The polyopisthocotylan responsible for anemia in the Japanese anchovy Engraulis japonicus has not previously been identified. In this study, specimens collected from both healthy wild Japanese anchovies and anemic cultured fish raised from eggs were identified as Pseudanthocotyloides mamaevi (Polyopisthocotyla: Mazocraeidae). This represents the first record of this species in Japan and provides a redescription accompanied by molecular data. Although P. mamaevi exhibits relatively high pathogenicity to Japanese anchovy, disease outbreaks have not been reported in aquaculture operations that use wild-caught larvae. This study therefore constitutes the first report of disease caused by this polyopisthocotylan in Japanese anchovy aquaculture.

The development of first to third stage larvae of Philometroides seriolae, the type species of the genus, was monitored. Hatched larvae were obtained from gravid females collected from Japanese amberjack Seriola quinqueradiata. The larvae in the uterus consisted of the first stage (18.4%) and second stage (81.6%). Larvae obtained from the uteri were exposed to the harpacticoid copepod Tigriopus japonicus, employed as a surrogate intermediate host. Infected copepods were maintained at 20°C and at 25°C for 28 days, during which larvae in the hemocoel were periodically examined. All larvae had developed into second stage by 5 days post exposure (5 dpe). Third stage larvae first appeared at 13 dpe at 20°C and at 8 dpe at 25°C. First to third stage larvae possessed two unicellular oesophageal glands located in the posterior region of the oesophagus. The second stage larvae possess single papilla-like projections at the surface of cephalic region and the caudal end. In the third stage larvae, these projections were liberated from the surface with peeling of the second stage sheath. This study provides the first description of the second and third stage larvae of P. seriolae and documents their experimental development in a copepod host.

ブリのレンサ球菌症ワクチンの追加接種に関するアンケートをブリ主産県に対して実施した。4県10業者30ロットを解析し，接種回数は1～3回，このうち接種回数が2回以上の追加接種は7業者22ロットで確認された。春種苗のワクチン接種時期は，種苗導入後に間をあけず夏までに2回のワクチン接種を完了させる連続接種と，導入直後に1回目を接種し冬から翌春の間に追加接種する越年接種に分けられた。越年接種では，1回目と2回目の接種の間に本疾病が発生すること，追加接種時の魚体重が用法外まで大型化し誤注射の危険性が高まることが確認された。それゆえ，接種時期は本疾病の発生が確認されず，魚体重が用法範囲内に収まる連続接種が推奨される。養殖業者の主観的な効果の判定では，追加接種を実施した約9割のロットで有効と回答された。本疾病発生時の投薬回数および累積死亡率は単回接種群と比べ追加接種群が低かった。これらの結果は，本疾病の予防を目的とした追加接種の有効性を示唆している。