First isolation of Miamiensis avidus (Ciliophora: Scuticociliatida) associated with skin ulcers from reared pharaoh cuttlefish Sepia pharaonis.

In the winter of 2015, a skin ulcer disease outbreak occurred in a pharaoh cuttlefish Sepia pharaonis population cultured on a land-based fish farm in China. Affected cuttlefish (about 60% of the population) were characterized as having developed ulcers on the dorsal skin, fin fringe, or distal mantle tip. Masses of a ciliated protozoan were isolated from skin ulcers. The ciliate was identified as Miamiensis avidus based on the morphological features of living and protargol-impregnated specimens. This identification was also supported by high sequence similarity of the small subunit ribosomal RNA gene (100%) and another ribosomal DNA region (including the 2 internal transcribed spacers and the 5.8S gene; 99%) with published sequences of fish parasitic M. avidus strains. M. avidus is known to be a histophagous marine fish parasite. This report describes the first case of M. avidus associated with skin ulcers in a cephalopod mollusk (Mollusca, Cephalopoda). This finding suggests that M. avidus may infect a phylogenetically broader range of hosts than what has previously been reported. Furthermore, M. avidus may pose a health risk to hatchery-reared cephalopods.