Effect of Propodus Excision on Growth and Survival in Giant Freshwater Prawn Macrobrachium rosenbergii

一般に甲殻類の飼育実験において共食いの発生は実験結果に重大な影響を及ぼし、共食いの防止が実験結果の信頼性を高めるので、本研究では体長6～7cmのオニテナガエビに、脱皮による再生の緩慢な鋏脚先端(掌部)の切除を行って60日間飼育し、成長、生残率、産卵に及ぼす影響を調べた。無処置のエビの60日間の生残率は共食いにより25%と著しく低かったが、鋏脚先端を切除した場合の生残率は92%であった。生残個体の平均サイズは無処置エビが鋏脚先端切除エビより優ったが、全成長量では著しく劣った。鋏脚先端を切除した雌エビの1尾当たりの産卵回数は1.83回であったが、無処置エビでは0.17回であった。以上のことから、鋏脚先端の切除はオニテナガエビの高密度飼育における共食いを防止し、生残率の向上に極めて有効であった。

Cannibalism often obscures the analysis of results of rearing experiments on nutritional requirement in prawn. The present study carried out in order to prevent cannibalism in high density culture of prawn under laboratory condition. Giant freshwater prawn, Macrobrachium rosenbergii, with a body length of 6-7 cm were reared for 60 days, The prawns that were excised the tip of propodus of both chelae (fixed finger) were compared with untreated group in terms of growth, survival, and spawning. In the excision of propodus, fixed finger could not be regenerated easily after consecutive molts rather than dactylus. The survival of the excised group was 92%, while that of untreated group was only 25%. Because of the mortality due to cannibalism, total production was impaired in the untreated group. The female of the excised group spawned a total of 11 times (1.83 spawnings/female), while the spawning rate of the unexcised group was 0.17/female. Thus it was concluded that the cannibalism can be markedly reduced by excision of the tip of propodus without spoilage of growth, molt, and spawning.