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Leclercq E.,University of Stirling | Taylor J.F.,University of Stirling | Hunter D.,Marine Harvest Scotland Ltd | Migaud H.,University of Stirling
Aquaculture | Year: 2010

Body size dimorphism between immature and early sexually recruited cohorts of farmed Scottish Atlantic salmon were investigated with the view to optimize the practical management of early maturation over the second-year at sea. Mixed-sex smolts from a single strain and freshwater source were stocked into four discrete commercial sites and sampled at harvest from June to December 2007, 15 to 22 months post-sea transfer. Individuals were sexed and their maturity status was determined based on gonado-somatic-index (GSI) and oocyte leading stage. Whole body weight (BW), fork length (FL) and Fulton condition factor (K) were measured and flesh quality analyzed. The immature mixed-sex population and each gender analyzed separately had an isometric weight-length relationship (WLR) but exhibited seasonal variations in K. Body size of immature Atlantic salmon were consistently sexually dimorphic with males exhibiting a higher BW (+ 13.4%) and FL (+ 5.9%) but a lower K (- 5.0%) than females. Individuals at an early stage of sexual maturation had a significantly higher BW (+ 35.2%) and K (+ 20.6%) than the immature cohort in June and July. During this period BW, FL and K together or BW alone was strong and standard indicators of early maturity in our discrete sites. Body size dimorphism described in this study shows that sex-ratio is an important parameter of farmed Atlantic salmon populations which is likely to vary following weight-grading and that population composition (sex-ratio and maturation rate) affects the seasonality in K typically observed at harvest. Importantly, the commitment of Atlantic salmon into maturation in spring can be rapidly and accurately estimated in a number of discrete populations by using simple weight-length morphological indicators characterized in a single rearing unit. Following maturation rate estimation, weight-grading implemented according to the predicted stock morphological structure could be used to selectively harvest a high proportion of maturing individuals at a stage where their flesh quality remains optimal. This could be applied as a powerful and practical on-site maturation management tool in the salmon industry as well as in other commercially important fish species. Crown Copyright © 2010.

Frenzl B.,University of Stirling | Stien L.H.,Norwegian Institute of Marine Research | Cockerill D.,Marine Harvest Scotland Ltd | Oppedal F.,Norwegian Institute of Marine Research | And 4 more authors.
Aquaculture | Year: 2014

This paper describes a study in which environmental manipulation of salmon swimming depth was tested in an attempt to reduce farm infection of Atlantic salmon, Salmo salar by the salmon louse, Lepeophtheirus salmonis. The effects of submerged artificial lighting (positioned at 10. m depth) in combination with submerged feeding (delivered at 5. m depth) were tested with respect to salmon swimming depth and sea lice infection, following the hypothesis that L. salmonis infection in a commercial salmon population is reduced when exposed to deep lighting and feeding. This is based on two assumptions, firstly that planktonic L. salmonis larvae principally remain in surface waters (top 4. m) and secondly, that deep lighting and feeding attract salmon to deeper water depths. Results from commercial scale trials confirmed that salmon swimming behaviour is altered under submerged feeding conditions with fish attracted to the feeding corridor during the feeding process. When the fish reached satiation or feeding ceased, they returned to the surface waters during the day. Submerged lighting attracted the fish to the illuminated water depths during the night. During the day, natural light overruled these effects to some extent. The number of L. salmonis on fish exposed to deep submerged lighting was significantly lower than the number of lice found on salmon in cages with surface lighting during the summer months. Submerged feeding showed no advantage over surface feeding with respect to the number of L. salmonis found in these trials. The results of the study suggest that swimming depth manipulation can be used at a commercial scale to reduce salmon lice burdens on Atlantic salmon stocks. © 2014.

Frenzl B.,University of Stirling | Migaud H.,University of Stirling | Fjelldal P.G.,Norwegian Institute of Marine Research | Shinn A.P.,University of Stirling | And 5 more authors.
Pest Management Science | Year: 2014

BACKGROUND: Sea lice infection is the most expensive disease factor for Atlantic salmon sea-cage farming. For triploid salmon to be accepted as a commercial possibility, investigation of susceptibility of triploid salmon to sea lice infection is a fundamental milestone. The susceptibility of diploid and triploid salmon to infection with Lepeophtheirus salmonis was examined in a tank trial in Scotla tank trial in Norway and a cage trial in Scotland. RESULTS: Following a single infection challenge, results indicated a significant correlation between fish size and the number of attached sea lice. Triploid fish were larger than diploids at the smolt stage. In the tank trials, no difference was found between infection levels on diploids and triploids after a single infection challenge. The tank trial in Scotland continued with a second infection challenge of the same fish, which also showed no infection differences between ploidies. A borderline correlation between first infection and re-infection intensity was found for PIT-tagged diploid salmon examined after each challenge. No significant difference in louse infection between diploid and triploid salmon (∼2kg) was found in the cage trial undertaken under commercial conditions. CONCLUSION: This study concludes that triploid Atlantic salmon are not more susceptible to sea louse infection than diploid fish. © 2013 Society of Chemical Industry.

Bell J.G.,University of Stirling | Pratoomyot J.,University of Stirling | Strachan F.,University of Stirling | Henderson R.J.,University of Stirling | And 5 more authors.
Aquaculture | Year: 2010

The present study compared the effects of diets formulated with reduced fishmeal (FM) content and either 100% fish oil (FO) or 100% of a vegetable oil (VO) blend in post-smolts of three family groups of Atlantic salmon. Two groups were selected as being either "Lean" or "Fat" based on estimated breeding values (EBV) for flesh adiposity of their parents derived from a breeding programme, while the third group (CAL) was a mix of non-pedigreed commercial families unrelated to the two groups above. The VO blend comprised rapeseed, palm and a new product, Camelina oil in a ratio of 5/3/2, and diets were fed to duplicate pens of each salmon group. After an ongrowing period of 55. weeks, to reach a mean weight of 3. kg, the fish from all treatments were switched to a decontaminated FO for a further 24. weeks to follow restoration of long-chain n-3 polyunsaturated fatty acids (LC-PUFA) in the fish previously fed VO. Final weights were significantly affected by family group and there was also an interaction between diet and group with Fat and Lean FO fish being larger than the same fish fed VO. Specific growth rate (SGR) was highest in CAL fish (1.01), feed conversion ratio (FCR) was highest in the Lean fish but there were no significant effects on thermal growth coefficient (TGC). Condition Factor (CF) was lowest in CAL fish while the hepato-somatic index (HSI) was highest in Lean fish and viscero-somatic index (VSI) highest in Fat fish. Flesh and viscera lipid content was affected by both family group and diet with a significant interaction between the two. Flesh lipid in fish fed FO was in the order Fat>CAL. >Lean although this order was Fat=Lean>CAL when fed VO. Flesh fatty acid compositions were affected mainly by diet although some minor fatty acids were also influenced by group. Fish fed VO had n-3 LC-PUFA reduced by ~. 65% compared to fish fed FO but this could be restored by a 16-week FO finishing diet phase. The differences observed in lipid and fatty acid deposition suggested that genetics affected lipid deposition and metabolism and that breeding programmes could select for fish that retained more n-3 LC-PUFA in their flesh, particularly when fed diets low in these fatty acids. © 2010 Elsevier B.V.

Leclercq E.,University of Stirling | Dick J.R.,University of Stirling | Taylor J.F.,University of Stirling | Bell J.G.,University of Stirling | And 2 more authors.
Journal of Agricultural and Food Chemistry | Year: 2010

The external coloration of fish is a key driver in consumer buying decisions and is typically altered during sexual maturation in salmonids. Farmed Atlantic salmon (Salmo salar L.) exhibiting distinct phenotypes from the typical silver and nuptial coloration were described in terms of sexual development, flesh quality, and skin pigment profiles. Reconditioning of skin coloration during storage was also tested (CIE[1976]L*a*b*) with the overall view to optimize quality management. The intermediary phenotype never reflected significant deteriorations of flesh quality. It originated from a lack of purine pigments (guanine and hypoxanthine), revealing the carotenoid compounds dominated by the yellow-orange β-carotene. The resulting distinctive lightness and yellowness were reduced by direct ice contact at a post-mortem stage. Storage conditions can be optimized to improve and standardize the coloration of whole-fish, yielding superior flesh quality parameters. This would facilitate product quality grading during primary processing and also increase product acceptance and attractiveness. © 2010 American Chemical Society.

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