sperm counted is linear (r = 0.996) from about K 

 = 10 to about K = 80 (Figure 1). Because this 

 method of estimation is sufficiently precise and 

 accurate and because attempts to minimize go- 

 nadal debris (and thus minimize a variable in 

 colorimetric evaluation) by gravity filtration or 

 centrifugation usually resulted in broken tails and 

 agglutination, respectively, we consider our 

 methods of sperm procurement and estimation 

 useful. Measuring light diffusion through a sample 

 of C. gigas eggs did not accurately estimate egg 

 numbers because they settled rapidly. 



We estimate that about one-half the number of 

 sperm counted had little or no observable motility; 

 we may have withdrawn immature sperm or 

 damaged mature sperm during extraction. Inac- 

 tive sperm were not agglutinated, an indication 

 that the acrosome reaction was not the major 

 cause of immotility. Although not directly equat- 

 ing fertilization capacity with high motility, our 

 assumption is that relatively immotile sperm are 

 incapable of fertilizing viable eggs. Similarly, 

 extractions from females often included small and 

 presumably immature eggs (Galtsoff 1964). Sperm 

 concentrations reported in Figure 1 and Tables 1 

 and 2 are observed values and do not reflect 

 estimates of immotile cells; only "mature-sized" 

 eggs were used because eggs less than 36 /xm were 

 rinsed through the cleaning screen. 



Within the limits of this investigation, mean 

 percent fertilization (%Zj:) increased as the. 

 number of sperm/ 100 eggs increased (Table 1). 

 The mean percent of larvae developing to the 

 D-shape stage {%I)j) increased until 7.3 x 10^ 

 sperm were used; %Dj: decreased with further 

 increases of sperm concentration (Table 1). 

 Because Glatsoff (1964) reported that high sperm 

 concentrations may result in polyspermy and 

 because in our experiments resulting in large 



I- 40 



» = 0.7 » ia.3(«) 

 r = 0.996 



15 2.0 2.5 3 



NUMBER OF SPERM /ml « lO' 



Figure 1. -Correlation between mean (A^ = 5) number of 

 Crassostrea gigas sperm and Klett units (light diffusion read- 

 ings) on a Klett-Summe.rson colorimeter. 



losses of larvae (Lf [where Lj = ?cZ^ minus %Dj]) 

 aberrant forms were observed (e.g., swimming 

 chains of cells, and trochophores persisting beyond 

 48 h), we assume polyspermy was responsible for 

 the increasing L^. 



Using 7.3 X 10-^ sperm/100 eggs, we observed 

 that %Zj increased as flodding time increased 

 (Table 2). Lf also increased as flooding time in- 

 creased, and maximum %Dj was obtained using a 

 flooding time of 5 min. 



Although most workers need only to maximize 

 %'Djr without regard to L?, some investigators may 

 need to minimize L? due to limited spawning stock 

 or other problems. Thus, to achieve maximum 

 efficiency it is necessary to maximize %!)? and 

 minimize L/. Under different conditions (e.g., 

 water quality and gamete viability may differ at 

 different locations or at different times), the 

 optimal sperm concentration and flooding time 

 will vary in response to the environment. In- 

 creases in ^Djr (by increasing sperm concentra- 

 tion or flooding time) also produce undesirable 

 increases in L^, thus a subjective decision usually 

 is made to evaluate the efficiency of fertilization 

 and larvae production. To reduce the subjectivity 

 of this evaluation, we suggest the following for- 

 mula reflects a compatability between maximum 

 %Dj and minimum L^: 



(%T) )' 

 Compatability index (CI) ===== x 10-^. 



/L; (%Zj) 

 In our lab, values greater than or equal to 1 were 

 desirable, and 1.16 was the maximim value ob- 

 tained (Table 1). CI values can be high for rela- 

 tively low %Dj: if L? is unusually low (e.g., where 

 %Zj = 30, and %Dj = 28, CI = 1.01). Low L, values 

 will normally be associated with low XD? ; however, 

 if a low Lj: occurs concommittantly with a "rea- 

 sonable" %l)j, we assume that the evaluation 

 would be based more on the desired %Dj rather 

 than on CI. Further, due to the often dramatic 

 differences in conditions at different labs and 

 hatcheries, or at different times, attempts to 

 establish a desirable CI value or range under 

 specified conditions may prove useful. 



During a 4- to 6-wk period we made 8-12 ex- 

 tractions from individual oysters, but did not 

 observe a deterioration of gametes. Data from 

 experiments using gametes from initial extrac- 

 tions were consistent with those of later extrac- 

 tions. The pooling of extractions may have reduced 

 observable changes. After about 8 wk, eggs were 

 easily broken and we noticed free yolk in extrac- 



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