The effect of temperature and ammonia exposure on swimming performance of brook charr (Salvelinus fontinalis) C. Tudorache ⁎, R.A. O'Keefe, T.J. Benfey Department of Biology, University of New Brunswick, Fredericton, New Brunswick, Canada, E3B 5A3 abstract article info Article history: Received 17 February 2010 Received in revised form 14 April 2010 Accepted 14 April 2010 Available online 29 April 2010 Keywords: Raceway Critical swimming speed Migration Toxicology Physiology Behaviour The effects of water temperature and ammonia concentration on swimming capacity of brook charr (Salvelinus fontinalis, Mitchill, 1814) were determined by measuring gait transition speed (U gt , cm s -1 ), maximum burst speed (U max , cm s -1 ), tail-beat amplitude (a, cm), tail-beat frequency (f, Hz), maximum acceleration of bursts (A max , cm s -2 ), number of bursts, distance of bursts (cm) and total swimming distance (cm) in a 4.5 m long experimental raceway with increasing upstream water velocity. Temperatures other than the acclimation temperature of 15 °C significantly reduced swimming characteristics of gait transition, i.e. U gt and A max , while increased ammonia concentration reduced the measures of swimming after U gt : U max , the relationship between f and swimming speed above U gt , a, A max and the distance travelled with each swimming burst above U gt . This study, using a novel raceway set-up shows various effects of temperature and ammonia exposure on the swimming performance of brook charr and can be used to establish threshold values for environmental management. © 2010 Elsevier Inc. All rights reserved. 1. Introduction Critical swimming speed (U crit ; Brett, 1964) is often used to assess the impact of environmental factors such as temperature, hypoxia, diseases or contaminants on fish performance (Brett and Glass, 1973; Beamish, 1978; Waiwood and Beamish, 1978; Thomas and Rice, 1987; Nikl and Farrell, 1993; Hammer, 1995). This is because it is generally assumed that maximum sustainable oxygen uptake occurs at U crit (Webb, 1975; Farrell and Steffensen, 1987; Keen and Farrell, 1994; Gregory and Wood, 1999). In the laboratory, U crit is commonly determined using increasing water velocity tests to measure the ability of fish to respond in confining swim tunnels. However, U crit measured in confining swimming tunnels can be influenced beha- viourally (McFarlane and McDonald, 2002; Peake and Farrell, 2006, Tudorache et al, 2007). Fish may refuse to continue swimming when forced to maintain position against a water speed too high for steady and too low for unsteady locomotory gait (Peake and Farrell, 2006, Tudorache et al, 2007). Also, burst-and-glide swimming, which involves the generation of a positive ground speed (Muller et al., 2000; Peake and Farrell, 2004), cannot be maintained efficiently within a confining swim tunnel (Tudorache et al, 2007). An alternative measurement of swimming energetics is the gait transition speed (U gt ), at which the transition from steady cruising to burst-and-glide swimming mode occurs (Videler, 1993). When swimming in cruising mode, the predominant muscle groups involved are red aerobically driven muscles, while at switching into burst-and- glide swimming mode white anaerobically powered muscles are engaged (Videler, 1993). Therefore, gait transition as an indicator for swimming performance bears both ecological and physiological importance (Peake, 2008, Tudorache et al., 2007). Gait transition is characterised by the first burst, typically as (1) a large and discrete increase in upstream motion, (2) increased tail-beat amplitude and (3) increased tail-beat frequency (Tudorache et al., 2007). Using a novel raceway that allows the fish to swim freely against increasing water speeds (see: Haro et al., 2004; Castro-Santos, 2004, 2005; Peake and Farrell, 2006; Peake, 2008), U gt can be a more reliable measurement of maximum aerobic swimming speed than U crit (Peake, 2008). White muscles used to power burst-and-glide swimming are very susceptible to ammonia (NH 3 ) toxicity, and ammonia exposure decreases swimming performance in both steady swimming (Beau- mont et al., 1995; Shingles et al., 2001) and unsteady swimming (Tudorache et al, 2008; McKenzie et al, 2009). Especially salmonids are known to be susceptible to even low ammonia concentrations in freshwater (Shingles et al., 2001). The potential for toxicity is determined by dissolved ammonia concentration since it diffuses into the fish across their gills (Shingles et al., 2001). As water ammonia level rises, plasma ammonia levels increase in the fish due to a decreased excretion by means of Rhesus (Rh) proteins (Weihrauch et al., 2009; Wright and Wood, 2009). Increased NH 3 levels within the fish alter the metabolic status, which may lead to premature muscle fatigue due to partial depolarisation of the Comparative Biochemistry and Physiology, Part A 156 (2010) 523–528 ⁎ Corresponding author. Tel.: + 1 31 6 20362185. E-mail address: christiantudorache@gmail.com (C. Tudorache). 1095-6433/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.cbpa.2010.04.010 Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part A journal homepage: www.elsevier.com/locate/cbpa