Because they grow in my yard, I was wondering if my fish would like them
I feed them to my hamsters, but I hear fish can't digest fruit as well?

Blackberries have seeds don't they? I would think the seeds would not be good for the fish, but I am not sure. I will be interested to see if you get a good answer.

perhaps you could blend them and sieve them to get rid of seeds, and add them to gel food? tho i suppose that takes all the convenience out of it!

they are probably right about the seeds. I know some people have tried grapes before, but my fish did not like them