View article

This study examined the osmoregulatory status of the euryhaline elasmobranch Carcharhinus leucas acclimated to freshwater (FW) and seawater (SW). Juvenile C. leucas captured in FW (3 mOsm l⁻¹ kg⁻¹) were acclimated to SW (980–1,000 mOsm l⁻¹ kg⁻¹) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l⁻¹ kg⁻¹. In SW, bull sharks had significantly higher plasma osmolarities (940 mOsm l⁻¹ kg⁻¹) than FW-acclimated animals and were slightly hypo-osmotic to the environment. Plasma Na⁺, Cl⁻, K⁺, Mg²⁺, Ca²⁺, urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and …