| CONTROL OF HATCHING WITH ENVIRONMENTAL OXYGEN
PRESSURES IN THE WALLEYE, STIZOSTEDION VITREUM Sarah M. Blank and John J. Just, School of Biological Science, University
of Kentucky, Lexington, KY 40506
Abstract. Most aquatic embryos grow inside a
proteinaceous egg case from which they must escape to complete development. Oxygen
consumption increases during embryonic development while surface area for gas exchange
remains constant thus hypoxia may be a natural stimulant for the release of hatching
enzymes. A repeated measures experiment was utilized to examine hypoxia as a stimulant of
hatching. Embryos, 6-20 day post-fertilization (PF), raised at 10-12oC were
exposed to nitrogen (0% O2), air (20% O2), oxygen (100% O2)
and mixture of air and nitrogen (10% O2) and percent hatch was recorded at 10
min. intervals for 90 min. A minimum of four experimental units consisting of 15 embryos
in a 50 ml vial containing 10 ml of pond water were used for each treatment at each
developmental time period. Control embryos first hatch on day 17 PF reaching 5% hatch with
100% hatch occurring on day 21 PF. Hypoxia (10% O2) induced premature hatching
on day 18 PF as the percent hatch of those embryos exposed to environments of 10% oxygen,
20% oxygen, and 100% oxygen was 67%, 54% and 13%, respectively. Percent induced hatching
increased in an age dependent fashion as demonstrated by comparing day 18 PF (above) to
day 19 PF embryos exposed to the same three oxygen environments (10, 20, or 100%)
resulting in 92%, 57% and 23% hatch, respectively. Walleye embryos were sensitive to
anoxia. Exposure of day 18 and 19 post-fertilized embryos to anoxia for 40 min. and 60
min. resulted in 33% and 100% mortality, respectively within 24 hours. Hyperopia (100% O2)
delayed hatching for at least three hours in 18, 19, and 20 day post-fertilized embryos.
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