A brief history of the study of fish osmoregulation: the central role of the Mt. Desert Island Biological Laboratory

Abstract

The Mt. Desert Island Biological Laboratory (MDIBL) has played a central role in the study of fish osmoregulation for the past 80 years. In particular, scientists at the MDIBL have made significant discoveries in the basic pattern of fish osmoregulation, the function of aglomerular kidneys and proximal tubular secretion, the roles of NaCl cotransporters in intestinal uptake and gill and rectal gland secretion, the role of the shark rectal gland in osmoregulation, the mechanisms of salt secretion by the teleost fish gill epithelium, and the evolution of the ionic uptake mechanisms in fish gills. This short review presents the history of these discoveries and their relationships to the study of epithelial transport in general.

Keywords: epithelial transport; fish osmoregulation; gill; kidney.

Figure 1

Basic pattern of marine teleost osmoregulation. To offset the osmotic loss of water across the gill epithelium, the fish ingests seawater and absorbs NaCl and water across the esophageal and intestinal epithelium. Urinary water loss is kept to a minimum by production of a low volume of urine that is isotonic to the plasma, but contains higher concentrations of divalent ions than the plasma. Excess NaCl is excreted across the gill epithelium. Redrawn from Evans (2008).

Figure 2

Working model for NaCl uptake and bicarbonate secretion by the fish intestine. Three intestinal cells, with connecting tight junctions are shown. See text, as well as recent reviews (Grosell, ; Marshall and Grosell, ; Grosell et al., 2009) for details.

Figure 3

Working model for NaCl secretion by the shark rectal gland and marine teleost gill epithelium. Three epithelial cells, with connecting tight junctions are shown. See text for details.

Figure 4

Working model for NaCl uptake and acid/base or ammonia secretion by the teleost gill epithelium. Two epithelial cells, with connecting tight junctions are shown. The distribution of the transport proteins in specific cells may vary with fish species. See text and Evans (2010) for details.