my partner and i have a fish tank which we bought last year, its got 2 corydoras and 2 platys in it. My partner has always wanted an Oscar but i said he had to wait untill we have a bigger tank and get rid of the smaller fish. However i came home 2 weeks ago to find a 1.5inch oscar in my tank and a silver doller with the other 4 fish... So far so good, he leaves the corys alone but is chasing the platys around the tank, not all the time but for the majority and especially when they go near him. (i only think it's a him) so far none have died or are harmed (i check daily to look for marks and evidence of a fight) the little fish are quite quick and tend to move out of his way but I am unsure whether to just leave it to fate or separate the fish???

I have always kept fish myself but this is the first time my partner has, i think he jus though it would be ok. I dont want to be cruel to the smaller fish so am a bit tied as to what to do as there has been no attacks so far???

My grandad has a 14inch oscar and the only tank mate he has is a 16inch catfish and his tank is the same size as mine...

Welcome to OFL.

What size is your tank?
99% chance your small fish will all end up eaten before long,
you cant home a oscar with them kind of small fish.
oscar's grow very quick.
your tank will need to be at least 55 gallons for 1 oscar.
i doubt it is if you had them small fish in there to begin with.
so you dont have to much time ahead of you.

my tank is 100 gallons, i know they grow quick but you didn;t really answer my question. Shall i leave them or separate and get another oscar or shark?

Well thats your choice, but me personally i wouldn't have any small fish with my oscar, because its just waiting to be eaten.
plus, its only stressing out your other fish.

Keeping Oscars and small fish together normally ends up with the Oscar eating all the small fish. If you want to keep your small fish, I would suggest that you separate them from the Oscar before it gets too big.

1.5 inches oscar is juvenile and eats like a pig.
your tank at 100 gal can cope up. the only consideration
i will give you so that you will have peace of mind is that
"as long as the size of the other specie is 1/2 of the oscar,
you can be at ease for the meantime. however, oscar grows fast
and once they reach 2/3 bigger that tankmates.... then your other
fishes will be in trouble.... they will become expensive meal.

your smaller fish could be in danger later on from your oscar but nothing is for sure. i have many small fish including 2 albino coreys living in my tank with a couple of 10 inch oscars. i also recently intoduced a 1 inch green terror into the same tank without any incedent. however not all oscars are the same so you should be aware of the fact that your oscar might look to the smaller fish as a meal some day.
in my experience if oscars grow up with small mates and you refrain from giving them feeders they tend to leave the smaller fish alone. but you never know waht will happen in any given situation so if you keep them all together be aware that it might not end up well for the smaller occupants.

I would never trust an Oscar with a smaller fish. I have never ever given any of my Oscars live fish to eat but that didn't stop them gobbling up my two bristle nose catfish as soon as I put them in the tank.

Also, when I first got Oscars I didn't really know anything about them. I got two Oscars and six Tiger barbs. Again, I never fed feeder fish, within the year, there are no tiger barbs left

Thanks for all your notes, they are much appreciated, since i have had no incidents as yet and the corys, platys and silver doller are all over half the size of the oscar i have decided to leave them, however have bought a larger tank for the oscar when he gets a bit bigger...

R.I.P start making funeral arangments ! in another 2 months or so he will eat em !

johnny dangerous, its not always the case, like some other people have said, it can work, but not always, your silver dollars will be ok, because they are good tank mates to have with oscars, BUT, the cory's and platy's could be in danger, what size tank did you buy for the oscar then?

can you not read... when he gets big i have another tank ready to transfer him...