Methods and compositions for increasing the growth rate of a prey fish are described. A method includes contacting the prey fish with a water-soluble growth promoting factor in an amount effective to increase the growth rate of the prey fish. The water-soluble growth promoting factor can be released through fish skin from the urine and/or feces of a predator fish that has eaten a prey fish. An aquaculture growth supplement includes a carrier and a water-soluble growth promoting factor. Also included are methods of making aquaculture growth supplements.
