Looking to start a semi-aggressive/agressive tank

[frieked]

First let me give a little background on myself.
I started out a couple years ago with a 10 gallon tank, I quickly graduated to a 20 gallon because I needed more space. I still have both tanks and both are community tanks with a mix of various tetra's, a couple cory's, a dwarf gourami, a blue lobster and a red clawed crab.
Well, it's been a couple of years and I've been doing pretty well maintaining the 2 tanks in my opinion, have only had one death in 2 years... so I want to now graduate to a 55gal. I got a great deal on a wood stand for only $65 on clearance at petsmart, still need the actual tank and supplies.
Basically I'm looking for beginners pointers on starting a semi-aggressive or aggressive tank. I'm thinking about either an oscar or a jack dempsey, maybe a green terror. What would go well with them, what do I need to know about starting out? What should I avoid?
Oh, I almost forgot to mention, I have another 10 gallon tank with an 8" pleco that I "saved" from a kid down the street from me recently because his mom made him give it away due to his lack of caring for it. The 10 gal is way too small for it so he'll most likely need a new home in my 55gal. I think he could hold his own since he is big and mostly just hides under a rock until feeding time.

 

[fish_freak]

I wouldnt do an oscar in a 55gal. It would survive but to be comfortabel it should be in a 75. You could do one of an assortment of aggresive cichlids but that would be about it the pleco should be fine though. A single Jack Dempsy or a Single Green Terror would be fine. You could also do a single african Like the malwali eye biter. Pretty much if it stays around 10" you will be ok in a 55.

 

[monkey_toes]

OK, you've got a choice to make — do you want an oscar, or do you want a community tank? It's no problem to choose tankmates for an oscar, but one oscar and one common pleco is about all you want to put in a 55g. I like oscars a lot, but I also like community tanks. For a community, I would choose single individuals of 3-4 cichlids with adult sizes between 5 and 8 inches. Territorial cichlids are more likely to have disagreements with members of their own species, plus if you ended up with a compatible male/female pair the tank would not be safe for any other inhabitants. Species that would work well include firemouths, jack dempseys, green terrors, festivums, sajicas, convicts, one of the smaller Geophagus species and keyholes. Buy your fish as juveniles and let them grow up together — don't throw a group of adults in together.

Whether you go oscar or community, plan to decorate with rockwork and driftwood, not plants. Most S.A. cichlids will feel inclined to rearrange the tank, uprooting any live or artificail plants. You may have some success with java moss and java fern (if you attach the fern to driftwood). Some people also use floating plants.