Two closely related ureotelic fish species of the genus Alcolapia express different levels of ammonium transporters in gills

Lewis J White, Matthew Rose, Michael Lawson, Domino Joyce, Alan M Smith, Gavin H Thomas, Kanchon K Dasmahapatra, Mary E Pownall

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Most fish excrete their nitrogenous waste across the gills as ammonia through the activity of the Rhesus glycoprotein ammonium transporters. In contrast, fish of the subgenus Alcolapia (Oreochromis) are the only vertebrates that survive the extreme conditions of the soda lakes of Natron and Magadi in East Africa and have evolved adaptations to the highly alkaline waters including the ability to excrete their nitrogenous waste as urea. Nevertheless, Alcolapia retain the Rhesus glycoprotein genes in their genomes and using two heterologous expression systems, we demonstrate that Alcolapia Rhbg is capable of moving ammonia. Comparing ammonia and urea excretion from two closely related Alcolapia species from the same aquarium, we found that while Alcolapia grahami remains fully ureotelic after many generations in lab conditions, Alcolapia alcalica excretes some of its nitrogenous waste as ammonia. Using in situ hybridisation, we demonstrate robust, localised gene expression of Rhbg, rhcg1 and rhcg2 in the gill tissue in both A. alcalica embryos and adults, similar to that in other ammoniotelic fish. In contrast, the expression of these genes in A. grahami gills is much lower than in A. alcalica, suggesting the rapid evolution of a molecular mechanism underlying the complete ureotelism of A. grahami.
Original languageEnglish
Article numberbio059575
Number of pages10
JournalBiology Open
Issue number11
Publication statusPublished - 1 Nov 2022

Bibliographical note

© 2022. Published by The Company of Biologists Ltd.


  • Animals
  • Gills/metabolism
  • Ammonia/metabolism
  • Ammonium Compounds/metabolism
  • Fishes/metabolism
  • Membrane Transport Proteins/genetics
  • Urea/metabolism
  • Glycoproteins/genetics

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