Please don’t judge me but I had a baby red tail cat in a 10 gallon long with some neons...one day we were missing one and found the catfish suspiciously fat with some traces of red and blue on its belly. He was promptly returned to the fish store right after.
My wife has several African cichlids in a 3.5 gallon tank.
There is a way to do this. I take the smallest babies, and drop them in her aquarium. When they get big enough, I move them to my much larger tanks.
The trick is to be able to move fish when they get big enough. Never give a kid with a 10 gallon baby Midas Cichlids (that easily grow to 18") without checking back in a year to see how they are doing.
My problem was when I got my 55 gallon years ago. I only got my fish from pet smart and said this was okay everyt ime I asked them. My stock was a dwarf blue gourami, 1 rainbow shark, 1 albino cory cat, 2 clown plecos, 1 rubber lip pleco, 1 twig catfish, 1 eclipse catfish, 1 angelfish, 1 synodontis eupterus, and 1 peacock eel. The gourami, rainbow shark, 2 clown plecos, and cory cat were from my first ever tank. Suprisingly the gourami, cory cat, and peacock eel survived this and lived for a long time. The gourami died in a cleaning accident about 2 years ago, cory cat died 6 months ago and the peacock I sold just a couple months ago since I got tired of only seeing him once every few weeks. This act of fish murder still haunts me to this day though.
At my ten gallons premier. I put in a dragon eel (which I now know as a dragon goby), a Bala shark, some upside down catfish, and a common pleco. When the “sharks” got big we gave them to my aunt (who had a 55) and the upsidown catfish went to the same aunt when I moved the tank. The pleco got to about 10 inches and no matter what method my family tried to euthanize it it still survived. (We left it out of water for a day and it swam back up the toilet when we tried to flush it) . And the dragon goby was buried under my zucchini plant when I found the pleco munching on it. The same 10 gallon is now a reef tank that houses only a clownfish a snail and a bunch of coral
I feel like I knew my stuff with fish when I was young. I liked researching fish a lot when I was young. I had a 10 gallon with 1 guppy,, 1 upsidedown catfish, 2 pepper cories, 2 harlequin rasboras, and 2 neon tetras, 2 oto's, all these fish were still young. I was always I remember begging my parents to get me a bigger tank so I could get cichlids(oscar, firemouth, convict) as I never known of any dwarf cichlids, and clown loaches and bala sharks. I did overcrowd that tank by getting more and more fish(tetras), making my parents buying me a bigger tank for my birthday.