Influence of feed ration size on somatic and muscle growth in landlocked dwarf and farmed Atlantic salmon Salmo salar

We examined the possible adaptation of the dwarf Bleke population of Atlantic salmon Salmo salar from Lake Byglandsfjord in southern Norway to limited food resources. The growth performance and muscle development in juvenile Bleke and farmed S. salar under satiated or restricted (50%) feeding were examined for 10 months, starting 3 weeks after first‐feeding stage. Four‐thousand fish were divided into four replicated groups and random samples of 16–40 fish per group were measured six times during the experiment. The two strains showed no significant difference in mean body mass when fed restricted ration, but the individual variation was considerably higher in the farmed fish. Both Bleke and farmed S. salar grew significantly faster when fed to satiation, but the farmed S. salar showed much higher gain in mass and were three times heavier (201.5 g v. 66.7 g) and possessed twice as many fast muscle fibres (179682 v. 84779) compared with landlocked S. salar after 10 months. Farmed fish fed full ration displayed both hypertrophic and hyperplasic muscle growth, while the increased growth in Bleke S. salar was entirely associated with a larger fibre diameter. The landlocked Bleke strain has apparently adapted to low food availability by minimising the metabolic costs of maintenance and growth through reduced dominance hierarchies and by an increase in average muscle fibre diameter relative to the ancestral condition.PostprintPeer reviewe

Rib abnormalities and their association with focal dark spots in Atlantic salmon fillets

publishedVersio

Gradually decreasing daylength after smoltification induced by “winter signal“ reduced sexual maturation in male Atlantic salmon

publishedVersio

Smoltification, seawater performance, and maturation in Atlantic salmon (Salmo salar) fed different fat levels

IntroductionThe use of recirculating aquaculture systems (RAS) to produce Atlantic salmon smolts has resulted in exceptionally high fish growth rates. However, there are potential negative trade-offs between fast growth and key physiological processes, such as inadequate smoltification and early sexual maturation, which can both be linked to body energy reserves.MethodsThis study determined the effect of i) dietary fat levels on Atlantic salmon whole-body fat and fatty acids composition, growth performance and smoltification and ii) a previous dietary regime on seawater growth performance and male early sexual maturation. In freshwater RAS, salmon parr (~19g) were fed 3 fat levels (20, 24, and 28%) over a 14-week period at 12°C. Subsequently, in seawater flow-through systems, smolt (~96g) were fed a control diet (26%) for 12 weeks at 2 temperatures (12 and 16°C).ResultsDietary fat levels resulted in differences in k-factor, fish whole-body fat and fatty acids composition; the low fat diet resulted in fish with a 23% lower whole-body fat when compared to the other two dietary groups at the end of the freshwater phase. These differences in whole-body fat faded at the end of the seawater phase. During the freshwater phase, all three feeds resulted in a comparable growth performance and smoltification indicator values, including k-factor, gill Na+, K+-ATPase, blood serum chloride and smolt index score. In contrast, water temperature resulted in fish body weight differences, where groups reared at 16°C were larger than those reared at 12°C. Nevertheless, both temperature regimes supported a similar thermal growth coefficient. Smolts grown at 16°C showed a higher level of the sex steroids androstenedione compared to those at 12°C. However, 11-ketotestosterone and testosterone levels did not differ despite a trend for higher levels at 16°C. Furthermore, testis histology at the final sampling indicated that some individuals showed initial signs of maturation (stage 3).DiscussionIn conclusion, varying dietary fat levels (20 - 28%) during the freshwater phase did not influence smoltification or male early sexual maturation during the subsequent grow-out phase. However, a temperature increase from 12 to 16°C resulted in larger fish and appeared to stimulate early male maturation in some fish individuals

PENGARUH KETERAMPILAN KERJA TERHADAP PRODUKTIVITAS KERJA ARSIPARIS BAPUSIPDA SE-BANDUNG RAYA

Penelitian ini dilakukan di Badan Perpustakaan dan Kearsipan Daerah (BAPUSIPDA) yang ada di sekitar Bandung raya. Penelitian ini mengkaji tentang rendahnya produktivitas kerja arsiparis Bapusipda se-Bandung raya yang diduga disebabkan oleh kurangnya tingkat keterampilan kerja para arsiparis. Metode yang digunakan dalam penelitian ini adalah metode survey eksplanasi, dimana data dikumpulkan dengan menyebarkan angket yang dikembangkan dengan menggunakan model skala likert pada 31 pegawai arsiparis di Bapusipda se-Bandung raya yang diambil sebagai sampel. Data yang terkumpul dalam penelitian ini diuji dengan menggunakan uji regresi linier sederhana. Hasil penelitian menunjukkan bahwa: (1) tingkat keterampilan kerja arsiparis berada pada kategori sedang; (2) tingkat produktivitas kerja arsiparis berada pada kategori cukup; (3) terdapat pengaruh yang sangat kuat dari keterampilan kerja terhadap produktivitas kerja arsiparis di Bapusipda se-Bandung raya. Penelitian ini menyarankan agar pihak Bapusipda memberikan dorongan motivasi yang lebih kepada para pegawai dengan cara memberikan penghargaan dan pengakuan yang tepat dan wajar kepada pegawai atas prestasi kerja yang telah dicapainya. Selain itu, pihak Bapusipda seyoganya mengadakan kegiatan pendidikan dan pelatihan dengan intensitas yang lebih tinggi, agar profesionalisme dan produktivitas kerja para arsiparis meningkat. ---------- This research was conducted in Agency for Library and Archives (henceforth, BAPUSIPDA). It investigates the low productivity of the archivists in the institution, which was assumed to have been caused by a lack of work skills. This research adopts survey-explanatory method, where data were collected by distributing a set of questionnaires using Likert scale to a sample of 36 archivists in BAPUSIPDA. The collected data were analyzed using simple linear regression. The results show that: (1) the level of archivists’ work skills was at the medium category; (2) the level of productivity of the archivists was at the moderate category; and (3) there was quite significant influence of work skills on work productivity of the archivists at BAPUSIPDA. This study recommends that BAPUSIPDA should further motivate the employees by giving adequate and appropriate rewards and recognition for their work achievements. In addition, BAPUSIPDA should also provide more intensive inservice educational activities and training in order to develop the archivists’ professionalism and work productivity

EX-spot: Mørke flekker i laksefilet. Årsak til dannelse og tiltak som hemmer utvikling

publishedVersio

Vekst, fôrutnyttelse, helse og biometriske parameter hos Atlantisk laks (Salmo salar L.) – Effekt av protein-til-fett forholdet i fôret og fettinnholdet i laksen

Today, commercial diets for large farmed Atlantic salmon (Salmo salar L.) commonly contain 30-35 % protein and 35-39 % lipids, i.e. a ratio of protein-to-lipids below 1. Such energy dense diets have generally been shown to improve feed utilization and growth. However, reducing the dietary protein-to-lipid ratio may lead to increased deposition of fat in the muscle and visceral cavity. There is evidence that high levels of body lipids may reduce feed intake and growth in salmonids, and is often referred to as lipostatic regulation. Thus, there is a risk of lowered growth prior to and during periods with increased feed intake and high fat accumulation when feeding high-fat diets. The present thesis test the hypothesis that increased dietary protein-to-lipid ratio, and the possible involvement of lipostatic regulation on body fat levels can be utilized to significantly improve fitness-related traits including growth, survival and nutrient deposition of farmed Atlantic salmon. Paper I describes the effects of isoenergetic diets with different protein-to-lipid (P/L) ratio on growth, feed intake, feed conversion, biometrics, nutrient retention and deposition in S1 Atlantic salmon post-smolt. The study was conducted during the early seawater phase from April to September. Significantly lower muscle fat, whole body lipid, and energy level was observed in the post-smolt fed high compared to low P/L ratio in July, approximately three months after the trial started. Reduced level of muscle fat/body fat in July significantly improved feed intake, growth and weight gain compared to fish fed low P/L ratio from July to September. The high P/L ratio group had also a significantly lower feed conversion ratio based on gutted weight (FCRg). In line with this, the visceral somatic index (VSI) of the group fed the high dietary P/L ratio was relatively stable during the experiment, whereas the VSI of the group fed the low dietary P/L ratio increased gradually, resulting in significantly higher VSI at the end of the trial. The increased protein content in the high P/L ratio diets was efficiently utilized for growth and weight gain, assessed by nutrient retention, particularly in the last period of the trial. In Paper II, low and high P/L ratios and restricted ration (~ 50%) of the high P/L diet were used to alter the lipid deposition prior to the autumn in large salmon. In this study, a clear treatment effect on body fat was observed after three months (May - August). The salmon fed low P/L ratio had higher fat content than those fed high P/L ratio, both in muscle (16.4 vs. 13.2 %) and viscera (39 vs. 29 %). Restricting the ration of the high P/L diet to 50 % further reduced the fat content to 11.3 % in muscle and 27 % in the viscera. Tagged individuals from the groups with different lipid content were restocked and mixed in the same pens, and then fed the same diet for seven months (August – March). As in Paper I, reducing the level of muscle fat prior to autumn significantly increased growth and weight gain from August to October. In other words, the weight gain was the highest for the restricted group, intermediate for the high P/L ratio and the lowest for the low P/L ratio group. In October, after two months of feeding a common diet, the muscle fat content was similar in fish from all three groups, whereas the differences in visceral fat content disappeared after four months (December). Although the differences in body weight, length and lipid content between the groups had been offset, the high P/L ratio and restricted group showed a significantly increased growth compared to the low P/L-ratio group in the latter stages of the trial (December – March), resulting in an overall weight gain difference of up to 1 kg. The high P/L ratio group had significantly higher final body weight, whereas the restricted group ended up with a numerically higher final body weight than in the low P/L ratio group. In addition, the variation in body weight and shape was significantly higher in the low P/L ratio group. The results from Paper I and II demonstrate that in early autumn, the salmon is able to replenish lipid stores rapidly after dietary lipid restriction and that energy intake and storage is of high priority. In Paper I, unlike Paper II, low and high P/L ratio were fed throughout the trial and it is therefore not possible to isolate the direct effect of diet on growth from the indirect effect caused by different body fat accumulation. Hence, paper I may also indicate that dietary P/L-ratio of 1.12 (DP/DE of 15.2 g MJ kg-1) was below the P/L ratio for optimal growth during the early seawater phase for S1 salmon. This result is in line with previous studies, although now verified using isoenergetic diets under ambient environmental conditions. Paper III describes the effects of increased dietary P/L ratio for S0 salmon on mortality rates, biometric and quality related parameters during the entire grow-out period in sea, within the SAV3 endemic zone. The low P/L group was fed a typical standard diet with 35% protein and 35% fat (P/L: 1), versus the high P/L group that was fed a diet with 47% protein and 24% fat content (P/L: 2). During the first summer at sea, a co-infection of SAV3 and PRV was detected and a natural PD outbreak was observed. The increased dietary P/L ratio improved survival during the natural outbreak of PD. In addition to diet, body weight and delousing mortality (induced stress) prior to the PD outbreak were also found to contribute significantly to explain the observed variation in PD associated mortality. The high P/L group had a mean mortality rate of 1.9 %, whereas the low P/L group had a mean mortality rate of 3.7 %. Subsequent to the PD outbreak, a large amount of fish failed to grow and caused an accumulation of runts (severely thin diseased fish). At the end of the trial, a significantly lower amount of runt fish was detected among fish fed high P/L ratio (12 vs. 21%) and among large compared to small body weight groups (11 vs. 20%) prior to PD. In Paper IV, an event of sudden mortality of large (2.5 kg) seemingly healthy farmed salmon during the winter period in northern Norway is reported. The experimental fish were reared in four net-pens and two dietary treatments were established; a high or low P/L ratio diets. An increased mortality (of 6 and 10%) was only observed within the two net-pens receiving the high P/L ratio experimental diets, following an abrupt reduction in dietary P/L ratio (increase in dietary fat level) six weeks earlier. The moribund/dying fish had significantly higher lipid content in the liver, altered hepatic fatty acid composition, and increased levels of ALT and AP in the blood plasma compared to non-dying fish, indicating impaired hepatic function. A possible hypothesis involving reduced recruitment of fat cells in high P/L-salmon is presented. Taken together, the results from this thesis show that alterations in dietary protein-to-lipid ratio have profound potential effects on growth, lipid deposition, nutrient retention and health of farmed Atlantic salmon. The results obtained during this work related to fat deposition and subsequent growth may be crucial knowledge when developing new dietary concepts in semi-closed and closed RAS production units, where water temperature and photoperiod can be manipulated.I dag inneholder kommersielle dietter for stor oppdrettet Atlantisk laks (Salmo salar L.) vanligvis 30-35% protein og 35-39% fett, dvs. et forhold mellom protein-til-lipider under 1. Slike energitette dietter har generelt vist seg å kunne forbedre fôrutnyttelse og vekst. Imidlertid kan en reduksjon av protein-til-lipid forholdet i fôret føre til økt deponering av fett i muskel og rundt innvollene. Det er vist at høye nivåer av kroppsfett kan redusere fôrinntak og vekst hos laksefisk og blir ofte referert til som lipostatisk regulering. Det er derfor en økt risiko for redusert vekst dersom man benytter et fôr med et høyt fettinnhold før og under perioder hvor fôrinntaket og fettakkumulering er høy. Denne avhandlingen tester hypotesen om at økt protein-til-lipid-forhold i fôret til laks, samt en mulig involvering av lipostatisk regulering ved å redusere kroppsfettet, kan utnyttes for å forbedre egenskaper som tilvekst, overlevelse og fôrutnyttelse hos oppdrettslaks. Artikkel I beskriver effekten av isoenergetiske dietter med forskjellig protein-til-lipid (P/L) forhold på vekst, fôrinntak, fôrutnyttelse, biometri og retensjon av næringsstoffer hos S1 post-smolt. Denne studien ble gjennomført fra sjø-utsett i april til september. Det ble funnet et signifikant lavere nivå av fett og energi i muskel og helkropp for laks gitt et fôr med høyt sammenlignet med lavt P/L forhold i juli, omtrent tre måneder etter at forsøket startet. Det redusert nivå av kroppsfett i juli forbedret fôrinntaket, veksten og vektøkningen betydelig sammenlignet med fisken som ble gitt et lavere P/L forhold i perioden juli til september. Gruppen gitt et høyt P/L forhold hadde også bedre fôrutnyttelse basert på sløyd vekt (FCRg). I tråd med dette var den relative innvollsvekten (viscerale somatiske indeksen, VSI) for gruppen gitt et høye P/L forholdet relativt stabilt under forsøket, mens VSI for gruppen gitt et lavere P/L forhold økte gradvis, noe som resulterte i signifikant høyere VSI på slutten av forsøket. Det økte proteininnholdet i diettene med høyt P/L forhold ble effektivt utnyttet for vekst og vektøkning, vurdert ved retensjonsberegninger, særlig i den siste perioden av forsøket. I artikkel II, ble lave og høye nivåer P/L forhold i fôret, samt begrenset rasjon (~ 50%) av det høye P/L fôret benyttet for å endre fettnivået/status før høsten i stor laks. I denne studien ble det påvist en klar effekt av de ulike fôrbehandlingen tre måneder etter forsøksstart (mai - august). Gruppen gitt et lavt P/L forhold hadde høyere fettinnhold enn gruppen gitt et høyt P/L forhold, både i muskel (16,4 vs. 13,2%) og innvollsmassen (39 vs. 29%). Ved å gi halv rasjon av fôret med et høyt P/L forhold ble fettet deponering reduserte ytterligere til 11,3% i muskel og 27% i innvollsmassen. Gruppene (markert med PIG-tagg) med forskjellig fett innhold ble deretter overført til samme enheter/merder oppsamlet og gitt lik diett (samme P/L forhold) i syv måneder (august - mars). I likhet med artikkel 1 ble det vist at gruppene med et redusert nivå av kroppsfett før høsten hadde økt tilvekst fra august til oktober. Vektøkningen var høyere for gruppene gitt halv rasjon og et høyt P/L forhold sammenliknet med gruppen gitt et fôr med lavt P/L forhold. I oktober, etter to måneder med fôring av lik diett, var det ingen forskjeller i muskelfett mellom de ulike gruppene og forskjellene innvollsfettet var borte etter fire måneder (desember). Selv om forskjellene i kroppsvekt, lengde og fettinnhold mellom gruppene var blitt kompensert, ble det observert en signifikant økning i tilvekst for gruppen gitt det høye P/L forholdet og halv rasjon av dette fôret (fra mai-august) sammenlignet med gruppen gitt et lave P/L forhold i den siste perioden av forsøket (desember - mars). Dette resulterte i en total relativt vektøkning for gruppene gitt halv rasjon og et høyt P/L forhold på opptil 1 kg. Gruppen gitt et høyt P/L forhold hadde derfor en signifikant høyere sluttvekt, mens gruppen gitt halvrasjon av dette fôret endte opp med en numerisk høyere sluttvekt sammenliknet med gruppen gitt et lave P/L forhold. I tillegg var variasjonen i fiskevekt og kroppsform signifikant høyere i gruppen gitt lavt P/L forhold. I artikkel III blir effekten av et økt P/L forholdet i fôret for S0 laks på overlevelse, biometriske registeringer og kvalitets parametere i løpet av hele sjøfasen, innenfor den SAV3-endemiske sonen testet. En gruppe ble fôret med et standard høyfett-fôr med 35% protein og 35% fett (P/L: 1), men den andre gruppen ble gitt et fôr med 47% protein og 24% fett (P/L: 2). I løpet av den første sommeren i sjø ble det oppdaget en samtidig infeksjon av SAV3 og PRV, og det ble observert et naturlig utbrudd av PD. Økt forhold mellom P/L i fôret forbedret overlevelsen under det naturlige utbruddet av PD. I tillegg til diett ble kroppsvekt og dødelighet ved avlusing (indusert stress) før PD utbruddet også funnet å bidra betydelig til å forklare den observerte variasjonen i PD-relatert dødelighet. Gruppen gitt et fôr med høyt P/L forhold hadde en gjennomsnittlig dødelighet på 1,9%, mens gruppen gitt lavt P/L forhold hadde en gjennomsnittlig dødelighet på 3,7%. Etter PD-utbruddet mislyktes en stor mengde fisk med å gjenoppta inntak av mat og forårsaket en kraftig akkumulering av såkalte «runts/taperfisk», som er alvorlig avmagret klinisk syk fisk. På slutten av forsøket ble det registrert en signifikant lavere mengde med runts blant gruppen gitt et fôr med høyt P/L forhold (12 vs. 21%) og blant stor sammenliknet med liten kroppsvekt (11 vs. 20%) før PD utbruddet inntraff (1.9 vs. 1.3 kg). Artikkel IV beskriver en hendelse med plutselig økt dødelighet av stor (2,5 kg) tilsynelatende frisk oppdrettslaks i løpet av vinteren i Nord-Norge. I dette forsøket ble fisken oppdrettet i fire merder, hvorav to ble gitt en fôrserie med høyt P/L forhold og de to andre et fôrserie med lavt P/L forhold. Den økte dødelighet (på 6 og 10%) ble kun observert i de to enhetene/merdene som ble gitt fôrserien med høyt P/L forhold først etter at fettinnholdet i denne fôrserien ble økt (reduserte P/L forholdet) seks uker tidligere. Den døende fisken hadde betydelig høyere fettinnhold i leveren, endret fettsyresammensetning, og økte nivåer av ALT og AP i blodplasma sammenlignet med ikke-døende frisk fisken. Dette kan indikere en nedsatt leverfunksjon hos den døende fisken, som trolig har negative konsekvenser for helse og robustheten til denne fisken. En mulig hypotese som involverer redusert rekruttering av fettceller i laks gitt et høy P/L forhold blir presentert. Samlet sett viser resultatene fra denne avhandlingen at endringer i protein-til-lipid forhold i fôr til oppdrettslaks har store effekter på fôrinntak, tilvekst, fett deponering og helse. potensielle effekter på vekst, lipidavsetning, næringsreservering og helse av oppdrettslaksatlantisk laks. Resultatene i denne avhandlingen knyttet til fettdeponering og påfølgende vekst, kan være viktig kunnskap ved utvikling av nye fôrkonsepter i semi-lukkede og lukkede RAS-produksjonsenheter hvor vanntemperatur og fotoperiode kan manipuleres

Growth, feed utilization, health and biometric parameters in Atlantic salmon (Salmo salar L.) - Influence of dietary protein-to-lipid ratio and body fat status

Today, commercial diets for large farmed Atlantic salmon (Salmo salar L.) commonly contain 30-35 % protein and 35-39 % lipids, i.e. a ratio of protein-to-lipids below 1. Such energy dense diets have generally been shown to improve feed utilization and growth. However, reducing the dietary protein-to-lipid ratio may lead to increased deposition of fat in the muscle and visceral cavity. There is evidence that high levels of body lipids may reduce feed intake and growth in salmonids, and is often referred to as lipostatic regulation. Thus, there is a risk of lowered growth prior to and during periods with increased feed intake and high fat accumulation when feeding high-fat diets. The present thesis test the hypothesis that increased dietary protein-to-lipid ratio, and the possible involvement of lipostatic regulation on body fat levels can be utilized to significantly improve fitness-related traits including growth, survival and nutrient deposition of farmed Atlantic salmon. Paper I describes the effects of isoenergetic diets with different protein-to-lipid (P/L) ratio on growth, feed intake, feed conversion, biometrics, nutrient retention and deposition in S1 Atlantic salmon post-smolt. The study was conducted during the early seawater phase from April to September. Significantly lower muscle fat, whole body lipid, and energy level was observed in the post-smolt fed high compared to low P/L ratio in July, approximately three months after the trial started. Reduced level of muscle fat/body fat in July significantly improved feed intake, growth and weight gain compared to fish fed low P/L ratio from July to September. The high P/L ratio group had also a significantly lower feed conversion ratio based on gutted weight (FCRg). In line with this, the visceral somatic index (VSI) of the group fed the high dietary P/L ratio was relatively stable during the experiment, whereas the VSI of the group fed the low dietary P/L ratio increased gradually, resulting in significantly higher VSI at the end of the trial. The increased protein content in the high P/L ratio diets was efficiently utilized for growth and weight gain, assessed by nutrient retention, particularly in the last period of the trial. In Paper II, low and high P/L ratios and restricted ration (~ 50%) of the high P/L diet were used to alter the lipid deposition prior to the autumn in large salmon. In this study, a clear treatment effect on body fat was observed after three months (May - August). The salmon fed low P/L ratio had higher fat content than those fed high P/L ratio, both in muscle (16.4 vs. 13.2 %) and viscera (39 vs. 29 %). Restricting the ration of the high P/L diet to 50 % further reduced the fat content to 11.3 % in muscle and 27 % in the viscera. Tagged individuals from the groups with different lipid content were restocked and mixed in the same pens, and then fed the same diet for seven months (August – March). As in Paper I, reducing the level of muscle fat prior to autumn significantly increased growth and weight gain from August to October. In other words, the weight gain was the highest for the restricted group, intermediate for the high P/L ratio and the lowest for the low P/L ratio group. In October, after two months of feeding a common diet, the muscle fat content was similar in fish from all three groups, whereas the differences in visceral fat content disappeared after four months (December). Although the differences in body weight, length and lipid content between the groups had been offset, the high P/L ratio and restricted group showed a significantly increased growth compared to the low P/L-ratio group in the latter stages of the trial (December – March), resulting in an overall weight gain difference of up to 1 kg. The high P/L ratio group had significantly higher final body weight, whereas the restricted group ended up with a numerically higher final body weight than in the low P/L ratio group. In addition, the variation in body weight and shape was significantly higher in the low P/L ratio group. The results from Paper I and II demonstrate that in early autumn, the salmon is able to replenish lipid stores rapidly after dietary lipid restriction and that energy intake and storage is of high priority. In Paper I, unlike Paper II, low and high P/L ratio were fed throughout the trial and it is therefore not possible to isolate the direct effect of diet on growth from the indirect effect caused by different body fat accumulation. Hence, paper I may also indicate that dietary P/L-ratio of 1.12 (DP/DE of 15.2 g MJ kg-1) was below the P/L ratio for optimal growth during the early seawater phase for S1 salmon. This result is in line with previous studies, although now verified using isoenergetic diets under ambient environmental conditions. Paper III describes the effects of increased dietary P/L ratio for S0 salmon on mortality rates, biometric and quality related parameters during the entire grow-out period in sea, within the SAV3 endemic zone. The low P/L group was fed a typical standard diet with 35% protein and 35% fat (P/L: 1), versus the high P/L group that was fed a diet with 47% protein and 24% fat content (P/L: 2). During the first summer at sea, a co-infection of SAV3 and PRV was detected and a natural PD outbreak was observed. The increased dietary P/L ratio improved survival during the natural outbreak of PD. In addition to diet, body weight and delousing mortality (induced stress) prior to the PD outbreak were also found to contribute significantly to explain the observed variation in PD associated mortality. The high P/L group had a mean mortality rate of 1.9 %, whereas the low P/L group had a mean mortality rate of 3.7 %. Subsequent to the PD outbreak, a large amount of fish failed to grow and caused an accumulation of runts (severely thin diseased fish). At the end of the trial, a significantly lower amount of runt fish was detected among fish fed high P/L ratio (12 vs. 21%) and among large compared to small body weight groups (11 vs. 20%) prior to PD. In Paper IV, an event of sudden mortality of large (2.5 kg) seemingly healthy farmed salmon during the winter period in northern Norway is reported. The experimental fish were reared in four net-pens and two dietary treatments were established; a high or low P/L ratio diets. An increased mortality (of 6 and 10%) was only observed within the two net-pens receiving the high P/L ratio experimental diets, following an abrupt reduction in dietary P/L ratio (increase in dietary fat level) six weeks earlier. The moribund/dying fish had significantly higher lipid content in the liver, altered hepatic fatty acid composition, and increased levels of ALT and AP in the blood plasma compared to non-dying fish, indicating impaired hepatic function. A possible hypothesis involving reduced recruitment of fat cells in high P/L-salmon is presented. Taken together, the results from this thesis show that alterations in dietary protein-to-lipid ratio have profound potential effects on growth, lipid deposition, nutrient retention and health of farmed Atlantic salmon. The results obtained during this work related to fat deposition and subsequent growth may be crucial knowledge when developing new dietary concepts in semi-closed and closed RAS production units, where water temperature and photoperiod can be manipulated

Influence of dietary tetradecylthioacetic acid (TTA) on lipid content and fatty acid composition in liver of 1+ Atlantic salmon (Salmo salar L.) and sex-specific differences in muscle fat provoked by TTA.

Tetradesyltioeddiksyre (TTA) er en modifisert fettsyre som har vist seg å ha en rekke biologiske og fysiologiske effekter hos pattedyr og fisk. I forsøk med Atlantisk laks (Salmo salar L.) har tilsetting av TTA i fôret vist seg å redusere fettreserver i kroppen og øke kapasiteten for fettoksidasjon i muskel og lever. Målet med dette forsøket var evaluere påvirkningen av TTA på fettinnhold og fettsyresammensetning i lever hos laks. Det ble også undersøkt hva salgs effekter TTA kan ha på fettreserver og om dette kan variere mellom kjønn. Forsøket ble utført med atlantisk laks (1+ smolt) satt ut i sjøen 14. april 2009 (snittvekt 105 g) og denne fisken ble fulgt inntil avslutningen av forsøket i begynnelsen av mai året etter. Fisken ble fordelt i 12 merder med tre gjentak per fôrbehandling. Under forsøket ble det fôret fire ulike fôrtyper; kontrollfôr (CONTR), kontrollfôr tilsatt 1.5 % glutamat (GLU), kontrollfôr tilsatt 1.5 % arginin (ARG) og kontrollfôr tilsatt 0.25 % TTA (TTA-SD). Innvirkningen av TTA tilsetning på vekst, fôrinntak, kondisjonsfaktor, fôrutnyttelse, fettsyresammensetning i lever, samt fettinnhold i både muskel og lever ble fastslått under forsøksperioden. Det ble også undersøkt om det var kjønns-spesifikke forskjeller mellom fisk gitt de ulike fôrtypene. Fôr tilsatt TTA ble gitt i to perioder under forsøket. I den første perioden ble TTA gitt fra og med sjøutsett og inntil fisken hadde spist den mengden av fôr tilsatt TTA som tilsvarer 0.2 prosent av den opprinnelige kroppsvekten (varighet 10 uker). I den andre perioden ble TTA gitt i 6 uker sent på vinteren. Etter de to periodene ble fôr tilsatt TTA erstattet med kontrollfôr (CONTR). Det ble ikke funnet negative signifikante effekter av TTA på gjennomsnittlig vekst eller fôrinntak. Det ble allikevel registrert at fisk gitt fôr tilsatt TTA hadde en signifikant lavere vekstrate og fôrinntak de første seks ukene etter sjøutsett, sammenlignet med fisk tildelt de andre fôrtypene (N-TTA-SD). Den hepatiske stomatic indeks (HSI) sammen med fettinnholdet i leveren til fisk gitt TTA var signifikant høyere ved slutten av første TTA fôring, 10 uker etter sjøutsett. Ved sluttuttaket i mai, etter den andre TTA fôringen, ble det derimot observert at fisk gitt TTA-SD, ARG og GLU hadde en signifikant lavere HSI sammenlignet med fisk gitt CONTR. Etter både den første og andre TTA fôringen hadde fisk gitt TTA-SD en tendens til økt andelen av n-3 flerumettede og mettede fettsyrer i leveren, mens nivået av oljesyre var redusert. TTA tilsetning førte til en signifikant reduksjon av fett i muskel og kondisjonsfaktor sammenliknet med N-TTA-SD. Kjønns-spesifikke forskjeller i muskelfett og kondisjonsfaktor ble også påvist i fisk gitt TTA etter de to fôringsperiodene. Siden det ikke ble påvist kjønns-spesifikke forskjeller i noen av de andre fôringsgruppene ble forskjellen trolig fremprovosert av TTA. En hypotese er at denne forskjellen mellom kjønn kan være nært knyttet opp mot energi og fett status, samt ønsket om å opprettholde fettreserver for å kunne initiere en kjønnsmodnings-prosess. Mer forskning er imidlertid nødvendig for å forstå underliggende og viktige faktorer som kan påvirke de observerte kjønnsspesifikke forskjellene