Why is it ‘odbornicí’ here? And not ‘odborníci’?
Is it because it is female?
Yes, odborník is male (sometimes used generically, odbornice is female.
Is "odbornice na" used with genitive here ?
No, na takes accusative or locative. Here it takes accusative (ryby). Genitive would be ryb.
"Ryby" is in accusative plural here, I get it now :) Thanks !