Miamiensis avidus (Ciliophora: Scuticociliatida) causes systemic infection of olive flounder Paralichthys olivaceus and is a senior synonym of Philasterides dicentrarchi

Abstract

The scuticociliate Miamiensis avidus was isolated from olive flounder Paralichthys olivaceus showing typical symptoms of ulceration and hemorrhages in skeletal muscle and fins. In an infection experiment, olive flounder (mean length: 14.9 cm; mean weight: 26.8 g) were immersion challenged with 2.0 × 10 3 , 2.0 × 10 4 and 2.0 × 10 5 ciliates ml -1 of the cloned YS1 strain of M. avidus. Cumulative mortalities were 85% in the 2.0 × 10 3 cells ml -1 treatment group and 100% in the other 2 infection groups. Many ciliates, containing red blood cells in the cytoplasm, were observed in the gills, skeletal muscle, skin, fins and brains of infected fish, which showed accompanying hemorrhagic and necrotic lesions. Ciliates were also observed in the lamina propria of the digestive tract, pharynx and cornea. The fixed ciliates were 31.5 ± 3.87 µm in length and 18.5 ± 3.04 µm in width, and were ovoid and slightly elongated in shape, with a pointed anterior and a rounded posterior, presenting a caudal cilium. Other morphological characteristics were as follows: 13 to 14 somatic kineties, oral ciliature comprising membranelles M1, M2, M3, and paroral membranes PM1 and PM2, contractile vacuole at the posterior end of kinety 2, shortened last somatic kinety and a buccal field to body length ratio of 0.47 ± 0.03. In addition, continuous PM1 and PM2, lack of M3 and variable kinetosome numbers in M2 and M3 were frequently observed. Specimens in the current study were compared with previous reports on M. avidus and Philasterides dicentrarchi and confirmed consistently that these 2 taxa are conspecific.KEY WORDS: Miamiensis avidus · Philasterides dicentrarchi · Ciliophora · Scuticociliatida · Pathogenicity · Olive flounder Resale or republication not permitted without written consent of the publisherDis Aquat Org 73: [227][228][229][230][231][232][233][234] 2007 describe, the morphometric characteristics of M. avidus cultured in Chinook salmon embryo (CHSE-214) cells and confirm M. avidus as a senior synonym for Philasterides dicentrarchi. MATERIALS AND METHODSNaturally infected fish. Wet preparations of skeletal muscle, gills and brain from Paralichthys olivaceus olive flounder showing typical symptoms of infection (ulceration and hemorrhage of skeletal muscle) were examined for the presence of ciliates. Small fish were fixed whole, in Bouin's solution; in the case of larger specimens, skeletal muscle, gills, liver, kidney, spleen, heart and brain were fixed in 10% formalin solution.Experimental infection. A cloned strain of Miamiensis avidus, YS1, was cultured for 6 d in CHSE-214 cells, then collected and centrifuged at 980 × g for 5 min. The ciliates were suspended in PBS (phosphate-buffered saline), and numbers were estimated using a hemocytometer. Olive flounder (mean total length: 14.9 cm; mean body weight: 26.8 g) were kept in an indoor tank for 2 wk prior to ciliate infection. Three groups of 20 fish were exposed to the ciliates for 45 min in 4 l of aerated water containing 2.0 × 10 3 , 2.0 × 10 4 , or 2.0 × 10 5 ...

Pathological Study on the Scuticociliatosis Affecting Farmed Japanese Flounder (Paralichthys olivaceus) in Japan

“…Severe epidermal degeneration and necrosis, myositis, encephalitis and myelitis were the most frequent changes in the present study. These histological findings are in accordance with those reported in marine fishes [3], turbot [4], Japanese flounder [6,7,9] and in silver pomfret [2]; skeletal muscle was the most severely damaged among the tissues affected; suggesting that the muscle is the most predisposed to the infection [3]. Ciliates containing numerous erythrocytes in the cytoplasm were observed in the hemorrhagic lesions in the skeletal muscle [2,6].…”

“…In the present fishes, macroscopic skin lesions including cutaneous ulcers and dark patches were observed; these findings are similar to those reported in turbot [5], Japanese flounder [7,9] and in silver pomfret in Kuwait [2]. Exophthalmia has not been reported in Japanese flounder.…”

“…Pathology of fishes affected with Uronema and Miamiensis has been reported to be similar to the present cases [4,12]. Moreover, it was reported that P. dicentrarchi and M. avidus are conspecific based on the careful morphological description and a wide range of reference comparisons [9]. Although, a detailed morphological study of the present ciliate is beyond the scope of this paper, some interesting findings were observed.…”

“…Several species of scuticociliates including M. avidus are known to be histophagous parasites causing severe infection in Japanese flounder [8,9] and can even exist in an aquarium rearing no fishes. Pathology of fishes affected with Uronema and Miamiensis has been reported to be similar to the present cases [4,12].…”

Strains of Uronema marinum (Scuticociliatia) co-isolated with amoebae of the genus Neoparamoeba

“…Philasterides dicentrarchi, which is considered to be a junior synonym of Miamiensis avidus (Jung et al 2007), has been frequently reported as an agent of systemic infections, including those that infect gills. This species has been characterized in detail, both morphologically and at a molecular level (Jung et al 2005).…”