Short communication Physiological responses of cobia Rachycentron canadum following exposure to low water and air exposure stress challenges J. Trushenski a, ⁎, M. Schwarz b , R. Takeuchi c , B. Delbos b , L.A. Sampaio d a Fisheries and Illinois Aquaculture Center, Southern Illinois University Carbondale, Carbondale, IL 62901, USA b Virginia Seafood Agricultural Research and Extension Center, Virginia Tech, Hampton, VA 23669, USA c International Initiative for Sustainable and Biosecure Aquafarming, Norfolk, VA 23503, USA d Marine Fish Culture Laboratory, Institute of Oceanography, Federal University of Rio Grande, Rio Grande, RS, 96201-900, Brazil abstract article info Article history: Received 17 March 2010 Received in revised form 14 June 2010 Accepted 13 July 2010 Keywords: Rachycentron Cortisol Stress Low water challenge Air exposure Prevention is the most viable disease management strategy in aquaculture, and prevention is primarily driven by strategies to avoid or minimize the effects of stress. Unfortunately, there is little information available regarding the stress physiology of emerging aquaculture species or appropriate experimental stressing protocols for these fishes, and thus very little context in which to evaluate mitigation strategies. Accordingly, the stress response of cobia was evaluated following exposure to 2 experimental stressors: low water and air exposure. Juveniles were exposed to air for 1 min (AIR EXPOSURE), held for 15 min in water lowered to the fish's lateral midline (LOW WATER), or unchallenged (CONTROL) prior to the collection of blood samples at 0 (pre-challenge), 0.5, 1, 2, 6, 12, 24, 48, and 72 h post-challenge. Both stressors elicited classical haematological changes indicative of the generalized stress response, however, the magnitude of the response was consistently greater in the AIR EXPOSURE group. Plasma cortisol, glucose, and lactate concentrations increased rapidly in the AIR EXPOSURE and LOW WATER groups, peaking within 1 h of challenge. Cortisol returned to basal levels rapidly, whereas glucose and lactate remained elevated for a longer period of time. Regardless of the stressor used, fish recovered within 12 h of the challenge. The primary and secondary responses of juvenile cobia challenged with low water and air exposure appear to respond in a similar fashion to other species exposed to these experimental stressors. Both low water and air exposure are suitable experimental stressors for use in cobia based on their ability to induce a classical stress response and ease of implementation. Published by Elsevier B.V. 1. Introduction Stress is inherent in all forms of livestock production, with aqua- culture being no exception. With industry trends consistently maximizing animal densities and production levels, animal stress levels are also increased. The effects of stress in animal production are varied, however, reduced survival and impaired growth rate, feed conversion efficiency, and immune status are commonly associated with chronic stressor exposure. The challenge in aquaculture is to develop strategies that minimize animal stress, while maximizing animal production, performance and welfare. In order to evaluate stress mitigation strategies, reliable stress challenge protocols must be established to allow for standardized experimentation. Cobia Rachycentron canadum L. is an emerging species for aquaculture (Liao and Leaño, 2007). In 2009, roughly 30,000 MT were produced worldwide (M. Schwarz, personal communication). Most cobia farms are in Asia, but culture activities are expanding in the Americas and Middle East in both open-water and land-based rearing systems. Cobia are well-suited to intensive culture because they are comparatively easy to spawn, rear (Arnold et al., 2002; Benetti et al., 2008), and feed train (Holt et al., 2007). Additionally, cobia exhibit rapid growth rates (Chou et al., 2001; Liao et al., 2004), efficient feed conversion, and desirable fillet characteristics, which make them ideal for food fish production (Shiau, 2007). However, cobia fingerlings appear to be quite sensitive to transport and handling stress, and may also be affected by chronic stressors associated with high-density culture in recirculating aquaculture systems (Schwarz et al., 2007) or cages (Benetti et al., 2008). Stress- related infections and infestations of Pasteurella, Vibrio, Amyloodinium, and Benedenia spp. are common (Chen et al., 2001; Lopez et al., 2002; Chi et al., 2003). Treatment options for cobia are severely restricted by practical and logistical constraints (cobia may be cultured in large cage systems in coastal or open ocean waters) and the limited number of therapeutants approved for food fish. Thus prevention is the most viable disease management strategy for cobia culture, and prevention is primarily driven by strategies to avoid stressor exposure or minimize Aquaculture 307 (2010) 173–177 ⁎ Corresponding author. E-mail address: saluski@siu.edu (J. Trushenski). 0044-8486/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.aquaculture.2010.07.015 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online