Meeting Abstract
The California grunion is an unusual fish because adults spawn on beaches during spring high tides and embryos develop within the sand until triggered to hatch by wave action during a subsequent spring high tide. Because hatching occurs quickly and the chorion is strong to protect the embryo within the sand, specializations for rapid chorion breakdown are expected in this species. Cells located laterally along the body are observed in embryos within, or after manual removal from, the chorion, but not after embryos are stimulated to hatch. It has been proposed that these cells contain the chorionase enzyme(s) required for hatching. This study characterized the density, distribution, and development of the putative chorionase-containing cells in California grunion embryos. Grunion gametes were stripped from adults collected while spawning in summer 2013 and 2014, fertilized, and maintained in laboratory incubators set at 20oC. Embryos and hatched larvae were examined by light and electron microscopy. Putative chorionase-containing cells appeared as early as five days post-fertilization (dpf). Cell density did not change significantly from 5 dpf to 12 dpf. The cells, within the one-cell-thick outer epithelium, are filled with protein and can release their contents into the space between the embryo and chorion. The cells are in a distinct pattern along the length of the embryo, starting anterior-dorsally near the head and continuing down the length of the body at the lateral midline. Assuming they contain chorionase, the placement of these cells at high densities along most of the body and rapid release of their contents would facilitate rapid chorion digestion and hatching.
