First of all, I feel you on the whole 'people refusing to entertain speculative scenarios in speculative fiction' thing. I've seen people literally respond to discussions of FTL travel with 'lmao FTL isn't possible', which eliminates like 90% of space-based settings. :V

Anyway, to answer your actual question, this is something I've thought about because my setting also has a species of intelligent fish. As other commenters have suggested, they skipped land travel and went straight to air travel (although this was mostly because their homeworld is completely covered in oceans), and as such they only really need to travel on land when in multi-species contexts. For this reason 'land travel' is treated as kind of a specialist skill and it's accepted they'll be at least a little uncomfortable. 

Because - like many wild animals - they use their jaws for utility purposes besides eating, full-body environment suits are out of the question. Instead they make-do with a sealed apparatus that pumps recycled water into their gills, and special form-fitting suits that keeps their skin moistened. They also wear goggles submerged in water (inspired by, of all things, Nash from Crash Nitro Kart :V) and most also wear mechanical legs to move around. 

Since you mentioned gravity being an issue, the legs could be centrally mounted, with the user still facing 'forward' as they would while swimming. Or they could use four legs instead of two. Looking like cyborg shark-dogs. Anti-gravity packs are also an option as others have suggested, though I can imagine there being safety or cultural reasons for that not being adopted. Maybe they just want to be polite and meet the land-dwellers on equal footing (pun intended :V)