SPEER, T.*; MARTIN, K.: Events at hatching in eggs of the California grunion fish, Leuresthes tenuis

The moment of hatching is a turning point in the life of any animal, but when an egg hatches quickly in response to an environmental trigger, the process is particularly intriguing. California grunion fish spawn terrestrially during semilunar high tides, and eggs incubate in sand for seven to nine days. At the next semilunar tide, the eggs wash from the sand and are catapulted into the ocean. The embryos must hatch almost instantaneously in order to survive the turbulent shift from terrestrial to aquatic life. This study provides a visual description of hatching in grunion. A digital video camera was attached to a dissecting microscope to visualize and record embryo appearance and movement. The videotapes were viewed and analyzed for comparison. Many of the events of the hatching process are consistent between individuals. Agitation of eggs in seawater provides the hatching trigger. Prior to agitation, grunion embryos show minimal movement within the egg. Upon being agitated, the chorion is distorted in a location superior to the caudal region. This distortion appears to be associated with a break in the surface of the chorion, as fluid escapes from this point. Grunion embryos show a significant increase in muscular activity and movement within the egg following agitation. This activity usually culminates in a whole body torsion and tail lash. Ultimately, usually within 5 minutes, the embryo emerges from the chorion and into its new larval aquatic environment. This work was supported in part by NSF DBI-99-87543.