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ShelterFish Review

Jokumsen, Alfred (2022) ShelterFish Review. [ShelterFish review.] .

[thumbnail of D1.19_Review article on project results.pdf] PDF - English


ShelterFish has addressed the currently main challenges for future development of organic trout production in Denmark, i.e. the parasitic disease costiasis (caused by Ichthyobodo necator) which is lethal for fry/smaller fish and the bacterial disease Red Mark Syndrome (RMS), which results in downgrading/rejection at slaughter. The issues were addressed by a holistic approach including interactions between the fish environmental conditions (water quality and welfare), the pathogens (health) and the fish.
Hence, fish welfare was evaluated in response to providing artificial shelters for the fish. Rainbow trout were exposed to two types of submerged shelters: Full screens or partial Semi screens, and fish welfare was assessed and compared to a control group (without shelters) by evaluating fish growth and condition, extent of external lesions, and the neuroendocrine responses to acute and repeated stress.
A separate study of potential effects of early exposure to shelters on the juvenile performance later in the life cycle showed, that shelter-grown fish performed less competitive compared to non-shelter-grown fish in challenging conditions favoring competition (low stocking density plus restricted feeding). However, this effect was clearly mitigated when letting shelter-grown fish to acclimate to non-shelter conditions before the competition tests.
Finally, a field study was performed in an organic rainbow trout farm with simply designed shelters to investigate rainbow trout fingerlings’ preference for shelter, and the behavioral response to farm related stress, as well as the cortisol
response and growth performance.
Overall the experiments showed:
• Fish showed a clear behavioral preference to use/get protected under the shelters, particularly when disturbed;
• Shelters had no deleterious effect on fish performance, welfare indicators or survival. Though, shelter resulted in reduced fin damages.
• Based on the results, in particular the field studies, it is suggested that future trials, designed to study the effects of shelter on rainbow trout welfare, would benefit from longer habituation period prior to stress testing and sampling.
Hence, the studies performed showed potential for shelters to be used as a welfare promoting strategy in trout farming, but further research is needed to optimize the shelter type and design and the proper timing for its application.
The serious parasitic pathogens Costia (Ichthyobodo necator), Ichthyopthirius multifilis (ICH-white spot disease) and different amoebae (Vanella sp.) have been identified in gill samples collected from trout in organic farms using Q-PCR array and histology. Test for establishment of Costia cultures have been performed at organic farm with positive results.
Extracts of oregano, thyme, coriander, garlic and astaxanthin were tested in vitro and in vivo against the ciliate, Costia. These natural compounds showed an effect on the infection in the early stage but not after 8 days.
Garlic exhibited the highest in vitro killing capacity towards theronts (the infective stage of the parasite), followed by oregano, thyme, and astaxanthin, whereas coriander had no in vitro parasiticidal effect. The results suggest that the investigated additives inhibit early parasite development directly as well as indirectly (i.e. by elevating the host immune response).
However, more promising results were found with a novel biological control agent, the surfactant from Pseudomonas H6, a kind of biological soap, which opens the cell membrane of the parasite so the content float out and the parasite dyes. It was found that this agent had a strong effect on a series of organisms colonizing gills, skin and fins of organic trout. The compound could kill many of the organisms but more importantly the surfactant seemed to clean off the colonizers (Amoebae, Ichthyobodo, Trichodina and Ambiphrya).
The auxiliary water treatment compounds, the biocides formalin, peracetic acid and hydrogen peroxide induced a strong inflammation in the fish but the surfactant H6 was very mild, although it induced mucus release from mucous cells in the skin. The biocides induced the mucus secreting cells on fish surfaces (gills, skin, and fins) to empty their content upon stimulation.
Experiments on prophylaxis/treatment of gill pathogens showed that amoebae were killed at the following concentrations: 16.9 mg/ml (raw garlic-extract), 100 mg/L (hydrogen peroxide), 250 microgram/ml (bacteria surfactant), 17.9 mg/ml (oregano extract), 7.5 ppt (NaCl).
No effect of shelters could be detected in gills, skin and fins on colonization of fish surfaces with amoebae and ciliates.
Red Mark Syndrome (RMS) is a disease affecting rainbow trout under farming conditions. The disease is not lethal but is costly for the fish farmer as the hallmark symptoms of the disease are large, red skin lesions, which often appear in fish of market size. There are currently no good treatment options for this disease.
RMS does rarely occur twice in the same fish population, therefore ShelterFish investigated whether early exposure to RMS as fingerlings could result in protective immunity throughout the remainder of the production cycle, thus preventing skin lesions in larger fish and thereby severely reducing the problems associated with RMS.
Naïve specific pathogen free (SPF) rainbow trout fingerlings were exposed to RMS by cohabitation. Most of the cohabitants developed clinical signs of RMS during the following three months. The fish were now maintained until 13 months after initiating the first round of cohabitation, at which time they were once again exposed to RMS via cohabitation. This time, non-exposed control fish were also added. The second cohabitation was terminated after 77 days. By then, all negative controls had developed several RMS-lesions, whereas no skin pathology was observed in the pre-exposed fish. All experimental procedures were carried out at 12°C.
The results showed that under the experimental conditions, protective immunity against RMS was induced in fingerlings and lasted for at least 13 months.
Use of chemical disinfectants and organic aquaculture may seem contradictory.
There are however no direct contradictions between these two terms, as long as they are developed and improved towards more sustainable solutions. A natural and immediate aversion to words like “sanitizers, chemicals and auxiliary compounds” are frequently met. Similarly, aquaculture production is often criticized and have a tarnished reputation. Organic aquaculture is a way to differentiate from conventional fish production. Some of the challenges still remain to be solved and during that process, ideally important knowledge and experience can also accelerate better management in the conventional aquaculture industry.
With particular reference to organic aquaculture the following recommendations are given:
• Reduce particulate organic matter, as the microbial water quality becomes improved by further removal of organic matter, i.e. lowered bacterial load, increased oxygen concentration and decreased dissolved CO2.
• Increase water flow and circulation/internal recirculation to improve oxygen conditions and reduce retention time and potentially dampen intra specific aggression to change fish behavior from erratic to more streamlined swimming (welfare).
• Proactively learn to use safe chemicals with caution to become confident with optimized chemical water treatment (dosages and fish behavior).
Future research and development of organic aquaculture is recommended to include organic feeds and fish nutrition, fish health and welfare, environmental aspects including sustainable management and use of disinfectants from an environmental, ethical and economical perspective, consumers’ needs, food safety and trade. Finally, there is also an urgent need to improve management practice towards more sustainable fish production. Increased collaboration and openness between industry, consumers, authorities and academia will facilitate that process

Summary translation

ShelterFish har adresseret de væsentligste udfordringer for udviklingen af økologisk ørred opdræt i Danmark, herunder parasitten Costia (forårsaget af Ichthyobodo necator), som er dødelig for yngel/mindre fisk og bakteriesygdommen Rødpletsyge (RMS), som resulterer i nedklassificering/kassation ved slagtning. Dette kan være en trussel mod tilstrækkelig udbud af økologisk yngel til videre produktion, da regelsættet for økologisk akvakultur kræver 100% økologisk yngel.
Med udgangspunkt heri fokuserede ShelterFish på løsninger i krydsfeltet: Fisk - Patogener – Opdrætssystem/miljø og vandkvalitet. Det omfattede 1) Test af skjul/skygge med henblik på at skabe bedre og robust opdrætsmiljø; 2) Test af urte ekstrakter og et nyt bakterielt overflade-aktivt stof til behandling af gæller/hud parasit infektioner; 3) Test af induceret immunitet mod rødpletsyge og 4) Test af metoder til reduktion af belastning med organisk stof i økologiske dambrug og herved forbedre vandkvalitet/miljø, fiske sundhed og velfærd.
Forsøg med simple skjul, der var enkle at fremstille, installere og flytte rundt viste i såvel laboratorie forsøg som forsøg på et økologisk dambrug, at fiskene havde en klar præference for skjul og at skjul ikke havde negative effekter på fiskevækst. Resultaterne kan anses for positive for fiske velfærd, idet dyre præferencer er et vigtigt velfærds aspekt. Ydre læsioner og den almindelige helbredstilstand var moderate, ligesom fiskenes stress tolerance ikke var påvirket af mulighed for skjul. Der er potentiale for optimering i brugen af skjul og andre typer ”miljøer” med henblik på øgning af velfærd hos opdrætsfisk. I forhold til anvendelse af skjul til opdræt af laksefisk, synes effekten af skjul at afhænge af mange forskellige faktorer og der er behov for yderligere forskning til optimering af typen af skjul, omfanget af skjul og relevante tidspunkter for brug af skjul gennem fiskens livscyklus.
De alvorlige parasitære patogener Costia (Ichthyobodo necator), Ichthyopthirius multifilis (fiskedræber/hvidpletsyge) og forskellige amøber (Vanella sp.) blev identificeret i gælleprøver fra økologiske ørreddambrug ved hjælp af Q-PCR teknik samt histologi.
Extrakter af oregano, timian, koriander, hvidløg og astaxanthin blev testet in vitro og in vivo mod ciliaten, Costia (Ichthyobodo necator). Disse naturlige stoffer viste en effekt mod infektionen i de tidlige stadier, men dog ikke efter 8 dage. Hvidløg viste størst effekt, men generelt tyder resultaterne på, at stofferne hæmmer tidlig udvikling af parasitten ved at øge fiskens immunrespons.
Et nyt biologisk overflade aktivt stof fra Pseudomonas H6 viste sig mere effektivt mod parasitten. Stoffet er en slags biologisk sæbe, som åbner parasittens cellemembran, så indholdet flyder ud og parasitten dør. Ud over tillige at være effektivt over for andre organismer på hud, gæller og finner rensede stoffet også overfladerne for disse parasitter.
Hjælpestofferne/biociderne formalin, pereddikesyre og brintoverilte inducerede en stærk inflammation hos fiskene, mens effekten af surfaktanten H6 var meget mild, men inducerede dog slim udskillelse i huden.
Forsøg viste, at følgende doser dræbte amøber i gællerne: 16,9 mg/ml (rå hvidløgs-ekstrakt), 100 mg/L (brintoverilte), 250 mikrogram/ml (bakterie overflade aktivt stof (H6), 17,9 mg/ml (oregano ekstrakt), 7,5 ppt (NaCl).
Skjul havde ingen effekt på forekomsten af amøber og ciliater i gæller, hud og finner.
Rødpletsyge (RMS) er en sygdom, der rammer regnbueørreder under opdræt. Sygdommen er ikke dødelig, men er alligevel kostbar for opdrætterne, da sygdommen – som navnet angiver – resulterer i store, røde pletter i huden, og det er desuden oftest fisk i salgsklare størrelser, der rammes. Der findes ingen vaccine mod RMS. Selvom sygdommen kan behandles med antibiotika, er der flere ulemper herved, bl.a. risiko for udvikling af antibiotikaresistens. Desuden er brug af antibiotika stærkt begrænset i regelsættet for økologisk akvakultur.
Da sygdommen sjældent optræder to gange i samme population og øjensynligt er ret mild, undersøgtes det, hvorvidt man kunne smitte små sættefisk, og om disse i så fald ville være beskyttede mod genudbrud af sygdommen indtil salg.
Små sættefisk blev smittet ved at sætte dem sammen med RMS-ramte fisk (kohabitering). De fleste af fiskene udviklede RMS-symptomer i løbet af de følgende tre måneder. Fiskene blev 13 måneder efter første kohabitering endnu engang kohabiteret med RMS-ramte fisk. Denne gang blev naive kontrolfisk også medtaget. Denne anden kohabitering blev afsluttet efter 77 dage. På dette tidspunkt havde alle de naive kontrolfisk udviklet adskillige RMS-hudlæsioner, hvorimod der ingen hudforandringer var at se hos de fisk, der tidligere var blevet smittet som sættefisk. Alle forsøg blev udført ved 12°C.
Konklusionen på forsøgene var altså, at beskyttende immunitet kunne induceres i sættefisk under de eksperimentelle forhold, og at disse fisk var beskyttede mod genudbrud af sygdommen i mindst 13 måneder.
Kemisk vandbehandling og økologisk akvakultur kan virke selvmodsigende. Men så længe udviklingen og forbedringer går imod bæredygtige løsninger er der ikke nogen direkte konflikt - tværtimod. Økologisk akvakultur adskiller sig fra konventionel fiskeopdræt ved de mere restriktive regler. Her er effektiv vandbehandling en udfordring og i den proces kan vigtig viden og erfaringer også understøtte forbedringer af driftsforhold i konventionel akvakultur.
Til forbedring af vandkvalitet anbefales:
• Reducer mængden af partikulært organisk stof, dvs. forbedret mikrobiel vandkvalitet/lavere bakteriel belastning og bedre ilt og CO2 forhold.
• Øge vand flow og cirkulation/intern recirkulation, dvs. bedre iltforhold, reduceret opholdstid og potentielt dæmpe aggression mellem fiskene i retning af mere strømlinet svømmeadfærd (velfærd).
• Proaktivt, at lære af anvende de let nedbrydelige hjælpestoffer med henblik på at blive mere fortrolig med sikre en mere optimal vandbehandling (dosering og fiske adfærd), når situationen opstår.
Kommende forsknings- og udviklings aktiviteter indenfor økologisk akvakultur foreslås at omfatte økologisk foder og fiske ernæring, fiske sundhed og velfærd, miljø aspekter inklusiv bæredygtig drift og brug af desinfektionsmidler i forhold til miljø, etik og økonomi, forbruger krav, fødevaresikkerhed og markedsforhold. Endelig er der behov for forbedret drifts praksis i forhold til mere bæredygtig fiske produktion. Denne proces kan få mere gennemslags kraft ved større samarbejde og åbenhed mellem industri, forbrugere, myndigheder og forskning.

EPrint Type:Report
Keywords:Organic aquaculture, trout, health, welfare, Red Mark Syndrome, water quality
Agrovoc keywords:
trout culture
water quality
Subjects: Environmental aspects > Air and water emissions
Animal husbandry > Health and welfare
Animal husbandry > Production systems > Aquaculture
Research affiliation: Denmark > Organic RDD 4 > ShelterFish
Deposited By: Jokumsen, Senior Advisory Scientist Alfred
ID Code:43856
Deposited On:07 Apr 2022 18:37
Last Modified:07 Apr 2022 18:37
Document Language:English
Refereed:Not peer-reviewed

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