文獻來源: Caruso D, Keith P, Palssiart G. 2009. Skin nodular neoplasm in the armoured catfish, cascarudo (Callichthys callichthys), in French Guiana, South America. Journal of Applied Ichthyology 19(2): 126-128. [網址]Microscopically, the lesions consisted of non-encapsulated dermal (sub-epithelial) mesenchymal proliferation. In the slide coloured with Masson's trichrome, the tumoral cells showed a fibroblastic phenotype and haphazardly scattered arrangements in collagen-rich stroma (Fig. 2). The surface of the tumour appeared to be covered by a hyperplastic epidermis devoid of simple cylindrical epithelium and was composed of the serous cells typical of the Siluriformes. This epithelium is well represented in the normal adjacent areas. Neither nuclear abnormality nor obvious mitotic activity was present. No parasitic structure was observed in the lesions at microscopic observation. The proliferating tissue occasionally infiltrated the underlying osseous dermal plaque (Fig. 3), but the osseous plaque structure appeared to be healthy. All examined lesions shared the same histological aspects (Fig. 4). Although a periostal origin of the tumour cannot be excluded, the histological findings of the lesions are consistent with a fibroma or benign fibrohystiocytoma in humans. Fibroma is considered one of the most frequently observed mesenchymal tumours in fish (Richards, 1977; Roberts, 1979). This neoplasm has been found in different marine species such as the striped mullet (Mugil cephalus) from Tunisia (Lopez and Ribaud, 1981) and the redband parrotfish (Sparisoma autofrenatus) in the Caribbean region (Grizzle and Williams, 1983). To the knowledge of the authors, few cases of fibroma have been reported on Amazonian freshwater fish in the literature. A fibroma localized in the branchial arc has been reported in pacu (Piaractus mesopotamicus) (Ferraz de Lima et al., 1993) from fish-pond facilities in Brazil, and another has been found in the abdomen of captive red piranha (Serrasalmus nattereri) (Heckman, 1994). Although the idiopathic origin cannot be excluded, the high prevalence observed (66%) and some histological features – such as the haphazardly disposed elongated cell – analogous to equine sarcoid caused by bovine papilloma DNA virus (Trenfield et al., 1985; Lancaster et al., 1997), could suggest an infectious aetiology, possibly of viral origin. Getchell et al. (1998) reported that at least 11 types of virus are implicated in skin tumours of wild fish, and different virus families have been involved in fish fibroma. Rhabdovirus carpio have been observed in the swim bladder fibroma in carp (Cyprinus carpio) (Inchausty and Heckman, 1996) and retrovirus particles were found in lip fibroma from captive Pterophyllum sp. (Francis-Floyd et al., 1993). Lentivirus-like particles have been responsible for skin tumours classified as fibroma or possible fibrosarcoma in another armoured fish, the hooknose (Agonus cataphractus) (Anders et al., 1991). Otherwise, the histological features observed in the fibroma of cascarudo allowed differential diagnosis from two other viral cutaneous tumours of fish: the fish lymphocystis disease (FLD) and the walleye dermal sarcoma (WDS). Indeed, the fibroblastic cells did not appear hypertrophied and surrounded by a hyaline capsule as typical for FLD (Paperna, 1982; Bowden et al., 1995; Williams Jr et al., 1996), and differed from WDS by the absence of vacuolar degeneration in the tumour cells and centrally located coagulation necrosis (Martineau et al., 1990; Earnest-Koons et al., 1996). No other species of fish collected in Marais de Panato showed similar skin lesions. This was also true for another sympatric armoured catfish, M. thoracata, very close to the cascarudo. This specificity could suggest a close relationship between the host and etiologic agent. Further study will be required to deepen epidemiological, histological and etiological considerations, but this note reports for the first time neoplastic skin lesions with high prevalence from a wild population of Amazonian fish.
