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

Lead Research Organisation: University of Exeter
Department Name: Biosciences

Abstract

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.

Technical Summary

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

Planned Impact

See Lead Proposal from Stirling

Publications

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