can i feed a long tentacle anemone small freshwater fish?

I guess you could, but why would you want to? The amount of money it would cost you to feed your anemone neon tetras would be unfeasible compared to buying a block of frozen silversides, and feeding your anemone those--not to mention it would be more humane. You can also get chopped frozen seafood at the grocery store.

An anemone will swallow anything from small bits like mysis to larger, meaty chunks of grocery store shrimp or small fish. It's really up to you on size, but larger chucks aren't likely to scatter and pollute water quality.

Hmmm, good question I don't know if that's the best idea because those are freshwater fish so they might die before they get to the anemone :D To tell you, I wouldn't do that that's so much salt for the fishes body the immune system will overload with salt related diseases and such, I'm not sure if that would pass on to the anemone. I wouldn't do it. Stick with saltwater fish, frozen silversides and the common diet for an anemone.

Depending on its appetite three times a week to once every 2 weeks. You should feed them a pice of shrimp, krill, scallop or other frozen food roughtly the size of their mouth.