I said the first thing that came into my head, 'Ciao.'
Fish looked puzzled. I guess it was my accent. I tried again with the only other bit of Italian I know. 'Buon appetito!'
That did the trick; he enthusiastically attacked the food flakes drifting round the bowl. I said it again for good measure and left him enjoying his dinner.
It does mean our conversation will be rather limited but it's only for a week while YS and Girlfriend are on holiday so I'm sure he'll survive.