Mixing Meanies?

So in LFS and on Youtubes I am seeing many people mixing fish that in me lil noggin... should kill each other. I have seen tanks with Dovii, Jags, Green Terrors and Plecos all living relatively peacefully. My Question is how the hell do you pull that off? Is it just sadistic people dumping all their fish into a large tank and hoping for the best? I have heard if the tank is overcrowded aggression is not an issue but it would seem that like Jags/Umbee/Dovii they are de facto killers. Can someone explain this artform to me? Would love to have an algae eater in with some of my S. American meanies.

in LFS fish probably aren't in the tank long enough to establish territories and get mean

I have plecos in with all of my Cichs except my Dovii. As for keeping them all together, the only issue I have ever had is with the Dovii. Once they get to a certain size they start to erase the population, but I have never had issues keeping several large Cichs together. That includes 12" Jags, 10" Umbee, 12" Zonatus, 13"Argentea, 13" Red Devil, 13" Hoga, 13" Hartwegi, 13" Bifa, 12" Fen, 10" Grammode, and so on. I have even had spawning amungst some of these while in the community tank. Festae, I was able to house them with other Cichs but once they spawned, it was war. I have a system, and have learned how to introduce fish and in what tank with what specie.

Looking at your selection it looks like keeping similar size is a definate eh? Im asking because the wife is getting upset I have all these 50+ gal tanks with 1 fish per when her 30 gal has prolly 50 in it. Was hoping to maybe try to see what I could cram into a 80 or 100gal. Thinking my jack dempsey and oscars could play nice even though the dempseys are a bit smaller. Oscars are the laziest/least aggresive of any "aggressive" fish breeds I have kept.

That is where it depends on your fish and what you know about it.  I know that my Hoga is a bull and he is the top dog in his tank, but he also doesnt seek out aggression but will step up when challenged.  My big RD shares his tank with 7 other RD's but those are smaller so there is no issue.  

When I say that I keep mine together, their tank is 250 gallons or larger.  Not sure a jump to just a 90 gal would be enough.  A 55 is 4'x13", a 90 is 4'x18", so the 90 is taller, big deal, with Cichlids its about floor space.  A 100 gal is 5'x18" thats a little better, but ideally going to 6'x18" or 6'x2' would work better.

I housed 3 x 10" RTM's, 1x 9" Freddie, 2 x 8" Jags, 2 x 5" Cubans in a 6'x2' 210 gal. tank.  They were in there until I separated the RTM and Cuban pairs and sold the rest.

As my tanks got bigger I noticed a lot less aggression in my fish. I had a Midas in a community setting that included a school of silver dollars. When he was growing up with them he would chase them pretty hard core when in a 65g breeder. When he got moved into a 120g 5ft tank, it eased up quite a bit. When he went into a 210g, he stopped chasing them altogether. Each fish is different but your chances of success increase with a larger tank.

I have also found that keeping the more aggressive species in a more peaceful setting, I tend to lower the temps to the lower 70s as with temps that are higher usually cause fish to live in a more spawning mindset which, in my humble opinion, means more aggression.


I'm currently keeping a number of top tier predators in with some plecos, and more community type cichlids.


Another thought of mine is that when my fish get out of the adolescent size, they also seem to mellow a bit.