著者らが分離してきたV.anguillarum 31株(PSh-3を除く)の性状をまとめてみたところ,海水株,淡水株別にみるとmethyl red, galactose,塩分耐性の点に多少違いはみられたが,他の多くの点で一致しており,それらの性状はHENDRIE, et al.のtype description,あるいはEVELYNのあげているarchtypeの性状にほぼあてはまることが確認された。しかし他の研究者の報告をも考察しながらHENDRIE, et al.の type descriptionをみていくと,彼女等の言うように＋もしくは－と規定できない性状があり,さらに彼女等は特には記していない項目で,oxidase, catalaseなど＋と定義付けできるものがあることがわかった。従来の魚病菌vibriosをまとめて“V. anguillarum”一種とすることには異論はないが,病原性を含めていくつかの重要な性状の違いに基づくタイプ分けの必要性があると思われた。V.anguillarumとV.parahaemolyticus, V. alginolyticusとの比較を行なったところ,前種と後二種との間にはarginine,lysine脱炭酸の点で明確な違いがあり,またNaCl7%～10%における発育に差があることがわかった。さらに前二種の間にはsucrose利用の点に違いがあり,MR, VP,2,3-butanediolの点でも例外的な株はあるにしても一応違いがあることがわかった。またこの三種につき,ウナギ,マウスに対する病原性を比較したところ,V.anguillarumはウナギに対し他の二種より強い病原性を示し, V.parahaemolyticusはマウスに対しV.anguillarumより強い病原性を示した。
White Spot Disease broke out among youngs (total length: 8-10 cm) of the European eel Anguilla anguilla in May 1970. The fishes had been reared in newly constructed ponds near Lake Hamana, Shizuoka Prefecture. In diseased fishes, covered with numerous white spots all over the body surface, the parasites Ichthyophthirius multifilis were also found situated in the gills and in the wall of the oral cavity. According to histological observations, swellings, and necrobiosis, were recognized in the cutis at the site of infection. In the gills, the parasites located under the respiratory epithorium in which augmentation was not observable, while, in the oral cavity, the epitherium augmented as in the skin. Although Ichthyophiriasis, with a heavy mortarity, was once observed among youngs of the Japanese eel Anguilla japonica reared in a pond at the Hamanako Branch, Shizuoka Pref. Fish. Expt. Stn. in April 1969, it is a generally accepted fact that the Japanese eel has a low sensitivity to this parasite.
Some 25 spores of Myxidium sp. were found out in an “Ich” Ichthyophthirius multifilis parasitic to the skin of a young cultured Euro pen eel Anguilla anguilla. The host eel was observed to be infested with not only a number of “Ich”s but also Myxidiian spores in the skin. Two other “Ich”s were found out which carried in their body digested Myxidiian spores. A few Myxidiian spores were found in the surface layer of the dermis just beneath one of the “Ich”s. These Myxidiian spores found in the “Ich”, seem to be taken by the ciliate while they were coming out from the surface of the dermis in the skin of the host. (The present author observed that matured spores of the present Myxidium come out from the skin of living eels. The detail will be reported elsewhere.)
Monthly investigations of bacterial infections among pond-cultured eels in the Yoshida area of Shizuoka prefecture were carried out in 1972 to 1973 (Table 1). Eels examined were collected from the ponds where mass mortalities had occurred just before each investigation. Isolation of bacteria from blood, liver, kidney, spleen and/or gill was attempted, using nutrient agar medium (Difco) and Cytophaga agar medium (modified). Among five established eel-pathogenic bacteria, Aeromonas hydrophila, Edwardsiella tarda, Pseudomonas anguilliseptica and Chondrococcus columnaris were isolated in these investigations, but not Vibrio anguillarum. Total incidences of the four bacterial infections and the mixed infections were calculated (Table 2 and 3). Seasonal distribution of each bacterial infection was shown in Fig. 1. Distribution of the eels of which any bacteria were not isolated from internal organs had a partiality for winter (Fig. 2). Most of the diseased eels in winter had symptoms of “branchionephritis”, from gill of which a myxobacterium was frequently isolated.