I have a 40 gallon pond. Please help with fish and pump ideas. No electricity available. Looking at solar.?

You need a filter, for fish, that runs 24/7. How ever you manage to do that is fine. You can fit 2 or 3 fancy goldfish in that pond, and nothing else. Depending on where you live that pond may not work at all, in 40 gallons you have large temperature swings unless you can regulate the temperature, and this kills fish.