Rainbow trout Oncorhynchus mykiss (Walbaum) are usually cultured at high densities to maximize production, but little is known about the physiological and behavioural consequences of high-density ®sh culture. The purpose of this study was to develop quantitative correlates of activity for ®sh held under conditions of increasing density. Fifteen hatchery-reared rainbow trout (mean fork length = 432.3 6 9.2 mm) were implanted with activity (electromyogram; EMGi) transmitters and randomly assigned to each of three replicate tanks. Original tank densities (15 kg m ±3 ) were then increased to 30 and ®nally to 60 kg m ±3 at weekly intervals by adding additional ®sh. Remote telemetry signals indicated that activity increased with increasing stocking density. Fish were relatively inactive during the middle of the day, with diel activity patterns not differing among treatments. Fish were more active during periods of darkness, with activity increasing with increasing stocking density. Relationships between swimming speed, EMGi activity and oxygen consumption were developed using a respirometer and used to estimate oxygen consumption of the ®sh in the density treatments. Average oxygen consumption estimates increased with increasing density treatments as follows: 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 quanti®-cation of the effects of increasing density on ®sh activity. Physiological telemetry devices may provide a useful tool for remotely monitoring animal welfare correlates under controlled conditions for ®sh exposed to different husbandry conditions and may prove a valuable tool for the aquaculture industry.

Behavioural and energetic responses of domesticated rainbow trout Oncorhynchus mykiss (Walbaum) (mean fork length 5 440 AE 45 mm) to a brief transportation episode were investigated. Fish implanted with radio transmitters measuring muscle activity (electromyogram; EMGi) were transported in a standard commercial shipping tank for 50 min by truck, and then allowed to recuperate for 48 h in stationary culture tanks. The EMGi telemetry data indicated that vigorous swimming activity occurred during transportation. Telemetry recordings also indicated that the ¢sh's swimming activity returned to baseline levels within the 48 h period after transport. However, even beyond the 48 h resting period, the swimming performance (measured as critical speed and endurance) of transported ¢sh was still impaired relative to non-transported controls (Po0.05). Respirometry measurements of ¢sh taken after transportation indicated that oxygen consumption (V O2 ) was signi¢cantly elevated. The rise in V O2 of posttransport ¢sh could be attributed to handling procedures, as well as the intense swimming behaviour observed during transportation. Therefore, the behavioural responses of ¢sh during transportation produced physiological consequences that persisted long after the transportation event. This study demonstrates the potential for utilizing behavioural measures, in concert with biotelemetry technologies, as tools to assess the impacts of routine aquacultural procedures on the health and welfare of captive ¢sh.