135-150 Gallon Tank with med to large size Oscars can live with no food for 1 month ?

Is this possible ? As I have to go back once a year for 1 month to visit family in France. Advise ? Help ?

That is really stretching it. Healthy fish may well survive the fast if everything is done to slow their metabolism (lights dimmed, temperature reduced, filters all perfect, etc.). The catch is that evaporation and /or equipment malfunction are difficult to predict. It would be advisable to hire a petsitter, preferably one who keeps fish. Maybe someone in the local aquarium society? Food can be pre-measured for feedings every 3-4 days. The sitter should be taught how to change water if needed, how to top up water, and how to monitor filters and fish health. It can be done, it just takes some planning to anticipate any contingency.

Jim