In Germany fishermen greet each other with "Petri Heil". I asked myself if this is only a German thing or is it kind of universal (at least in developed countries like EU countries, US etc.) for fishermen?
I grew up in Italy, in a fishermen's village on the Adriatic Sea. I never heard this expression, and I am pretty sure I've never heard it anywhere in the Mediterranean. Furthermore, I think that a "HEIL" in the southern European seas is one of the most non-local and foreign-sounding expressions that I can imagine. So please don't even try it :-)
This answer is based on the meaning of "Petri Heil", I have hardly any first hand knowledge of the use of this phrase.
For starters it is certainly restricted to countries where the majority religion is christianity, as "Petri" is a reference to the biblical fisherman Petrus (Luke 5.1-11 and John 21.1-14).
Then "Heil" is a somewhat outdated German noun used as a greeting. In general it is positive expression, meaning a broad range of things like good fortune, health, success, ... It is derived from "heilig" which is "holy". So the German origin makes it likely that this is only used in German speaking parts of the world. However there are German expressions in English and probably other languages. Generally in technical language you can often find terms from foreign languages. So this is not conclusive.
Combining the two "Petri Heil" means something like "I wish you just as much success as fishing as the biblical Petrus had". At least technically, I guess hardly any fisherman will actually know this.
In case you do not mind a regional-based mutation, among Czech fishermen a very similar greeting can be heard: "Petru zdar!" or "Petrův zdar", which has the same meaning as "Petri Heil". However, I suppose the Czech analogue actually comes from German as the Czech language used to be influenced by German in the past.
I'm a Canuck. My father in law is German and lives there. Whenever he speaks to my wife, he has her tell me Petri Heil, knowing we both fish. Neither of us speak the other's language though I have picked-up on a few, ahem, choice words here and there. The common greeting here is "Tight Lines", the meaning should obvious. Tight lines meaning "fish on" or, I wish you much luck :) And I do believe the answer to Petri Heil is Petri Danke.