id go with a common single tailed goldfish and a shubunkin. They look cool when they get big both single tailed since they are very hardy and active.
Sajica and clown loaches. Or maybe Bartoni.
Yoyo Loach stay pretty small but they are greedy and aggressive eater, it will chase off smaller fish and try grab all the food, some even dare to try to steal a piece of food from a predator mouth too, my Yoyo always try to steal a piece of smelt from my crayfish and it almost lost it live last night but lucky enough the crayfish was aimed to grab back his own smelt piece of meal lol...Most information in internet said crayfish too slow to catch other fishes for meal lol I doubt about that...its lightning fast to grab anything within its claw range....Love clowns, could be a problem long term though depending on how fast they grow methinks.
Love clowns, could be a problem long term though depending on how fast they grow methinks.