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Dry mass of yolked oocytes of the southwest african pilchard sardinops ocellata in relation to maturity stages and spawning cycles



Dry mass of yolked oocytes of the southwest african pilchard sardinops ocellata in relation to maturity stages and spawning cycles



South Africa Sea Fisheries Branch Investigational Report (119): 1-29



In the pilchard S. ocellata mean oocyte dry mass was determined for 737 females in all stages of ovarian development. The fish were collected from June 1972-Oct. 1974 off the South West African coast, mainly between Palgrave Point and Walvis Bay. The oocyte dry mass reached an asymptote by the time last-mode yolked oocytes (the most advanced mode) were 0.09 mm3 in volume. Mean oocyte mass was 39.8 .mu.g for fish with oocyte volumes greater than 0.09 mm3. The monthly oocyte masses were combined into 2 spawning cycles within each spawning season: winter-spring (June-Oct.) and summer-autumn (Nov.-March). The average oocyte mass of winter-spring was higher (44.2 .mu.g) than the overall mean and that of summer-autumn was lower (36.7 .mu.g). The oocyte mass of the months within each spawning cycle did not differ significantly except in summer 1972-1973. There were significant differences in oocyte dry mass between corresponding spawning cycles. No relation was found between oocyte dry mass and the length, mass, age or condition index of the fish. A slight difference in oocyte dry mass suggested that the intermediate-mode oocytes of 1 spawning cycle may be the early active oocytes of the next spawning cycle. Both the density index and the oocyte volume of intermediate-mode oocytes were less in March 1973 than in Jan. 1973 and June-Sept. 1972. At the end of the spawning season intermediate-mode oocytes might be more easily rejuvenated into yolkless reserve-stock oocytes. The possible effects of temperature on seasonal and annual differences in oocyte dry mass are discussed.

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Accession: 005197524

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