Salmon In Seawater Research Articles

Salmon lice--impact on wild salmonids and salmon aquaculture.

Salmon lice, Lepeophtheirus salmonis, are naturally occurring parasites of salmon in sea water. Intensive salmon farming provides better conditions for parasite growth and transmission compared with natural conditions, creating problems for both the salmon farming industry and, under certain conditions, wild salmonids. Salmon lice originating from farms negatively impact wild stocks of salmonids, although the extent of the impact is a matter of debate. Estimates from Ireland and Norway indicate an odds ratio of 1.1:1-1.2:1 for sea lice treated Atlantic salmon smolt to survive sea migration compared to untreated smolts. This is considered to have a moderate population regulatory effect. The development of resistance against drugs most commonly used to treat salmon lice is a serious concern for both wild and farmed fish. Several large initiatives have been taken to encourage the development of new strategies, such as vaccines and novel drugs, for the treatment or removal of salmon lice from farmed fish. The newly sequenced salmon louse genome will be an important tool in this work. The use of cleaner fish has emerged as a robust method for controlling salmon lice, and aquaculture production of wrasse is important towards this aim. Salmon lice have large economic consequences for the salmon industry, both as direct costs for the prevention and treatment, but also indirectly through negative public opinion.

A Novel Betaproteobacterial Agent of Gill Epitheliocystis in Seawater Farmed Atlantic Salmon (Salmo salar)

Epitheliocystis, a disease characterised by cytoplasmic bacterial inclusions (cysts) in the gill and less commonly skin epithelial cells, has been reported in many marine and freshwater fish species and may be associated with mortality. Previously, molecular and ultrastructural analyses have exclusively associated members of the Chlamydiae with such inclusions. Here we investigated a population of farmed Atlantic salmon from the west coast of Norway displaying gill epitheliocystis. Although ‘Candidatus Piscichlamydia salmonis’, previously reported to be present in such cysts, was detected by PCR in most of the gill samples analysed, this bacterium was found to be a rare member of the gill microbiota, and not associated with the observed cysts as demonstrated by fluorescence in situ hybridization assays. The application of a broad range 16 S rRNA targeted PCR assay instead identified a novel betaproteobacterium as an abundant member of the gill microbiota. Fluorescence in situ hybridization demonstrated that this bacterium, tentatively classified as ‘Candidatus Branchiomonas cysticola’, was the cyst-forming agent in these samples. While histology and ultrastructure of ‘Ca. B. cysticola’ cysts revealed forms similar to the reticulate and intermediate bodies described in earlier reports from salmon in seawater, no elementary bodies typical of the chlamydial developmental cycle were observed. In conclusion, this study identified a novel agent of epitheliocystis in sea-farmed Atlantic salmon and demonstrated that these cysts can be caused by bacteria phylogenetically distinct from the Chlamydiae.

Growth, osmoregulation and endocrine changes in wild Atlantic salmon smolts and post-smolts during marine migration

We have examined physiological parameters associated with seawater adaptability, growth and energetics, as well as major endocrine regulators of these processes in wild migrating Atlantic salmon smolts and post-smolts from the river through the fjord, coastal areas and the open ocean. Muscle RNA/DNA ratio suggests that growth rate increases soon after entry into seawater and continues to increase after the post-smolts reach the offshore banks and the feeding grounds in the Norwegian Sea. Post-smolts prioritize rapid growth and protein deposition in spring and summer, and their energy intake during this period is so high that deposition of energy is possible in addition to muscle growth. An increase in thyroxine (T4) and triiodothyronine (T3) levels was observed, suggesting a major activation of hepatic conversion of T4 to T3 in post-smolts in seawater, probably related to the high metabolic activity and rapid growth and development of the post-smolts. Decreased plasma growth hormone (GH) levels were observed from the river through the fjord, with levels around 2ngml−1 in rapidly growing post-smolts, concurrent with an increase in circulating insulin-like growth factor I (IGF-I). An increase in pituitary GH expression levels and hepatic GH receptor (GH-R) and local IGF-I mRNA levels suggest a physiological basis for the changes in circulating GH and IGF-I levels. Receptor expression in brain and pituitary suggests that both hormones are actively involved in the growth and differentiation of these tissues during the critical early marine phase. Gill Na+,K+-ATPase (NKA) activity increased to post-smolt levels above 20μmol ADP mgprot.÷1h÷1, probably representing long-term NKA activity levels of Atlantic salmon in seawater. Concurrent with the changes in NKA activity the expression of the NKA α1b isoform remained high in post-smolts, while the expression of the NKA α1a decreased from smolts to post-smolts. Both cystic fibrosis transmembrane conductance regulator (CFTR) I and II showed a reduction in mRNA levels from smolts to post-smolts, and remained stable at low expression levels in seawater.

FXYD-11 associates with Na+-K+-ATPase in the gill of Atlantic salmon: regulation and localization in relation to changed ion-regulatory status

The Na(+)-K(+)-ATPase is the primary electrogenic component driving transepithelial ion transport in the teleost gill; thus regulation of its level of activity is of critical importance for osmotic homeostasis. In the present study, we examined the dynamics of the gill-specific FXYD-11 protein, a putative regulatory subunit of the pump, in Atlantic salmon during seawater (SW) acclimation, smoltification, and treatment with cortisol, growth hormone, and prolactin. Dual-labeling immunohistochemistry showed that branchial FXYD-11 is localized in Na(+)-K(+)-ATPase immunoreactive cells, and coimmunoprecipitation experiments confirmed a direct association between FXYD-11 and the Na(+)-K(+)-ATPase α-subunit. Transfer of freshwater (FW)-acclimated salmon to SW induced a parallel increase in total α-subunit and FXYD-11 protein expression. A similar concurrent increase was seen during smoltification in FW. In FW fish, cortisol induced an increase in both α-subunit and FXYD-11 abundance, and growth hormone further stimulated FXYD-11 levels. In SW fish, prolactin induced a decrease in FXYD-11 and α-subunit protein levels. In vitro cortisol (18 h, 10 μg/ml) stimulated FXYD-11, but not FXYD-9, mRNA levels in gills from FW and SW salmon. The data show that Na(+)-K(+)-ATPase expressed in branchial mitochondrion-rich cells is accompanied by FXYD-11, and that regulation of the two proteins is highly coordinated. The demonstrated association of FXYD-11 and α-subunit strengthens our hypothesis that FXYD-11 has a role in modulating the pump's kinetic properties. The presence of putative phosphorylation sites on the intracellular domain of FXYD-11 suggests the possibility that this protein also may transmit external signals that regulate Na(+)-K(+)-ATPase activity.

Distinct hormonal regulation of Na+,K+-atpase genes in the gill of Atlantic salmon (Salmo salar L.)

It has recently become evident that maintenance of ionic homoeostasis in euryhaline salmonids involves a reciprocal shift in expression of two isoforms of the gill Na(+),K(+)-atpase alpha-subunit when the surrounding salinity changes. The present study investigated the regulation of this shift between the alpha1a (freshwater (FW) isoform) and the alpha1b (seawater (SW) isoform) by cortisol, Gh, prolactin (Prl) and Igf 1. Injection with cortisol into FW salmon increased alpha1a expression, while Gh had no effect. Conversely, both cortisol and Gh stimulated alpha1b expression, and a significant synergy was observed. igf1 expression was increased by Gh in both gill and liver, and inhibited by cortisol in the liver. Gill igf1 and gh receptor expression increased in response to cortisol. Injection with Prl into SW salmon compromised their hypo-osmoregulatory performance, selectively reduced the expression of the alpha1b isoform and decreased enzymatic Na(+),K(+)-atpase activity in the gill. Cortisol and Prl reduced gill and liver igf1 expression, and both hormones stimulated gill igf1 receptor expression. In a short-term experiment with incubation of FW gill cell suspensions, cortisol stimulated alpha1a and alpha1b expression, while Igf1 stimulated only alpha1b. The data elaborate our understanding of Prl and Gh as being antagonists in the control of gill ion regulation, and support a dual role for Gh involving endocrine and paracrine Igf1 action. Gh and Prl may be the decisive stimuli that direct cortisol-aided mitochondrion-rich cell development into either secretory or absorptive types.

An experimental investigation on aspects of infectious salmon anaemia virus (ISAV) infection dynamics in seawater Atlantic salmon, Salmo salar L.

This study investigated infection dynamics of infectious salmon anaemia virus (ISAV) by conducting two experiments to examine minimum infective dose and viral shedding of ISAV. In terms of minimum infective dose, the high variability between replicate tanks and the relatively slow spread of infection through the population at 1 x 10(1) TCID(50) mL(-1) indicated this dose is approaching the minimum infective dose for ISAV in seawater salmon populations. A novel qPCR assay incorporating an influenza virus control standard with each seawater sample was developed that enabled the quantity of ISAV shed from infected populations to be estimated in values equivalent to viral titres. Viral shedding was first detected at 7 days post-challenge (5.8 x 10(-2) TCID(50) mL(-1)kg(-1)) and rose to levels above the minimum infective dose (4.2 x 10(1) TCID(50) mL(-1)kg(-1)) on day 11 post-challenge, 2 days before mortalities in ISAV inoculated fish started. These results clearly demonstrate that a large viral shedding event occurs before death. Viral titres peaked at 7.0 x 10(1) TCID(50) mL(-1)kg(-1) 15 days post-infection. These data provide important information relevant to the management of ISA.

Effects of Gastric and Surgical Insertions of Dummy Ultrasonic Transmitters on Juvenile Chinook Salmon in Seawater

AbstractThe objective of this study was to develop guidance for tagging methods for juvenile Chinook salmon Oncorhynchus tshawytscha in their first ocean year by evaluating the effects of tagging during this critical life stage. We compared survival over 42 d among juvenile hatchery Chinook salmon receiving surgically implanted dummy ultrasonic transmitters (equivalent to VEMCO V7‐1 L tags) ranging from 2.6% to 8.8% of body mass with that of fish receiving gastrically implanted tags. Survival was significantly lower in fish receiving gastrically implanted transmitters (21%) than for the gastric‐sham (66%), surgery (61%), surgery‐sham (58%), and control treatments (90%). Survival was also significantly higher in the control treatment than in all other treatments. The results of this study indicate that surgical insertion into the peritoneal cavity is the preferred method of transmitter implantation in juvenile Chinook salmon in their first ocean year and that the transmitters should be less than 5.8% of the fish's body mass to reduce transmitter‐related mortality.

Multiplicity of expression of Na+,K+–ATPaseα-subunit isoforms in the gill of Atlantic salmon (Salmo salar): cellular localisation and absolute quantification in response to salinity change

The ability to reverse the net direction of gill ion transport in response to a salinity change is critical for euryhaline teleosts and involves a complex cellular and molecular remodelling of the gill epithelium. The present study aimed to clarify the cellular localisation and exact quantitative inter-relationship of Na(+),K(+)-ATPase alpha- and beta-subunit transcripts in Atlantic salmon gill during salinity change. The combined expression level of all alpha-isoforms in the gill increased by 100% after freshwater (FW) to seawater (SW) transfer. The alpha(1a) and alpha(1b) isoforms were both in the range 1-6 amol 20 ng(-1) total RNA; alpha(1a) decreased and alpha(1b) increased after SW-transfer, their ratio changing from 5:1 in FW to 0.26:1 in SW. The alpha(1c) and alpha(3) levels were 10- and 100-fold lower, respectively. The beta(1)-subunit mRNA level was 0.1-0.3 amol 20 ng(-1) total RNA, thus much lower than the sum of alpha-subunits. Even though increasing 3-fold after SW-transfer, beta-subunit availability may still limit functional pump synthesis. The mRNAs of the predominant alpha(1a) and alpha(1b) isoforms were localised by in situ hybridisation in specific gill cells of both FW and SW salmon. Labelling occurred mainly in presumed chloride cells and cells deep in the filament but occasionally also on lamellae. Overall, the salinity-induced variation in labelling pattern and intensity matched the quantification data. In conclusion, the predominant switching of Na(+),K(+)-ATPase alpha-subunit isoform mRNA during salinity acclimation reflects a marked remodelling of mitochondrion-rich cells (MRCs) in the gill and probably tuning of the pump performance to accomplish a net reversal of gill ion transport in hypo- and hypertonic environments.

Identification of FXYD protein genes in a teleost: tissue-specific expression and response to salinity change

It is increasingly clear that alterations in Na+-K+-ATPase kinetics to fit the demands in specialized cell types is vital for the enzyme to execute its different physiological roles in diverse tissues. In addition to tissue-dependent expression of isoforms of the conventional subunits, alpha and beta, auxiliary FXYD proteins appear to be essential regulatory components. The present study identified genes belonging to this family in Atlantic salmon by analysis of expressed sequence tags. Based on the conserved domain of these small membrane proteins, eight expressed FXYD isoforms were identified. Phylogenetic analysis suggests that six isoforms are homologues to the previously identified FXYD2, FXYD5, FXYD6, FXYD7, FXYD8, and FXYD9, while two additional isoforms were found (FXYD11 and FXYD12). Using quantitative PCR, tissue-dependent expression of the different isoforms was analyzed in gill, kidney, intestine, heart, muscle, brain, and liver. Two isoforms were expressed in several tissues (FXYD5 and FXYD9), while six isoforms were distributed in a discrete manner. In excitable tissues, two isoforms were highly expressed in brain (FXYD6 and FXYD7) and one in skeletal muscle (FXYD8). In osmoregulatory tissues, one isoform was expressed predominantly in gill (FXYD11), one in kidney (FXYD2), and one equally in kidney and intestine (FXYD12). Expression of several FXYD genes in kidney and gill differed between fresh water and seawater salmon, suggesting significance during osmoregulatory adaptations. In addition to identifying novel FXYD isoforms, these studies are the first to show the tissue dependence in their expression and modulation by salinity in any teleosts.

Spinal deformation in commercially cultured Atlantic salmon, Salmo salar L.: a clinical and radiological study

A clinical and radiographic study was carried out on 2016 randomly selected Atlantic salmon parr from six farms, which weighed between 55 and 100 g. In addition, 86 fish from six marine farms were similarly studied. Radiographically detectable vertebral lesions were found in 3.8-8.8% of the parr. The changes ranged from a single vertebra showing features, such as demineralization, increased density and slight loss of structure, to fish with multiple vertebrae affected by collapse, fusion and change in intervertebral space that could give rise to lordosis or kyphosis or abnormal vertebrae at several locations. The predominant location was the vertebral region V21-27, and rarely V44 caudad. The radiographic changes in seawater salmon mirrored those found in parr, but vertebrae V35 caudad were more frequently involved. Very few parr were found to have abnormal vertebrae in the peduncle area which suggests that the development of lesions at this location occurs de novo in the seawater phase, given that 'stumpy' fish are most frequent reported deformity at slaughter. It was concluded that minor vertebral change could be detected radiographically in many parr with no observable effect on external morphology. Whether such minor radiographic alteration would proceed to observable morphological change at slaughter weight is open to question.

Screening of nutrient digestibilities and intestinal pathologies in Atlantic salmon, Salmo salar, fed diets with legumes, oilseeds, or cereals

Ten different plant protein and/or starch sources were studied in a 5-week experiment with triplicate groups of 0.7-kg Atlantic salmon in seawater, pre-adapted to a diet with fish meal, faba beans, sunflower cake, and wheat gluten as sources of protein and starch. The experimental ingredients were corn gluten, defatted soybean, defatted sunflower, dehulled lupin, defatted double-low rapeseed, whole field pea, whole and dehulled faba bean, whole wheat and naked oat, tested one at a time (14–24% inclusion). The diets were balanced by addition of pure wheat starch and/or pure cellulose, to obtain equal macro nutrient compositions. The control diet consisted of fish meal, wheat starch, cellulose and fish oil. The results showed reduced faecal dry matter content in fish fed the soybean diet and to a lesser extent in those fed the sunflower, lupin and rapeseed diets. Diets containing lupin and rapeseed resulted in a moderate increase in the viscosity of the digesta, while diets with wheat and oat increased viscosity of digesta more. Apparent digestibility of lipid decreased linearly with increasing dietary cellulose level. A significant reduction in the digestibility of crude protein was seen for the soybean, sunflower, rapeseed and oat diets, reflecting reduced digestibilities of most amino acids. The salmon fed the corn gluten, lupin, pea, bean and wheat diets had protein digestibilities comparable to the control group. The digestibility of phosphorus was highest for salmon fed the rapeseed diet and lowest for fish fed the oat diet. Faecal excretion of sodium was highly elevated for salmon fed the soybean diet, and moderately elevated for fish fed the corn gluten and sunflower diets. Faecal excretion of zinc was elevated in the fish fed the oat diet. None of these observations were significantly related to the dietary concentration of phytic acid. A histological examination of the stomach, mid- and distal intestine of all groups showed no other irregularities than enteritis in the distal intestine of salmon fed soybean meal. The present study demonstrated a potential for several plant ingredients, such as field pea and faba bean, partly replacing high-quality fish meal in diets for Atlantic salmon, based on nutrient digestibilities and absence of pathologies in the stomach and intestine.

Non-invasive measurement of cortisol and melatonin in tanks stocked with seawater Atlantic salmon

This study examined the potential for non-invasive assessment of cortisol and melatonin status of seawater Atlantic salmon, by measurement of hormone release into the water using methodology developed recently for freshwater rainbow trout. Validation experiments demonstrated good recoveries of spiked cortisol (ca. 95%) and melatonin (ca. 85%) from seawater, that oxygenation of seawater did not affect recovery, and that only small losses occurred during freeze storage of samples. When groups of seawater Atlantic salmon were transferred to experimental tanks, water cortisol concentrations reduced over the first few days — indicating an acclimation response. Subsequent exposure to a handling stress caused a rapid 50-fold increase in water cortisol concentration, followed by a decrease. In a separate experiment, water cortisol levels were elevated in tanks of fish previously exposed to infectious pancreatic necrosis virus, and cortisol release rate was correlated to plasma cortisol level. Water sampling from tanks holding seawater salmon showed that water melatonin concentrations were elevated at night, conforming to expectation. These experiments demonstrate that the cortisol and melatonin status of seawater Atlantic salmon in tanks can be monitored non-invasively by water sampling, with the particular advantage that hormonal status can be tracked over time as the fish are not disturbed by sampling.

Nutritive value of partially dehulled and extruded sunflower meal for post-smolt Atlantic salmon (Salmo salar L.) in sea water

This study determined the digestibility of protein in partially dehulled sunflower meal (SFM) and then, as the main goal, the nutritive value of high-temperature extruded (≤149°C) partially dehulled SFM (SFMEX) for post-smolt Atlantic salmon Salmo salar in sea water. The digestibility study was conducted using the settling column approach (‘Guelph system’) for faeces collection as described by Hajen, Higgs, Beames and Dosanjh. In the nutritive value study, triplicate groups of 50 salmon (mean weight ∼116 g) in 4000-L outdoor fibreglass tanks supplied with 25–40 L min−1, filtered, oxygenated (dissolved oxygen, 7.0–8.5 mg L−1), 11–12°C sea water (salinity, 29–31 g L−1), were fed twice daily to satiation one of five steam-pelleted dry diets that contained 422 g of digestible protein (DP) kg−1 and ∼16.4 MJ of digestible energy (DE) kg−1 on a dry weight basis for 84 days. Low-temperature-dried anchovy meal (LT-AM) comprised 68.2% of the basal diet protein whereas in four test diets, SFMEX progressively replaced up to 33.0% of the DP provided by LT-AM in the basal diet (SFMEX≤271 g kg−1 of dry matter). Sunflower meal had 87.9% DP. Diet treatment did not significantly affect specific growth rate (1.39–1.45% day−1), feed efficiency (1.19–1.26), percentage of dietary protein retained (45.8–47.5), gross energy utilization (46.5–49.4%), per cent survival (96.0–99.3) or terminal whole body and muscle proximate compositions. We conclude that SFMEX can comprise ≥271 g kg−1 of the dry diet or ≥22.7% of the digestible dietary protein of post-smolt Atlantic salmon in seawater without any adverse effects on their performance.

Efficacy of an equal blend of canola oil and poultry fat as an alternate dietary lipid source for Atlantic salmon (Salmo salar L.) in sea water. I: effects on growth performance, and whole body and fillet proximate and lipid composition

This study assessed the suitability and cost efficacy of an equal blend of canola oil (CO) and poultry fat (PF) as a supplemental dietary lipid source for juvenile Atlantic salmon. Quadruplicate groups of Atlantic salmon (∼400 g) held in 4000 L outdoor fibreglass tanks supplied with running (35–40 L min−1), aerated (dissolved oxygen, 7.88–10.4 mg L−1), ambient temperature (8.6–10.9°C) sea water (salinity, 26–35 g L−1) were fed twice daily to satiation one of three extruded dry pelleted diets of equivalent protein (488–493 g kg−1 dry matter) and lipid (267–274 g kg−1 dry matter) content for 84 days. The diets were identical in composition except for the supplemental lipid (234.7 g kg−1) source viz., 100% anchovy oil (AO; diet COPF-0), 70.2% AO and 29.8% CO and PF (diet COPF-30), and 40.3% AO and 59.7% CO and PF (diet COPF-60). Atlantic salmon growth rate, feed intake, feed efficiency, protein and gross energy utilization, percent survival and whole body and fillet proximate compositions were not affected by diet treatment. Cost per kilogram weight gain was about 10% less for fish fed diet COPF-60 than for diet COPF-0. Percentages of saturated fatty acids in dietary and fillet lipids varied narrowly. Moreover, percentages of 18:1n-9, monounsaturated fatty acids, 18:2n-6, n-6 fatty acids, 18:3n-3, and ratios of n-6 to n-3 fatty acids in the flesh lipids were directly related to the dietary level of CO and PF whereas 22:6n-3, the total of 20:5n-3 (eicosapentaenoic acid; EPA) and 22:6n-3 (docosahexaenoic acid; DHA), and n-3 fatty acids revealed the opposite trend. Percentages of 22:6n-3, EPA and DHA, and n-3 fatty acids were significantly depressed in fish fed diet COPF-60 versus diet COPF-0. We conclude that a 1:1 blend of CO and PF is an excellent cost-effective dietary source of supplemental lipid for Atlantic salmon in sea water.

Endocrine growth regulation of adult Atlantic salmon in seawater: The effects of light regime on plasma growth hormone, insulin-like growth factor-I, and insulin levels

Plasma growth hormone (GH), insulin-like growth factor-I (IGF-I), and insulin were measured in two groups of Salmo salar L. during a one-year study. The fish were reared under either a simulated natural photoperiod (SNP) from January to December or a regime of continuous light from January to June, followed by SNP until December (LL/SNP). Plasma GH levels during spring were low, and lower in the LL/SNP fish (< 0.9 ng ml − 1 ) than in the SNP fish (> 1.9 ng ml − 1 ), although the LL/SNP grew better (0.8% per day) than the SNP fish (0.5% per day). Plasma IGF-I levels increased transiently from January (64.7 ng ml − 1 ) to maximum in late September in the LL/SNP (85.8 ng ml − 1 ) and in November in the SNP group (87.3 ng ml − 1 ). The ratio GH:IGF-I was lower in the LL/SNP group during spring when this group grew better than the SNP group.

Atlantic salmon, Salmo salar, utilizes wax ester-rich oil from Calanus finmarchicus effectively

Against a background of decreasing availability of fish oils for use in aquaculture, the present study was undertaken to examine whether a wax ester-rich oil derived from the calanoid copepod Calanus finmarchicus, could be used effectively by Atlantic salmon when supplied in their diet. Individually tagged Atlantic salmon of initial weight around 500 g were divided into replicate tanks of two dietary groups and fed either a fish oil supplemented diet, or an experimental diet coated with Calanus oil. Wax esters accounted for 37.5% of the lipids in the Calanus oil diet but were absent from the fish oil diet in which triacylglycerols (TAG) were the major lipid class. Over the feeding period (140 days) the salmon fed fish oil displayed a greater increase in length, but there was no significant difference between the two groups in weight gained. The specific growth rates (0.75) and the feed conversion ratio of fish fed the two diets were similar throughout the study. No differences were observed in the apparent digestibility coefficients (ADC) of fish fed Calanus oil or fish oil. The ADC of fatty acids decreased with chain length and increased with unsaturation. Long-chain alcohol utilization showed a similar tendency although there was a notable difference in that saturated long-chain alcohols were utilized better than the comparable fatty acid homologue. In fecal lipid of fish fed Calanus oil, the content of 16:0 alcohol decreased in both the free long-chain alcohol and wax ester fractions, while the corresponding fatty acid increased in the feces of both dietary groups of fish. In contrast, the proportion of the 22:1 n−11 alcohol increased in both fecal wax esters and free long-chain alcohol fractions whereas 22:1 n−11 fatty acid displayed no accumulation. The observed patterns of fatty acid and long-chain alcohol compositions in fecal lipid compared to those of the initial dietary lipid are consistent with the digestive lipases of salmon preferentially hydrolyzing esters containing polyunsaturated fatty acid (PUFA) moieties. The wax esters of Calanus oil contained substantial amounts of the n−3 PUFA, 20:5 n−3 and 22:6 n−3, that were effectively deposited in muscle and liver tissues. No major differences were seen in either lipid content/lipid classes or in gross fatty acid composition of these tissues between the two dietary groups. It is concluded that that Atlantic salmon in seawater can effectively utilize diets in which a major lipid component is derived from zooplankton rich in wax ester without any detrimental change in growth or body lipid composition. This finding gives support to the use of lipid from zooplankton from high latitudes as an alternative or as a supplement to fish oil and a provider of long-chain n−3 PUFA in diets for use in salmon aquaculture.

Efficacy of chloramine-T as a treatment for amoebic gill disease (AGD) in marine Atlantic salmon (Salmo salar L.)

AbstractAtlantic salmon with amoebic gill disease (AGD)weretreatedwithchloramine-Ttocompareitseiect-iveness with that of freshwater bathing. In 250-Ltanktrials, treatmentof seawater withchloramine-Treducedamoebadensityonthegillstolevelssigni¢c-antly lower than when treated with seawater alone.Therewasnofurtherchangeinamoebalevelsin¢shbathed for 3 or 6h compared with1h of treatment.Plasma lactate levels in ¢sh bathed in chloramine-Tfor 6h showed no diierences across treatments. In1000-L tank trials using freshwater alone or sea-water with chloramine-T, signi¢cant reductions inamoeba density occurred compared with pre-bathlevels. Histological analysis of gill tissue revealedAGD lesion levels to increase, then to return to pre-bath levels within1week for freshwater-treated ¢sh,while chloramine-T- and seawater-treated ¢sh hadhigher levels of AGD lesions from 2 weeks post bath-ing.Immunodot-blotdataindicatedaninitialsigni¢c-antincreaseinprevalenceof lesionsinseawaterandchloramine-T-treated ¢sh, which declined to levelssigni¢cantly lower than pre-bath levels by 3 weekspost bathing, compared with the freshwater-treated¢sh, which had signi¢cantly lower levels than con-trols by 2 weeks post bathing. At reducing amoebadensity, it is apparent that bathing AGD-aiectedAtlantic salmon in seawater with chloramine-Tprovedatleastaseiectiveasfreshwater.Keywords: amoebic gill disease, Atlantic salmon,Neoparamoeba pemaquidensis, chloramine-T, seacagesIntroductionAmoebicgilldisease (AGD) is a signi¢cant infectiousdiseaseaiectingculturedAtlanticsalmon,Salmosal-arL., inTasmania,Australia. However, AGDhasbeenreported in salmonids from around the world andin non-salmonids primarily in the Mediterranean(Munday, Zilberg & Findlay 2001). The causativeagentofAGDistheamphizoicamoebaNeoparamoebapemaquidensis (Page) (ex Paramoeba pemaquidensis)(Kent, Sawyer & Hedrick 1988; DykovaŁ,Figueras&Peric 2000). The disease presents grossly as raisedwhite mucoid patches on the gills and histologicallyasmultifocalregionsof hyperplasiaandfusionofthesecondary branchial lamellae (Adams & Nowak2001). The presence of gill lesions with associatedamoebae is seenas the ultimate determinant of AGDstatus.The treatment of choice for AGD is freshwaterbathing for 3^4h (Parsons, Nowak, Powell & Dix2001). However, this has limitations particularly inits e⁄cacy (Parsonsetal.2001) with reinfectionandincreases ingillamoeba numbers to pre-bath levelswithin10days(Clark,Powell&Nowak2003).Fresh-water bathing is a time consuming and costly pro-cess involving the moving of cages and pumping of¢sh into freshwater-¢lled liners, all resulting in alossofgrowthduetothecessationoffeedingandin-creased handling stress. In addition, freshwater isnot always readily available, and some times needstobepurchasedfrommunicipalsupplies.Thetrans-port of such large volumes of water is a labour-intensive exercise, which also adds to the cost oftreatment. The use of additives to seawater baths

Influence of Oxygen on the Toxicity of Chloramine‐T to Atlantic Salmon Smolts in Freshwater and Seawater

AbstractChloramine‐T is a widely used disinfectant for the treatment of gill diseases of fish in freshwater, and more recently attention has turned to its use in seawater. However, despite the wide use of chloramine‐T, few studies have examined its acute toxicity to fish. In this study we examined the acute (within 12 h) toxicity of freshwater‐ and seawater‐acclimated Atlantic salmon Salmo salar smolts under aerated (100% air saturation with O2) and oxygen supersaturation conditions (200% air saturation with O2). Chloramine‐T was more acutely toxic to salmon in seawater than to those in freshwater, and oxygen supersaturation enhanced the toxicity in both sea‐ and freshwater. In aerated freshwater the median lethal times (LT50s) for chloramine‐T concentrations of 50 and 25 mg/L were 166.8 and 474.3 min, respectively; in aerated seawater they were 119.1 and 297.3 min, respectively. However, in freshwater at 200% air saturation with oxygen, the 50 and 25 mg/L LT50s were 133.6 and 190.9 min, respectively; in seawater at 200% air oxygen saturation, the values were 85.3 and 158.9 min, respectively. Freshwater Atlantic salmon appear to be as sensitive as rainbow trout Oncorhynchus mykiss and more sensitive than channel catfish Ictalurus punctatus to chloramine‐T toxicity. Seawater‐acclimated salmon, however, appear to be more sensitive to chloramine‐T than are trout and catfish. The primary mechanism of toxicity in both seawater and freshwater appears to be extensive oxidative necrosis of the gill filament and lamellar epithelium, causing acute osmoregulatory dysfunction.

Replacement of dietary fish oil with increasing levels of linseed oil: modification of flesh fatty acid compositions in Atlantic salmon (Salmo salar) using a fish oil finishing diet.

Five groups of salmon, of initial mean weight 127 +/- 3 g, were fed increasing levels of dietary linseed oil (LO) in a regression design. The control diet contained capelin oil (FO) only, and the same oil was blended with LO to provide the experimental diets. After an initial period of 40 wk, all groups were switched to a finishing diet containing only FO for a further 24 wk. Growth and flesh lipid contents were not affected by dietary treatment. The FA compositions of flesh total lipids were linearly correlated with dietary FA compositions (r2 = 0.88-1.00, P < 0.0001). LO included at 50% of added dietary lipids reduced flesh DHA and EPA (20:5n-3) concentrations to 65 and 58%, respectively, of the concentrations in fish fed FO. Feeding 100% LO reduced flesh DHA and EPA concentrations to 38 and 30%, respectively, of the values in fish fed FO. Differences between diet and flesh FA concentrations showed that 16:0, 18:1n-9, and especially DHA were preferentially retained in flesh, whereas 18:2n-6, 18:3n-3, and 22:1n-11 were selected against and presumably utilized for energy. In fish previously fed 50 and 100% LO, feeding a finishing diet containing FO for 16 wk restored flesh DHA and EPA concentrations, to approximately 80% of the values in fish fed FO throughout. Flesh DHA and EPA concentrations in fish fed up to 50% LO were above recommended intake values for humans for these EFA. This study suggests that LO can be used as a substitute for FO in seawater salmon feeds and that any reductions in DHA and EPA can be largely overcome with a finishing diet high in FO before harvest.

Dietary fatty acid composition affects the repeat swimming performance of Atlantic salmon in seawater

Repeated critical swimming performance trials ( U crit) were performed on Atlantic salmon ( Salmo salar) to test the null hypothesis that the source of dietary lipids (fish-based, poultry-based, and plant-based) does not influence exercise and recovery performance. Four diets were prepared by extensively replacing supplemental lipid from anchovy oil (AO; 100% AO at 150 g/kg) with cold pressed flaxseed oil (FO; 25% AO, 75% FO), sunflower oil (SO; 25% AO, 75% SO), or poultry fat (PF; 25% AO, 75% PF). These diets had equivalent protein and energy concentrations, but due to the different supplemental lipid sources, varied widely in their fatty acid composition. Fish fed AO had a significantly higher ( P<0.05) first U crit (2.62±0.07 body lenght s −1) than those fed PF (2.22±0.12 body lenght s −1) that had low muscle ratios of n-3 highly unsaturated fatty acids (n-3 HUFA) to saturated fatty acids (SFA) and arachidonic acid (AA), and high levels of oleic acid. Fish in the FO and SO diet groups swam as well as AO-fed fish in both swimming trials. The performance of fish fed AO decreased significantly ( P<0.05) during the second swimming trial (i.e. U crit2/ U crit1=0.92±0.02). No significant differences occurred between diet groups for the second swim trial. There was a positive correlation between both n-3 HUFA/SFA and n-3 HUFA/AA ratios, and U crit1. A negative correlation was found between dietary AA and oleic acids, and U crit1. The present study suggests that low dietary n-3 HUFA/ SFA and n-3 HUFA/AA ratios may negatively affect swimming performance. The former possibly can be offset by increasing linoleic acid in the presence of nutritionally adequate n-3 HUFA (e.g. SO diet). Lipid supplements consisting largely of vegetable oils did not compromise fish cardiorespiratory physiology under the conditions of this study.