Fisheries Research 169 (2015) 1–7 Contents lists available at ScienceDirect Fisheries Research j ournal homepage: www.elsevier.com/locate/fishres Behavioral responses of a highly domesticated, predator naïve rainbow trout to chemical cues of predation a,b,∗ b,c a a Christopher J. Kopack , E. Dale Broder , Jesse M. Lepak , Eric R. Fetherman , b,c Lisa M. Angeloni a Colorado Parks and Wildlife, Aquatic Research Section, 317 W. Prospect, Fort Collins, CO 80526, USA b Department of Biology, Colorado State University, Fort Collins, CO 80523-1878, USA c Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523-1878, USA a r t i c l e i n f o a b s t r a c t Article history: Fisheries management agencies allocate significant proportions of available resources to rear fish for Received 23 July 2014 stocking in lakes, rivers, and reservoirs. However, domesticated fish reared in a hatchery environment Received in revised form 10 April 2015 may fail to exhibit normal antipredator behavior and can have relatively low survival when released Accepted 12 April 2015 into natural habitats. Exposing hatchery fish to natural predator cues can provide information about Handling Editor B. Morales-Nin their capacity to exhibit appropriate behavioral responses and has the potential to enhance antipredator behavior and subsequent survival in the wild. We investigated immediate behavioral responses to an Keywords: acute exposure to chemical cues of predation in highly domesticated, hatchery-reared rainbow trout Alarm cue Oncorhynchus mykiss. We used a frequently stocked and economically important strain of rainbow trout, Antipredator behavior the German Rainbow (GR), which is resistant to whirling disease but particularly susceptible to predation. Oncorhynchus mykiss Predator kairomones We exposed individual rainbow trout to alarm cues from conspecifics, kairomones from brown trout Salmo trutta Salmo trutta predators, and a combination of the two cues. Fish exposed to these cues exhibited changes Trout in behavior expected to reduce predation risk, including a reduction in time spent actively swimming and exploring, and an increase in time spent frozen. Thus, these highly domesticated, hatchery-reared fish retain the innate ability to express appropriate responses to the threat of predation. Future research should investigate whether repeated exposure to predation cues in a hatchery setting could translate to long-term enhancement of antipredator behavior and increased survival rates, as this would provide a rapid, simple and low cost way to increase the efficiency of stocking programs for recreational purposes and, more importantly, native fish restoration and conservation. © 2015 Elsevier B.V. All rights reserved. 1. Introduction be hindered when piscivores (introduced and native) consume stocked native fish (Karam and Marsh, 2010). Thus, techniques In the US, fisheries management agencies stock millions of that increase post-stocking survival may be beneficial for native fish annually in rivers, lakes, and reservoirs. Because these efforts fish restoration and conservation efforts (e.g., Hutchison et al., are costly (Johnson and Martinez, 2000), an increase in effi- 2012). ciency of rearing or stocking practices has the potential to benefit Stocked fish tend to have relatively low survival rates, especially hatchery and management programs. Specifically, techniques that immediately after they are stocked, presumably in part because increase survival of hatchery fish post-stocking can increase the naïve hatchery fish do not exhibit natural behavior important for number of fish available for anglers while reducing the num- survival in the wild, including appropriate foraging and antipreda- ber of fish required for rearing and stocking (Olson et al., 2012; tor behavior (Brown and Laland, 2001; Brown et al., 2003; Suboski Vilhunen, 2006). In addition, invaluable fish restoration efforts can and Templeton, 1989). Poor post-stocking survival associated with reduced antipredator behavior may be due to hatchery- selection, differential experience with ecologically relevant cues, ∗ or a combination of the two (Jackson and Brown, 2011). Many ani- Corresponding author at: Colorado Parks and Wildlife, Aquatic Research mals, including fish, exhibit innate antipredator behavior (Ferrari Section, 317 W. Prospect, Fort Collins, CO 80526, USA. Tel.: +1 970 412 3843; et al., 2010b). However, experience with predators and their cues fax: +1 970 491 0649. E-mail address: [email protected] (C.J. Kopack). can allow for higher potential survival after stocking through http://dx.doi.org/10.1016/j.fishres.2015.04.005 0165-7836/© 2015 Elsevier B.V. All rights reserved. 2 C.J. Kopack et al. / Fisheries Research 169 (2015) 1–7 enhancement of antipredator behavior (Brown and Smith, 1998; have a greater influence on behavior than either cue alone due to Hawkins et al., 2008; Vilhunen, 2006). their potential additive effects. In the second experiment, GR fish There are many ways to evaluate and enhance ecologically rele- from the first experiment were immediately exposed to a brown vant behavior in hatchery fish, including providing access to habitat trout predator. If prior exposure to predator cues enhances subse- structure (Braithwaite and Salvanes, 2005) and direct exposure to quent antipredator behavior, we expected fish previously exposed predators or to predator models (Brown and Magnavacca, 2003), to chemical cues of predation to be more likely to use a protec- but experience with chemicals of predation has shown particular tive structure compared to control fish. The ability of this highly promise (Vilhunen, 2006). Chemical cues that elicit antipredator domesticated strain to respond to chemical cues of predation and behavior include both conspecific alarm cues (Ferrari et al., 2010b) the short term persistence of antipredator behavior post exposure and predator produced kairomones (Hawkins et al., 2008). Expos- to these cues, during a live predator encounter, would provide ing hatchery-reared fish to these chemical cues prior to release additional support to suggest that the GR may benefit from train- can reveal their ability to exhibit appropriate responses and has ing. the potential to enhance antipredator behavior (Chivers et al., 2002 in fathead minnow Pimephales promelas; D’Anna et al., 2012 2. Materials and methods in white seabream Diplodus sargus sargus; Hutchison et al., 2012 in Murray cod Maccullochella peelii; Mirza and Chivers, 2000 in 2.1. Fish husbandry brown trout Salmo trutta). Pairing conspecific alarm cues with predator kairomones may allow fish to more effectively asso- We obtained 70 GR fingerlings from the Colorado Parks and ciate the predator kairomone with danger (Berejikian et al., 2003; Wildlife (CPW) Bellvue Fish Research Hatchery (Bellvue, CO) that Brown et al., 2013; Ferrari et al., 2005). The coupling of these cues ranged in size from 54 to 88 mm total length (TL). They were held has also shown to have additive effects resulting in a stronger in a 76 L recirculating tank in the CPW Toxicology Laboratory (Fort behavioral response when compared to the use of alarm cue or ◦ Collins, CO), maintained at 10.5 ± 1 C, and fed trout starter feed predator cue alone (Brown and Smith, 1998). These techniques TM (Rangen Inc. , Idaho) at 1% of the total mass of fish in the tank, may be particularly useful for domesticated fish strains since once daily. responses to predators decline with each generation in captiv- Eighteen brown trout, each approximately 140 mm TL, were ity (Brown and Laland, 2001; Jackson and Brown, 2011). Both acquired from the CPW Bellvue-Watson Fish Hatchery (Bellvue, laboratory and field experiments have shown that experience rec- CO) for use in the predator encounter trials. Brown trout preda- ognizing predators leads to increased survival during predator tors were selected because they are the most common predator encounters highlighting the importance of providing appropriate of rainbow trout in the state of Colorado, and they were free experience with predators to hatchery-reared fish (Brown et al., of disease, readily available, and easy to maintain. The brown 2013; Brown and Laland, 2001; Chivers et al., 2002; Mirza and trout were housed in three, 133 L recirculating tanks that were Chivers, 2000). Fish exposed to these cues exhibit an increase in subdivided into six sections by transparent, porous dividers and natural antipredator behavior, including spending more time in ◦ maintained at 10.5 ± 1 C. Each tank and corresponding brown trout a frozen posture or hidden under cover and less time foraging or was assigned a number that was used to systematically choose a exploring (Brown et al., 2003; Brown and Laland, 2001; Brown and predator for encounter trials so that each predator was used only Smith, 1998). These differences in behavior can result in decreased once. vulnerability because of decreased conspicuousness (Mesa et al., To ensure that brown trout would exhibit natural predator 1994). behavior, we provided them with experience feeding on live prey The German Rainbow (GR) is a hatchery-derived rainbow trout prior to the study. Each fish was allowed three opportunities to Oncorhynchus mykiss that has developed resistance to Myxobolus eat live fingerling rainbow trout within a five-day period when cerebralis, the parasite responsible for salmonid whirling disease, their normal food, commercial pellets, was withheld. Only brown as a result of decades of exposure to the parasite in a German hatch- trout (n = 16) that