In vivo and in vitro initiation of sperm motility using fresh and cryopreserved gametes from the pacific herring, <i>Clupea pallasi</i>

Abstract

Abstract Pacific herring ( Clupea pallasi ) gametes were cryopreserved in a simple extender (15% dimethyl sulfoxide in herring Ringers). Sperm remained viable for over 7 months when kept at liquid nitrogen temperature. A rapid cooling rate by directly plunging into liquid nitrogen allowed a majority of the cells to remain viable after subsequent thawing at 26°C. Cryopreserved sperm initiated motility (activation) under both in vivo (in the micropyle area of the egg) or in vitro (in the presence of isolated sperm motility initiation factor or low sodium seawater) conditions. In addition to their ability to undergo activation, cryopreserved sperm were capable of fertilizing fresh eggs in a concentration dependent manner resulting in &gt; 90% fertilization and embryonic development. Herring eggs cryopreserved in a similar manner as sperm remained intact in gross morphology. Although cryopreserved eggs were not fertilizable, both fresh and previously frozen sperm were activated in the micropyle areas of the chorions. The method we describe to cryopreserve gametes from this species is simple and is useful for future experimental studies of sperm‐chorion interaction when fresh material is unavailable. © Wiley‐Liss, Inc.