as long as there fresh and not canned with oil and more salt then fish no problem they are a little oily naturally so don't use them as a staple but once in a while mixed with other foods there fine
They will take it. Just be patient. I was feeding my dats blue anchovies until I switched to Hikari FD krill. Now the primadonna dats of mine won't take San Francisco brand krill. Too bad for them 'coz its a pretty big jar.
I am also thinking switching to anchovy again though just to make it different. Krill-anchovie-krill-anchovy diet.