary societies that grow plant foods in soil, and medieval (or even Iron Age-like) cities arise from the social stratification and role differentiation that agricultural surpluses permit.

An aquatic society could hunt (fish) and gather almost everything they'd concievably need, and since fish, sea mammals, and whales are highly mobile, so would be our merfolk. They might need tools and weapons to successfully hunt, but those would likely be bone from whales, not wood or metal. They might possibly cultivate or farm some shellfish, the way some hunter-gatherers cultivate small garden plots to supplement, but they wouldn't have a need for large-scale agriculture. No sedentary societies would evolve and no agriculture would be necessary or possible given the incredible diversity and availability of ocean resources. They'd just fish, and optionally might gather kelp. They might form federations and alliances of tribes, but overall, if you absolutely need a terrestrial analogue, think about precontact North American plains Indian tribes living off the buffalo, not medieval feudalism.

But really, nothing would be analogous to a society we'd see on the surface. In fact, they wouldn't even look human - even based on a humanoid body plan, they'd quickly evolve blubber and camouflaging skin tones, legs would become vestigial or fused, genitalia would be protected and internal, voices would likely become like those of whales....picture humanoid seals and whales, not humans with tails.

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    $\begingroup$ "Quickly evolve" made me chuckle. $\endgroup$
    – The Nate
    Aug 7, 2017 at 18:43
  • $\begingroup$ It's kind of an odd phrase, but evolution can and does happen on pretty rapid timeframes - especially when ecosystems change rapidly and lots of new niches open up, significant evolution and phenotypic change can happen on the timeframe of a generation or two. Epigenetic shifts can happen even faster. $\endgroup$
    – Snark218
    Aug 14, 2017 at 18:51

Let's start from a simple society, for sure they will need to trade on food: seaweeds, various fishes, fresh meat caught by local "grounder" daring to venture to the border of the sea.

Then, what else may they need? Anything made of wood can be used as "lighter than water" device, as it will float up, so no fancy ebony furnitures but a great help in carrying around heavy stuff.

For similar reason they won't be able to forge metals, as having a fire underwater is pretty much impossible. But at least they can trade worked metals with the people above waters.

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    $\begingroup$ Actually, wood may be sought after - not for furniture, but for heavy lifting and transport of goods (e.g. it's easier to tow a slab of rock if you make it buoyant, not enough to escape up to sea level, but enough so you don't need to support its full weight on your own). $\endgroup$
    – G0BLiN
    Aug 7, 2017 at 11:08
  • $\begingroup$ If they can reach geothermal vents, then they can be masters of metallurgy for all we know... $\endgroup$
    – Maciej
    Aug 7, 2017 at 11:10
  • $\begingroup$ Geothermal vents do not outlow molten iron or other metals.. $\endgroup$
    – L.Dutch
    Aug 7, 2017 at 11:14
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    $\begingroup$ @G0BLiN good point, edited my answer to embed it $\endgroup$
    – L.Dutch
    Aug 7, 2017 at 11:15

I imagine toolmaking would be important and so would any good material for making tools like suitable types of stone, bone, wood. Also rope and material for fishing nets.

Even if fishing is not the main food source fishing would be an important skill, including the knowledge of where to find fish, in what seasons etc. Going after big fish might be more akin to hunting and require special tools & techniques. From them you would get the big bones for making bigger tools or weapons and even things like whale oil from whales.

Manufactured items from the surface that could not be made underwater would be close to invaluable. Maybe harvesting resources from land would also be a thing? A society like you describe might have developed techniques to fell trees into the water to get at the valuable wood. Even if that takes digging channels into the land where trees are. They might go to great lengths to harvest the "plenty of the land" in creative ways similar to how human civilizations have exploited the sea.

Fortress building could also be a science in itself. Underwater stone fortresses with gates opened by moving trapped air bubbles or other mechanisms to produce lift.

Instead of horses dolphin breeding/training could be a major part of the economy. Fish farming inside giant nets or in ponds at the coast would also be doable.

Since you mention different dietary needs I think the base trade would center around food since your gatherers would often be able to find some that would fetch a better price elsewhere. Consider that dead fish will spoil quickly. So preservation or even moving around live fish might also be a business.

For more ideas along the same lines I recommend thinking of underwater alternatives to what our own civilizations developed on land in pre-industrial times.


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