Preliminary development and evaluation of an aquaponic system for the American Insular Pacific

Abstract

Integrated fish and plant culture may minimize resource usage, a valuable characteristic for the American Insular Pacific Islands. The goal of this work was to develop and evaluate a simple integrated lettuce and tilapia production system suitable for this region. The system consisted of a plant growing tray and an aerated fish tank, with water exchanged manually. A literature review suggested that plant nutrient requirements must be matched by fish nutrient production. A tray of 48 lettuce plants, Lactuca sativa (red sails variety of leaf lettuce), was provided a standard nutrient formulation and nutrient uptake was quantified over time. In a follow up trial, lettuce trays were provided modified nutrient formulations. Lettuce head weights were reduced when provided one fourth nutrients, one half nutrients, or one half potassium but not when provided one half calcium and magnesium or double nitrogen. These results suggested that the nutrient amounts observed to be taken up by lettuce were required for growth. Hybrid tilapia, Oreochromis sp., were grown in a 200 L aerated tank with 20 L of water removed and replaced with tap water daily. The nutrient amounts in the water removed daily were quantified as fish biomass and daily feed consumption increased. Nutrient production appeared adequate for a tray of 48 lettuce plants using 2.3--2.5 kg of tilapia consuming 39--53 g of feed/day. Lettuce trays exchanging 20 L of water/day with fish tanks operated as suggested grew as well as those provided the standard nutrient formulation, demonstrating the technical feasibility of the system. A breakeven analysis was conducted for hypothetical systems based on the present work. Systems appeared profitable, but no economical benefit was gained by integrating tilapia and lettuce production. Additional research is required to confirm the findings of this study.