Once the tank has been cycled properly, I’d recommend freshwater pufferfish (Figure 8’s) , or if you’re up for more of a challenge, a brackish tank with Green Spotted pufferfish
Puffers are basically puppies with fins, they are extremely intelligent fish (highest brain/body ratio in the industry), recognize their owners, will beg for food, and have their own unique personalities.
just to give you an example, i had a Green Spotted pufferfish, i named him Zaphod, his favorite food was crawfish, and he’d literally hunt them, he had a plan for attack, and would literally stalk the crawfish…
first step, he’d hover around it, just out of claw range, sizing up his prey, figuring out the best plan for attack, the first strikes were always to remove the claws, rendering the craw defenseless, then… (spoilers for the queasy)
depending on how hungry he was, he’d either bite it’s eyes off first, to make hunting easier, then go for the killing bite at the base of the carapace, or just go for the killing bite, then feed at his leisure
crawfish were a rare treat, his normal food was Ramshorn snails, freeze dried krill (which i would hand feed him), and the occasional ghost shrimp.
to give you an example of his personality;
first thing in the morning, he’d wake me up by splashing at the surface of the water, so i’d feed him his morning krill, then he’d follow my motions around the room from his tank, his colors vivid fluorescent green, brown spots and a pure white belly, then i’d go to work…
when i got home, i’d se him resting on the gravel bottom of the tank, his colors were muted, his belly a dark gray, his expression almost…sad, he looked bored and sad (and he did have some tankmates, he just preferred his pet human)….
The veryINSTANT he saw me, his colors brightened up instantly, his belly pure white, his back iridescent green, and he’d swim around the tank happily, and start begging for dinner…