Freshwater aquaculture systems have requirements for improved instrumentation to monitor water quality. Closed loop control of water quality will provide additional advantages to this growing worldwide industry. The objective of the proposed program is to develop systems to monitor and control water quality in freshwater aquaculture. These systems will be based on the use of novel fiber optic chemical sensors or optrodes. This type of sensor is especially well suited to the requirements of continuous in-situ monitoring of aqueous solutions. The systems that will be developed under this program promise to increase aquaculture growth rates, productivity and efficiencies in environmentally safe facilities. In the Phase I program, the requirements for chemical sensors in freshwater aquaculture will be assessed. An ammonia optrode will be designed, fabricated, and calibrated in the laboratory. This sensor will then be evaluated in a recirculating aquasystem. Concepts for chemical sensors to detect other chemical species or water parameters identified in the requirements assessments will be developed. Additionally, a concept for a system that will both monitor and control water quality in freshwater aquaculture systems will be developed.