Do river sharks (genus Glyphis) have reduced rectal glands for salt removal?
I contacted Richard Pillans, the primary author of the article linked to in the question. He told me that he did not know whether the rectal gland was reduced. Researchers are hesitant to capture and dissect the freshwater sharks because of their endangered status.  

He did tell me that they have gathered much more data on the movement of the sharks since the 2009 paper was published.  Apparently, river shark is a bit misleading (my words, not Dr. Pillans). Glyphis does occur in freshwater (no salt) but tends to be found in the middle range of brackish water. Brackish water is considered to be anything that is not purely freshwater nor purely salt water, with typical values between 0.5 and 30 parts per thousand (ppt). Freshwater is 0 ppt and open ocean salt water is 35 ppt, the equivalent of 35 grams of salt in one liter of water. 

If Glyphis is found primarily in the mid-range of brackish water, then I would expect the rectal gland not show signs of reduction. Pillans and Franklin (2004) showed that rectal gland mass of brackish water bullsharks (Carcharhinus leucas) in Australia did not differ significantly from either freshwater or saltwater individuals.  So, pending further evidence, I would conclude that Glyphis, which in the same family as bull sharks, probably does not show rectal gland reduction.


  Pillans, R.D. and C.E. Franklin, 2004.  Plasma osmolyte concentrations and rectal gland mass of bull sharks Carcharhinus leucas, captured along a salinity gradient.  Comparative Biochemistry and Physiology, Part A 138: 363-371.