Can feeding status and stress level be assessed by analyzing patterns of muscle activity in free swimming rainbow trout (Oncorhynchus mykiss Walbaum)?

This study involved monitoring the activity levels of three groups of adult rainbow trout that were either fasted on a weekly cycle, fed to satiation, or fed to satiation and then acutely stressed by overcrowding twice weekly. A subsample of fish was implanted with electromyogram (EMG) radio-transmitters that broadcast a signal proportional to muscle activation levels, allowing for the continuous recording of swimming activity by a remote receiver. These EMG transmitters did not affect the swimming performance of fish, but did reveal variation in activity as a result of feeding status. The results of this study clearly illustrate differences in activity levels in fish of differing feeding and stress status in cultured fish. Ultimately, fish may be able to control feed availability using their behaviour patterns, with feed being presented upon demand. This type of technology may enhance the automation of intensive fish culture operations while simultaneously minimizing feed wastage as well as overall production costs. (C) 2004 Elsevier B.V. All rights reserved.