The unlikely combination of freshwater fish and cannabis is producing outsized medical marijuana crops that Green Relief Inc aims to capitalize on, as the Canadian company plots a stock market listing and global expansion.In an underground southern Ontario facility surrounded by farmland, Green Relief operates a cutting-edge aquaponic farm, using filtered fish waste to fertilize cannabis plants, which in turn clean the water for the fish.The company says it is the world’s only licensed producer to grow medical marijuana this way, a pesticide-free process that took 2-1/2 years to fine tune. The only signs of this operation, which is built into a hill and insulated by some three feet of dirt and grass, is above-ground ventilation equipment sticking out of the ground.