I have sailed through parts of Croatia.
It is amazingly clear waters and beautiful old towns.
Unfortunately, the Mediterranean has been extensively fished out and there is really little around.
Even the fish they showcase at restaurants are a very poor second to Australian equivalent.
Also don't expect any Tackleworld or similar type shops stocking the latest Shimano gear, it is more likely a local shop with a few rods and sods.
Hope that doesnt dishearten you, as Croatia is really amazing, just not the fishing.