The saying, "Trout jump high when a rain is nigh," could have some truth to it. When air pressure drops, it could cause trapped gases on the bottom of a body of water to be released.
This release causes microscopic organisms to disperse into water, which prompts small fish to start feeding. The small fish attract larger fish that prey on them. Eventually, all this feeding can cause such a stir that the fish start jumping.
20 Surprising Ways to Predict the WeatherFrom coffee cups to crickets, discover these unusual weather predictors