Yeah, agreed. I have been experimenting with a brackish tank (Decently large but far from monster) with some mini-monsters and I am growing more and more interested in brackish/salt. Those are pretty good ideas. What's really selling me is the needlefish, as I know a collection spot where you can find the babies in summer.B BillyMaysChickenWings I think it is time to set up an estuary tank and accept they need some salt. You are always looking at really cool and difficult to obtain borderline freshwater fish. If you embrace the salt you will make your life a lot easier. You could set up a Gulf of Mexico tank and I am guessing you would enjoy it a lot and not have to wait on really rare fish. Having strong captive raised gulf pipefish would be a great contribution to the hobby even if they live in salt water. I have done tanks with fish that live on the grass flats and it was a lot of fun. Breeding catsharks, bamboo sharks, or even bonnethead sharks is also a good contribution. While none of these fish are rare, they also aren't as available in all areas as plenty of hobbyist would like.
If you want to go all out an above ground swimming pool in a greenhouse with southern puffers, bonnet head, spadefish, yellow rays or skates, gulf killis, needlefish a flounder, and a bunch of mangroves growing on one end would be a ton of fun. The cost of salt will be less than buying insanely rare fish.
Granted I really appreciate the effort and I am enjoying the conversations. I would love to see you succeed with one of these projects. If you want a cool freshwater/marine fish top hat blennies have been bred in captivity. That would be a cool project. While hatch was significantly lower in freshwater, it wasn't zero and who knows what would happen over 10-15 generations. These are also imported fairly frequently so a good LFS should be able to get them. Successful Captive Breeding of the "Freshwater" Tophat Blenny (reef2rainforest.com)
About the blennies, that is very interesting. I saw some in an LFS a few months ago and I was kind of dumbfounded because I had never heard of a blenny in freshwater. I will definately consider them.
Good insight as always