juvenile striped bass {Morone saxatilis). J. Fish. Res. 

 Board Can. 32:1864-1866. 

 Pachares, J. 



1959. Table of the upper 10% points of the studentized 

 range. Biometrika 46:461-466. 

 Parr Instrument Co. 



1969. Instructions for D41 and D42 adiabatic calorimeters. 

 Man. 142. Parr Instrum. Co., 211 53d St., Moline, 111., 23 p. 



Sid Korn 



Southwest Fisheries Center Tiburon Laboratory 



National Marine Fisheries Service, NOAA 



Tiburon, Calif. 



Present address: 



North west Fisheries Center Auke Bay Fisheries 



Laboratory, NMFS, NOAA 



P.O. Box 155, Auke Bay, AK 99821 



Jeannette W. Struhsaker 

 Pete Benville, Jr. 



Southwest Fisheries Center Tiburon Laboratory 

 National Marine Fisheries Service, NOAA 

 3150 Paridise Drive 

 Tiburon, CA 91920 



Marine Science Center (MSC) at Newport, exposed 

 to ultraviolet light (3.785 liters/min), diluted 

 (when necessary) to 25"/uo with distilled water, and 

 stored in Nalgene carboys. This salinity is within 

 the range recommended for C. virginica by Davis 

 and Calabrese (1964), and was used for mainte- 

 nance of oysters and for experiments on fertiliza- 

 tion and early larval development. In laboratory 

 procedures, all glassware was initially acid- 

 washed; used glassware was carefully cleaned and 

 rinsed several times first in tap water and then in 

 distilled water; all polyethylene tubing was 

 Tygon^ R3606 (nontoxic by bioassay, Breese, MSC, 

 unpubl. data); gametes and larvae were confined in 

 glass containers only (except for momentary 

 exposure to stainless steel syringe needles and 

 nylon screen); all seawater used in fertilization 

 experiments was Millipore-filtered (0.47 jum) and 

 stored in glass screw-cap bottles with Parafilm- 

 lined caps (nontoxic by bioassay, Breese unpubl. 

 data). 



FERTILIZATION METHOD QUANTIFYING 



GAMETE CONCENTRATIONS AND 



MAXIMIZING LARVAE PRODUCTION 



IN CRASSOSTREA GIG AS 



Most workers obtain oyster larvae by using ex- 

 perimental methods similar to those reported by 

 Galtsoff" (1964). Although useful in most hatchery 

 or laboratory investigations, these methods do not 

 quantify gamete concentrations. To obtain 

 specific larval concentrations, most researchers 

 dilute dense postfertilization concentrations. 



This paper reports on a method of estimating 

 sperm concentrations of Pacific oyster, Crassos- 

 trea gigas, using colorimetric techniques, and on a 

 method of fertilization using small volumes of 

 seawater and known gamete concentrations. We 

 also present an index which may be useful in 

 evaluating the efficiency of fertilization. These 

 methods were developed during 1973 and should 

 prove useful in the study and production of cul- 

 tured oysters. 



Materials and Methods 



Pacific oysters were obtained from Fowler Oys- 

 ter Co. on Yaquina Bay, Newport, Oreg. Sand- 

 filtered seawater of 25-32"/(ki salinity and pH 7.0-8.1 

 was collected at the Oregon State University 



Procurement of Gametes 



To enhance gonad development, we conditioned 

 mature oysters in seawater at 16.0° ± 1.0° C for 3-6 

 wk (Loosanoff and Davis 1963). To identify test 

 oysters, we drilled a 0.8-mm (1/32-inch) hole in the 

 umbo and attached a 6.4- x 15.9-mm numbered 

 plastic tag (Howitt Plastics Co., Mollala, Oreg.) 

 with monofilament. After conditioning, access to 

 the gonads was made by drilling a 1.2-mm 

 (3/64-inch) hole in the posterodorsal region of the 

 right valve. We extracted gametes with a 2.5-cm^ 

 glass syringe fitted with a 20-gauge 38-mm needle 

 containing about 0.5 ml of seawater (Lannan 

 1971). Oysters containing either intensively motile 

 sperm or eggs greater than or equal to 36 jum were 

 kept for fertilization experiments. To prevent 

 spawning after extractions, we isolated individual 

 oysters for 12-24 h in 3-liter beakers containing 

 seawater at 12°C. 



Prior to gamete extraction we raised the tem- 

 perature of all donor oysters to 27.0° ± 0.5°C, a 

 temperature within the range recommended by 

 Davis and Calabrese (1964) for fertilization and 

 larval development. Oysters were transferred 

 from the conditioning tray to an 18.9-liter 

 (5-gallon) tank containing 11.4 liters (3 gallons) of 

 seawater at 16.0° ± 1.0°C; a 100-W aquarium heater 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



698 



