Phenotypic methods have traditionally been used to identify clinically important Mucor spp. (Wang et al., 1990; Fingeroth et al., 1994; Chandra & Woodgyer, 2002). However, the fact that most published reports refer only to the genus Mucor underlines the difficulties in species identification (Ribes et al., 2000). Although observation of zygospores enhanced the identification of heterothallic Zygomycetes (Weitzman et al., 1995; Iwen et al., 2005), maintaining a library of tester strains is not easy for many laboratories and mating tests do not always yield a positive result (Schipper, 1976; Sigler et al., 2002). The Mucor isolate FM07 in yellow catfish was more like oomycete

species or some other filamentous fungi by gross examination. Under the microscope,

uniform nonseptate, broad and right-angled Lapatinib concentration branched hyphae, globose sporangia and sporangiophores could be seen. Based on the morphological characteristics, the strain FM07 was identified as M. circinelloides. Interestingly, the ITS rRNA gene fragment of FM07 showed 100% similarity to both M. circinelloides (EF583641) and Rhizomucor variabilis (DQ118990). Voigt et al. (1999) found R. variabilis was phylogenetically very close to Mucor spp. However, R. variabilis has rhizoids and stolons and can grow well above 40 °C. These characteristics are very different from those of Mucor Selumetinib spp. and were not found in strain FM07. The results identified strain FM07 as M. circinelloides. Infection trials showed that strain FM07 was pathogenic for yellow catfish by intraperitoneal and wound infection. However, the trials also revealed some differences between the two routes of infection (cf. results in Table 1). When the concentrations of sporangiospore suspension were increased, the cumulative mortality from different concentration groups went up correspondingly (30%, 45% and 90%) and the time to death of fish was

reduced (45, 28 and 19 days) in intraperitoneal crotamiton infection. In wound infection, the beginning time of death of fish from different concentration groups was similar to that in the intraperitoneal infection group, but the cumulative mortality was 100% in all wounded groups. In both experiments, when the concentration of sporangiospore suspension was increased the infected fish died more quickly. In immersion infection, there were no fish dead, although the strain FM07 was isolated from the mucus of some fish. These results suggest M. circinelloides is pathogenic to yellow catfish if a portal of entry is provided. Their infection may be associated with some primary pathogenic factor, for example trauma such as wound infection or poor environmental conditions. This phenomenon was consistent with the disease caused by M. circinelloides in humans (Chandra & Woodgyer, 2002; Iwen et al., 2007). In these cases, although M. circinelloides was reported as primary cutaneous zygomycosis, the patients all were known or suspected to have been exposed to trauma in different parts of body.