Aquatic creatures: Saltwater vs. Freshwater list, what if one enters the other?

There are quite a few Aquatic creatures in 5e, but (at least per their history in prior editions) they don't all thrive or live in the same kind of water. Koa-Toa, for instance, only seem to live in freshwater pools (and underground, at that), whereas I believe Sahuagin are only found in the seas, which is saltwater. Sadly, the DMG fails to differentiate between these two watery environments or specific what creature goes in which type, except by inference. Also, it doesn't state what happens in a creature that is native to saltwater goes into a freshwater environment, or visa-versa.

So, does anybody have (or care to make) a list showing what Aquatic critters belong where? The categories would be Freshwater, Saltwater, and Any (for creatures that thrive in either type of water).

Also, this isn't a 5e book, but I think the 3.5 book "Stormwrack" had a rule stating penalties for creatures entering the wrong type of water - anybody have this book and care to quote it (or summarize if a direct quote would violate copyright)?

A freshwater fish put in saltwater should suffer dehydration as the water leaves its body; a saltwater fish in freshwater will absorb water until it explodes. (Well, its cells explode, which is not as spectacular.)

According to teh interwebz, it is a matter of minutes before the fish dies. I think the closest analog in the 5E core rules are the rules for "holding your breath," which gives you 1 + Con mod minutes (min 30 seconds). In theory bigger creatures should have a higher Con but you could do some sort of size modifier if you want to get fancy (a bigger creature should last longer as its surface-area-to-volume ratio is lower).

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OK, I just fished my copy of Stormwrack out of the library. The rule in question is a bottom-bar on one of the first few pages: When a creature is in the wrong kind of water, it must make a Con check every hour (DC 10, +1 per previous check), or take 1d6 nonlethal damage, and become fatigued until it gets rid of the nonlethal damage.

5E doesn't have nonlethal damage, and tends to use exhaustion levels to represent environmental hazards, so I'd adapt this rule as follows: When a creature is in the wrong kind of water, it must make a Con check every hour (DC 10), or take a level of exhaustion that it can't be rid of until it is back in the correct type of water. Note that the very first level of exhaustion will give disadvantage on Con checks, so I don't think the increasing DC is important. Plus only the very largest and toughest of creatures will have a +10 Con mod, and I'm OK with them surviving in the wrong water.

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Now, this is all based on real-world fish biology. It wouldn't apply to reptilians, and might not apply to aberrations like aboleths (who knows with those guys), and I'm not sure about arthropods. And merfolk and sea elves are their own thing, so maybe?

I feel that worrying about this might hinder game play a bit. However, hand-waving it completely might be unsatisfactory ("Why is there a shark in the lake?" or "Why is there a frog in the ocean?"). One potential solution is that there are certain fish that can exist in both fresh and salt water, salmon being the most famous example. So you could say that merfolk, merrows, sahaguin, etc. are this type of fish. In fact, I'd say any aquatic creature that doesn't clearly belong in one type of water can survive in both.

Based on cursory web research, it appears that you can't just dump the fish from one kind of water into the other; in nature the salinity adjusts gradually, and so the fish can't adjust its osmosis thingies right away. So for these fish, I'd adjust the rule so that they still need to make Con checks or get exhaustion, but as soon as they pass a Con check, they've adjusted and the exhaustion goes away at a rate of one level per hour.

Also, I am trying not to go to sleep because then I would have to wake up on time and do things tomorrow, and making a list of fresh/salt creatures sounds like the perfect waste of time to me.

Freshwater only: Bullywug (I'm assuming an amphibian's permeable skin is just as sensitive to salt as a freshwater fish's), Crab, Frog, Giant Crab, Giant Frog, Giant Toad, Quipper, Swarm of Quippers

Saltwater only: Crab, Giant Crab, Giant Octopus, Giant Sea Horse, Giant Shark, Hunter Shark, Octopus, Quipper, Reef Shark, Sea Horse, Swarm of Quippers

Transitional: (These are the ones that can live in either, but take a while to adjust) Kuo-Toa, Merfolk, Merrow, Sahuagin, Sea Hag (yes I know it says SEA hag, but a lot of adventures have them in lakes and such)

Any other creature not listed can survive just fine in either water. (E.g. Aboleths -- they are covered in mucous; Chuul -- they are covered in chitin; Water Elemental -- they are water; Killer Whale -- they are covered in blubber; also why are we calling them "Killer Whale" again when I thought the proper term was "Orca?")

Note that a few creatures appear on both the freshwater and saltwater lists (e.g. Crab, Quipper) because these stat blocks represent multiple species but most of them either stick to freshwater or saltwater and don't transition between them. Quippers are generally thought of as analogs of piranhas, which are freshwater, but I think in a D&D world there will be plenty of saltwater quippers.

A freshwater fish put in saltwater should suffer dehydration as the water leaves its body; a saltwater fish in freshwater will absorb water until it explodes. (Well, its cells explode, which is not as spectacular.)

(Edit)

Now, this is all based on real-world fish biology. It wouldn't apply to reptilians, and might not apply to aberrations like aboleths (who knows with those guys), and I'm not sure about arthropods. And merfolk and sea elves are their own thing, so maybe?

(Edit)

“Why is there a shark in the lake?"

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While accurate in general, some RW critters are known rulebreakers.

You asked about the shark in the lake. Well, in the real world, some species of shark ARE found in fresh water. They have evolved to deal with both types. Most notorious- and dangerous- are bull sharks. Adults average out around 6’ in length, but they’re extremely aggressive, and account for the majority of attacks on humans. While primarily oceanic, they’ve been found in the Mississippi River, the Trinity River, Lake Ponchartrain, the Great Lakes, and an Australian golf course.

It’s also not just a question of concern for the water breathers. Air-breathing reptiles and mammals- as well as water-dwellers of all kinds- are also affected by the density differences in the water. Salt water provides more buoyancy than does fresh. Crossing from salt to fresh water- say, from an unexpected rush of fresh water from the surface- will result in an unplanned dive. And going the other way, a creature would rise. Depending on the specifics, either situation could mean death: one by drowning or pressure related causes for both.

Dannyalcatraz said:

While accurate in general, some RW critters are known rulebreakers.

You asked about the shark in the lake. Well, in the real world, some species of shark ARE found in fresh water. They have evolved to deal with both types. Most notorious- and dangerous- are bull sharks. Adults average out around 6’ in length, but they’re extremely aggressive, and account for the majority of attacks on humans. While primarily oceanic, they’ve been found in the Mississippi River, the Trinity River, Lake Ponchartrain, the Great Lakes, and an Australian golf course.

It’s also not just a question of concern for the water breathers. Air-breathing reptiles and mammals- as well as water-dwellers of all kinds- are also affected by the density differences in the water. Salt water provides more buoyancy than does fresh. Crossing from salt to fresh water- say, from an unexpected rush of fresh water from the surface- will result in an unplanned dive. And going the other way, a creature would rise. Depending on the specifics, either situation could mean death: one by drowning or pressure related causes for both.

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Bull Sharks have the record for the furthermost shark attack from the coast.
https://worldnewsdailyreport.com/fisherman-captures-3000-pound-great-white-shark-in-great-lakes/

Seems to survive for a bit, may not be real IDK. .

Zardnaar said:

Bull Sharks have the record for the furthermost shark attack from the coast.
https://worldnewsdailyreport.com/fisherman-captures-3000-pound-great-white-shark-in-great-lakes/

Seems to survive for a bit, may not be real IDK. .

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As of the filming of this clip in 2011, the bull sharks had been in the water hazard for 17 years, and there was evidence of breeding.
[video=youtube;dn41Odq8hyc]https://www.youtube.com/watch?v=dn41Odq8hyc[/video]

77IM said:

Also, I am trying not to go to sleep because then I would have to wake up on time and do things tomorrow, and making a list of fresh/salt creatures sounds like the perfect waste of time to me.

Freshwater only: Bullywug (I'm assuming an amphibian's permeable skin is just as sensitive to salt as a freshwater fish's), Crab, Frog, Giant Crab, Giant Frog, Giant Toad, Quipper, Swarm of Quippers

Saltwater only: Crab, Giant Crab, Giant Octopus, Giant Sea Horse, Giant Shark, Hunter Shark, Octopus, Quipper, Reef Shark, Sea Horse, Swarm of Quippers

Transitional: (These are the ones that can live in either, but take a while to adjust) Kuo-Toa, Merfolk, Merrow, Sahuagin, Sea Hag (yes I know it says SEA hag, but a lot of adventures have them in lakes and such)

Any other creature not listed can survive just fine in either water. (E.g. Aboleths -- they are covered in mucous; Chuul -- they are covered in chitin; Water Elemental -- they are water; Killer Whale -- they are covered in blubber; also why are we calling them "Killer Whale" again when I thought the proper term was "Orca?")

Note that a few creatures appear on both the freshwater and saltwater lists (e.g. Crab, Quipper) because these stat blocks represent multiple species but most of them either stick to freshwater or saltwater and don't transition between them. Quippers are generally thought of as analogs of piranhas, which are freshwater, but I think in a D&D world there will be plenty of saltwater quippers.

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- You just made me realize that some RW critters - such as crabs - come in separate saltwater and freshwater versions, so that while "Crabs" as a group might be found in either environment, it won't be the SAME crabs and putting one type in the other's water will have the usual negative effect....

Yup!

In my world 77IM would be taken out for a swim by 5 level Bullywug Barbarian and 6th level rogue octopus. The swim would be in the kings olypmic size pool.

jasper said:

In my world 77IM would be taken out for a swim by 5 level Bullywug Barbarian and 6th level rogue octopus. The swim would be in the kings olypmic size pool.

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Promises, promises...