Changes in ion content and transport during development of embryonic rainbow trout

K.J. Barrett, D.G. McDonald, M.J. O'Donnell-2001

Journal of Fish Biology, 59(5): 1323-1335

Abstract:

Wet mass and water content of four lots of whole eggs did not change throughout embryonic development of rainbow trout Oncorhynchus mykiss. Eggs in all four lots accumulated Na⁺. Eggs in lots 2 and 4 also accumulated Ca²⁺and Cl^-, whereas eggs in lot 1 showed no significant change in Ca²⁺or Cl^-, and eggs in lot 3 showed no change in Cl^-and a small loss of Ca²⁺. Although the Na⁺content of embryonic tissues increases in the later stages of development, the yolk sac content remained constant, indicating uptake of Na⁺from the environment. Na⁺uptake by whole eggs was non-saturable, consistent with diffusion of Na⁺across the chorion into the perivitelline fluid. Na⁺uptake in dechorionated embryos was saturable, as was Ca²⁺uptake by both whole eggs and dechorionated embryos, consistent with active uptake or facilitated diffusion mechanisms at the surface of embryos. Very low Ca²⁺uptake rates in dechorionated embryos suggest that the Ca²⁺uptake mechanism is not fully developed until after hatching.

(Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada, L8S 4K1, Tel.: +1 905 525 9140; fax: +1 905 522 6066; email of D.G. McDonald: mcdonald@mcmaster.ca)

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