How can I get a fish, that is used to brackish water, to get used to freshwater?

[Yanni]

Hi! I recently got some guppies that were originally kept in a brackish water kind of setting. They are all getting kind of sick with fungus and one of them had dropsy. What can I do to get them used to freshwater? I'm really trying to get them healthy but they aren't doing that good for me.

[b_ball34]

I would get them back to the salinity they are used to asap. Then treat the fungus and after its cleared up to slowly drop the salinity over time.

[Yanni]

Quote

I would get them back to the salinity they are used to asap. Then treat the fungus and after its cleared up to slowly drop the salinity over time.

Ok, so I just put that amount of salt and then slowly take it out with waterchanges? Also, is aquarium salt usually used to make brackish water? The guy I bought them from said he used aquarium salt

[b_ball34]

I would talk to whoever you got the guppies from and find out how much and what type of salt they were kept in and start with that. Then slowly lower the salinity after you get the fungus treated by changing water and adding less and less salt back each time until you are not adding anymore. Say you have a 10 gal tank and he kept them at 1tbsp of salt per gal and you did a 50% water change, add 5 tbsp of salt and every week drop that by 1 tbsp until you are not adding any extra salt.

Hope this helps.

[Yanni]

Thank you so much for your help! Appreciate it!

[gardenman]

Since guppies are a fresh water fish, transitioning them from brackish water back to freshwater shouldn't be overly challenging. Just do so gradually.

I've been intrigued by the idea of a long-term experiment with seahorses to see if you could develop a freshwater seahorse over the course of multiple generations. Seahorses breed fairly easily (by marine fish standards anyway) in aquariums. Start with a largish breeding colony at full salinity then over the course of a few years gradually reduce the salinity generation by generation. Those best suited to survive in the lower salinity would survive while others would die. It could take ten, twenty years to finish, but the ultimate goal would be a full freshwater seahorse that would thrive and reproduce in freshwater. It might not be possible at all, but it could be an interesting experiment. If you could pull it off, the market for a freshwater seahorse could be huge.  You could try the same thing with clownfish and other easier to breed marine species also.  (The tank space to try and create a freshwater great white shark would be more challenging.) We've seen discus go from only being able to be bred and kept in very acidic, very soft water to fish that can now be kept and bred in nearly any water over multiple generations. Why not try transitioning some popular marine species into freshwater over multiple generations? Freshwater seahorses, freshwater clown fish, I'd keep them if they were available.

[Eric R]

30 minutes ago, gardenman said:

Since guppies are a fresh water fish, transitioning them from brackish water back to freshwater shouldn't be overly challenging. Just do so gradually.

I've been intrigued by the idea of a long-term experiment with seahorses to see if you could develop a freshwater seahorse over the course of multiple generations. Seahorses breed fairly easily (by marine fish standards anyway) in aquariums. Start with a largish breeding colony at full salinity then over the course of a few years gradually reduce the salinity generation by generation. Those best suited to survive in the lower salinity would survive while others would die. It could take ten, twenty years to finish, but the ultimate goal would be a full freshwater seahorse that would thrive and reproduce in freshwater. It might not be possible at all, but it could be an interesting experiment. If you could pull it off, the market for a freshwater seahorse could be huge.  You could try the same thing with clownfish and other easier to breed marine species also.  (The tank space to try and create a freshwater great white shark would be more challenging.) We've seen discus go from only being able to be bred and kept in very acidic, very soft water to fish that can now be kept and bred in nearly any water over multiple generations. Why not try transitioning some popular marine species into freshwater over multiple generations? Freshwater seahorses, freshwater clown fish, I'd keep them if they were available.

I'm not a biologist, but I would imagine that it would take a lot more than 10-20 years to adapt most fully marine fish to full freshwater. I don't know the specific biological differences that salinity versus water hardness has on fish, but I imagine that there's a significant biological difference. If you want to keep saltwater fish, setup a saltwater tank. Also, even if certain hardy fish in our aquariums have been adapted to different water conditions than their native environs, they often can still do better when returned to their native parameters, in terms of longer lifespans, more natural behavior, more readily breeding, and being less susceptible to stress and disease.

Have you researched fish biology and learned about the evolution of various freshwater and saltwater species, as well as their anatomical differences? Could be a good learning opportunity.

[gardenman]

8 minutes ago, ererer said:

I'm not a biologist, but I would imagine that it would take a lot more than 10-20 years to adapt most fully marine fish to full freshwater. I don't know the specific biological differences that salinity versus water hardness has on fish, but I imagine that there's a significant biological difference. If you want to keep saltwater fish, setup a saltwater tank. Also, even if certain hardy fish in our aquariums have been adapted to different water conditions than their native environs, they often can still do better when returned to their native parameters, in terms of longer lifespans, more natural behavior, more readily breeding, and being less susceptible to stress and disease.

Have you researched fish biology and learned about the evolution of various freshwater and saltwater species, as well as their anatomical differences? Could be a good learning opportunity.

The thought behind seahorses is that they're a shallow water fish in the wild. Shallow water is more prone to fluctuations in salinity due to things like heavy rain. Seahorses can be found in the Thames estuary which is brackish due to the Thames River flowing into it. You don't hear of tens of thousands of dead seahorses washing ashore after every heavy rainstorm, so there's some adaptability already there. Seahorses only live 1-5 years, but a female can lay as many as 1500 eggs at a go. That's a lot of fry with some level of genetic variation from fry to fry. Over a ten to twenty year period you could have a hundred generations or more of fry born. A gradual decrease in the salinity over those ten to twenty years, might just produce a true freshwater seahorse. Would it be easy? No. Is it even possible? Maybe not. It could be interesting though.