I'll offer a bit of unique perspective as a native fish enthusiast.

Mummichogs. They are a very common North American killifish which lives in conditions anywhere from freshwater to marine. I have about 10 in my brackish tank. These things are no joke. According to some articles, these have been found in salinities of up to and including 110 grams per liter, (more than 3x the salinity of seawater,) as well as literally being sent to outer space and coming back alive. These things aren't tiny, either. They can get about 5-6" at full size. Not to mention, they eat everything from flakes, to worms, to shrimp, to live fish.
So yeah. They are impossible to kill, usually not very interesting in appearance (the one in the picture is def one of the more colorful specimens,) and very voracious. Not exactly the funnest fish to keep.

Mummichogs. They are a very common North American killifish which lives in conditions anywhere from freshwater to marine. I have about 10 in my brackish tank. These things are no joke. According to some articles, these have been found in salinities of up to and including 110 grams per liter, (more than 3x the salinity of seawater,) as well as literally being sent to outer space and coming back alive. These things aren't tiny, either. They can get about 5-6" at full size. Not to mention, they eat everything from flakes, to worms, to shrimp, to live fish.
So yeah. They are impossible to kill, usually not very interesting in appearance (the one in the picture is def one of the more colorful specimens,) and very voracious. Not exactly the funnest fish to keep.