Dheltzel, many people keep Oscars in brackish tanks. I have not owned any brackish ponds, but many people who do keep Oscars. The pipefish are most definitely not for beginners or those who aren't ready to take care of such a complex fish. Thank you for your input, I will certainly research more before purchasing any brackish fish or tanks. Do you personally keep Oscars or pipefish? I know almost no one that manages to take care of them successfully, let alone breed them.
While it may be that oscars survive in brackish water, they never encounter that in their native habitat, unlike Poecilieds like "mollies" that live in coastal areas and can (fairly) rapidly adapt to changes in salinity. I believe that it would be stressful to the oscar's physiology to keep them in brackish water, so my recommendation would be to keep them in pure fresh water.
I've had Oscars, though I have never bred them. I have bred dozens of other species, including a lot of cichlids. As for pipefish, I have never had the time to properly care for them (or seahorses), so I avoid them. My personal philosophy is to keep fish only if I can provide really great conditions for them, another reason I avoided Oscars, they require large tanks and powerful filtration or abundant water changes to keep the water conditions good. They also don't coexist well with live plants and those are very important to me, so I tend to go with small, plant friendly fish like killifish, white clouds and bristlenose catfish. All those breed abundantly in planted tanks with little attention other than abundant food and great water quality.
I am not trying to be antagonistic, I just cringe when I think of either pipefish or oscars being recommended for beginners. They both take exceptional care and it does not serve a new aquarist well to suggest they start with either. There are far better species that are easy to maintain, leave these for the dedicated hobbyists who fully understand what they are getting themselves into. I despise the "throw away" attitude I find in pet shops, especially the chains. Just because a creature is cold blooded does not mean it's life is worth less attention than a cuddly animal like a dog, cat, or chicken.
I am (probably temporarily) out of the aquarium hobby, all my time is taken up with poultry now. But I am happy to help anyone with their aquariums. It's a shame that people get started in this hobby and fail to keep their fish alive. It's "easy" if you understand what is going on biologically, but it's doomed if you are just blindly following the directions of the pet shop helpers.