No tanks. Fish(tilapia, rest stay oustide year round) only go inside for winter, in IBC 330 gallon tanks with tops cut off....winter here is about 5-6 weeks. The rest of the time they are in outdoor ponds. I used to own a company installing water gardens, had some parts I had left over from a variety of jobs and started digging. Not pretty, as built with NO budget and from remnants. Never seem to be able to afford one of the ponds I put in other people's yards @ 10K+.
But....I get off topic. It's utilitarian. But works, and produces fish like a factory.
Koi, fancy goldfish, catfish, prawns, tilapia, green back minnows, and bull frogs(big enough they are eating doves now...I put an aluminum pie plate on the water and add birdseed to coax the doves down. Find if I don't keep them fed I lose fish. Not very nice. But fish are worth more than doves). It's a multi tiered pond with 2 waterfalls at the moment. This produces lots of water plants and still has enough nutrients to pump into another 330 tank I use as a staging tank. From there into gutters I use as growbeds.....then back to pond.