Proliferative gill disease (PGD) was first reported in channel catfish Ictalurus punctatus at commercial farms in 1981 and is caused by the myxozoan parasite Henneguya ictaluri. The disease affects the gills and is characterized by severe branchial inflammation, epithelial hyperplasia, lamellar fusion, and lysis of chondrocytes. Presumptive diagnosis is based on the presence of lytic areas in the cartilage of the primary lamellae on microscopic examination and is confirmed histologically by the presence of the organism. In these trials, PGD was induced by exposing channel catfish fingerlings to fresh or aged infectious water collected from a pond containing fish diagnosed with severe PGD. The severity of disease was graded by histological scoring and microscopic examination of wet mounts to determine the percentage of gill filaments containing chondrolytic lesions. Exposure of fish to infectious pond water was shown to produce pathological lesions consistent with PGD, and the percentage of gill filaments containing chondrolytic lesions was positively correlated with histological scoring of gill pathology. The number of trophozoite stages in the gills was shown to increase with the severity of the disease. In most cases, however, parasitic cells were not observed in tissue samples with chondrolytic lesions during the early stages of infection. These observations indicate that pathology and lysis of chondrocytes can occur prior to detection of the organism by histopathology. Exposing fish to infectious pond water that was aged for 1 d produced negligible gill pathology and implies that the infectivity of the H. ictaluri actinospore stage is short lived. Removing fish from the source of infection promoted repair of damaged gill tissue; within 14 d of fish transfer to clean water, gill pathology associated with the acute infection was negligible.

中文翻译：

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沟鲶鱼种增殖性鳃病的诱发与评价

增殖性鳃病 (PGD) 于 1981 年首次在商业养殖场的沟鲶 Ictalurus punctatus 中报道，由粘虫寄生虫 Henneguya ictaluri 引起。该疾病影响鳃，其特征是严重的鳃炎症、上皮增生、板层融合和软骨细胞溶解。推定诊断基于在显微镜检查时初级薄片软骨中溶解区的存在，并通过生物体的存在进行组织学确认。在这些试验中，PGD 是通过将沟鲶鱼种暴露于从含有被诊断为严重 PGD 的鱼的池塘收集的新鲜或老化的传染性水中来诱导的。疾病的严重程度通过组织学评分和湿贴的显微镜检查进行分级，以确定含有软骨溶解病变的鳃丝的百分比。鱼暴露于传染性池塘水被证明会产生与 PGD 一致的病理损伤，并且含有软骨溶解损伤的鳃丝百分比与鳃病理学的组织学评分呈正相关。鳃中滋养体阶段的数量随着疾病的严重程度而增加。然而，在大多数情况下，在感染的早期阶段，在具有软骨溶解病变的组织样本中没有观察到寄生细胞。这些观察结果表明，在通过组织病理学检测生物体之前，可以发生软骨细胞的病理学和裂解。将鱼暴露于老化 1 天的传染性池塘水中产生的鳃病理可忽略不计，这意味着 H. ictaluri 放线孢子阶段的传染性是短暂的。将鱼从感染源中剔除，促进受损鳃组织的修复；在将鱼转移到干净的水后 14 天内，与急性感染相关的鳃病理可以忽略不计。