Nippon Suisan Gakkaishi 65 (4), 661-664 (1999)

Decline of Infectivity of Oomycetes in Diluted Seawater to the Larvae of Greasyback Shrimp Metapenaeus ensis

Koichi Izumikawa,*1 Tadashi Oda,*1
Hideo Yamanoi,*1,*2 and Kishio Hatai*3

Haliphthoros milfordensis and Halocrusticida panulirata (Oomycetes, Lagenidiales) isolated from diseased greasyback shrimp larvae, Metapenaeus ensis, were examined in order to determine the ability of zoospore formation and their infectivity to greasyback shrimp larvae in diluted seawater at 25°C. The numbers of zoospores released from both species in 2/3 seawater (salinity between 21.3~21.7‰) were reduced to about 102 zoospores/ml from 104 zoospores/ml in undiluted seawater (salinity between 32.0~32.5‰). Experimental infection by bath method showed that oomycetes killed second zoea (mortality 55%) and second mysis (mortality 5.9%) but not post-larval stages in undiluted seawater. In 3/4 seawater (salinity between 24.4~25.1‰) oomycetes of the two species had low infectivity to the zoea and mysis stages. Judging from these results, it was considered that using diluted seawater at the initial stage of mass producting of greasyback shrimp larvae may be a useful preventive method against mycosis caused by the above species.


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