"The birds eat fish."
Translation:Los pájaros comen pescado.
Because the given sentence said "fish" and not "the fish." Your second sentence would translate to "The birds eat the fish." The given sentence didn't specify an article for the fish, so there isn't one used when you translate it.
Mybsentence saidnl exactly what it said i messes up. This has been the case multiple times
Is it possible you're making typos in your translations? I know you made a few here in your comment. Maybe type slower and be more aware of what keys you're pressing?