Fish produce nitrogenous wastes through catabolism of amino
acids (Wood, 1993). The majority of fresh water and marine teleost
fish are ammonioteles and excrete most of their nitrogenous wastes as
ammonia across the gills to the water (Wilkie, 2002). The mechanisms
involved in branchial ammonia excretion remain controversial. In the
most recently proposed model for branchial ammonia excretion,
simple NH3 diffusion down the partial pressure gradient is the
predominant mechanism under normal conditions. At high water
ammonia concentrations, when NH3 diffusion is impaired or even
reversed, several active NH4
+ excretion pathways, involving Rhesus
(Rh) glycoproteins as membrane transporters, facilitate ammonia
efflux (Wright and Wood, 2009).
Fish produce nitrogenous wastes through catabolism of aminoacids (Wood, 1993). The majority of fresh water and marine teleostfish are ammonioteles and excrete most of their nitrogenous wastes asammonia across the gills to the water (Wilkie, 2002). The mechanismsinvolved in branchial ammonia excretion remain controversial. In themost recently proposed model for branchial ammonia excretion,simple NH3 diffusion down the partial pressure gradient is thepredominant mechanism under normal conditions. At high waterammonia concentrations, when NH3 diffusion is impaired or evenreversed, several active NH4+ excretion pathways, involving Rhesus(Rh) glycoproteins as membrane transporters, facilitate ammoniaefflux (Wright and Wood, 2009).
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