fishing biting other fish

Question
i have a  10 gallon tank with 3 fish, a catfish, a moor fish, and the other one i'm not sure of yet (but is related to the moor fish just it doesn't have the large eyes) i just got the smaller fish yesterday and i noticed today it chases the LARGER moor fish around.. and bites at his face/fins/and under belly... she even swims up under his back fin so he cant shake her off. i not sure if this is okay or not? She's been chasing him for over an hour now. and i'm afraid she's going to hurt him because he has missing scales now... what is going on here and what should i do?

Answer
Hey Samantha,

Its quite possible the two gold fish are fighting for territory, or for alpha status. If the fighting continues more then 48 hours, I'd return the newer fish saying it's inable to live in your aquarium. All pet stores will take it back for an exchange, or a refund within a week.

Your black moor really needs that tank to himself anyway, because on average, goldfish will grow into a hefty 13-15" (about half of your tank!) after just a few short years. In indeal conditions, he can live upto 35 years+ as well. For the time being, it may be best to keep him alone while he heals and recovers too. If you're absolutely set on getting two fish, consider a larger tank, and a tank divider to keep them separate.