Syuzo Egusa

Detection of Resistance Factors in Fish Pathogen Aeromonas liquefaciens

SUMMARY: Thirty-nine out of 72 drug-resistant strains of Aeromonas liquefaciens isolated from cultured fish and soft-shelled turtles (Trionyx sinensis japonicus) in various districts of Japan carried transferable drug resistance factors. The fish included eel (Anguilla japonica), carp (Cyprinus carpio), ayu (Plecoglossus altivelis) and goldfish (Carassius auratus). The most common type of resistance factors had the markers of resistance to sulphanilamide and tetracycline and all belonged to the fi - type. Transferable drug resistance was not found in any of 12 strains of A. liquefaciens isolated from wild eels. The high incidence of resistance factors in A. liquefaciens from cultured fish is assumed to be due to the selective pressure exerted by chemotherapeutics used in fish culturing.

Detection of R Factors in Naturally Occurring Vibrio anguillarum Strains

R factors were detected in Vibrio anguillarum strains from vibrio-diseased freshwater fish, ayu (Plecoglossus altivelis), in Japan. It was found that 65 out of the 68 random isolates from epidemics of vibrio disease in 1973 carried transferable drug resistance factors. The most common type determined resistance to sulfonamides, streptomycin, chloramphenicol, and tetracycline and belong to the fi− type. The high incidence of R factors in Vibrio anguillarum from cultured fish is assumed to be due to selective pressure exerted by chemotherapeutic agents used in fish culturing.

Detection of R Plasmids in Naturally Occurring Fish-Pathogenic Bacteria, Edwardsiella tarda

The conjugative R plasmids were detected from fish‐pathogenic Edwardsiella tarda isolated from cultured eels. These R plasmids were resistant to sulfonamide and tetracycline, or sulfonamide, streptomycin, chloramphenicol, tetracycline and kanamycin. There were no inhibitions in growth of phages W‐31, P1, T1, T3, T7, and λ. They were classified into incompatibility group A.

The systematic position of the genus Anoplodiscus (Monogenea: Anoplodiscidae)

SummaryRedescriptions are given of the monogeneans Anoplodiscus spari (Yamaguti, 1958) n. comb. (syn.: Pseudomicrobothrium spari) from Acanthopagrus schlegeli (Teleostei: Sparidae) in Japan and Anoplodiscus australis Johnston, 1930 from Acanthopagrus australis in Australia; the developmental stages of Anoplodiscus spari are described. Anoplocotyle Palombi, 1943 and Pseudomicrobothrium Yamaguti, 1958 are synonymized with the genus Anoplodiscus Sonsino, 1890. These monogeneans have the following morphological characteristics in common: (i) the opisthaptor in form of an unarmed, disc-shaped sucker, (ii) the single and asymmetrical intestine, and (iii) the prohaptor in the form of a pair of bothria opening anteroterminally. It is reasonable to assume that these are generic characteristics because they agree in essentials with the previous descriptions of the type species, A. richiardii Sonsino, 1890. The oncomiracidium of A. spari n. comb. also bears eight pairs of marginal hooks, which disappear during the post-oncomiracidial development and no further chitinous structures appear on the opisthaptor. From these characteristics of both the adult and oncomiracidium it is concluded that the genus Anoplodiscus represent an independent family, Anoplodiscidae Tagliani, 1912 (formerly a subfamily in the invalid family Anisocotylidae Monticelli, 1903). The family Anoplodiscidae is emended in this paper. ac]19800623

Studies on a New Trypanorhynchan Larva, Callotetrarhynchus sp., Parasitic on Cultured Yellowtail-XII

Observations were made on the movement and gravidity of free proglottides of Callotetrarhynchus sp. separated from the strobila of the adult in the valvular intestines of Triakis scyllia. The results are as follows: 1) Mature proglottides which still joined to the terminal of the strobila are 4.05-6.50×1.28-2.14mm in size and have no sperms either in the vas deferens or in the vagina and no ova in the narrow uterus. 2) Mature proglottides separate from the strobila before fertilisation at the posterior part of the valvular intestine. 3) In the initial stage, free proglottides immediately after separation, often have the cirrus protruded and the ductus ejaculatorius filled with sperms. 4) Free proglottides after receiving sperms move toward the anterior part of the valvular intestine and many fertilized eggs appear in the spread uterus of the proglottid. 5) All the free proglottides in the anterior part of the valvular intestine are completely gravid and larger in size than mature proglottides, being 5.33-7.65×2.00-3.75mm. 6) When the number of the fertilized eggs reaches about 40-60 thousand in the uterus, gravid proglottides start to return to the posterior part of the valvular intestine and finally escape into the sea from the anus of the host. 7) When gravid proglottides contact with sea water, the spawning pore is opened immediately on the dorsal side of the vertex of the uterus and the majority of the fertilized eggs are jetted out from the pore instantly. 8) Free proglottides are found in the valvular intestine of host sharks 12 to 30 days after administration of the bladder worms, plerocercus of Callotetrarhynchus sp.. 9) From these observations, it is concluded that the present species is hyperapolytic.

Studies on a New Trypanorhynchan Larva, Callotetrarhynchus sp., Parasitic on Cultured Yellowtail-VI

In a previous paper, it was reported that the anchovy worm which shows up in the body cabity of Engraulis japonica (HOUTTUYN) is a pre-staged larva of the bladder worm found in Seriola quinqueradiata TEMMINCH et SCHLEGEL. The present investigation was carried out so as to elucidate seasonal changes in the occurrence of anchovy worms in the Bungo Channel and the Hyuga Sea in connection with the migration of the 3 seasonal groups of anchovies, spring-, summer-and autumn-hatched in the mentioned areas. Seventy one samples of anchovies (17, 017 fishes in total) were collected at various seasons, from March 1968 to November 1970, from different localities. The study revealed that the incidence of worm carring fishes differed definitely among the 3 anchovy groups. The occurrence rate of fishes carring the worms estimated with samples consisting of 7 to 11 months old fishes were 10.8 ?? 25.0% (average 19.2%) in spring-hatched group (12 samples), 4.2 ?? 15.4% (9.5%) in summer-hatched group (14 samples) and 1.1 ?? 7.7% (3.8%) in autumn-hatched group (17 samples). The incidence in the other 28 samples which were estimated to be under 6 or over 12 months old was relatively low, and no worm was found in the 3 and 4 months old samples. The smallest fish which harboured the worm was 7.6cm in body length (sample No. 7). Out of the 71 sample groups, 53 samples were caught in the Uwa Sea, the north eastern part of the Bungo Channel. A definite seasonal variation in the incidence of the worm was noticed in this area throughout the 3 years, being highest in autumn and winter and lowest in summer. These seasonal variations were satisfactorily explained from the annual migration modes of the 3 hatching groups which markedly differed from each other in the incidence of the worm.