Summary
Although locomotory performance in vertebrates is related to fitness, most performance tests are conducted in a laboratory setting, or in a manner that forces the organism to move not of their own volition. Biotelemetry offers the possibility to measure voluntary activity in a natural setting and provides the opportunity to combine laboratory-derived data with field studies on wild fish. In this study, it was found that laboratory- and field-based measurements of swimming performance and voluntary activity resulted in similar general seasonal trends, though each measurement assessed a different swimming type. In the field, all swimming metrics were lower at cooler water temperatures and were lowest during early winter (mean daily activity = 0.016 BL/s; mean voluntary swimming activity = 0.04319 BL/s; maximum swimming speed = 0.17 BL/s). In the laboratory, fish acclimatized to 25.0, 14.0, and 7.5 °C decreased swimming performance (Ucrit) with water temperature (25.0 °C (2.17 BL/s); 14.0 °C (1.69 BL/s); 7.5 °C (1.17 BL/s). Although some species and tissues have been shown to exhibit different degrees of thermal adaptation, these results show that swimming, one of the most important functions in fish, is largely dependent on environmental temperature, at least in largemouth bass (Micropterus salmoides (Lacepède, 1802)).
Methodology
Warner Lake (8.3 ha), located entirely within the property of the Queen’s University Biological Station, is a freshwater lake with a maximum depth of 7 m. Warner Lake is equipped with a fixed-station, submerged acoustic telemetry array consisting of a CDMA-based telemetry system that is able to monitor the three-dimensional position of telemetered fish. The system consists of 2 multiport MAP 600 receivers (one for each basin) and 13 hydrophones moored approximately 2 m below the water surface (Lotek MAP 600; Lotek Wireless Inc., Newmarket, Ontario) (Cooke et al. 2005). Each hydrophone has a cable extending to a central location on shore where it is connected to a receiver. Receivers are connected to a desktop computer controlled by MAP 600 PC HOST software (version 3.09; Lotek Wireless Inc., Newmarket, Ontario). Fish position data are stored on flash cards and are later transferred to personal laptops for interpretation and positioning in BioMAP (version 2.1.12.1; Lotek Wireless Inc., Newmarket Ontario). Filters within BioMAP process raw position data, remove erroneous positions using wavelet-based analysis (Hess-Nielsen and Wickerhauser 1996; Akay and Mello 1997), and provide daily estimates of both mean and maximum swimming speeds for each fish (Niezgoda et al. 2002).
Temperature thermochrons (DS1921Z, iButton; Maxim Integrated Products and Dallas Semiconductor, Sunnyvale, California) were deployed to record ambient temperature at 4 h intervals from November 2005 to November 2006. The thermochrons were attached to floating ropes and anchored at numerous depths (0–5 m) and at multiple locations to ensure complete coverage of the lake.
In October 2005, nine largemouth bass (39.9 ± 0.65 cm) were angled from Warner Lake and implanted with CDMA temperature–pressure sensing acoustic transmitters (Lotek MA-TP 16-25, 16 mm × 65 mm, repetition rate 59.5 s, life expectancy of 3 years, weighing 30.0 g in air; Lotek Wireless Inc., Newmarket, Ontario), using surgical approaches outlined in Cooke et al. (2003). Each fish was released following surgery and tracking by the telemetry system began immediately. Tracking of all fish continued into the following summer, with the exception of one fish that was no longer being tracked after April 2006.