Influence of salinity on the energetics of gill and kidney of Atlantic salmon (Salmo salar)

The effect of seawater acclimation and adaptation to various salinities on the energetics of gill and kidney of Atlantic salmon (Salmo salar) was examined. Smolts and non-smolts previously reared in fresh water were exposed to a rapid increase in salinity to 30 ppt. Plasma osmolarity, [Na⁺], [Cl^–], [K⁺] and [Mg⁺⁺] increased in both groups but were significantly lower in smolts than non-smolts. Gill Na⁺, K⁺-ATPase specific activity, initially higher in smolts, increased in both groups after 18 days in seawater. Kidney Na⁺, K⁺-ATPase specific activity was not affected by salinity in either group. Gill and kidney citrate synthase specific activity was not affected by seawater exposure in smolts but decreased in non-smolts. In a second experiment, Atlantic salmon smolts reared in fresh water were acclimated to 0, 10 or 30 ppt seawater for 3 months at a temperature of 13–14°C. Gill Na⁺, K⁺-ATPase was positively correlated with salinity, displaying 2.5- and 5-fold higher specific activity at 10 and 30 ppt, respectively, than at 0 ppt. Kidney Na⁺, K⁺-ATPase specific activity was not significantly affected by environmental salinity. Citrate synthase and cytochrome c oxidase specific activities in gill were slightly (6–13%) lower at 10 ppt than at 0 and 30 ppt, whereas kidney activities were lowest at 30 ppt. Oxygen consumption of isolated gill filaments was significantly higher when incubated in isosmotic saline and at 30 ppt than at 0 ppt, but was not affected by the prior acclimation salinity. The results indicate that although high salinity induces increased gill Na⁺, K⁺-ATPase activity, it does not induce substantial increases in metabolic capacity of gill or kidney.     

Mycobacterium salmoniphilum infection in farmed Atlantic salmon, Salmo salar L

Multiple greyish‐white visceral nodules containing abundant rapidly growing and acid‐fast bacteria, subsequently identified as Mycobacterium salmoniphilum, were detected in moribund and newly dead market‐sized fish during a period of increased mortality in an Atlantic salmon, Salmo salar, farm in western Norway. Isolates cultured from diseased fish were phenotypically consistent with Mycobacterium sp. previously isolated from Atlantic salmon [MT 1890 (= NCIMB13533), MT1892, MT1900 and MT1901] in the Shetland Isles, Scotland. Partial sequences of 16S rDNA, ribosomal RNA internal transcribed spacer (ITS1), 65‐kDa heat‐shock protein (Hsp65) and β subunit of RNA polymerase (rpoB) revealed 97‐99% similarity with M. salmoniphilum type strain ATCC 13758^T. The source of infection was not confirmed. Koch’s postulates were fulfilled following experimental challenge of Atlantic salmon with field isolate NVI6598 ( FJ616988 ). Mortality was recorded in experimentally infected fish; however, the infection remained subclinical in the majority of affected fish over the 131‐day challenge period.     

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 (SFM_EX) 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, SFM_EX progressively replaced up to 33.0% of the DP provided by LT‐AM in the basal diet (SFM_EX≤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 SFM_EX 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.     

Characterisation of the microbiota associated with intestine of Atlantic cod (Gadus morhua L.): The effect of fish meal, standard soybean meal and a bioprocessed soybean meal

Populations of aerobic heterotrophic bacteria present in the gastrointestinal (GI) tract of healthy Atlantic cod (Gadus morhua L.) fed three different diets, fish meal, standard or a bioprocessed soybean meal (BPSBM), were estimated using the dilution plate technique. A total of 944 isolates were characterised by biochemical and physiological properties and 425 isolates were identified further by sequencing the 16S rRNA genes. Our results showed that gut microbiota were affected by dietary manipulation. The GI tract of fish fed fish meal was dominated by Gram-positive bacteria of the genera Brochothrix and Carnobacterium. The Gram-negative bacteria Chryseobacterium spp. and Psychrobacter glacincola, and Gram-positive bacteria belonging to Carnobacterium, dominated in the digestive tract of fish fed soybean meal. In contrast to these results, genus Psychrobacter dominated in the GI tract when fish were fed BPSBM.Until recently, it was generally suggested that the gut microbiota of fish were less diverse than in homoeothermic animals. However, the present study identified several “new” bacterial species isolated from the alimentary tract of Atlantic cod. These “new” bacterial species are not normally isolated from the GI tract of fish. Based on our finding we suggest that the GI tract microbiota of fish might not be as simple as believed.Antagonistic activity of carnobacteria regarding inhibition of growth of two fish pathogens (Aeromonas salmonicida ssp. salmonicida and Vibrio anguillarum) was observed. However, some difference in the antibacterial activity of Carnobacterium spp. was observed. Whether this antagonistic activity has any effect in challenge studies will be discussed, especially in relation to the finding that the digestive tract is one of the major infection routes in fish.     

Use of stable isotopes to distinguish farmed from wild Atlantic salmon, Salmo salar

Abstract –  Stable isotopes of carbon and nitrogen ( δ ¹³C and δ ¹⁵N) were examined in wild and aquaculture origin Atlantic salmon, Salmo salar , to evaluate their utility to identify escaped farmed fish. Samples of muscle tissue obtained from wild Conne River, Newfoundland, salmon were significantly more enriched in nitrogen ( δ ¹⁵N: mean = 12.75; SD ± 0.38‰) but depleted in lipid corrected carbon ( δ ¹³C': mean = −20.51; SD ± 0.23‰) by comparison with aquaculture specimens obtained from Bay d'Espoir, Newfoundland ( δ ¹⁵N = 10.96 ± 0.19‰;  δ ¹³C' = −19.25 ± 0.17‰) resulting in a complete separation of the two groups. Aquaculture specimens differed in δ ¹³C' from analyses of commercial salmon diet by 0.24‰, within the enrichment range associated with trophic transfers, while the δ ¹⁵N values in salmon muscle were enriched by 5.01‰. Although differences occurred in direct comparisons of white muscle and adipose tissue ( N  = 49), the average δ ¹³C' and δ ¹⁵N signatures varied in absolute amounts by only 0.5‰, supporting the use of adipose tissue as a nonlethal means to determine isotopic signatures of Atlantic salmon.     

Bluefin tuna (Thunnus thynnus) distribution in relation to sea surface temperature fronts in the Gulf of Maine (1994–96)

Fishery‐linked aerial surveys for bluefin tuna (Thunnus thynnus) were conducted in the Gulf of Maine (GOM) from July through October, 1994–96. Each year, from 507 to 890 surface schools were detected and their locations examined in relation to oceanographic conditions. Correlations between bluefin tuna presence and environmental variables were explored for sea surface temperature (SST), distance to a SST front, frontal density (relative density of all SST fronts seen in a given 1 km area for 2 weeks prior to each tuna sighting), and bottom depth and slope. Mean SST associated with bluefin schools was 18.1°C (±2.8). Schools were located at a mean distance of 19.7 km (±19.6) from SST fronts, and in water masses with an average frontal density of 28.2 m km^?2 (±35.7). Mean bottom depth of detected schools was 139.0 m (±70.3), and mean bottom slope was 0.7% rise (±0.7). A binomial generalized linear model fit to these variables indicated that bluefin are seen closer to fronts than locations in which no tuna were seen. Using simple and partial Mantel tests, we investigated the spatial correlation between bluefin tuna presence and the environmental variables, controlling for spatial autocorrelation. For each day that schools were sighted, we performed 24 Mantel tests, on a combination of response and predictor variables. The spatial relationship between bluefin tuna and SST fronts was inconsistent. Our analysis identified significant spatial structure in the bluefin school locations that had no significant correlation with any of the measured environmental features, suggesting that other untested features, such as prey density, may be important predictors of bluefin distribution in the GOM.     

New invasive predator reduces the abundance of native prey in a cold-temperate marine fouling community

1. Invasive species threaten the conservation of marine environments, and urgent management strategies are needed to prevent their introduction, establishment and spread. Specifically, marine invasive predators destabilize ecological interactions and alter community structure and function. However, most of the evidence showing the effect of these predators is restricted to a few species and regions, while for others the information remains scarce.
2. This study experimentally evaluated the ecological effects of the sea slug Pleurobranchaea maculata, a recently introduced invasive predator, on the fouling communities of a cold-temperate port in the South-western Atlantic.
3. The results show that increasing predation pressure reduces significantly the abundance of sea anemones, which are among the preferred prey items.
4. This study reveals new evidence to help better understand the effects of P. maculata on the biological communities of a recently invaded region. Furthermore, it provides the first experimental evidence supporting the hypothesis that marine invasive predators can induce a significant decrease in the abundance of native species in benthic communities of cold-temperate marine environments in the South-western Atlantic.

     

Full-fat soybean meal in diets for Atlantic halibut: growth, metabolism and intestinal histology

Isonitrogenous and isocaloric diets containing 0, 18 or 36% toasted full-fat soybean meal (FFSM) were fed to Atlantic halibut. The diets were fed to five tanks of fish each for 34 days (period 1). Four tanks from each treatment were then retained in the growth experiment for a further 32 days (period 2), while the groups of fish from one tank from each of the 0 and 36% FFSM groups were split and transferred to two metabolism tanks each. The initial weight of the fish in the growth trial was 169 ± 1 g (mean ± SEM, n =12; weight range 89–253 g) and the final weight was 317 ± 5 g. There was no significant effect of dietary treatment on specific growth rate (range, 0.8–1.1% day⁻¹), feed consumption (0.5–0.7% body weight day⁻¹), feed efficiency (1.3–1.6 g wet gain g dry feed⁻¹), protein retention (48–55%) or energy retention (49–57%). The fat, protein and energy concentrations in the fish increased during the trial and were not affected by the diet. The hepatosomatic index in fish fed with 36% FFSM diet was significantly lower (1.7%) than in the other groups (2.2%) ( P  < 0.05). No differences in intestinal morphology were observed between dietary treatments and no pathological reactions were identified in any of the samples. In the metabolism trial, there were no significant differences in oxygen consumption or ammonia excretion between fish fed with 0 and 36% FFSM diets. In conclusion, up to 36% FFSM may be added to diets for Atlantic halibut without negative effects on growth, feed efficiency or intestinal morphology.     

Enhanced production of the sea urchin Paracentrotus lividus in integrated open-water cultivation with Atlantic salmon Salmo salar

Survivorship and performance was investigated for two size classes of the sea urchin Paracentrotus lividus grown adjacent to open-water Atlantic salmon (Salmo salar) cultivation on the north-west coast of Scotland. Juvenile P. lividus were maintained for 12 months at 0 m, 50 m and 2.5 km from the mariculture activity. The sea urchins at the 0 m station showed higher survivorship than at the 50 m and 2.5 km stations and had significantly greater test diameter than at the 50 m station. Only urchins at 0 m developed gonads and, although small, these were of acceptable or excellent colouration in terms of their marketability. Adult P. lividus were maintained for 3 months at 0 m and 15 m from the mariculture activity, either with or without additional macroalgae Laminaria spp. Sea urchins at the 0 m station and fed additional macroalgae showed higher gonadal growth than sea urchins at the 15 m station held without additional food. Gonad colouration in the adult urchins, irrespective of the treatment, was acceptable or excellent. The 0 m station also received significantly greater quantities of particulate organic matter (POM) than the other stations in both the juvenile and adult experiments. At the 0 m station, the presence of the fatty acid 22:1n-11 and elevated levels of the long chain n-3 fatty acid DHA 22:6n-3 in the gonadal tissue of the urchins confirmed the consumption of fish farm derived POM and highlighted the potential human health benefits from consuming sea urchin roe.The results show that P. lividus can thrive in the salmon culture environment and suggests that the integration of P. lividus with Atlantic salmon can provide a viable means to culture this species, even at this northerly latitude. Salmon-sea urchin co-culture would enable fish farms to diversify into producing a second highly valuable product and would reduce the increasing worldwide pressure of sea urchin fisheries on wild stocks.     

Control of phosphorus homeostasis of Atlantic salmon (Salmo salar) in fresh water

Studies were conducted to determine the absorption, excretion and requirement of dietary phosphorus (P) by Atlantic salmon (Salmo salar). Triplicate groups of salmon parr, initial weight 15 ± 0.5±g , were fed, diets containing 4, 5, 6, 7, 8, 9, 11 and 13 mg P and 20 KJ of digestible energy (DE) per±g of diet (dry matter basis, DMB) to satiation for 16 weeks. The basal diet containing 4 mg P g^-1 (0.15 mg available P per KJ DE) was supplemented with graded levels of calcium phosphate, Ca(H₂PO₄)²H₂O to formulate the eight experimental diets. The fish were reared in fresh water at a temperature of 15 °C on a 12 h photoperiod. Vertebrae ash increased from 316 to 516 mg g^-1 fat-free dry matter with an increase in dietary P content. P requirement was estimated by using a four-parameter sigmoidal equation. The data suggests that a diet of 0.28 mg available P per KJ DE is needed for Atlantic salmon. Phosphate and calcium levels in plasma and bone increased, whereas levels of magnesium and liver cholecalciferol decreased, with an increase in dietary P.Phosphate excretion in urine and apparent availability of P were determined in deficient and replete fish. In deficient fish, the urine phosphate concentration was 0.10 mmol L^-1 before feeding and 0.25 mmol l^-1 after feeding, whereas in replete fish these concentrations were 1.09 and 5.11 mmol l^-1, respectively. The increase in urine phosphate concentration was higher in replete fish than in deficient fish, however, the apparent absorption of P was found to be significantly lower in replete fish than in deficient fish. These results suggest that similarly to terrestrial vertebrates, P homeostasis in Atlantic salmon is controlled by absorption in the intestine, conservation in the kidney and storage in the bones.