Fertilization, Meiosis and Cleavage in Eggs from Large Mass Spawnings ofCrassostrea VirginicaGmelin, the Commercial American Oyster

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Abstract
A cytogenetic study was made of over 1600 eggs from 17 mass-spawned groups of 835 wild spawners of the commercial American oyster, Crassostrea virginica. Composition of the several groups varied from all Long Island Sound oysters to two-thirds from other geographic areas, ranging from Prince Edward Island, Canada, to Virginia. The addition of oysters to the spawning groups from outside of Long Island Sound did not have any adverse effects on rate of fertilization, meiosis, cleavage, development to the first larval stage, or metamorphosis to the adult form. Polyspermy though was increased. Abnormalities of fertilization, meiosis, cleavage and heteroploidy occurred in 10 to 86% of the different mass-spawned populations. Evolution must tolerate considerable wastage of eggs and zygotes in a species such as the oyster where a single adult can produce as many as 35 to 65 million eggs. However, this zygotic wastefulness assumes a practical importance now. This is because of the decline of oyster populations due to the activities of man, and because of interest in commercial production of oysters in hatcheries. The eggs and larvae of the oyster must be adversely affected by any number of sea water pollutants which cause abnormalities of meiosis, fertilization and cleavage, and often kill larvae which do develop from genetically normal zygotes. The oyster egg is a good assay cell type for cytogenetically damaging marine contaminants.