Physiological responses to hypersalinity correspond to nursery ground usage in two inshore shark species (Mustelus antarcticus & Galeorhinus galeus)

Abstract

Shark nurseries are susceptible to environmental fluctuations in salinity because of their shallow, coastal nature; however, the physiological impacts on resident elasmobranchs are largely unknown. Gummy sharks (Mustelus antarcticus) and school sharks (Galeorhinus galeus) use the same Tasmanian estuary as a nursery ground; however, each species has distinct distribution patterns that are coincident with changes in local environmental conditions, such as increases in salinity. We hypothesized that these differences were directly related to differential physiological tolerances to high salinity. To test this hypothesis, we exposed wild, juvenile school and gummy sharks to an environmentally relevant hypersaline (120% SW) event for 48 h. Metabolic rate decreased 20-35% in both species, and gill Na + /K + -ATPase activity was maintained in gummy sharks but decreased 37% in school sharks. We measured plasma ions (Na + , K + , Cl − ) and osmolytes [urea and trimethylamine oxide (TMAO)], and observed a 33% increase in plasma Na + in gummy sharks with hyperosmotic exposure, while school sharks displayed a typical ureosmotic increase in plasma urea (∼20%). With elevated salinity, gill TMAO concentration increased by 42% in school sharks and by 30% in gummy sharks. Indicators of cellular stress (heat shock proteins HSP70, 90 and 110, and ubiquitin) significantly increased in gill and white muscle in both a species-and a tissue-specific manner. Overall, gummy sharks exhibited greater osmotic perturbation and ionic dysregulation and a larger cellular stress response compared with school sharks. Our findings provide physiological correlates to the observed distribution and movement of these shark species in their critical nursery grounds.

Diel cycling hypoxia enhances hypoxia-tolerance in rainbow trout (Oncorhynchus mykiss): evidence of physiological and metabolic plasticity

“…Hematocrit levels were determined by measuring the height of packed erythrocyte versus that of total blood [(height of packed red blood cells/total blood height)×100%] following centrifugation in micro-hematocrit capillary tubes. Mean corpuscular hemoglobin concentration (MCHC) was calculated as described in Tunnah et al (2016a). Plasma cortisol levels were measured by ELISA according to the manufacturer's instructions (Neogen Corp., KY, USA).…”

Pass the salt: physiological consequences of ecologically relevant hyposmotic exposure in juvenile gummy sharks (Mustelus antarcticus) and school sharks (Galeorhinus galeus)

“…We did not observe significant effects of time or sampling; thus, control data are not presented here. These control animals were also used in a companion study ( Tunnah et al ., 2016 ).…”

“…The concentrations of HSP70 and HSP90 (in nanograms per microgram of total protein) were determined using immunoblotting. Samples were prepared according to Tunnah et al . (2016 ) and compared with a commercially available standard (recombinant rat HSP70/72, SPP 758; human native HSP90, SPP770; Enzo Life Sciences) to quantify the specific HSP in each sample.…”

“…Plasma, gill and white muscle urea concentration (in millimoles per litre) were analysed on perchloric acid-extracted samples using the method of Rahmatullah and Boyde (1980) in quartz cuvettes using a Spectronic Unicam UV1 (Thermo Fisher Scientific, Waltham, MA, USA). Plasma, gill and white muscle TMAO concentrations were determined with liquid chromatography–mass spectrometry (LC-MS) as described by Tunnah et al . (2016) .…”

“…Routine metabolic rate was measured in separate groups of school sharks (~450 g) and gummy sharks (~750 g) in control and hyposmotic environments in a similar manner to Tunnah et al . (2016) using a Fibox O 2 probe (PreSens Fibox).…”