The metabolic rate response to feed withdrawal in Atlantic salmon post-smolts

Feed withdrawal is a widespread practice in Atlantic salmon (Salmo salar) aquaculture to empty the gut prior to major farming operations, while certain pathogens and suboptimal environmental conditions in production cages are known to induce prolonged fasting. However, these fasting periods may be in conflict with ethical and legal obligations to farm animals. Presently, science-based recommendations on responsible fasting times that consider fish welfare are lacking. In this study, we measured the standard metabolic rate (SMR) and metabolic rate following acute handling and confinement stress in Atlantic salmon post smolts (~575 g, ~38 cm) following 1, 2, 3 and 4 weeks of feed withdrawal and 1 week of subsequent refeeding at 12 °C. The purpose was to identify when changes in metabolic mode occurred and assess whether the capacity to respond to stress eventually was compromised, since such observations could serve as potential welfare indicators. The SMR decreased significantly from 84.4 ± 4.7 mg O2 kg h−1 in control fish to 71.0 ± 1.8 mg O2 kg h−1 following 1 week of fasting. A further significant decrease to 65.0 ± 3.7 mg O2 kg h−1 was measured after 3 weeks, while refeeding returned SMR to control levels. The increase in MO2 following acute stress was unaffected for the first three weeks of fasting. However, the 4 week group showed a reduced peak response compared to the preceding weeks (278 ± 13 vs. 310 ± 7 mg O2 kg h−1). Weight, fork length and condition factor did not change significantly during the fasting period, and the fish immediately resumed eating upon refeeding. We conclude that up to 4 weeks of feed withdrawal had negligible effects on fish welfare. Moreover, an improved aerobic scope owing to a reduced SMR may be advantageous prior to certain farm operations.publishedVersio

Thaw rigor in Atlantic salmon (Salmo salar) fillets, as affected by thawing rate and frozen storage time

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Increasing Dip Net Mesh Size Results in More Fin Splits in Post-Smolt Atlantic Salmon (Salmo salar)

Dip nets are widely used to retrieve fish from the water but can cause injuries to the fish. The objective of this study was to document the potential effects of dip net mesh size with respect to external injuries, more specifically fin splits and scale losses, in Atlantic salmon (Salmo salar). The study included 273 post-smolt Atlantic salmon from two fish batches referred to as the Tank group (w¯¯¯ = 178 ± 36 g, n = 198) and the Cage group (w¯¯¯ = 1319 ± 334 g, n = 75). Four identical dip nets with mesh sizes of 5, 10, 15, and 20 mm, respectively, were used to net fish out of their enclosures before the external injuries were assessed by visual inspection. The results showed that the number and severity of fin splits increased with dip net mesh size, but no effect of mesh size on the percentage of scale losses was found. Dip-netting of five fish at a time instead of one with the 20 mm dip net, had no statistically significant effect on the examined injuries. It is concluded that the use of dip nets with smaller mesh sizes can be positive for fish welfare by reducing fin splitting.publishedVersio

Assessment of long-term implementation of sea lice prevention technologies: efficiency in reducing infestations and impact on fish welfare

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Part of CAC2016G Vindsvik: Integrated lice management -test of various combinations of preventive measures against lice.

Source at https://www.hi.no/en/hi/nettrapporter/rapport-fra-havforskningen/2018/45-2018_assessment_of_long-term_implementationSalmon lice prevention strategies are steering towards passive implementation, and this study aimed to monitor these strategies in commercial cages over time, to determine the efficiency of these approaches and their effect on welfare. Four strategies were tested at a commercial scale at the Centre for Aquaculture Competence (CAC; funded by CAC and FHF), over a 13-month period. The additive effect of multiple treatments was established in 12 cages, which were assigned to a prevention strategy of either cleaner fish only (A group), cleaner fish and functional feed (B group), the previous two factors plus deep attractant lights and submerged feeding (C group), or the previous three factors plus a lice skirt (D group). Environmental profiles and school swimming depth were monitored throughout the study period, and sampling events occurred every 3 –5 weeks to assess the infestation and welfare status of salmon. The rate of infestation fluctuated with season, however the group with all prevention strategies (D) maintained a lower rate of new infestations compared to the groups with in-cage prevention (A and B groups). However, even with strong differences in new infestations and swimming behaviour, the level of mobile lice was similar among all groups, thus incurring a similar frequency of delousing events. This is potentially due to unrepresentative sampling of salmon or reduced cleaner fish efficiency in treatment cages. There was no overall effect of these prevention strategies on welfare status of salmon during the study period. Thus, the tested prevention strategies have promising potential for commercial implementation; however, improved and consistent efficiency is likely to be achieved with flexible operation that changes with specific environmental conditions.I de senere år har det vært økt fokus på økt bruk av er en rekke forebyggende strategier mot lakselus i oppdrettsmerder. Dette studie dokumenterer hvordan ulike tiltak gjennom en produksjonssyklus egner er seg for bruk, med fokus på den lusereduserende effekt og laksens velferd. Forsøket ble gjennomført i kommersiell skala ved «Centre for Aquaculture Competence» (CAC, finansiert av CAC og FHF 901243), ved lokaliteten Vindsvik i Rogaland og varte i 13 måneder. Den adderende/ økende effekten av flere samtidige tiltak ble undersøkt i 12 merder. Forebyggende tiltak besto av enten bare rensefisk (gruppe A), rensefisk + funksjonelt fôr (gruppe B), rensefisk + funksjonelt fôr + dype lys og fôring (gruppe C) eller rensefisk + funksjonelt fôr + dype lys/ fôring + skjørt (gruppe D). Hver 3.-5. uke ble det tatt ut fisk for lusetelling av alle stadier og skåring av fisk for å vurdere laksens velferd. Miljøprofiler ble tatt daglig og ekkolodd ble benyttet i lange perioder. Påslag av lakselus varierte betydelig med sesong. Fiskegruppen som ble gitt samtlige forebyggende tiltak (D) hadde konsekvent lavere påslag enn gruppene som kun hadde rensefisk og funksjonelt fôr (A og B). Selv om det var store forskjeller i lusepåslag og svømmedyp var nivået av bevegelige lus likt mellom gruppene, og dermed var behovet for avlusing det samme. Potensielle årsaker kan være sammensatt og mangesidig, eksempelvis at rensefiskens effektivitet er redusert eller at representativiteten i uttakene ikke har vært lik mellom gruppene som svømmer på ulike dyp. Overordnet velferd hos laksen var lik mellom gruppene. De ulike forebyggende tiltakene hadde kommersielt potensial for å bli benyttet i forhold til velferd og produksjon. Men, det er behov for å etablere og vise mer stabil og bedre effekt mot lusepåslag. Muligens kan dette oppnås ved å kombinere bruken av tiltakene i takt med de varierende miljøforhold, med fokus på brakkvannslag, og laksens valg av svømmedyp

Lusepåslag og velferd hos dypfôret og overflatefôret laks på lokalitet Skrubbholmen midtvinters. – Delrapport fra FHF-prosjekt 901154 «Dypelysogfôring»

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Snorkelmerd: Produksjonseffektivitet, adferd og velferd. Sluttrapport FHF-prosjekt 900884

English: The snorkel cage creates a mismatch between the salmon lice infestative larvae stage and the salmon, thus minimizing infestations. The snorkel cages comprise a roof of net to keep the fish down, but with a tarpaulin dressed passage to the surface. Through this the salmon have access to surface air and can refill the swim bladder while still avoiding surface waters where lice larvae are most abundant. The idea was initiated in one of the Norwegian Research Council Centre’s for Research-based Innovation, CREATE, and further development of the principle has been supported by The Norwegian Seafood Research Fund since 2013. Egersund Net AS has been responsible for the design and manufacture of snorkels. Bremnes Seashore AS was the first to use commercial snorkels. In medium-scale experiments sea lice infestation was reduced by 84 to 66% through the summer in spring-transferred smolts, but growth was declined as a result of underfeeding. In a follow-up study with low stocking density and medium-sized fish, minimal growth differences were noted, but slightly increased snout wear and only partly swim bladder re-filling. With a brackish layer as deep as the snorkel depth there was no mitigating effects on infestations. Next trial on slaughter-sized fish, commercial stocking density, medium-scale cages and 4 m deep snorkels in coastal waters showed recurring reduction in sea lice infestation ranging 24-65%. Concurrently, production efficiency, behaviour and welfare were adequately maintained. "Proof of concept" was thus proven for medium-scale cages. The final trial displayed clearly that lice reduction increased with deeper swim depth of the fish (snorkel depth) and were virtually zero when the salmon had to swim deeper than 12 m in winter. At commercial scale, 50% lower lice levels were noted at a snorkel site compared to a neighbouring site during autumn 2014. In 2015, 100-65% less lice was counted in snorkel compared to normal cages within the same site. In snorkel cages, treatments against amoebic gill disease were avoided by introducing a fresh water layer in the top of the snorkel. There have been some challenges with deployment, management and maintenance of the water quality of the snorkels. There is still room for optimization of design, use, and handling at large scale. However, most normal operations in large-scale snorkels may be performed (e.g. net changing, chemical lice treatment, sampling). Use of commercial snorkels needs further developed and documented the next few years, and applications are submitted for scientific testing of using a surface freshwater layer against AGD this autumn. Overall, the snorkel cage trials and commercial tests have repeatedly shown that salmon swimming deeper becomes less infested by the salmon lice, Lepeophtheirus salmonis. Such also opens up for the use of a variety of other methods to reduce sea lice infestation, for example submerged cages with air domes, repetitively submerged cages, lighting and feeding strategies that lure salmon deeper. The data also verifies that the present use of skirts around the cages is prone to have a lice inhibitory infestative effect. In summary, deep enough snorkels have the potential for salmon in cages to be infested by close to zero lice. Such would lead to that today's demanding operations with de-licing, general negative environmental impact and potentially reduced fish welfare can be decimated. The snorkel method is innovative, sustainable and environmentally friendly while the farmed salmon needs and welfare is safeguarded. Norsk: Snorkelmerd skaper avstand/ ”mismatch” mellom lakselusens frittlevende, infesterende larver (kopepoditter) og laksen. Dermed blir lusepåslaget minimalisert. Snorkelmerden består av et tak av not for å holde fisken nede, men med en presenningskledd passasje til overflaten. Gjennom denne har laksen tilgang til luft og etterfylling av svømmeblæren, uten at fisken kommer i kontakt med overflatevannet hvor de infesterende luselarvene oppholder seg mest. Ideen ble initiert i et av Forskningsrådets sentre for forskningsdrevet innovasjon, CREATE, og videreutvikling av prinsippet er støttet av FHF siden 2013. Egersund Net har stått for design og produksjon av snorkler. Bremnes Seashore var først ute med å bruke kommersielle snorkler. I innledende mellomskala forsøk ble lusepåslag redusert med 84 til 66 % gjennom sommeren på vårutsatt fisk, men tilvekst redusert som følge av underfôring. I oppfølgende studie med lav tetthet og mellomstor fisk, så vi minimale forskjeller i tilvekst, men noe økt snuteslitasje og ikke fullstendig svømmeblærefylling. Med brakkvannslag like dypt som snorkelen var det ingen reduserende effekt på lusepåslaget. Med slaktestørrelse fisk, kommersiell tetthet i mellomskala merder og 4 m dype snorkler ble det på kystlokalitet vist gjentagende reduksjon i lusepåslag i størrelsesorden 24-65 %. Samtidig var produksjonseffektivitet, normal atferd og velferd opprettholdt tilstrekkelig. ”Proof of concept” var dermed bevist i mellomskala merder. Siste mellomskala forsøk viste at effekten av snorkelmerd øker med laksens påtvungne svømmedyp (snorkeldypet) og at påslag var tilnærmet null når laksen måtte svømme dypere enn 12 m om vinteren. Hos Bremnes Seashore var det 50 % lavere lusenivå enn ved sammenlignbart naboanlegg på H14 utsett. Ved V15-utsett var det 100-65 % mindre lus i to snorkelmerder sammenlignet med to normale kontrollmerder på samme anlegg. Snorkelanlegget med høstfisk klarte å unngå behandling mot amøbisk gjellesykdom ved å introdusere ferskvannslag i toppen av snorkelen. Det har vært en del utfordringer med utsetting, håndtering og opprettholdelse av et godt miljø i snorkelen. Fremdeles er det rom for optimalisering av design, bruk og ikke minst håndtering i stor skala. Det er likevel mulig å gjennomføre de fleste normale operasjoner i storskala snorkler (eksempelvis notskift, kjemisk lusebehandling, uttak). Bruk av kommersielle snorkler videreutvikles og dokumenteres de neste årene, og planer er lagt for vitenskapelig uttesting av ferskvannslag i overflaten mot AGD denne høsten. Totalt sett er det gjentagende vist at laks som svømmer dypere blir mindre infestert av lakselus, Lepeophtheirus salmonis. Dette åpner også opp for bruk av en rekke andre metoder for redusert lusepåslag, eksempelvis nedsenkete merder med luftlomme, repetitivt nedsenkete merder, lys og fôringsstrategier som lokker laksen dypere. Samtidig verifiserer dataene at bruk av skjørt/duk rundt merdene vil ha en påslagshemmende effekt. Oppsummert så kan dyp nok snorkelmerd ha potensial for at laksen i merdene kan få bortimot null lus og dagens krevende operasjoner med avlusing, generell negativ miljøpåvirkning og potensielt nedsatt fiskevelferd kan desimeres. Snorkelmetoden er innovativ, bærekraftig og miljøvennlig, samtidig som laksens behov og velferd er ivaretatt

Is it advantageous for Atlantic salmon to be triploid at lower temperatures?

Marine organisms living at low temperatures tend to have larger genomes and larger cells which suggest that these traits can be beneficial in colder environments. In fish, triploidy (three complete sets of chromosomes) can be induced experimentally following fertilization, which provides a model system to investigate the hypothesis that larger cells and genomes offers a physiological advantage at low temperatures. We tested this hypothesis by measuring metabolic rates and swimming performance of diploid and triploid Atlantic salmon (Salmo salar) post smolts acclimated to 3 or 10.5 °C. At 10.5 °C, triploids had significantly lower maximum metabolic rates which resulted in a lower aerobic scope compared to diploids. In addition, triploids initiated ram ventilation at lower swimming speeds, providing further evidence of a reduced capacity to meet oxygen demands during strenuous activity at 10.5 °C. However, at 3 °C, metabolic rates and critical swimming speeds were similar between both ploidies, and as expected substantially lower than at 10.5 °C. Therefore, triploidy in colder environments did not provide any advantage over diploidy in terms of metabolic rate traits or swimming performance in Atlantic salmon. We therefore conclude that traits, other than aerobic scope and swimming performance, contribute to the trend for increased cell and genome size in marine ectotherms living in cold environments.publishedVersio

Differential effects of internal tagging depending on depth treatment in Atlantic salmon: a cautionary tale for aquatic animal tag use.

Electronic tags are widespread tools for studying aquatic animal behavior; however, tags risk behavioral manipulation and negative welfare outcomes. During an experiment to test behavioral differences of Atlantic salmon Salmo salar in different aquaculture cage types, including ones expected to elicit deeper swimming behavior, we found negative tagging effects depending on whether cages were depth-modified. In the experiment, data storage tags implanted in Atlantic salmon tracked their depth behavior and survival in unmodified sea-cages and depth-modified sea-cages that forced fish below or into a narrow seawater- or freshwater-filled snorkel tube from a 4 m net roof to the surface. All tagged individuals survived in unmodified cages; however, survival was reduced to 62% in depth-modified cages. Survivors in depth-modified cages spent considerably less time above 4 m than those in unmodified cages, and dying individuals in depth-modified cages tended to position in progressively shallower water. The maximum depth that fish in our study could attain neutral buoyancy was estimated at 22 m in seawater. We calculated that the added tag weight in water reduced this to 8 m, and subtracting the tag volume from the peritoneal cavity where the swim bladder reinflates reduced this further to 4 m. We conclude that the internal tag weight and volume affected buoyancy regulation as well as the survival and behavior of tagged fish. Future tagging studies on aquatic animals should carefully consider the buoyancy-related consequences of internal tags with excess weight in water, and the inclusion of data from dying tagged animals when estimating normal depth behaviors.publishedVersio