HI, Although i am new to the world of Oscars i have had a nice community tank for a number of years. Anyway, I have set up a 300 litre tank 48 inch tank just for an oscar.
I already have a 4.5 inch Red tailed Black Shark and a 4.5 inch Pleco (i think a sail fin)in my community tank.
Will it be ok to add these two fish into my larger tank with an Oscar??? as tank mates or will i face problems with fighting/ territorial issues or any things which i might not be aware of?????
Any advice is appreciated.
Thank You.

firstly welcome to the site

now as to tankmates the pleco can grow to huge sizes(if you weren't aware up to 24"). but they are fine as tankmates for oscars. your redtail can be quite aggressive but oscars grow really quickly and will outgrow the redtail in a short time. it might not seem like an issue now but remember that if it can fit into an oscar mouth they probably will eat it.

luck to you with your new oscar

I think that a 4.5in red tailed shark would be too big for even a full sized oscar to eat. As said the shark may bully a small oscar, altho the oscar may stand up for itself. Oscars grow quick so any bullying by the shark wont last for long. The plec will be fine, they can reach 2ft however they take a very long time to get that big

actually delboy i have a 4" (total lengh)rainbow shark and my big oscars can easily fit something his size in there mouth. im growing the rainbow to hopefully one day put in with my o's

Fair enough. It depends on the type of fish and how big your oscars mouth is, i still think a 4.5 in red tail shark might be ok.

There is another problem and that is if your oscar tries to eat a fish but it wont fit, the oscar gives up but in the process of trying kills the smaller fish

if u get small os, i think they will be ok with the shark. the shark might bully it a little, but they have small mouths on the bottom. so i dont see it killing an o. when os grow up with a fish ( with my experience at least) they wont eat the fish if they end up out-growing it. i think youll be ok but the best thing to do is to try it out and separate them if needed.