California Sea Grant College Program

The effects of an environmental stressor (salinity) and an anthropogenic stressor (creosote-derived compounds) on sperm motility, fertilization and early development were investigated in the Pacific herring. In the laboratory, the optimal salinity for sperm motility initiation in response to an egg-derived factor, sperm motility initiating factor (SMIF), was 16-24 parts per thousand (ppt), while the optimal salinity for both fertilization and development was 12-24 ppt. These salinities are approximately one-half that of full-strength seawater. These laboratory data correlated with the optimal salinity for development (16-20 ppt) for embryos deployed at field sites in San Francisco Bay. The effect of individual cations on fertilization was also assessed. Sodium (Na·) inhibited fertilization at concentrations ≤55 or ≥440 mM. Alterations in calcium or magnesium had no effect on fertilization unless omitted from the medium. A similar effect was seen for potassium (K·), but elevated K. in combination with elevated Na· inhibited fertilization to a greater degree than Na· alone.

To characterize the mechanism for the effects of altered salinity on sperm motility, changes in intracellular ions in response to SMIF or by manipulation of extracellular ions were investigated. SMIF induced a membrane depolarization that was inhibited by increasing either salinity or the Na' concentration. SMIF, and an activator of protein kinase C. induced an increase in intracellular Ca2+ ((Ca2+]i), which along with motility initiation required the presence of extracellular Ca2+ ((Ca2+]o). An efflux of Na· was observed in response to SMIF, or in the absence of SMIF, in low sodium media. again requiring [ca2+]o. Membrane depolarization. increase in [Ca2+]i, and Na· efflux were inhibited by calcium channel and sodium-calcium exchange inhibitors.

Finally, the effects of creosote-derived compounds on development were investigated. Exposed embryos exhibited significant mortality, delay in development, cardiac abnormalities, abnormal movement within the chorion. and edema. Hatching success of exposed embryos was also decreased, and all larvae exhibited severe morphological deforinities (scoliosis, pericardia! and/or yolk-sac edema. Less than optimal salinities (8 and 28 ppt) enhanced the effects of creosote-derived compounds on development.