Osmolarity Problem in Western Gulls

   I was studying the osmolarity problem of sea gulls. How do these beautiful animals maintain a constant level of sodium chloride in their bodies ? They must live in and drink sea water to survive. How do they get rid of the extra salt so their cells do not swell and burst ? And how does this compare with the same osmolarity problem in salmon which swim from fresh water into salt water and then back into fresh water during their life cycle.

   According to Macfarland, Martin and Freedman¹ in the Journal of Cellular and Comparative Physiology, Western Gulls (Larus occidentalis) use various enzymes in its beak to secrete salt through the avian nasal salt gland. The salt gland is stimulated to secrete its highly concentrated fluid (700–800 mm Na) by enzymes which cause a nerve reflex in the back part of the eye. The tears from both eyes then mix in the nasal septum. The excessive NaCl excretes from these orifices on the beak of the gull.

Monterey Gull

   In this photograph of gull's head, you can see the small dimpled orifice on the upper side portion of its beak. That is the avian nasal salt gland. When it discharges saline waste, it looks like the gull is weeping or has sinus problems.

   According to Mark Briffa², a marine biologist at the University of Plymouth, the Atlantic Salmon (Salmo salar) does the same osmolarity trick using different means. The surface cells of the gills secrete the salt. As the salmon enters the sea, there is an involuntary change in the cellular structure of the gills which enables them to start secreting salts. This is not strange, in that all marine fish must do. The salmon's trick is that he turns it on in salt water and turns it off in fresh.

Atlantic Salmon

Robert

photos courtesy of jurvetson, pnicklen

¹McFarland, L. Z., Martin, K. D. and Freedland, R. A. (1965), The activity of selected soluble enzymes in the avian nasal salt gland. Journal of Cellular and Comparative Physiology, 65: 237–241. doi: 10.1002/jcp.1030650210

²Mark Briffa, forum administrator,
http://www.thenakedscientists.com/