施氏鲟水霉病病原的初步研究

Isolation of Saprolegnia parasitica as a pathogen from Acipenser schrenckii

从患水霉病的施氏鲟(Acipenser schrenckii)幼鱼肌肉中分离获得一株优势水霉菌株XJ001。大麻籽上水霉XJ001培养物的形态观察表明,菌丝透明无间隔,分枝少;新孢子囊以层出方式产生或从旧孢子囊根部长出,游动孢子按水霉属方式释放;在7℃、15℃和25℃条件下不能产生有性器官,但能够产生大量的厚垣孢子。电镜观察发现第二孢孢子表面具有大量弯曲的长毛,其在25%GY培养液中呈现出间接萌发。根据形态及生理学特征将水霉XJ001鉴定为寄生水霉(Saprolegnia parasitica)。水霉XJ001的最适生长温度为25℃,对NaCl敏感,当PDA培养基中NaCl质量分数为1%和2%时,水霉生长抑制率分别为37.4%和75.6%;质量分数大于3%时,生长被完全抑制。用水霉XJ001对异育银鲫(Carassius auratus gibelio)进行人工感染,结果表明XJ001有较强的致病力,异育银鲫感染严重,体表出现棉花状白毛,感染率为83.3%,感染后的死亡率为100%,可见XJ001是施氏鲟水霉病的病原菌。

Saprolegniois has been one of the common diseases and caused great damage to aquaculture. This study aimed to investigate the pathogen of saprolegniois in the aspests of morphological, physiolical and pathogenic characteristics to help control the disease. Saprolegnia XJ001 was isolated from the muscle of cultured juvenile Acipenser schrenckii with saprolegniois. Observation on the morphology of Saprolegnia X J001 cultured on hemp seed showed that the hyphae were transparent and non-septate with sparing branches, zoosporangium renewed by internal proliferation or basipetalous succession, zoospores were released in Saprolegnia fashion through the exit pores, sexual structure could not form at 7 ℃, 15℃ and 25 ℃, and considerable gemmae were produced. The presence of long, hooked hairs in bundles on the secondary encysted spores were observed by using transmission electron microscopy, and the spores showed indirect germination in 25% GY broth. According to the morphological and physiological characteristics, Saprolegnia XJ001 was identified as Saprolegnia parasitica. The optimal culture temperature for Saprolegnia parasitica XJ001 was 25℃ . In addition, the Saprolegnia parasitica XJ001 was sensitive to NaCl. At NaCl concentrations of 1% and 2%, the inhibition rate of hyphae growth on PDA agar was 37.4% and 75.6%, respectively, while the growth was inhibited completely at the concentration of 3%. The result of artificial infection of Carassius auratus gibelio with Saprolegnia parasitica X J001 indicated that Saprolegnia parasitica X J001 was highly pathogenic to Carassius auratus gibelio, which displayed serious fungal infection symptom with cottonlike mycelia on body surface after challenge. The infection rate was 83.3% and the mortality of infected fish was 100%. It can be concluded that Saprolegnia parasitica XJ001 was the causative agent of saprolegniosis in the juvenile Acipenser schrenckii.