hi i am setting up a 40 gallon tank and want a semi-aggresive to aggresive tank
You may be able to put a few barbs or mbuna cichlids in that, but for most semi-aggressive and aggressive fish it's too small. Smaller barbs should do fine, and as long as you have a nice "cave" setup then the smaller cichlids should do fine as well. Anything else of the types you want either get too big individually, or need a lot larger space for their schooling requirements.
