Swimming activity and energetic expenditure of captive rainbow trout Oncorhynchus mykiss (Walbaum) estimated by electromyogram telemetry

Rainbow trout Oncorhynchus mykiss (Walbaum) are usually cultured at high de nsities to maximize production, but little is known about the physiological and behavioural consequences of high-density fish culture. The purpose of this study was to develop quantitative correlates of activity for fish held under conditions of increasing density, Fifteen hatchery-reared rainbow tr out (mean fork length = 432.3 +/- 9.2 mm) were implanted with activity (ele ctromyogram; EMGi) transmitters and randomly assigned to each of three repl icate tanks. Original tank densities (15 kg m(-3)) were then increased to 3 0 and finally to 60 kg m(-3) at weekly intervals by adding additional fish. Remote telemetry signals indicated that activity increased with increasing stocking density. Fish were relatively inactive during the middle of the d ay, with diel activity patterns not differing among treatments. Fish were m ore active during periods of darkness, with activity increasing with increa sing stocking density. Relationships between swimming speed, EMGi activity and oxygen consumption were developed using a respirometer and used to esti mate oxygen consumption of the fish in the density treatments. Average oxyg en consumption estimates increased with increasing density treatments as fo llows: low density = 75.6 mg kg(-1) h(-1): medium density = 90.0 mg kg(-1) h(-1); and high density = 102.6 mg kg(-1) h(-1). Telemetry permits quantifi cation of the effects of increasing density on fish activity. Physiological telemetry devices may provide a useful tool for remotely monitoring animal welfare correlates under controlled conditions for fish exposed to differe nt husbandry conditions and may prove a valuable tool for the aquaculture i ndustry.