In this study, we isolated, identified and characterized isolates of Tenacibaculum dicentrarchi in Atlantic salmon (Salmo salar) farmed in Chile for the first time. In 2010 and 2014, mortalities were observed in Atlantic salmon (average weight 25-30 and 480-520 g, respectively) at an aquaculture centre in Puerto Montt, Chile. Severe tail rots, frayed fins and, in some cases, damaged gills were detected. Wet smear analyses of these lesions revealed a high occurrence of Gram-negative, filamentous bacteria. Microbiological analysis of infected gill and tail tissues yielded six bacterial isolates. All were identified as T. dicentrarchi through polyphasic taxonomy, which included phenotypic characterization, 16S rRNA sequencing and multilocus sequence typing. The latter method revealed a close relationship of the Chilean genotype with the T. dicentrarchi type strain and two Norwegian Atlantic cod (Gadus morhua) isolates. The pathogenic potential of the TdChD05 isolate was assessed by challenging Atlantic salmon and rainbow trout (Oncorhynchus mykiss) for one hour, which resulted in mean cumulative mortality rates of 65% and 93%, respectively, as well as clinical signs 14 days post-challenge. However, challenged Coho salmon (Oncorhynchus kisutch) presented no mortalities or clinical signs of infection. These findings indicate that the geographical and host distribution of T. dicentrarchi is wider than previously established and that this bacterium may have negative impacts on salmonid cultures.

Eight bacterial strains isolated from diseased rainbow trout (n55) and Atlantic salmon (n53) were characterized by phenotypic and molecular taxonomic methods. The isolates were negative for the Gram-reaction, non-motile, rod-shaped and catalase-and oxidase-positive. Colonies on solid media were yellow, smooth, shiny and circular with regular edges. Growth occurred at 4-28 6C (optimum, 15 6C) and with 0-3 % NaCl (optimum, 0.5 %). Analysis of the 16S rRNA gene sequence allocated the micro-organisms to the genus Chryseobacterium, with Chryseobacterium soldanellicola PSD1-4 T and Chryseobacterium soli JS6-6 T as their closest relatives (96.9 and 97.1 % sequence similarity, respectively). The levels of DNA-DNA hybridization towards these nearest phylogenetic neighbours were below 17.1 %. The DNA G+C contents of strains VQ-6316s T and VQ-4836s were 32.5 and 32.3 mol%, respectively. The predominant menaquinone was MK-6 and the major fatty acids were iso-C 15 : 0 , anteiso-C 15 : 0 , iso-C 17 : 1 v9c, iso-C 17 : 0 3-OH and summed feature 3 (comprising C 16 : 1 v7c and/or C 16 : 1 v7t and/or iso-C 15 : 0 2-OH). The eight isolates were classified as representatives of a novel species, Chryseobacterium piscicola sp. nov., with strain VQ-6316s T (5CECT 7357 T 5DSM 21068 T ) as the type strain.

The present study reports on the first isolation of Tenacibaculum maritimum in rainbow trout (Oncorhynchus mykiss) farmed in Chile. In March 2020, two cages raising rainbow trout (~250 g) in the Los Lagos Region suffered a disease outbreak. In total, 17,554 fish died (3.5%-4.8% accumulated mortality). Microbiological analysis of the diseased fish obtained two representative isolates (i.e. Tm-035 and Tm-036). These were obtained from the external gross skin lesions-typical of tenacibaculosis-of two fish. Phenotyping, PCR tests and sequencing of the 16S rRNA and housekeeping genes confirmed the isolates as T. maritimum. The pathogenic potential of Tm-035 was further assessed by bath challenging Atlantic salmon (Salmo salar), which killed 70 ± 15% of fish within 11 days. Dead fish presented the same external clinical signs as did the farmed rainbow trout specimens. This research further broadens the known host distribution of this pathogen. Furthermore, the virulence experiments demonstrated that T. maritimum does not have a specific host. Additional studies are needed to evaluate the risk of T. maritimum for the O. mykiss farming industry.

No abstract

Strawberry disease is a chronic, nonlethal skin condition that affects Rainbow Trout Oncorhynchus mykiss in the United States and several European countries, where it is also known as red-mark syndrome. We provide the first identification and characterization of three strawberry disease outbreaks occurring at two aquaculture farms in southern Chile. Clinically affected fish weighing an average of 400 g presented multiple bright-red, usually raised, skin lesions on the flank, ventral surface, and dorsal surface. A PCR using Rickettsia-like-organism (RLO)-specific primers was performed on nine affected fish, and all skin samples were positive for the RLO 16S ribosomal RNA sequence. All PCR results for Flavobacterium psychrophilum and other bacterial and viral pathogens were negative. Histopathological examination of the skin lesions revealed extensive dermatitis, with severe lymphocytic infiltration in advanced cases. This report is the first to describe strawberry disease in farmed Chilean Rainbow Trout. Additional studies are needed to evaluate the risk for Rainbow Trout culture; fish challenge experiments should be performed to fulfill Koch's postulates and to demonstrate that RLO is the cause of this disease. Received December 27, 2014; accepted October 23, 2015.