Vol. 28: 137–147, 2019 AQUATIC BIOLOGY Published October 17 https://doi.org/10.3354/ab00715 Aquat Biol OPENPEN ACCESSCCESS Effects of acclimation temperature on critical thermal limits and swimming performance of the state-endangered bigeye chub Hybopsis amblops Qihong Dai*, Cory D. Suski Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana-Champaign, Urbana, IL 61801, USA ABSTRACT: Thermal stress can directly affect the survival of fishes and indirectly impact fish populations through several processes, including impaired swimming performance. Bigeye chub Hybopsis amblops is a state-endangered species in Illinois and is disappearing in the northern portion of its native range in North America. Limited temperature tolerance information exists on this species. The aim of this study was to define the impacts of 2 acclimation temperatures on the performance and behavior of bigeye chub. To accomplish this, we conducted 2 assays: critical thermal maximum (CTmax) testing for upper thermal tolerance limits, and swimming performance testing for critical swimming speed (Ucrit) and burst swimming ability. With a 5°C acclimation tem- perature increase from 21 to 26°C, the CTmax of bigeye chub increased from 32.8 ± 0.4°C to 36.4 ± 0.9°C. Ucrit was not different across acclimation temperatures, and fish from both acclimation groups could swim up to over 10 body lengths (BL) s−1. Burst swimming duration also did not differ statistically across groups, but bigeye chub from the 26°C group swam 27% longer in duration rel- ative to fish from the 21°C group. Results from this study can help guide the protection and resto- ration of bigeye chub populations from thermal stressors. KEY WORDS: CTmax · ATmax · Thermal tolerance · Ucrit · Burst swimming · Global warming · Range distribution · Endangered 1. INTRODUCTION tect and restore populations of various fish species, it is therefore important to be able to quantify thermal For ectothermic organisms including fish, tempera- tolerance and predict the possible impacts of thermal ture is one of the most critical abiotic factors, and is challenges. recognized as an important ecological resource Bigeye chub Hybopsis amblops is a member of the (Magnuson et al. 1979). Although acclimation to Leuciscinae subfamily (Page & Burr 2011), and these higher temperature can increase the upper thermal fish are commonly known as small minnows (Avise & tolerance of fish, the scope of this enhanced tolerance Ayala 1976). The species once had a widespread dis- decreases at higher tolerable acclimation tempera- tribution in North America, from the drainages of tures (Beitinger et al. 2000). As a result, with expo- Lakes Ontario and Erie in the north to the Tennessee sure to sustained elevated temperatures or more River drainage in the south (Page & Burr 2011). It is intermittent heat waves, fish can suffer negative con- typically found in clear, gravel-bottomed streams sequences including increased energy use, impaired with permanent flow and little silt, preferring to swimming performance, reductions in fitness, altered reside at the base of riffles or in quiet pools (Pfleiger range limits, or even death (Huey 1991, Beitinger et 1997). The presence of bigeye chub has been viewed al. 2000, Xia et al. 2017, Morgan et al. 2018). To pro- as an indicator of excellent water quality (Boschung © The authors 2019. Open Access under Creative Commons by *Corresponding author: [email protected] Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com 138 Aquat Biol 28: 137–147, 2019 & Mayden 2004). Bigeye chub distributions have Bei tinger & Lutterschmidt 2011), suggesting that the been greatly reduced, particularly in the northern physiological plasticity of fish could help reduce the portion of their native range (Tiemann et al. 2004). At im pacts of thermal challenges (Underwood et al. 2012). present, the species is believed to have been extir- In addition to directly quantifying thermal limits pated from Michigan and Virginia and is listed as an using CTmax tests, quantifying temperature- regulated endangered species in Illinois (Warren & Burr 1988, swimming is an efficient way to define how thermal Angermeier 1995, Berendzen et al. 2008, Illinois acclimation can impact performance and survival of Endangered Species Protection Board 2015). The ex- fish in a laboratory setting (Plaut 2001) because tirpation of bigeye chub in parts of its range has been swimming ability is critical for activities such as prey attributed to bank siltation and release of fertilizers capture, predator avoidance, and reproduction in and pesticides from poor agricultural practices (Page natural populations (Killen et al. 2010). Fish typically & Retzer 2002); thermal stressors could also be con- have a thermal optimum for swimming, and tempera- tributing to its decline. For example, for stream fish, tures that exceed this optimum result in decreased loss of riparian habitats is known to exacerbate the swimming performance that can have negative con- impacts of thermal challenges (Naiman & Décamps sequences for survival and fitness (Lee et al. 2003). 1997) under more frequent heat waves and elevated Thus, better understanding of the thermal tolerance temperatures (IPCC 2018). At present, however, of bigeye chub, as well as an improved ability to pre- there is one study on thermal tolerance of bigeye dict the response of bigeye chub to thermal chal- chub, using only one fish acclimated to a single tem- lenges, can be achieved using CTmax and swimming perature (Lutterschmidt & Hutchison 1997). Addi- performance testing across a range of acclimation tional data on the thermal tolerance of bigeye chub temperatures. are therefore essential to better understand and pro- To better protect and restore bigeye chub popula- tect this rare species in the face of thermal stressors. tions, the objectives of this study were to (1) quantify To quantify the direct and indirect impacts of ther- the upper critical thermal limits, (2) define the influ- mal stressors on fishes, critical thermal maximum ence of acclimation temperatures on swimming per- (CTmax) (Lutterschmidt & Hutchison 1997, Beitinger & formance, and (3) compare the thermal tolerance and Lutterschmidt 2011) and swimming performance (Xia swimming performance of bigeye chub to other Leu - et al. 2017) testing, respectively, are commonly used. cis cinae species. These 3 objectives will combine to CTmax is a laboratory-based procedure commonly improve our ability to quantify how ther mal chal- used to define upper thermal tolerance limits of lenges can influence bigeye chub populations. aquatic ectothermic animals and determine species’ distributions (Sears et al. 2011). Compared to other dynamic or static assays, CTmax has emerged as the 2. MATERIALS AND METHODS mostly widely used procedure, with the number of thermal tolerance studies using CTmax increasing 2.1. Fish sampling and release 500% from 1990− 2000 to 2010−2017 (Morgan et al. 2018). The procedure to define tolerance limits for fish On 25 October 2018, an initial group of bigeye using CTmax consists of increasing water temperature chub (n = 12) were collected from the Middle Fork at a constant rate until a sublethal endpoint, such as Vermilion River (40° 12’ N, 87° 44’ W) at Kennekuk the loss of equilibrium or the onset of spasms, is Cove County Park near Danville, IL, USA. Fish were reached (Lutter schmidt & Hutchison 1997). Compared sampled using a seine net, placed in coolers with to other methods, such as incipient upper lethal tem- aerators, and brought back to the University of Illi- perature, CTmax has 2 main advantages: (1) it is a non- nois Aquatic Research Facility in Urbana-Cham- lethal method that requires relatively small sample paign. These 12 individuals were held in a single sizes, which makes it ideally suited to the study of aerated aquarium to confirm their transition to con- threatened species; and (2) it is very effective when suming dry fish flakes (Freshwater Flakes; Omega evaluating the impacts of biotic (e.g. competition) and One) in the laboratory. Following successful transi- abiotic factors (e.g. pollution) on thermal tolerance tion to flaked food within 1 d, an additional 28 bigeye (Becker & Genoway 1979, Beitinger & Lutterschmidt chub were then sampled at the same site on 31 Octo- 2011). To date, different abiotic factors have been in- ber 2018 using the same sampling techniques de - corporated in thermal tolerance tests, and among scribed above. Species identification of individual these acclimation temperature has shown a positive fish was confirmed by biologists working for the Illi- relationship with CTmax (Bennett & Beitinger 1997, nois Department of Natural Resources. Dai & Suski: CTmax and swimming performance of bigeye chub 139 After all experiments described below, all live fish ammonia-N was quickly reduced to 0 ppm by nitrify- were released back to the original sampling site after ing bacteria (Currie et al. 1998, Carveth et al. 2006, cooling acclimation temperature to match environ- Xia et al. 2017) (Table 1). During holding, there was mental temperatures. no sign of any fungus on the fish, and all animals appeared to be robust, healthy, and vigorous. Nei- ther total length (TL), total weight (TW), nor condi- 2.2. Fish holding and acclimation tion score (Fulton’s condition factor, K, calculated as: TW / TL3 × 105) (Neumann et al. 2012) differed