Yersinia ruckeri challenge on rainbow trout fed different diet types

A challenge for sustainable rainbow trout production is an increasing use of plant sources in fish feed due to shortage of marine protein and oil sources. Diets with high plant content are known to cause enteritis and injury to the intestine, which will affect the absorption of nutrients, affecting the overall health status and welfare of the fish. The result is a higher risk of disease following exposure to pathogenic microorganisms. The aim of this study was to elucidate how different feed types with varying amounts of marine versus organic plant protein and oil sources affected the survival of rainbow trout in connection with an infection. Enteric redmouth disease caused by Yersinia ruckeri is an economically important disease which causes problems in rainbow trout. Experimental infections (intraperitoneal injection of 150-200 g fish fed the different diets over a two month period) were done and mortalities in the different diet groups were recorded. Two weeks post challenge the mortalities in the different groups were between 50 and 89 %. The mortalities were lowest in the group fed the diet where half of the fish oil was replaced by organic plant oil. Unfortunately, the results were blurred due to a natural infection with Y. ruckeri that had occurred in the diet groups two months prior to the experimental infection (mortalities between 2 and 9 % in the different groups), and the half fish oil half plant oil group had had the highest cumulative mortality percentage in connection with this natural infection

OptiFish: Probiotika og foders betydning for sundheden hos økologisk regnbueørred

Formålet med OPTIFISH er at sikre optimale betingelser og høj overlevelse for regnbueørreder i økologisk akvakultur. Regnbueørreden er den dominerende opdrætsfisk i dansk akvakultur, hvoraf en mindre del produceres økologisk. Pt. er der ingen produktion af økologisk yngel, da en økologisk fisk igennem livsforløbet højst må behandles med antibiotika to gange, hvilket kan være svært at overholde pga. gentagne sygdomsudbrud specielt forårsaget af bakterien Flavobacterium psychrophilum på yngelstadiet. Endvidere vides det fra lakseopdræt, at vegetabilske proteinkilder (f.eks. sojamel) i foderet påvirker tarmslimhinden, hvor der ses betændelse med en efterfølgende svækkelse af immunstatus. OPTIFISH vil se på, hvordan økologiske fodertyper med indhold af forskellige mængder af marine og vegetabilske foderemner samt med og uden probiotika (mælkesyrebakterier) påvirker regnbueørredens tarm, den bakterielle tarmflora samt overlevelsen hos fisk i forbindelse med infektioner. Brugen af probiotika til ynglen forventes at resultere i øget sundhed. Resultaterne vil skabe en mere bæredygtig produktion ved en bedre udnyttelse af de tilgængelige økologiske naturressourcer og ikke mindst muligheden for, at erhvervet ved brug af den mest optimale fodring opnår en robust og sund fisk. Dette vil ikke bare kunne bruges ved opdræt af økologisk fisk, men også i det traditionelle opdræt. En mere robust og sygdomsfri yngel vil være nødvendig for en højere produktion, især i forbindelse med økologisk opdræt. The aim of OPTIFISH is to optimize growth and survival for organic cultured rainbow trout, the dominant fish species produced in Denmark. A minor part of the rainbow trout is produced as organic fish. Currently there is no production of organic fry, as the classification organic only can be given to fish that have been treated with antibiotics no more than twice in a lifetime. This is hard to achieve as recurrent disease outbreaks, especially with the bacterium Flavobacterium psychrophilum, are seen during the fry stage. A further challenge known from salmon culture is that diets with high plant contents cause enteritis and injury to the intestine, which will affect the absorption of nutrients, affecting the overall health status and welfare of the fish. The result is a higher risk of disease following exposure to pathogenic microorganisms. OPTIFISH will investigate how organic diet types with varying amounts of fish and plant sources as well as with or without probiotics (lactic acid bacteria) will affect the intestine, the intestinal microbial flora and survival rates of rainbow trout following exposure to pathogens. The use of probiotics for fry are assumed to result in a higher health level. The overall result will be a sustainable production with an optimal utilization of the available organic ressources as well as the scope for the industry that they by using the optimal diet type will achieve a robust and healthy fish, something that can be achieved not only in organic but also in traditional farming. A robust and disease-free fry is the most important factor for a higher production in organic aquaculture in the future

Infection models with Flavobacterium psychrophilum

High mortalities among rainbow trout (Oncorhynchus mykiss) fry are often the result of infections caused by Flavobacterium psychrophilum, and in Denmark this pathogen can be found in nearly all freshwater fish farms. The infection can be treated with antibiotics, but lower sensitivity against the infection is an increasing problem for some of the used drugs, wherefore alternative treatment methods (e.g. bacteriophages) are investigated. Prophylactic measures (e.g. feed additives) are another approach, so infections with the bacterium can be avoided, before they become a problem. No matter if the focus is on prophylactic or alternative treatment, reliable infection models are needed to evaluate the treatments as well as to get more knowledge about infections with F. psychrophilum. Experimental infection models will be presented, among them a reproducible intraperitoneal injection model as well as different bath models, and the potential for using the models will be discussed

Økologisk yngelfoder til regnbueørred - et sundere alternativ for fisken?

Regnbueørreden er den dominerende produktionsfisk i Dansk akvakultur, og der produceres årligt ca. 30.000 tons i ferskvandsopdræt. I de senere år er der igangsat produktion af økologiske fisk og mængden er stigende. I 2013 er der yderligere opstartet produktion af økologisk regnbueørred yngel, og dette medfører nogle ekstra udfordringer i forhold til forebyggelse af sygdomme og behandling. En af betingelserne for at en fisk kan sælges som værende økologisk er, at der er en begrænsning for hvor mange gange den kan behandles med antibiotika i løbet af dens liv, for ellers mister den sin økologiske status. Det er derfor vigtigt at sikre optimale forhold, så fisken undgår at blive syg. I Organic RDD projektet OPTIFISH undersøges det bl.a. hvordan foder indeholdende forskellige typer af olie og protein påvirker fiskeynglens evne til at overleve smitte med to af de bakterier, der hyppigt giver årsag til dødelighed på yngelstadiet; Flavobacterium psychrophilum og Yersinia ruckeri.Dette med henblik på derefter at kunne udpege en fodersammensætning, der kan sikre sundere fiskeyngel, der bedre kan modstå sygdom. Udover at evaluere overlevelsen i forbindelse med smitte, måles effekterne på forskellige immunparametre samt på bakteriefloraen i tarmen også.Forsøg samt resultater og konklusion beskrives

THE INTESTINAL MICROBIOTA IN RAINBOW TROUT (ONCORHYNCHUS MYKISS) IS INFLUENCED BY DIET TYPE AND YERSINIA RUCKERI CHALLENGE

In recent years it has become more and more evident that the bacterial flora in the gut of warm-blooded animals modulates physiological processes and the immunological status of the host. Besides effects on growth parameters, commensal intestinal bacteria balance the immune system and prevent colonization of pathogenic bacteria. The question is if the gut microbiota is also important in lower vertebrates such as fish? Is the microbiota related to the diet type and does it play a protective role in connection to pathogenic challenge? To examine these questions rainbow trout fry were fed two different diets of either a marine or vegetable origin from first feeding and onwards. At a size of about four gram the fish were bath challenged by Yersinia ruckeri serotype O1 and intestines were then sampled 5 days post challenge for subsequent metagenomic examination. Next-generation sequencing was applied for the metagenomic studies using the Illumina HiSeq 2000 platform. The results showed two distinctly different microbial patterns in the intestines dependent on the diet type. Fish fed a marine based diet overall had a significantly higher amount of the class β-proteobacteria, while the amount of reads belonging to phylum Firmicutes were significantly higher in the intestines of vegetable fed fish. The genera within phylum Firmicutes present in significantly higher amounts in vegetable fed fish were Weissella, Leuconostoc and Streptococcus. Genus Aeromonas from the γ-proteobacteria class was also present in significantly higher amounts in the vegetable fed fish. When challenged with Yersinia ruckeri, fish with a high amount of sequence reads belonging to genus Yersinia had a significantly lower amount of reads from the order Burkholderiales relative to non-infected control fish and fish with a low amount of Yersinia specific sequences. Further, these infected fish further clustered separately when analyzing the bacterial community on a PCA plot. The immunological examinations using RT-qPCR showed similar constitutive expression between the two diet groups, but the response differed between the two diet groups in challenged fish. Here, the general pattern was a pro-inflammatory response in the intestine of marine fed fish challenged with Yersinia ruckeri relative to non-infected control fish, while several immune genes were down-regulated in vegetable fed fish relative to non-infected control fish. Overall, the results indicate that the gut microbiota in rainbow trout is highly plastic according to the type of diet and does further seem to be involved in the immunological response in connection to pathogenic challenge

Foder skal sikre økologisk ørredyngel

Et optimalt sammensat foder til regnbueørredyngel forventes at kunne øge overlevelse og mindske sygdomsudbrud hos yngel. En af betingelserne for, at en regnbueørred kan sælges som værende opdrættet økologisk, er, at den højst har været behandlet to gange med antibiotiak i forbindelse med sygdomsudbrud. En af udfordringerne i økologisk regnbueørredproduktion er derfor at undgå, at fisk bliver syge, bl.a. ved at sørge for, at fiskene får optimalt foder, der styrker deres immunforsvar og dermed evne til at modstå sygdomme