Since MRC are generally quite large,
proliferation on the lamellae results in the
thickening of the epithelium, and, consequently,
the blood to water diffusion distance is increased
(reviewed by Perry, ’98). This has negative
consequences for gas exchange as blood PO2 and
hypoxia tolerance are reduced in fish with lamellar
MRC proliferation. It should be noted, however,
that ion-poor conditions are not always associated
with the such massive numbers of lamellar MRC
as is evident in the neon tetra (Paracheirodon
innesi), which is native to the ion poor waters of
the Amazon (Wilson et al., ’96).