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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 1518

Hagiwara Atsushi, Hoshi Nobuyuki, Kawahara Fumiko, Tominaga Kayoko, and Hirayama Kazutsugu; Resting eggs of the marine rotifer Brachionus plicatilis Muller: development, and effect of irradiation on hatching. Hydrobiologia 313/314:223-229, 1995

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Diapause and hatching of Brachionus plicatilis Muller resting eggs were examined through histological and optical approaches. Compound microscope observations on 1% toluidine blue-stained embryo sections suggests that the total number of nuclei in an embryo during the internal diapause period increased from 22 on Day 2 to 39 (each n=1) on Day 6. The outer layer on embryo membrane gradually thickens from 1.2 (Day 0) to 4.0 um (Day 8) (each n=10). Resting eggs that have completed maturation and are in the external diapause period require light for hatching. The threshold of light (halogen lamp) intensity for hatching was estimated to be 4400 lux for 30 min. Hatching rate decreased with longer wavelength irradiation (mercury lamp). Irradiation at more than 350 nm caused 1-25% hatching, but it reached 50-60% at 250-310 nm light. The addition of hydrogen of peroxide or prostaglandis (E1, E2 or F2 alpha) caused resting egg hatching even in darkness. The production of peroxide in seawater caused by light as well as the oxidation of fatty acid to prostaglandins inside the embryo is a possible mechanism of resting egg hatching.