(3D) understanding of their interactions has been hampered by difficulties in sample preparation and lack of technologies for visualizing microstructure and microassociations. We have used cryo-electron microscopy, microfocus computed tomography and synchrotron radiation tomography to investigate the tessellated skeleton down to submicron thicknesses but without damage to the delicate relationships between phases or among tesserae. Our digital tomographic methods are non-invasive and thus provide non- destructive investigations of never before appreciated hard tissue anatomy on any virtual slice plane and in both extant and fossil species. Our data reveal structural features (e.g. canalicular passages linking cells within tesserae, mineralized cross-bridges connecting adjacent tesserae) that are likely important for the growth and mechanics of elasmobranch skeletons. We discuss these and other microanatomical features in the context of models we have generated of tessellated cartilage function and address where these “typical” morphologies are modified, such as high-stress or curved regions of the skeleton. We also highlight our 3D methodologies, which present several compliments and advantages to traditional dissection or chemical preparation of heterogeneous tissues such as tessellated cartilage. Email Address for correspondence: mdean@uci.edu doi:10.1016/j.cbpa.2009.04.019 A1.18 Poster Session — Tuesday 30th June 2009 Does the stress associated with catch-and-release angling of bonefish (Albula vulpes) affect predation by juvenile lemon sharks (Negaprion brevirostris)? Lorna J. Dallas (University of Plymouth), Aaron D. Shultz (Cape Eleuthera Institute), A. John Moody (University of Plymouth), Andy J. Danylchuk (Cape Eleuthera Institute), Katherine A. Sloman (Uni- versity of Plymouth) Predation by juvenile lemon sharks (Negaprion brevirostris) is the main cause of short-term mortality for bonefish (Albula vulpes) following catch-and-release angling. Previous studies suggested that these predators appeared to home in on stressed bonefish using olfaction. This study used a combination of field and laboratory work to investigate the possibility that lemon sharks detect stress chemicals associated with the angling event. To examine the response of predators to these chemicals, the behaviour of juvenile lemon sharks (n =12) held in captivity was quantified when exposed to 30 s pulses of ammonia (500 mM), cortisol (20 μg L -1 ), lactate (6 mM), and urea (3 mM), as well as water from a cooler that had contained bonefish and control tank water. To quantify the release of stress chemicals, wild bonefish (n =7) were angled, fought to exhaustion, and exposed to air for 1 min. Bonefish were then placed in an aerated cooler and water samples were taken at 0,1, 5, 10 and 30 min to be later analysed for ammonia, cortisol, lactate and urea. It was found that bonefish excrete both ammonia and urea during the first 30 min after angling; but cortisol and lactate were below detectable levels. Lemon sharks were significantly more active when exposed to ammonia and urea than when exposed to control water. Combined, these results show that products excreted by bonefish, particularly ammonia and urea, may provide an olfactory cue for the post-release predation of bonefish by lemon sharks during catch-and-release angling events. Email Address for correspondence: lorna.dallas@plymouth.ac.uk doi:10.1016/j.cbpa.2009.04.020 A1.19 Poster Session — Tuesday 30th June 2009 Development of embryonic gill vasculature in the yellow stingray, Urobatis jamaicensis Bethany L. Basten (Nova Southeastern University), Robin L. Sherman (Nova Southeastern University), Alois Lametschwandtner (University of Salzburg), Richard E. Spieler (Nova Southeastern University) As part of a series of studies examining gill vascularization in batoid elasmobranchs, we used corrosion casting to examine the development of gill vasculature in embryonic yellow stingrays, Urobatis jamaicensis (formerly Urolophus jamaicensis). The most marked changes in vascular configuration of the gills occur in the earliest castable stages of gestation. These changes included devel- opment of afferent external gill filament vessels and progression from paired dorsal aortae to a single fused dorsal aorta. Internal gill vasculature was found to nearly match that of an adult by the time the external gill filaments had fully regressed and yolk sac had been exhausted (>47 mm disk width). Examination of embryo casts also revealed characteristics of the branchial vasculature not previously reported in adult specimens. These include the presence of prelamellar sph 2 sphincters, intertrematic branches, afferent dis- tributing arteries which supply blood to many afferent filament arteries, resulting in greater interconnection of the filaments, and observation that the afferent branchial artery in the first hemibranch supplies blood directly to afferent filament arteries on the dorsal half of this arch. The physiological significance of these early structures is not clear. Email Address for correspondence: spielerr@nova.edu doi:10.1016/j.cbpa.2009.04.021 A1.20 Poster Session — Tuesday 30th June 2009 The role of the caudal fin in the common thresher shark, it's not just for swimming Diego Bernal (University of Massachusetts Dartmouth), Scott Aalbers (Pfleger Institute of Environmental Research), Chugey Sepulveda (Pfleger Institute of Environmental Research) The thresher sharks comprise a monophyletic group of pelagic sharks most commonly recognized by their elongate upper lobe of the caudal fin. It has been hypothesized that thresher sharks utilize the elongate fin to stun small-schooling prey while feeding. The bi- functional role of the caudal fin for both thrust production and predation represents a unique adaptation that has not been described for any elasmobranch species. Despite the commercial importance of the thresher sharks, there are no published accounts on how the caudal fin is used during feeding. Field and laboratory studies were conducted to acquire video recordings of feeding common threshers, examine the caudal fin morphology, and investigate the ocular morphology which potentially enables vision in the posterior field. Of the 140 specimens captured 3% were hooked in the mouth while the remainder were hooked in the caudal fin. Video of feeding threshers yielded footage from 25 individual caudal fin-feeding events. Morphological examination of the common thresher caudal fin revealed that the upper lobe is predominantly comprised of tendinous and cartilaginous support tissues. The dissections also revealed the presence of locomotor muscle fibers throughout the entire length of the caudal fin. In general, the caudal fin structural architecture appears to be similar to that of lamnid sharks, but with Abstracts / Comparative Biochemistry and Physiology, Part A 153 (2009) S64–S70 S69