ProtoNutrition, Robustness, Oxygen and Omega-3 in Salmon (ProtoROOS)

Fish are an important component of a healthy human diet providing high quality protein, key minerals and vitamins, and are an almost unique source of omega-3 long-chain polyunsaturated fatty acids (LC-PUFA) - EPA and DHA. Increased dietary intake by humans of these omega-3 fatty acids are associated with beneficial health effects, including reducing incidence and severity of inflammatory and pathological conditions including cardiovascular, neurological and developmental diseases. However, all marine fisheries are fully exploited and, since 2015, more than half of all fish and seafood is now supplied by aquaculture. Paradoxically, farmed fish, such as salmon, are themselves reliant on dietary supply of the LC-PUFA. However, there are finite and limited supplies of the marine resources such as fishmeal (FM) and fish oil (FO) that supply these nutrients. Alternative, more sustainable feeds have been developed over the past decade with much of the FM and FO now being replaced by plant proteins and oils. The level of replacement has now reached a critical point where it is having potentially detrimental effects on fish growth, feed efficiency and, importantly, fish health and robustness. Therefore, the key aim of the present research will be to refine our understanding of the needs for these nutrients by Atlantic salmon and thereby refine our recommendations on the need for LC-PUFA in the diets of these animals.
Requirements by salmon have been estimated at ranging somewhere between 1.0% and 1.5% of diet. Given that global salmon farming presently uses about one third of global fish oil production any upward revision of those requirements may cause some significant constraint issues with supplies. Recently, studies undertaken in Norway have suggested that, under challenging environmental conditions, the requirements for LC-PUFA by Atlantic salmon are elevated to about 1.7%. However, there are various flaws with this study including a lack of statistical robustness, formulation covariates, and different nutritional backgrounds of the stock used in the study. Additionally, the use of the term "challenging environmental conditions", wasn't qualified in terms of specific environmental variables but rather a collective of various conditions. Because of that Norwegian study, there is now a perception across the industry that there is a need for higher omega-3 LC-PUFA in the diets of salmon under sea-cage conditions than previously thought, which adds considerably to production cost and undermines the sustainability of modern feeds. Therefore, the present project proposes to re-assess this link between environmental challenge and omega- 3 requirements in a more robust and structured manner, as well as assessing the implications of proto-nutrition on subsequent nutritional responses and whether this prior nutrition link can be used as a means of reducing subsequent demands by fish later in life.
The studies proposed in this project include increased statistical robustness, combined with a more carefully structured experimental approach with a clear definition of the challenging environmental conditions as a decline in water oxygenation (usually the key environmental challenge in sea-cages conditions), which will be used to provide robust quantitative data on this issue. The project will also aim to separate oxygenation issues from feed intake issues, as typically fish respond to low oxygen levels by reducing appetite, which is a further confounding factor with how oxygen affects nutrition.
The proposal is timely and highly relevant as it responds to an important industrial need with cutting edge research. This research will have clear deliverables to improve the utilisation of limiting marine resources in the use of modern feeds in aquaculture. In doing so it will help enhance production and feed efficiency, while maintaining the health and nutritional quality of farmed fish, delivering greater sustainability and food security.

Our hypotheses are that prior nutritional history (proto-nutrition) has an impact on subsequent nutritional requirements as the fish seeks to obtain a net level of key nutrients in their system to sustain growth. Additionally, that the occurrence of "challenging" environmental conditions, through hypoxia (and reciprocal CO2 increase), impacts nutritional responses, not by changing the animals demands per se, but rather by an overall down-regulation of feed intake resulting in an apparent need for an increased nutrient concentration in the feed. These hypotheses contend that nutritional requirements for fish should be expressed as a function of their daily nutrient demand relative to total energy intake and growth demands (akin to a recommended daily intake, RDI), not as a proportion of the diet as has historically been the case. This is a major conceptual shift in the notion of nutritional requirements in the aquaculture domain.
By addressing both hypotheses, we will improve our ability to manage the nutritional requirements of Atlantic salmon more effectively and efficiently through their lifecycle. This will enable greater utilisation of sustainable feeds formulated with very low levels of marine ingredients, through that better understanding the complexities associated with essential nutrient demands and how to supply them. There are elements of the nutritional programming concept in parts of this project in that we will, for the first time, test the hypothesis that proto-nutrition during the salmon's freshwater phase of life will have an impact on subsequent requirements. Specifically, that the potential fortification of a salmon's diet when it is young may allow a reduction in demands later in life during a more resource demanding stage. This will have huge implications for how much of the finite marine resources will need to be used in satisfying the animals requirements at the more resource-use-intensive later stages during the seawater phase of production

Outcomes from this research will impact at many levels, including academia, the salmon feed and production industry, fish consumers and the public. The primary exploitation will be through development and production of improved feed formulations designed to optimise the production efficiency of fish to better utilise sustainable feeds. It will also help facilitate improved levels of replacement of the dwindling and expensive marine ingredients, fishmeal and fish oil, currently used in UK aquafeeds, largely from imported sources. This project will therefore provide industry with strategies with the potential to improve both the economic viability and sustainability of UK aquaculture. Key tangible outcomes will include the more effective use of sustainable feeds formulated with low marine ingredients. By fine-tuning our ability to formulate closer to the fish's demands, whatever the environment or nutritional history, we will be able to better use this valuable resource. However, our exploitation strategy will be far wider than just the feed manufacture sector, as we will target the fish production sector as a whole and increase awareness of the potential of nutritional management through a combination of nutritional and environmental strategies to mitigate fish health and production issues associated with sustainable feeds. There are two main industrial beneficiaries, the UK salmonid farming and aquaculture feed industries. The aquafeed industry itself will play a key central role in the commercial application and uptake of the feed formulation and feeding strategies to be developed and evaluated, with project partner Marine Harvest taking a lead role. The Universities of Stirling (UoS) and Exeter (UoE) have both worked extensively with the feed and salmonid farming sector for more than a decade, collaborating on several research studies including recent BBSRC IPA and BBSRC-NERC projects. This project with Marine Harvest Feed is, however a new collaboration with a newly established feed producer in the UK. Moreover, both UoS and UoE have long and established histories as centres of excellence for fish nutrition, health and physiology research and are recognised as trusted sources of independent research. However, UoS and UoE have extensive links with all sectors and key stakeholders in the UK aquaculture industry that involve regular direct contact, engagement and discussion. Thus, we will use these well-established links including the industry-led Scottish Aquaculture Innovation Centre (SAIC), to engage with potential end-users including major fish farming companies, to ensure industry-wide dissemination and engagement. UoS and UoE membership of the BBSRC ARCH-UK network ensures that the research and inter-disciplinary collaborations it involves strengthen basic and strategic aspects of aquaculture science in the UK. Project results will not only be published as usual in scientific peer-reviewed literature (conference proceedings and papers in high impact journals), but also disseminated widely to industry through contributions to trade and professional magazine articles and online sites such as FISHupdate, and the public via Institutional web pages, and social media as well as mainstream media articles in local and national press and interviews.