Described herein are methods of use of purified preen oil, food and feed compositions containing purified preen oil, food and feed additives containing purified preen oil, and pharmaceutical compositions containing purified preen oil. Methods include treatment of chronic joint inflammation in humans and animals by orally administering purified preen oil. Also included are methods of feeding a growing fish by feeding the feeding the growing fish purified preen oil in amounts effective to improve survival and/or stimulate growth in the growing fish. Further included are methods of feeding live prey organisms purified preen oil, and feeding the live prey organisms to growing fish.