Development of an optical communication type biosensor for real-time monitoring of fish stress

Expanding our understanding of the physiologic conditions, including stress, that affects fish health will facilitate the development of practices to improve fish health. Toward this aim, we previously developed a radio transmission-type biosensor for real-time monitoring of glucose levels, which are an important indicator of stress in fish. The use of this system is restricted in seawater, however, because seawater greatly attenuates radio waves. Therefore, we designed another transmission method for use in seawater. In the present study, we developed a novel wireless biosensor system using optical technology through the application of a light-emitting diode (LED) as the transmission device, which was attached to the body of the fish (Oreochromis niloticus) and stress was monitored in fish under free-swimming condition. The LED transmitter was used to deliver a digital signal that was based on the output current of the sensor. The transmission efficiency is influenced by the relative position of the optical axis of the LED and receiver. The communication success rate remained stable for approximately 94% of the total monitoring time when the LED was attached to the head of the fish and the receiver was placed above the water tank. The stress response of the fish was also measured by loading a stressor, such as chemical (ammonium nitrogen compounds, pH), physical (strobe flash) and biologic (threat behavior) stressor. Successful real-time monitoring of fish stress indicated that the new biosensor system worked well and is a promising tool for monitoring on fish condition.