First Report of Tenacibaculum dicentrarchi in Diseased Palm Ruff (Seriolella violacea, Guichenot 1848) From an Experimental Culture in Chile.

Abstract

Palm ruff (Seriolella violacea, Guichenot 1848) has been identified as a promising candidate for aquaculture in northern Chile. During the winter of 2023, an outbreak of an external infectious disease affected 3740 juvenile Palm ruff at the Marine Fish Farming Laboratory of the Universidad Católica del Norte. The macroscopic signs, particularly external ulcers, were consistent with tenacibaculosis. Microbiological, genomic and typing analyses were conducted to determine the cause of fish mortality. Sixteen isolates were recovered from four moribund fish, primarily from external lesions organs such as the mouth (n = 4), skin lesions (n = 4) and gill (n = 1). All isolates exhibited phenotypic traits characteristic of Tenacibaculum dicentrarchi: Gram-negative, motile rods, positive catalase and oxidase activity, Congo red absorption and an absence of flexirubin pigment. PCR analysis confirmed the identity of the isolates as T. dicentrarchi, with 16S rRNA and fusA gene sequencing clustering the isolates with the T. dicentrarchi type strain 35/09^T. Multiplex PCR-based O-AGC typing classified all 16 Chilean isolates as Type 1, which could aid in the development of an autogenous vaccine to prevent future tenacibaculosis outbreaks. RAPD analysis revealed clear genetic heterogeneity among all isolates, with a dominant genetic group comprising 11 isolates, regardless of the primer used. This study represents the first report of a bacterial disease in Palm ruff, expanding the list of endemic species susceptible to tenacibaculosis caused by T. dicentrarchi.