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Yersiniosis, caused by Yersinia ruckeri, has become the most common disease in farmed rainbow trout Oncorhynchus mykiss in Peru, affecting Puno and Junín Regions, important aquaculture areas in the country. Florfenicol (FLO) and oxytetracycline (OXY) are the antimicrobials most frequently used to mitigate losses attributed to this pathogen. This study presents an analysis of the susceptibility patterns of 60 Y. ruckeri isolates (30 isolates each from Puno and Junín), including the type strain CECT 4319T and the strains CECT 955 and CECT 956, against FLO and OXY. Minimum inhibitory concentrations (MICs) were determined following the guideline for standard broth dilution method published by the Clinical and Laboratory Standards Institute. MIC results ranged from 4.0 to 8.0 µg ml-1 for FLO and 0.5 to 4.0 µg ml-1 for OXY. Normalized resistance interpretation (NRI) analysis identified epidemiological cut-off values of ≤16.0 µg ml-1 for FLO and ≤4.0 µg ml-1 for OXY. All Peruvian isolates, including the collection strains, were categorized as wild-type for both antimicrobials. Even though the number of Y. ruckeri isolates with MIC values of 8 µg ml-1 for FLO is more than double in Puno than in Junín (15 vs. 7 isolates), the NRI analysis showed the same epidemiological cutoff of 16 µg ml-1; while for OXY, it was 4.0 µg ml-1 for Puno and 2.0 µg ml-1 for Junín. This study establishes the basis for monitoring susceptibility to FLO and OXY in new Y. ruckeri isolates in Peruvian rainbow trout farming.

Tilapia is one of the most important farmed fish in the world and the most cultivated in Brazil. The increase of this farming favors the appearance of diseases, including bacterial diseases. Therefore, the aim of this study was to evaluate the bactericidal activity of copaiba oil, Copaifera duckei, against Streptococcus agalactiae and Flavobacterium columnare and the dietary effect of copaiba oil on zootechnical performance, hematological, biochemical, immunological, and histological analysis before and after an intraperitoneal infection (body cavity) with S. agalactiae in Nile tilapia. For this, fish were randomly distributed into 15 fiber tanks in five treatments (0, 0.25, 0.50, 0.75, and 1.0%) and fed with a commercial diet supplemented with copaiba oil for 30 days. After this period, the fish were randomly redistributed for the experimental challenge with S. agalactiae into six treatments (T0, T1, T2, T3, T4, and T5), the fish were anesthetized, and blood samples were collected to assess hematological, biochemical, immunological, and histological parameters. Copaiba oil showed bactericidal activity against Streptococcus spp. and Flavobacterium spp. in vitro. In addition, concentrations of 0.75 and 1.0% of copaiba oil have an anti-inflammatory effect and improve hematological and immunological parameters, increasing leukocyte numbers, albumin, and serum lytic activity. Furthermore, there is an increase in the intestinal villus length and tissue damage in groups at concentrations of 0.75 and 1.0% of copaiba oil. In conclusion, copaiba oil presented bactericidal activity against Streptococcus spp. and Flavobacterium spp. in vitro, and oral supplementation at concentrations of 0.75 and 1.0% compared to the control group enhanced non-specific immune parameters and digestibility in Nile Tilapia., (© 2024. The Author(s).)

Diphyllobothriosis, a fish-borne zoonosis in South America, is mainly caused by the Pacific broad tapeworm Adenocephalus pacificus Nybelin, 1931, a parasite of considerable concern in fishery resources due to its impact on public health. A new diphyllobothrid, Diphyllobothrium sprakeri Hernández-Orts et al. Parasites Vectors 14:219, 2021, was recently described from sea lions from the Pacific Coast, but marine fish acting as intermediate hosts are unknown. The objective of this study was to confirm the presence of plerocercoid larvae of Diphyllobothriidae Lühe, 1910 (Cestoda: Diphyllobothriidea) in nine fish species of commercial importance in Peru. Of a total of 6999 fish (5861 Engraulis ringens, 853 Sciaena deliciosa, 6 Sciaena callaensis, 171 Scomber japonicus, 40 Trachurus murphyi, 40 Ariopsis seemanni, 18 Merluccius peruanus, 5 Sarda chiliensis, and 5 Coryphaena hippurus), 183 were infected with plerocercoid larvae, representing a total prevalence of 2.61% and a mean intensity of 3.2. Based on mtDNA cox1 sequences of 43 plerocercoids, a phylogenetic analysis revealed that 41 belong to A. pacificus and two to D. sprakeri. These findings are first molecular data for D. sprakeri larvae, and the infections of E. ringens and T. murphyi by plerocercoid larvae represent the first records of intermediate/paratenic hosts for this species. Hence, the findings of the current study enhance our understanding of the presence of diphyllobothriid species in commercial fish from the Southeastern Pacific Ocean and their potential impact on seafood safety for local human populations., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The global ornamental fish trade carries important risk factors for spreading pathogens between different countries and regions, not only for ornamental fish but also for cultured fish and even other animal species. In the current study, we reported the capacity of Aeromonas veronii and A. hydrophila isolated from ornamental fish to experimentally infect the reared Amazonian fish Colossoma macropomum. For this, those bacteria were identified, and a primary characterization was performed. Fish were inoculated with 0.1 mL of increasing concentrations of A. hydrophila or A. veronii (C1 = 1 × 10 2 ; C2 = 1.8 × 10 4 ; C3 = 2.1 × 10 6 ; C4 = 2.4 × 10 8 bacterial cells per mL) in the coelomic cavity. In the control group, fish received the same volume of sterile saline solution (0.9 %). Fish presented petechiae, skin suffusions, and mortality rates up to 100 % according to the inoculum concentration. Histopathologically, fish presented necrosis with karyolysis, loss of the cytoplasmic delimitation of cells of the renal tubules and hepatocytes, hemorrhage, cellular edema, and the presence of bacterial cells. The LD 50-96h of A. veronii on C. macropomum was estimated at 2.4 × 10 6  CFU mL -1 and of A. hydrophila at 1.408 × 10 5  CFU mL -1 . The results demonstrated that it is possible that Aeromonas species isolated from ornamental fish affect C. macropomum, causing similar clinical signs and lesions. This shows the importance of promoting risk control measures worldwide regarding the trade of ornamental fish., Competing Interests: Declaration of competing interest The authors declare as no conflict of interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Yersinia ruckeri causes important economic losses for rainbow trout (Oncorhynchus mykiss) farms worldwide. This bacterial disease is likely the most common among trout in Peru; however, no commercial vaccine is available nationally, which is, in part, due to a lack of information on the bacterium. The aim of the current study was to characterize 29 Y. ruckeri isolates sampled from seven cage-reared farms in the Puno Region, the focal point for aquaculture activities in Peru. For this, samples were taken from fish with clinical signs (i.e. haemorrhages, uni- or bilateral exophthalmia, hyphaemia and/or melanosis). Notable among our findings was the existence of both Y. ruckeri biotype 1 (9 isolates) and biotype 2 (20 isolates; negative for sorbitol and Tween 80). The isolates further differed in API profiles 5307100 (21 isolates), 1307100 (4 isolates), 1305100 (2 isolates), 1307120 (1 isolate) and 5305100 (1 isolate), with the main differences being in the tests for lysine decarboxylase, gelatine hydrolysis and D-saccharose fermentation. Despite these differences, all isolates shared identical ERIC-PCR and REP-PCR profiles and belonged to the O1a serotype. Fingerprints were identical to the reference strain CECT 955 (serotype O1a). The information obtained will be used for epidemiological purposes by health authorities and for the development of a vaccine against Y. ruckeri, a prominent request made by fish farmers in Peru., (© 2022 John Wiley & Sons Ltd.)