Environmental influences on growth, maturation and smoltification in Atlantic salmon parr, Salmo salar

The maturation of Atlantic salmon (Safmo safar) parr, and its effects on growth and smoltification, causes significant economic losses to commercial aquaculture. The current thesis investigates the role of environmental factors on freshwater development, with the aim of providing information which would help reduce the currently observed levels of maturation in farmed salmon. The effects of short day "winter" photoperiods were investigated by exposing three replicated groups of fish to an 8 week "winter" photoperiod (LDlO:14) commencing in May, August or September, in an otherwise continuous light (LD24:0) regime. A further group was held on LD24:0 throughout. 200 to 300 individuals were PIT tagged in each group in order to follow the growth of fish undergoing different developmental strategies, with the retrospective analysis of such development also possible. The highest incidence of maturation (>20%) was observed in the May winter photoperiod group, with low levels recorded in the August and September fish «4%), suggesting that maturation may be influenced during a "critical" period in early development. Maturation levels were intermediate «9%) in the continuous light group indicating that seasonally-changing photoperiodic cues are not necessarily required for gonadal development. The size of mature fish was initially the same as both immature parr and smolts, although the growth of mature individuals subsequently declined, and at the conclusion of the experiment they were significantly smaller. The August photoperiod resulted in the highest incidence of smoltification, with all other treatments resulting in low levels. In a second experiment, PIT tagged fish were reared under an 8 or 12 week ''winter'' photoperiod (LD 10: 14) starting in Mayor June, in an otherwise continuous light (LD24:0) regime. The highest incidence of maturation (> 11 %) was found in the 12 week May fish, with intennediate levels in the 8 week May and 8 week June groups «8%). Low levels were found within the 12 week June group «0.6%) and it is suggested that a critical period when maturation is influenced may occur during a specific, short period in early development. Throughout the experiments, mature individuals maintained the same size as their immature siblings. The 12 week June photoperiod appeared to result in the highest level of smoltification, although those exposed to the 12 week May photoperiod showed the greatest seawater survival. In both photoperiod experiments, fish showing some signs of smoltification were also found to be undergoing gonadal development, indicating that maturation and smoltification are not completely mutually exclusive processes. Possible nutritional effects were considered using different dietary lipid inclusions (either 12.5% or 25%) and variable rations of feed (either full, 2/3 or 113 rations). Different dietary lipid inclusions had no effect on growth, although the whole body fat content of individuals was affected, with a switch in dietary fat content during development resulting in a rapid change in body composition. Fish size increased with ration and, although at the lowest ration of feed whole body fat levels were reduced, they were maintained at a set level under the high and intennediate rations, implying a lipostatic control of growth. Maturation levels were low throughout the nutrition experiments, suggesting that genetic influences may have been important. Dietary lipid level had a negligible effect on smoltification, although increases in ration resulted in a greater incidence of smoltification. Using a 0+ photoperiod regime (i.e. LD24:0 applied from March until December, with the exception of an 8 week period of LD17:7 applied from August), smolting individuals showed a reduction in smolt status when compared to those developed under a natural photoperiod. It is suggested that such regimes restrict the mobilisation of long-tenn energy stores, with the subsequent development of seawater tolerance affected. However, it was noted that the 0+ regime had increased the incidence of smolts. In summary, it has been shown that environmental factors such as photoperiod, nutrition and temperature can play an important role in the developmental strategies taken by juvenile Atlantic salmon. Such factors are likely to greatly influence the attainment of size and/or nutritional thresholds necessary for various developmental strategies, in particular if such thresholds occur during seasonally-sensitive "critical" periods when development can be influenced. Furthermore, the life history strategy undertaken by an individual may be affected by endogenous rhythms, cued by seasonally-changing environmental factors. However, there are clear indications that the underlying genetic control of maturation may also be of importance

The growth of a Welsh strain of Arctic charr Salvelinus alpinus (L.) and investigations into its aquaculture potential

The growth in captivity of a wild Welsh strain (Llyn Cowlyd) of Arctic charr (Salvelinus alpinus) was compared to that of a commercial Scottish strain over the course of a 12 month experiment. At the conclusion of the study, the Welsh strain had a lower mass and condition factor than the commercial fish, but a similar length. Aspects of the growth and population structure of the Welsh strain imply that it could be a subject for aquaculture development, but such practises will be dependant on further work on selection and broodstock development

Photoperiodic effects on precocious maturation, growth and smoltification in Atlantic salmon, Salmo salar

Current Atlantic salmon farming practice induces early smoltification with artificial photoperiod regimes, however the importance of these photoperiods on parr maturation and interactions with smoltification are poorly understood. These questions were addressed in the present investigation, which examined the effects of photoperiod manipulation on the development, maturation and smoltification of individually tagged parr. Approximately 9000 salmon parr from a high grilsing stock were exposed to continuous light (LL) from first feeding. Three sub-groups of 2400 parr, each sub-group in triplicate tanks, were then exposed to an 8 week “winter photoperiod” (LD 10:14) starting on either the 18th May, the 9th August or the 20th September (defined respectively as the May, August and September groups). Following the artificial winter each group was returned to LL. A fourth group of 1600 fish was maintained in replicate tanks on LL throughout. The highest levels of maturation (approx. 20%) were recorded in the May group. August and September groups showed low levels of maturity

The influence of dietary lipid inclusion and daily ration on growth and smoltification in 1+ Atlantic salmon (Salmo salar) parr

The effects of diet regime on growth and smoltification in 1+ Atlantic salmon parr were studied. Two groups of approximately 400 salmon parr, in triplicate, were fed diets containing either 25% or 12.5% lipid from first-feeding. Two further treatments were fed either the 25% or 12.5% lipid diet for 98 days, after which they were fed the alternate diet. In a second experiment three groups of 550 parr, in duplicate, were fed at full, two-thirds or one-third of the manufacturers’ recommended ration, from first-feeding. All groups were maintained on their respective diet regimes until smoltification approximately one year after first-feeding. In experiment 1, lipid level had a significant effect on whole body lipid content. However growth and the incidence of smoltification was not affected by dietary lipid inclusion, with upper modal group fish from each treatment achieving a similar smolt status (in terms of condition factor and Na+, K+-ATPase) at seawater transfer. In experiment 2, growth and the incidence of smolt transformation increased with ration. Full and two-thirds ration fish maintained similar body lipid contents throughout the experiment, with that of the one-third ration fish lower only during early development, indicating that growth was controlled by the maintenance of a distinct lipid level. It is concluded that ration, and not dietary lipid inclusion, has a significant effect on growth and the decision to undergo smoltification in salmon parr

Bio-economic costs and benefits of using triploid rainbow trout in aquaculture: Reduced mortality

Analysis of data collected from rainbow trout farms in the United Kingdom found that mortality levels in triploid rainbow trout were lower than those in diploids. The consequences of rearing triploids, as opposed to diploids, as an intervention to reduce mortality in the U.K. trout farming industry were quantified using a bio-economic model. The model showed that growing triploids could be more profitable than growing diploids, and this was achieved through improvements in productivity (in terms of better survival) and potential for increased product value, and despite the extra costs attributed to purchasing triploid fingerlings

Mortality and fish welfare

Mortality has received insufficient attention as a fish welfare topic. Here, we aim to prompt fish farming stakeholders to discuss fish mortalities in relation to welfare. Mortality in farmed fish populations is due to a variety of biotic and abiotic causes, although it is often difficult to differentiate between underlying and immediate causes of mortality. Most mortality appears to occur during episodes associated with disease outbreaks and critical periods (in development or production). Most causes of mortality can be assumed to be associated with suffering prior to death. As mortality rates in farmed fish populations are suspected to rank amongst the highest in commonly farmed vertebrate species, mortality should be a principal fish welfare issue. Long-term mortality rates can be used as a retrospective welfare performance indicator and short-term mortality rates as an operational welfare indicator. Scrutiny of mortality records and determining causes of death will enable action to be taken to avoid further preventable mortality. The welfare performance of fish farms should only be judged on levels of predictable and preventable mortality. Fish farmers will already be monitoring mortality due to commercial and legal requirements. As profitability in fish farming is directly linked to survival, confronting mortality should ultimately benefit both fish and farmers

Towards a standard protocol in coastal aquaculture biomonitoring: an interlaboratory study to assess reproducibility of the wet lab protocol and of Illumina sequencing

Salmon aquaculture is one of the fastest growing food sectors in the world. Because aquaculture can have a significant impact on the benthic environment, frequent monitoring is required by law. Recently, eDNA (environmental DNA) metabarcoding of benthic bacterial communities emerged as a very powerful tool to infer ecological quality based on amplicon sequence variants (ASVs) and their analyses. To exploit this monitoring approach and enable implementation into routine monitoring programs and official regulations, a high reproducibility of a standardized protocol among different laboratories is a prerequisite. Therefore, sediment samples from a compliance monitoring of a Scottish salmon farm were split into aliquots and distributed to two different laboratories for the wet lab procedure prior to independent Illumina sequencing of the two datasets. We then conducted pattern matching analyses and used supervised machine learning to predict ecological quality for each sample in the two datasets. Results were compared among the two datasets and to the reference data (ecological quality status as obtained from traditional macrofauna-based benthic monitoring). The obtained results demonstrate the high degree of congruence between the ecological quality assessments from the two laboratories. We conclude that the standard wet lab protocol used in our study is sufficiently robust across different laboratories, which meets a milestone criterion for practical routine application in industry

Achieving consensus on current and future priorities for farmed fish welfare: a case study from the UK

The welfare of farmed fish has attracted attention in recent years, which has resulted in notable changes within the aquaculture industry. However, a lack of communication between stakeholders and opposing ethical views are perceived as barriers to achieving consensus on how to improve farmed fish welfare. To address these issues, we developed an interactive approach that could be used during stakeholder meetings to (1) improve communication between different stakeholder groups, (2) build consensus on priorities for farmed fish welfare and (3) establish mechanisms to address welfare priorities. We then applied this approach during a meeting of stakeholders to identify current and future priorities for farmed fish welfare in the UK. During the meeting in the UK, stakeholders initially identified 32 areas that they felt were in need of development for future improvements in farmed fish welfare. These were further refined via peer review and discussion to the seven most important "priority" areas. Establishing a "better understanding of what good fish welfare is" emerged as the highest priority area for farmed fish welfare. The second highest priority area was "the need for welfare monitoring and documentation systems", with mortality recording proposed as an example. The other five priority areas were "[improved understanding of] the role of genetic selection in producing fish suited to the farming environment", "a need for integration and application of behavioural and physiological measures", "the need for a more liberal regime in Europe for introducing new medicines", "a need to address the issues of training existing and new workers within the industry", and "ensuring best practise in aquaculture is followed by individual businesses". Feedback from attendees, and the meeting outputs, indicated that the approach had been successful in improving communication between stakeholders and in achieving consensus on the priorities for farmed fish welfare. The approach therefore proved highly beneficial for future improvements in fish welfare in the UK

Modeling the economic impact of welfare interventions in fish farming—A case study from the UK rainbow trout industry

Actions that aim to improve animal welfare are likely to involve costs for the producer, although at the same time such actions may improve the profitability of production. In this article we introduce a quantitative bio-economical approach for estimating the economic consequences for improving animal welfare in the aquaculture industry; for farmers and the industry as a whole. The decision tool can be used with different welfare indicators, different species and production systems. It can be used to rank the economic consequences of different techniques that aim to improve welfare. We illustrate the decision tool with a case study relating to the use of triploids in rainbow trout farming. We highlight the probability how the benefits gained from changes in bio-economical productivity factors, and consumers' willingness to pay can overcome the costs associated with implementing a specific welfare intervention