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Hatching Events in the California Grunion, Leuresthes tenuis
Tara M. Speer-Blank and Karen L. M. Martin
Vol. 2004, No. 1 (Feb. 9, 2004), pp. 21-27
Stable URL: http://www.jstor.org/stable/1448633
Page Count: 7
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This study provides the first detailed description of the events at hatching for an anamniotic vertebrate egg. California Grunion are ideally suited for this study, because these fish eggs incubate fully terrestrially and delay hatching until presented with an environmental trigger. Grunion eggs can be induced to hatch on demand within a few minutes, by mechanical agitation in seawater. We suggest that the process of hatching in grunion involves an enzymatic weakening of the chorion followed by the embryo's active efforts to escape. Using a dissecting microscope, microscope camera, and digital video camera, we compared embryonic movements within the chorion prior to hatching. Then, we recorded the exact moment of hatching with digital video to identify events that occur consistently. Prior to exposure to the hatching trigger, Grunion embryos move minimally within the egg. After the hatching trigger, embryos significantly increase the amount and types of movements within the egg. The chorion distorts in a location superior to the caudal region, and fluid escapes from the egg. Embryonic activity usually culminates in a vigorous tail lash that splits the chorion open. Ultimately, usually within two minutes, the Grunion larva emerges from the chorion into its new aquatic environment.