NOVELTY - Producing eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA)-containing oil, by (i) growing one or more algae species capable of producing EPA and/or DHA in first enclosed-container system or open-pond system, (ii) harvesting algae, controllably feeding algae to one or more zooplankton and/or fish species in first enclosed-container system or open-pond system, or in second enclosed-container system or open-pond system, and (iii) extracting EPA- and/or DHA-containing lipids from fish.    USE - The method is useful for producing EPA and/or DHA-containing oil used as liquid fuel composition, human consumption and animal feeds (all claimed). Can also be used for treating cardiovascular disease, arthritis, sleep disorders, high blood pressure, high cholesterol, heart arrhythmias, coronary heart disease, insomnia, depression, anorexia, schizophrenia, hypertension and attention deficit hyperactivity disorder (ADHD).    ADVANTAGE - The method is inexpensive.    DETAILED DESCRIPTION - Method for producing eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA)-containing oil, involves (a) (i) growing one or more algae species capable of producing EPA and/or DHA in a first enclosed-container system or open-pond system, (ii) harvesting the algae, controllably feeding the algae to one or more zooplankton and/or fish species in the first enclosed-container system or open-pond system, or in a second enclosed-container system or open-pond system, and (iii) extracting EPA- and/or DHA-containing lipids from the fish, where the EPA- and/or DHA-containing lipids are processed into concentrate and purified into EPA and/or DHA, or (b) (i) providing a multi-trophic system comprising algae and a population of fish in several enclosures, where the enclosures are on land adjacent to a coast, (ii) growing the algae in one or more of the enclosures, (iii) harvesting the algae by controllably feeding the algae to the population of fish, where at least a portion of the population of fish grows from fry to adulthood, (iv) gathering at least a portion of the population of fish, (v) extracting lipids from the gathered fish, and (vi) separating and purifying the lipids to form EPA and/or DHA-containing products. An INDEPENDENT CLAIM is included for multi-trophic system for producing an EPA and/or DHA feedstock, which comprises (i) algae and fish in several enclosures, (ii) unit for controllably feeding the algae to the fish, and (iii) unit for extracting lipids from the fish.