How about Swordtails? As you know, they are live-bearers. I would buy pregnant females and get 15 fish for the price of one.
I did have swordtails I had a variety of aquariums, in one of the aquarium's I made a mistake by putting a snakehead in it, it attacked everything in the tank. I had algae eaters trying to keep the glass clean, snails, I wish I could remember the names of the fish I had so long ago I was Young. I did have a large tank I believe it's 29 gallons that was a mix of a silver dollar fish, Mississippi red ear slider turtles, had a caiman which is South American alligator. It was by far the most interesting tank to observe. It was about two-thirds full of water I had Flat Rocks stacked under a light so the turtles and Caiman could bask under.
As an adult, I got my aquariums started again and took the advice of some teenage kid in the pet shop when stocking it. Aquarium frogs DO eat tropical fish. Don't let them tell you otherwise.
Don't remember much about it, but my cousin and I found two baby raccoons that we kept. They were kept at his house, but somehow, a Fish & Game Warden found out about them, came to my cousin's house and told him that we had to give them up. So, he took them. From what I member, "taking them" didn't upset either of us. When I met my first wife, she had a white cat, named Annabelle. We got a white male Samoyed Husky and name him King. Annabelle and King got along fine. When we split up, I guess she got rid of Annabelle and King. My second wife and I decided to get a dog. Got a female from local County Animal Shelter that was a 3 year old combo "Sibi" and Malamute. She was a great dog and absolutely loved the snow here in Colorado. Unfortunately, she was also, and Huskies are very well known for this, being an "escape artist" and runners. After escaping from us twice, the third time, local police picked her up and took her to a shelter 35 miles from our house. We both decided we'd had enough of the "escaping" and took her back to the County Shelter we got her from. Have plenty of pictures of her at home and on the boat we had at the time. Our last pet was a Betta fish. Bought a 5-gallon aquarium, a beautiful Betta, a few mini-shrimp (for cleaning), some real plants and colored gravel. Had it for a year or so, then it got sick and died. Bought some medicine, but it didn't work. Bought another Betta, but same thing happened. So, sold the tank and all accessories. Very good chance, our last pet will be a Shih Tzu pup, after we get rid of our boat. We already have a Play Pen, some grooming items and toys for one. Will get a female and name it Daisy.
Almost forgot but some of the above posts reminded me, I did have two baby raccoons and raised them to adulthood.
A pet that don't want to forget is an iguana we called Iggy. When we first got him he was six or seven inches long from nose to tip of tail, years later when he passed he was between 2 1/2 and 3 ft long. He got to know us, we'd take him out of his pen, he would hang out on our shoulder for a while. He had a way of cocking his head when you would bring him nice soft banana or lettuce that reminded me of birds.
Besides several cats and one dog... As an adult, long past the age of knowing better... 14 goats, 2 baby squirrels and one flying squirrel. Turned the squirrels loose when they became adults. As a kid... we tried guppies once. Mean little fish. They would eat their young. You had to put them in separate bowls when they gave birth. Not a pleasant experience. One tiny little turtle, the kind they sold at the 5 & dime store in the fish section. It didn't live very long {sniff}. Can't think of anything else.
I agree fish are not a cuddly pet or the friendliest. About 30 years ago my son-in-law installed a pond in my yard it had two waterfalls and a stream. I stocked it with Koi, shubunkin, and channel catfish. At first the fish were skittish when I put my hands in the water with food, eventually the koi and shubunkin we're taking the food out of my hand.
Most fish will eat their own young. They are not very smart. When my live-bearing aquarium fish would start to spew out fry, I would put it in its own tank (because all the fish thought it was meal time) floating in this special v-shaped plastic container that had a slot in the bottom for the babies to fall through. The babies would be freely swimming in the dedicated tank, and the mother would be captive in the floating plastic container. When she was finished, she would go back with the other adult fish and the babies would be raised in that tank until they were large enough to not be swallowed. Then they would go in with the other fish.