AJP - Regulatory, Integrative and Comparative Physiology, Vol 238, Issue 1 36-R41, Copyright © 1980 by American Physiological Society
Water balance in embryos of Fundulus heteroclitus and F. bermudae in seawater
W. B. Guggino
The purpose of this study is to examine the mechanisms of osmoregulation in
embryos of Fundulus heteroclitus and F. bermudae. The turnover rate of
tritiated water in intact embryos of F. heteroclitus increases from 0.05 to
0.013 h-1 at 4 days to 0.12 +/- 0.030 h-1 at 7 days and to 0.18 +/- 0.060
h-1 at 10 days, corresponding to estimated diffusional water permeabilities
of 0.4, 1.0, and 1.6 x 10(-6) cm . s-1, respectively. These values are low
when compared to other organisms but not sufficiently low to maintain
embryos in water balance. The osmolality of the embryonic extracellular
fluids decreases during development from 362 +/- 9.2 mosmol . kg-1 at 4
days to 344 +/- 6.9 mosmol . kg-1 at 10 days. Water loss is balanced by
drinking seawater at a rate of 600 pl . mg-1 . h-1 for 7- to 8-day embryos.
The embryo possesses a pair of branchial chambers that communicate
anteriorly with the pharynx through embryonic gill slits and posteriorly
with the perivitelline space by means of pores. In the absence of a mouth
it is probably through these pores that seawater is injested.
