Osmoregulation by juvenile brown-banded bamboo sharks in hypo- and hyper-saline waters
Published online on 11. April 2015
Osmoregulation by juvenile brown-banded bamboo sharks, Chiloscyllium punctatum, in hypo- and hyper-saline waters
R.L. Cramp, M.J. Hansen, C.E. Franklin
While there is a considerable body of work describing osmoregulation by elasmobranchs in brackish and saltwater, far fewer studies have investigated osmoregulation in hypersaline waters. We examined osmo- and ionoregulatory function and plasticity in juvenile brown-banded bamboo sharks, Chiloscyllium punctatum, exposed to three experimental salinities (25, 34 and 40‰) for two weeks. C. punctatum inhabits sheltered coastal areas and bays which can naturally become hypersaline as a consequence of evaporation of water but can also become hyposaline during flood events. We hypothesised that C. punctatum would demonstrate a phenotypically plastic osmoregulatory physiology. Plasma osmolality, urea, Na+ and Cl− levels increased significantly with increasing environmental salinity. Rectal gland and branchial sodium–potassium ATPase (NKA) activities were unaffected by salinity. Using immunohistochemistry and Western Blotting we found evidence for the presence of the key ion-regulatory proteins vacuolar H+-ATPase (VHA), pendrin (Cl−/HCO3− co-transporter) and the Na+–H+ exchanger isoform 3 (NHE3) in discrete cells within the branchial epithelia. These results indicate that C. punctatum is a partially euryhaline elasmobranch able to maintain osmo- and ionoregulatory function between environmental salinities of 25‰ and 40‰. As suggested for other elasmobranchs, the gills of C. punctatum likely play a limited role in maintaining Na+ homeostasis over the salinity range studied, but may play an important role in acid–base balance.
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology
Volume 185, July 2015, Pages 107–114