h As global aquaculture fish production continues to expand, an improved understanding of how environmental factors interact in fish health and production is needed. Significant advances have been made toward economical alternatives to costly fishmealbased diets, such as grain-based formulations, and toward defining the effect of rearing density on fish health and production. Little research, however, has examined the effects of fishmeal-and grain-based diets in combination with alterations in rearing density. Moreover, it is unknown whether interactions between rearing density and diet impact the composition of the fish intestinal microbiota, which might in turn impact fish health and production. We fed aquacultured adult rainbow trout (Oncorhynchus mykiss) fishmeal-or grain-based diets, reared them under high-or low-density conditions for 10 months in a single aquaculture facility, and evaluated individual fish growth, production, fin indices, and intestinal microbiota composition using 16S rRNA gene sequencing. We found that the intestinal microbiotas were dominated by a shared core microbiota consisting of 52 bacterial lineages observed across all individuals, diets, and rearing densities. Variations in diet and rearing density resulted in only minor changes in intestinal microbiota composition despite significant effects of these variables on fish growth, performance, fillet quality, and welfare. Significant interactions between diet and rearing density were observed only in evaluations of fin indices and the relative abundance of the bacterial genus Staphylococcus. These results demonstrate that aquacultured rainbow trout can achieve remarkable consistency in intestinal microbiota composition and suggest the possibility of developing novel aquaculture strategies without overtly altering intestinal microbiota composition.

We hypothesized that low concentrations of H2O2 could be generated through the electrochemical conversion of oxygen by applying an electric potential to a conductive scaffold and produce a low, but constant, concentration of H2O2 that would be sufficient to destroy biofilms. To test our hypothesis we used a multidrug-resistant Acinetobacter baumannii strain, because this species is often implicated in difficult-to-treat biofilm infections. We used conductive carbon fabric as the scaffold material (“e-scaffold”). In vitro experiments demonstrated the production of a maximum constant concentration of ~25 μM H2O2 near the e-scaffold surface. An e-scaffold was overlaid onto an existing A. baumannii biofilm, and within 24 h there was a ~4-log reduction in viable bacteria with an ~80% decrease in biofilm surface coverage. A similar procedure was used to overlay an e-scaffold onto an existing A. baumannii biofilm that was grown on a porcine explant. After 24 h, there was a ~3-log reduction in viable bacteria from the infected porcine explants with no observable damage to the underlying mammalian tissue based on a viability assay and histology. This research establishes a novel foundation for an alternative antibiotic-free wound dressing to eliminate biofilms.

Strawberry disease (SD) in the USA is a skin disorder of unknown etiology that occurs in rainbow trout Oncorhynchus mykiss and is characterized by bright red inflammatory lesions. To identify a candidate bacterial agent responsible for SD, we constructed 16S rDNA libraries from 7 SD lesion samples and 2 apparently healthy skin samples from SD-affected fish. A 16S rDNA sequence highly similar to members of the order Rickettsiales was present in 3 lesion libraries at 1%, 32% and 54% prevalence, but this sequence was not found in either healthy tissue library. Based on phylogenetic analysis, this Rickettsia-like organism (RLO) sequence is most closely related to 16S rDNA sequences of bacteria that may form a novel lineage within the Rickettsiales. We used nested PCR assays to screen 25 SD-affected fish for RLO or Flavobacterium psychrophilum DNA. Sixteen lesion samples were positive for the RLO sequence and 4 of the matched healthy samples were positive resulting in a significant association between SD lesions and presence of RLO DNA. While F. psychrophilum is reportedly associated with 'cold water strawberry disease' in the UK, we found no significant association between SD lesions and the presence of F. psychrophilum DNA. The statistical association between SD lesions and presence of RLO DNA is not proof of etiology, but these data suggest that RLO may play a role in SD in southern Idaho, USA. KEY WORDS: Strawberry disease · Oncorhynchus mykiss · Rickettsia · 16S rDNA library · CWSD · WWSD · RMS Resale or republication not permitted without written consent of the publisherDis Aquat Org 82: [111][112][113][114][115][116][117][118] 2008 strawberry disease' (CWSD) in the UK (Fleury et al. 1985, Ferguson et al. 2006, Verner-Jeffreys et al. 2008.Results from Idaho producer surveys show no consistent management practices or facility, diet, or water conditions that predispose trout to SD, although stress is thought to aggravate the condition (Olson et al. 1985, Oman 1990. While previous surveys did not control for potentially confounding variables, there is evidence that SD is caused by a transmissible agent. Oman (1990) reported some success in transmitting the condition by experimental inoculation with SD lesion homogenate. Verner-Jeffreys et al. (2008) were able to demonstrate repeatable transmission of RMS/CWSD by cohabitation. Oral treatment with oxytetracycline (OTC) is used to manage the disease at some farms and is thought to reduce recovery time by as much as 50% (Erickson 1969, Olson et al. 1985, Oman 1990. Limited transmission studies and apparent response to chemotherapeutic treatment (OTC) are consistent with the hypothesis that SD results from a primary or secondary bacterial infection. Consequently, we investigated the bacterial community associated with SD lesions by constructing and comparing 16S rDNA libraries from SD lesions and matched healthy skin samples from SD-affected fish. MATERIALS AND METHODSSample collection. Fish were sampled from 4 different trout farms in southern Idaho, USA ...

Farmed and wild salmonids are affected by a variety of skin conditions, some of which have significant economic and welfare implications. In many cases, the causes are not well understood, and one example is cold water strawberry disease of rainbow trout, also called red mark syndrome, which has been recorded in the UK since 2003. To date, there are no internationally agreed methods for describing these conditions, which has caused confusion for farmers and health professionals, who are often unclear as to whether they are dealing with a new or a previously described condition. This has resulted, inevitably, in delays to both accurate diagnosis and effective treatment regimes. Here, we provide a standardized methodology for the description of skin conditions of rainbow trout of uncertain aetiology. We demonstrate how the approach can be used to develop case definitions, using coldwater strawberry disease as an example.

Previously we described a new member of the Neoparamoeba genus, N. perurans, and showed that it is an agent of amoebic gill disease (AGD) of Atlantic salmon Salmo salar cultured in southeast Tasmania, Australia. Given the broad distribution of cases of AGD, we were interested in extending our studies to epizootics in farmed fish from other sites around the world. Oligonucleotide probes that hybridise with the 18S rRNA of N. perurans, N. branchiphila or N. pemaquidensis were used to examine archival samples of AGD in Tasmania as well as samples obtained from 4 host fish species cultured across 6 countries. In archival samples, N. perurans was the only detectable amoeba, confirming that it has been the predominant aetiological agent of AGD in Tasmania since epizootics were first reported. N. perurans was also the exclusive agent of AGD in 4 host species across 6 countries. Together, these data show that N. perurans is a cosmopolitan agent of AGD and, therefore, of significance to the global mariculture industry. KEY WORDS: Amoebic gill disease · Neoparamoeba perurans · In situ hybridisation · Aquaculture Resale or republication not permitted without written consent of the publisherDis Aquat Org 78: [217][218][219][220][221][222][223] 2008 cases of AGD reported elsewhere, it is not known what role N. perurans, N. pemaquidensis and/or N. branchiphila play. Therefore, our objective was to use species-specific molecular probes to determine the aetiological agent or agents of AGD in 4 host species in 6 countries. MATERIALS AND METHODSParaffin-embedded gill tissues were obtained from 4 fish species predominantly during or following epizootics at commercial fish farming operations in 6 countries (Table 1). An epizootic was not reported from Chinook salmon Oncorhynchus tshawytscha cultured in New Zealand; however, the smallest fish (runts) within the healthy population were observed to have gill lesions that corresponded with AGD and these fish were used in this study. Gill tissues were sectioned (3 to 7 μm), stained with haematoxylin and eosin (H&E) and examined with light microscopy. Alternatively, sections (7 μm) of gill tissues were placed onto Polysine glass slides (Menzel-Gläser) and dried overnight at 37°C. Sections were hybridised with a digoxigenin (DIG)-labelled 'universal' 18S rRNA oligonucleotide probe to verify the integrity of rRNA as previously described (Young et al. 2007). All gill tissues with suitable host and amoeba rRNA were serially sectioned, placed onto Polysine glass slides and incubated with Neoparamoeba perurans, N. branchiphila and N. pemaquidensis DIG-labelled oligonucleotide probes as previously described (Young et al. 2007). Positive and negative (no probe) controls were run in parallel with each in situ hybridisation experiment by hybridising each probe with a section containing representative strains of each Neoparamoeba species termed an 'amoebae array' as previously described (Young et al. 2007). Tissue sections were incubated for up to 1 h with in a premixed solution of 5-b...