Hi ewa
You were asking about fish restraunts
1 Captain cooks next to the happy bar and grill in s/b last year the meals there did not seem to be as good as the previous year (possibly different cook)
2 As tony says try the Kapitanska Shreshka in Nessebar above the harbour the fish there is brilliant and the waiters are great (not to eat)
3 The pirate ship (fregatta) at the far south end of s/b behind the Amphibia hotel (can get a mini train to it) is also great for fish hope this gives you some ideas