エビジャコの抱卵数

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書誌事項

タイトル別名
  • エビジャコ ノ ホウランスウ
  • Fecundity of the Sand Shrimp, Crangon affinis

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In relation to the fact that the hatchlings of the sand shrimp, Crangon affinis, have been used for a live food in the rearing experiments of the early larval stage of the several cephalopods in Japan, fecundity expressed as the number of eggs carried on the pleopods was estimated for the shrimp collected from the Omura Bay, western Kyushu. Embryonic development of the shrimp could be classified into five stages by the external appearance. Average weight of the single egg was inquired for each stage. Then, numbers of eggs carried were estimated gravimetrically for the females collected in May and June, 1985. Following three equations were calculated from the relationships between carapace length (CL; in mm) and number of eggs carried (EN): Maximum EN per female: EN=-15459+2084.5CL Average EN per female in May: EN=-7246+1037.5CL Average EN per female in June: EN=-2025+273.1CL It was estimated from the relationships between the total weight of the females and the total EN that 240,000 and 68,000 hatchlings are expected from 100g females in May and June respectively, under the condition that hatching rate is 100 %. In addition, the biological minimum size of the female was estimated to be between 7.0 and 7.4mm CL from the intercepts of the above three equations on the X axis.

大村湾産の長期世代のエビジャコの抱卵数を調べ次の結果を得た。1. 卵発生は外観から5段階に分け得る。2. 卵は発生が進むにつれて重量を増す。発生初期の卵重量は平均29.4μgで変異が大きいが,終期のそれは44.7μgで変異が小さい。3. 重量法による推定と実数計数とを併用して抱卵数を求め,CLと,最大卵数・5月の平均卵数・6月の平均卵数との3つの関係式を得た。4. 上記の3式のX軸切片から,雌の生物学的最小形はCL7.0-7.4mm (BL34.8-36.5mm)と推定された。5. 総体重と総卵数の関係から,100gの雌親から期待できる孵化稚仔数は,5月では約240,000,6月では約68,000と推定された。

長崎大学水産学部研究報告, v.61, pp.1-5; 1987

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