Lipids and their constituent fatty acids are, along with proteins, the major organic constituents of fish, and they play major roles as sources of metabolic energy for growth including reproduction and movement, including migration. Furthermore, the fatty acids of fish lipids are rich in ω3 long chain, highly unsaturated fatty acids (n-3 HUFA) that have particularly important roles in animal nutrition, including fish and human nutrition, reflecting their roles in critical physiological processes. Indeed, fish are the most important food source of these vital nutrients for man. Thus, the longstanding interest in fish lipids stems from their abundance and their uniqueness. This review attempts to summarize our present state of knowledge of various aspects of the basic biochemistry, metabolism, and functions of fatty acids, and the lipids they constitute part of, in fish, seeking where possible to relate that understanding as much to fish in their natural environment as to farmed fish. In doing so, it highli...

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Metabolism and Functions of Lipids and Fatty Acids in Teleost Fish

Physical, chemical and perceived stressors can all evoke non-specific responses in fish, which are considered adaptive to enable the fish to cope with the disturbance and maintain its homeostatic state. If the stressor is overly severe or long-lasting to the point that the fish is not capable of regaining homeostasis, then the responses themselves may become maladaptive and threaten the fish's health and well-being. Physiological responses to stress are grouped as primary, which include endocrine changes such as in measurable levels of circulating catecholamines and corticosteroids, and secondary, which include changes in features related to metabolism, hydromineral balance, and cardiovascular, respiratory and immune functions. In some instances, the endocrine responses are directly responsible for these secondary responses resulting in changes in concentration of blood constituents, including metabolites and major ions, and, at the cellular level, the expression of heat-shock or stress proteins. Tertiary or whole-animal changes in performance, such as in growth, disease resistance and behavior, can result from the primary and secondary responses and possibly affect survivorship.Fishes display a wide variation in their physiological responses to stress, which is clearly evident in the plasma corticosteroid changes, chiefly cortisol in actinopterygian fishes, that occur following a stressful event. The characteristic elevation in circulating cortisol during the first hour after an acute disturbance can vary by more than two orders of magnitude among species and genetic history appears to account for much of this interspecific variation. An appreciation of the factors that affect the magnitude, duration and recovery of cortisol and other physiological changes caused by stress in fishes is important for proper interpretation of experimental data and design of effective biological monitoring programs.

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Stress in Fishes: A Diversity of Responses with Particular Reference to Changes in Circulating Corticosteroids

Aquaculture's pressure on forage fisheries remains hotly contested. This article reviews trends in fishmeal and fish oil use in industrial aquafeeds, showing reduced inclusion rates but greater total use associated with increased aquaculture production and demand for fish high in long-chain omega-3 oils. The ratio of wild fisheries inputs to farmed fish output has fallen to 0.63 for the aquaculture sector as a whole but remains as high as 5.0 for Atlantic salmon. Various plant- and animal-based alternatives are now used or available for industrial aquafeeds, depending on relative prices and consumer acceptance, and the outlook for single-cell organisms to replace fish oil is promising. With appropriate economic and regulatory incentives, the transition toward alternative feedstuffs could accelerate, paving the way for a consensus that aquaculture is aiding the ocean, not depleting it.

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Feeding aquaculture in an era of finite resources

https://www.cell.com/trends/biotechnology/pdf/S0167-7799(00)01433-5.pdf

Commercial potential for Haematococcus microalgae as a natural source of astaxanthin.

Unsustainable fishing practices have placed a heavy emphasis on aquaculture to meet the global shortfalls in the supply of fish and seafood, which are commonly accepted as the primary source of health-promoting essential omega-3 (n-3 highly unsaturated fatty acids). However, dietary fish oil is required for the production of omega-3-rich farmed fish and this commodity, in a vicious circle, is at present derived solely from wild fisheries. Decreasing global availability coupled with the highly variable price of this resource has forced the aquaculture industry to investigate the possibilities of alternative dietary lipid sources. This review attempts to compile all principal information available regarding the effects of fish oil replacement for the diets of farmed finfish, analysing the findings using a comparative approach among different cultured fish species. The review initially focuses on the present situation with regard to the production, availability and main nutritional characteristics of fish oil and the principal alternative lipid sources (such as vegetable oils and animal fats). Following this, the effects of fish oil replacement in finfish nutrition on feed quality, fish performance, feed efficiency, fish lipid metabolism, final eating quality and related economic aspects are presented and discussed.

Fish oil replacement in finfish nutrition

Triplicate groups of Atlantic salmon (Salmo salar L.) were fed four diets containing different oils as the sole lipid source, i.e., capelin oil, oleic acid-enriched sunflower oil, a 1:1 (w/w) mixture of capelin oil and oleic acid-enriched sunflower oil, and palm oil (PO). The beta-oxidation capacity, protein utilization, digestibility of dietary fatty acids and fatty acid composition of lipoproteins, plasma, liver, belly flap, red and white muscle were measured. Further, the lipid class and protein levels in the lipoproteins were analyzed. The different dietary fatty acid compositions did not significantly affect protein utilization or beta-oxidation capacity in red muscle. The levels of total cholesterol, triacylglycerols, and protein in very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL), and plasma were not significantly affected by the dietary fatty acids. VLDL, LDL, and HDL fatty acid compositions were decreasingly affected by dietary fatty acid composition. Dietary fatty acid composition significantly affected both the relative fatty acid composition and the amount of fatty acids (mg fatty acid per g tissue, wet weight) in belly flap, liver, red and white muscle. Apparent digestibility of the fatty acids, measured by adding yttrium oxide as inert marker, was significantly lower in fish fed the PO diet compared to the other three diets.

Lipid metabolism and tissue composition in Atlantic salmon (Salmo salar L.)--effects of capelin oil, palm oil, and oleic acid-enriched sunflower oil as dietary lipid sources

Atlantic salmon (Salmo salar L.) juveniles were fed either 100% fish oil (FO), 75% vegetable oil (VO), or 100% VO throughout their life cycle to harvest weight followed by a finishing diet period when all groups were fed 100% FO. The two experimental VO diets were tested at two different locations (Scotland and Norway) against the same control diet (100% FO). The VO blend was composed of rapeseed oil, palm oil, and linseed oil using capelin oil as a control for fatty acid class compositions. Flesh fatty acid profiles were measured regularly throughout the experiment, with the times of sampling determined by changes in pellet size/lipid content and fish life stage. Growth and mortality rates were not significantly affected by dietary fatty acid compositions throughout the life cycle, except during the seawater winter period in Norway when both growth and protein utilization were increased in salmon fed 100% VO compared to 100% FO. Flesh fatty acid composition was highly influenced by that of the diet, and after the finishing diet period the weekly intake recommendations of very long chain n-3 polyunsaturated fatty acid (VLCn-3 PUFA) for human health were 80 and 56% satisfied by a 200 g meal of 75% VO and 100% VO flesh, respectively. No effect on flesh astaxanthin levels was observed in relation to changing dietary oil sources. Sensory evaluation showed only minor differences between salmon flesh from the dietary groups, although prior to the finishing diet period, flesh from 100% VO had less rancid and marine characteristics and was preferred over flesh from the other dietary groups by a trained taste panel. After the finishing diet period, the levels of typical vegetable oil fatty acids in flesh were reduced, whereas those of VLCn-3 PUFA increased to levels comparable with a 100% FO fed salmon. No differences in any of the sensory characteristics were observed between dietary groups. By blending VOs to provide balanced levels of dietary fatty acids, up to 100% of the fish oil can be replaced by the VO blend without compromising growth or flesh quality. At the same time, 75% of the dietary fish oil can be replaced without compromising flesh VLCn-3 PUFA content, thereby providing a beneficial nutritional profile for human consumption.

Tailoring of Atlantic salmon (Salmo salar L.) flesh lipid composition and sensory quality by replacing fish oil with a vegetable oil blend.

Blood samples from healthy adult Atlantic salmon fed an optimal diet in net sea pens were collected at intervals from October to May Haematological determinations and biochemical serum analyses were carried out on 20 fish in each of seven samples The ranges of haemato-logical values for sample means were: haematocrit 44–49%, haemoglobin 89–104 g 100ml−1, red blood cell count 085–110 × 1012 l−1, MCV 441–553 × 10−15 1, MCH 94–106 × 10−6 g, MCHC 194–217 g 100ml−1 and leucocrit 043–096% The ranges of enzyme activities in serum, for sample means, were: alkaline phosphatase 647–988Ul−1, aspartate aminotrans-ferase 202–351 Ul−1 and alanine aminotransferase 4–8 Ul−1 The ranges of the other parameters analyzed in serum were: total protein 416–566 gl−1, albumin 183–243 gl−1, albumin/total protein ratio 393–440%, creatinine 26–46 μmol, triglycerides 253–498 μmol and cholesterol 93–128 μmol These values are considered to be the normal ranges in healthy fish Variations due to seasonal changes, and the clinical significance of the selected parameters, are discussed Data showing the reproducibility of the biochemical analyses in serum are presented

Normal ranges of some blood chemistry parameters in adult farmed Atlantic salmon, Salmo salar

Six groups of Atlantic salmon, initial weight 142 ± 1 g, were fed increasing dietary inclusion of rapeseed oil (RO) in a regression design and one group was fed a 50% olive oil/50% capelin oil diet. Fatty acid composition was measured in red and white muscle, liver, and fatty acid and lipid class composition was measured in plasma and in the lipoproteins; very low density lipoprotein, low density lipoprotein, high density lipoprotein and nonlipoprotein fraction after 22 and 42 weeks of feeding. Further, the activities of liver NADH-isocitrate dehydrogenase (ICDH), malic enzyme, glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase were measured at each sampling point. After 42 weeks of feeding the experimental diets, the tissue and lipoprotein fatty acid composition was highly affected by dietary fatty acid composition. Regressions showed that 22:1n − 11, 18:1n − 9, 18:3n − 3 and 18:2n − 6 are readily metabolized in all tissues analysed. Further, 20:5n − 3 seems to be metabolized in muscle and retained in liver. 22:6n − 3 was selectively retained in all the analysed tissues, and with higher retention in liver and plasma with higher polar lipid/neutral lipid ratio compared to white and red muscle. Liver from salmon fed 100% RO showed decreased G6PDH and increased ICDH activities compared to the other dietary groups; however, no linear relationship related to increased RO inclusion was detected. The amount of plasma lipoproteins, liver monoene fatty acid level and lipogenic enzyme activity decreased from the autumn to the winter sampling with concomitant decrease in temperature.

Replacing dietary fish oil with increasing levels of rapeseed oil and olive oil – effects on Atlantic salmon (Salmo salar L.) tissue and lipoprotein lipid composition and lipogenic enzyme activities

Øyvind Lie

Papers

Lipid metabolism and tissue composition in Atlantic salmon (Salmo salar L.)--effects of capelin oil, palm oil, and oleic acid-enriched sunflower oil as dietary lipid sources

Tailoring of Atlantic salmon (Salmo salar L.) flesh lipid composition and sensory quality by replacing fish oil with a vegetable oil blend.

Normal ranges of some blood chemistry parameters in adult farmed Atlantic salmon, Salmo salar

Replacing dietary fish oil with increasing levels of rapeseed oil and olive oil – effects on Atlantic salmon (Salmo salar L.) tissue and lipoprotein lipid composition and lipogenic enzyme activities

Starch as an energy source in feed for cod (Gadus morhua): digestibility and retention