58i|e 



WOELKE ON PACIFIC OYSTER EMBRYO BIOASSAY 



115 



a sexually mature, sacrificed male oyster is added to the water. The 

 combination of increased temperature and sperm will induce one or more 

 of the female oysters to spawn. Eggs from a single female are selected 

 for use in the bioassay, and the number of eggs per unit volume are 

 determined by sampling tiie sperm-egg suspension. Glass or plastic 



TABLE 2 — yVastes rcinked and grouped from most toxic to least toxic, based on 

 estimated dilution level which produced 20 per cent abnormal larvae. 



beakers containing the water to be bioassayed are each inoculated with 

 a sufficient amount of the egg suspension to give 20,000 to 30,000 

 fertilized eggs per liter. Approximately 10 per cent of the cultures in a 

 given bioassay are controls. The culture containers are placed in a 20 C 

 water bath for 48 hr. At the end of this time the cultures are poured 

 through a 37 /i sieve to collect the oyster larvae. Samples containing 

 about 150 to 250 larvae taken from each culture are preserved and later 

 examined under a microscope. The number of normal and abnormal 



