Hypothetical effects of too much freshwater immersion on an intelligent, marine, fish-like entity

[Tired]

So, bit of an unusual question. I'm doing some research for a work of fiction, not for any real-life animal. I like to ground fantasy biology in reality. 

 

I have a character named Drava. He's an entity created when a dead body, actively being eaten by eels, drifted into a magical hotspot, during a hurricane, under a full moon. The hotspot, stirred up by everything, turned said corpse and eels into a single, living creature. I don't know too much about his biology, but I think the closest comparison, in terms of breathing and body composition, is something along the lines of some of the particularly air-hardy fish. Walking catfish, mudskippers, the sorts that can go on land for hours. He can definitely tolerate more air than they can, and I think he's warm-blooded, but he breathes water when given the chance. Does a job of looking humanish, and he doesn't need his skin to stay as wet as fish do. 

 

I'm working on a story snippet where he gets mistaken for a river creature of some sort, and a biologist/collector shuts him in a cage in a lake. Given the gills, I'm sure that's a bad thing for him. 

 

What happens to saltwater fish when they stay in freshwater for too long? I know they retain too much water, and their cells eventually swell and burst. What does that do to them? What shuts down first? 

 

I'm reading about the effects of water poisoning on humans. Nausea, confusion, muscle cramps, all the fun lack-of-electrolyte symptoms, and then seizures and eventually death in severe cases. Does that track with what happens to fish? It's the same idea, though fish, of course, have things worse. What with the gills. 

[mcarroll]

Personally, I can't answer your question based on anything but conjecture, but I think (traumatic) shock would set in very quickly.

 

Anadromous fish don't have a problem with the switch.  

 

Sorry, that's the opposite of what you wanted to know...but maybe there's more info you can research in that direction?  

 

 

[Ratvan]

I would think that the a kidneys and or liver would shut down first. 

 

Seawater is hypertonic to the fishes living in the ocean, which means that water is continually being sucked out of their bodies. To survive, saltwater fishes continually drink lots of water to compensate for water loss caused by osmosis. They filter out excess salt from their bloodstream through their gills and kidneys by urinating.

 

For the freshwater fish, they don't need to drink water, but they do have to urinate. Because freshwater is hypotonic to the fishes living in it, water is continually entering their bodies through their gills, skin, or their mouths when they eat. To balance the amount of water in their bodies, all they have to do is urinate frequently.

 

Wait! What? Does it mean than seawater fishes just have to pee more to live in freshwater?

Yes, but no! The cells of the seawater fish will be saturated faster than it is able to pee (or faster than its kidneys can handle).

[Tired]

What I'm getting from this is, he's going to have a very bad time. 

 

So the new question is: what do you do about this? The modern treatment for water poisoning in humans mostly involves sodium IVs and stopping you from drinking more water. If this is a time period that doesn't have IVs, and also the sick person is sort of a fish, I'd imagine the proper route is "immerse in saltwater and hope". That's what I would do with a fish that had been in freshwater for too long, at least, just put it back in saltwater and hope it worked. I don't know what else would help.

[Ratvan]

I mean Medieval Medical techniques pretty much were leeches, and herbal remedies. So really you are looking at ways in which you can remove water from a body quickly you'd be looking at things like Peppermint, sweating remedies. They would probably try and use some form of burn remedy on him?

 

"In the early stages of treatment there was an attempt to stop the formation of blisters. The burn was prevented from becoming dry by using anointments placed on the burn. These anointments typically consisted of vinegar, egg, rose oil, opium, and a multitude of different herbs"

[Tired]

I'm trying to figure out what the roughly-medieval version of a marine biologist would think to try as a solution. Figure out what's possible, first of all, and what would come to mind. Saltwater immersion seems relatively obvious- if a sea creature is sick because it's been in freshwater, put it back where it belongs. Maybe try to get him to drink especially strong saltwater, too, though I wonder if he might be inclined to do that on his own. Water poisoning seems like it'd give someone a major salt craving. 

 

No idea if this guy can sweat, but given that it's only mammals that can, I don't think so. Don't know what this guy is, but I'm pretty sure he's not a mammal. I would also worry that sweating, if it was possible, would lose him what little electrolytes he might have left. Something to physically draw the water out is interesting. 

[mcarroll]

36 minutes ago, Tired said:

roughly-medieval

Are we pre-or post microscope in this world? That was early 1700s I think.

 

The same guy that wrote the first marine aquarium handbook (1850’s) wrote an amazing microscope book as well.  It is basically a written account of what he sees through the scope while looking at a (highly organized) variety of natural things.*  Hypothetically he could be your prototype marine biologist.  
 

His last name is Gosse, but the rest if his name is eluding me (his dad was also an author, but not on this subject) and I can’t link well from where I am. If you check out the “aquarium history” article on my blog I talk about him and have links to his aquarium handbook there.  I think the title of the microscope book is something like “an evening at the microscope“.
 

* In 2020 it’s probably hard to imagine a microscope book without photos. I get the feeling that many folks might even find that irritating. But I’ve read some of it and it’s an amazing read.  Just sayin’.  At the same time, he hand illustrated his aquarium handbook and it’s amazing art.

[Tired]

I hadn't thought about it. I'd guess post-, if only because I like the idea of my biologist character getting to look at everything under a microscope. It might have some bearing on figuring out exactly why lack of salt is so bad for a saltwater animal, I suppose.