My oto at C.E.S will not stop harassing the larger goldfish! It is constantly trying to suck on him, and he does not like it AT ALL.

We got a new filter not too long ago, and since then, the tank has been cleaner then it ever has.

You need to feed the oto, it's hungry and looking for something to eat. Get it some algae wafers or veggies. Veggies that you can sue include blanched romain lettace, cucumber and zuchinni. Your goldfish will like them as well.

I wonder if it might be hungry, there isn't as much algae as there used to be, because of the new filter.

I can almost guarantee that thats the case, it's trying to eat off your fishes slime coat.

Sandtiger's right, this only seems to happen when the oto is starving. An average tank will not usually produce enough algae for the oto to eat and it will become ravenous. Drop in the supplemented foods at night and watch for a while to make sure the goldfish does not eat all the oto's food. You can also start growing a mini "algae farm" outdoors for a constant supply of algae. Set a shallow pale of water and stones in the sun and wait for algae to grow. Switch a few in and out of your tank as needed. The goldfish is less likely to eat this than the wafers or veggies. Feed him those foods now though!

I agree with all of the above. I like to keep some plants that grow algae in my tanks that have otos ... I never seem to have trouble growing algae on my live plants

I can't risk having plants, the larger goldfish would surely destroy them!

What is the best thing I could feed the oto?(which is still attacking the larger GF)

Feed blanched spinach and zuccini slices now. Head to the store to buy a quality algae wafer. Set up the outdoor algae farm if you can to supplement the oto later.

Also, I hate to say this, but some otos remain aggressive even with an adequate food supply. You will have to keep an eye on this fellow and if necessary house him with some fast moving tropicals if possible.

The oto was NEVER aggresive before. It now lives in it's own bowl as feeding it in the tank was impossible because the larger goldfish would take the wafer.

How big is the bowl? Is there any way you could buy a small filter for it? Otos are very sensitive to ammonia.

The oto is dead now, so it doesn't matter. I won't be getting another, the new filter does a good enough job keeping the tank clean.

That's good, because oto's don't clean tanks anyway.