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Utilising novel ingredients in aquafeeds is necessary for the continued expansion and intensification of aquaculture production. Microalgae are utilised widely in aquaculture for a variety of purposes; as live feed for fish and shellfish larvae and juveniles, for the production of algae‐based meals and oils to replace marine derived raw materials in aquafeeds, and for the production of astaxanthin, the carotenoid that gives salmon flesh its characteristic reddish colour. Notably, long‐chain polyunsaturated fatty acids, amino acids, proteins, fibres, antioxidant pigments, vitamins and minerals are among the compounds in microalgae with great biological value. A growing collection of experimental data has demonstrated that these substances are crucial for increasing larval survival and enhancing the growth and well‐being of fish and shellfish. In this review, the processing of microalgae utilised as aquafeed ingredient, the health promoting compounds in microalgae and their role in growth, immunity and disease resistance of fish and shellfish are described and discussed. Simultaneously, major hurdles in the commercial use of microalgae in aquafeed, and future research and development perspectives are all critically discussed. [ABSTRACT FROM AUTHOR]

Choline plays a crucial role in lipid metabolism for fish, and its deficiency in aquafeed has been linked to compromised health and growth performance. A 56-d experiment was conducted to examine the effects of dietary choline on lipid composition, histology and plasma biochemistry of yellowtail kingfish (Seriola lalandi; YTK; 156 g initial body weight). The dietary choline content ranged from 0·59 to 6·22 g/kg diet. 2-Amino-2-methyl-1-propanol (AMP) (3 g/kg) was added to diets, except for a control diet, to limit de novo choline synthesis. The results showed that the liver lipid content of YTK was similar among diets containing AMP and dominated by NEFA. In contrast, fish fed the control diet had significantly elevated liver TAG. Generally, the SFA, MUFA and PUFA content of liver lipid in fish fed diets containing AMP was not influenced by choline content. The SFA and MUFA content of liver lipid in fish fed the control diet was similar to other diets except for a decrease in PUFA. The linear relationship between lipid digestibility and plasma cholesterol was significant, otherwise most parameters were unaffected. When AMP is present, higher dietary choline reduced the severity of some hepatic lesions. The present study demonstrated that choline deficiency affects some plasma and liver histology parameters in juvenile YTK which might be useful fish health indicators. Importantly, the present study elucidated potential reasons for lower growth in choline-deficient YTK and increased the knowledge on choline metabolism in the fish. [ABSTRACT FROM AUTHOR]

• Temperature changes altered fish ectoparasite reproductive traits. • Neobenedenia girellae laid larger, more nutritionally-rich eggs under cool conditions. • Reproduction rates increased under warm conditions. • Egg volume showed strong, positive correlations with several high-energy materials. This study quantified the effects of temperature on reproduction and maternal provisioning of the ectoparasite, Neobenedenia girellae (Platyhelminthes: Monogenea), a species known to cause detrimental impacts to aquaculture fishes in tropical and subtropical environments worldwide. At 20 and 25 °C, parasites exhibited relatively slower production of larger eggs that were energy-dense. In contrast, parasites at 30 °C attained sexual maturity faster, were reproductively active over a shorter period, grew to a smaller size and laid smaller, less energy-rich eggs at a faster rate. As such, parasites exhibited two distinct reproductive patterns in response to temperature: parasites at lower temperatures produced larger eggs with higher energy content, while those at the higher temperature had a higher rate of egg production. Larger eggs produced under cooler conditions were better provisioned with energetic reserves and important, membrane-bound lipids that would likely facilitate larval longevity and development success. This is commensurate with previous observations of epizootics of this parasite species in aquaculture systems during winter. Meanwhile, eggs produced at 30 °C contained higher proportions of saturated fatty acids compared with polyunsaturated fatty acids, likely reflecting metabolic regulation of cell membrane fluidity, which is necessary for larvae to survive warm conditions. This study demonstrates that fish ectoparasites have evolved substantial reproductive and metabolic flexibility to maximise infection success under variable environmental conditions. [ABSTRACT FROM AUTHOR]

A more efficient utilisation of marine-derived sources of dietary n -3 long-chain PUFA (n -3 LC PUFA) in cultured Atlantic salmon (Salmo salar L.) could be achieved by nutritional strategies that maximise endogenous n -3 LC PUFA synthesis. The objective of the present study was to quantify the extent of n -3 LC PUFA biosynthesis and the resultant effect on fillet nutritional quality in large fish. Four diets were manufactured, providing altered levels of dietary n -3 substrate, namely, 18 : 3 n -3, and end products, namely, 20 : 5 n -3 and 22 : 6 n -3. After 283 d of feeding, fish grew in excess of 3000 g and no differences in growth performance or biometrical parameters were recorded. An analysis of fatty acid composition and in vivo metabolism revealed that endogenous production of n -3 LC PUFA in fish fed a diet containing no added fish oil resulted in fillet levels of n -3 LC PUFA comparable with fish fed a diet with added fish oil. However, this result was not consistent among all treatments. Another major finding of this study was the presence of abundant dietary n -3 substrate, with the addition of dietary n -3 end product (i.e. fish oil) served to increase final fillet levels of n -3 LC PUFA. Specifically, preferential β -oxidation of dietary C18 n -3 PUFA resulted in conservation of n -3 LC PUFA from catabolism. Ultimately, this study highlights the potential for endogenous synthesis of n -3 LC PUFA to, partially, support a substantial reduction in the amount of dietary fish oil in diets for Atlantic salmon reared in seawater. [ABSTRACT FROM AUTHOR]

Fatty acids (FA) play a vital role in coral physiology, metabolism and stress resistance. Optimal health requires a balance of fatty acids, and more specifically essential polyunsaturated fatty acids (PUFA), for efficient biochemical and physiological functioning. Therefore, it is necessary to fully assess and evaluate the viability of FA as biomarkers for monitoring the health of coral populations. This study explores seasonal and spatial variation in the abundance of 17 FA in the coral Acropora tenuis, along two water quality gradients on the central Great Barrier Reef. Ratios of key FA varied similarly along the two water quality gradients and were highest in corals from comparatively good water quality conditions. Strong differences in PUFA composition were found between wet and dry seasons, with high percentage n-3 PUFA defining the dry seasons (June 2013 and October 2013) and high percentage n-6 PUFA defining the wet seasons (February 2013 and 2014). Saturated FA and monounsaturated FA concentrations varied with season, positively correlated with Symbiodinium density, and had highest concentrations in corals exposed to relatively poor water quality. Overall, results demonstrate that essential FA and their derived ratios support FA as a potential indicator of coral holobiont health; however, strong seasonal variation may negate FA and their derived ratios as water quality indicators. [ABSTRACT FROM AUTHOR]

Abstract There is a growing trend of 'replacing' long-chain omega-3 polyunsaturated fatty acid (n-3 LC PUFA) rich oils with C 18 shorter-chain omega-3 polyunsaturated fatty acid rich oils in Atlantic salmon aquafeed formulations. n-3 LC PUFA, including 20:5n-3 and 22:6n-3, play contrasting physiological roles and are metabolised differently in comparison to C 18 PUFA. Accordingly, the present study recorded the effect of replacing n-3 LC PUFA rich dietary fish oil with C 18 n-3 PUFA rich camelina oil at two inclusion levels in commercial-like diets fed to market-sized Atlantic salmon. This assessment was achieved by an analysis of industry relevant production parameters including growth performance, fatty acid composition and metabolism, nutrient digestibility and consumer acceptance (liking and attribute analysis of fillet). The trial was conducted over the final 150 days of an on-farm grow-out period in seawater. The dietary replacement of n-3 LC PUFA with C 18 n-3 PUFA resulted in a significant decrease in fillet n-3 LC PUFA and a poorer growth performance. However, in the absence of fish oil, the inclusion of camelina oil at high levels (40%) contributed to an improved n-6/n-3 ratio and partially ameliorated low dietary n-3 LC PUFA by providing added substrate for endogenous n-3 LC PUFA synthesis in comparison to a 20% camelina oil inclusion. Furthermore, consumer acceptance of Atlantic salmon was unaffected by the dietary addition of camelina oil. Highlights • The dietary replacement of n-3 LC PUFA with C18 n-3 PUFA resulted in a decrease in fillet n-3 LC PUFA and poorer growth. • Camelina oil at a diet lipid level of 40% provided an improved n-6/n-3 ratio in the fillet compared to a 20% inclusion level. • High dietary provision of camelina oil provided added substrate for endogenous n-3 LC PUFA synthesis in Atlantic salmon. • Consumer acceptance including overall taste of Atlantic salmon fillet was unaffected by the dietary addition of camelina oil. [ABSTRACT FROM AUTHOR]

Nutritional strategies are currently developed to produce farmed fish rich in n-3 long-chain PUFA (LC-PUFA) whilst replacing fish oil by plant-derived oils in aquafeeds. The optimisation of such strategies requires a thorough understanding of fish lipid metabolism and its nutritional modulation. The present study evaluated the fatty acid bioconversion capacity of rainbow trout (Oncorhynchus mykiss) fry previously depleted in n-3 PUFA through a 60-d pre-experimental feeding period with a sunflower oil-based diet (SO) followed by a 36-d experimental period during which fish were fed either a linseed oil-based diet (LO) (this treatment being called SO/LO) or a fish oil-based diet (FO) (this treatment being called SO/FO). These treatments were compared with fish continuously fed on SO, LO or FO for 96 d. At the end of the 36-d experimental period, SO/LO and SO/FO fish recovered >80 % of the n-3 LC-PUFA reported for LO and FO fish, respectively. Fish fed on LO showed high apparent in vivo elongation and desaturation activities along the n-3 biosynthesis pathway. However, at the end of the experimental period, no impact of the fish n-3 PUFA depletion was observed on apparent in vivo elongation and desaturation activities of SO/LO fish as compared with LO fish. In contrast, the fish n-3 PUFA depletion negatively modulated the n-6 PUFA bioconversion capacity of fish in terms of reduced apparent in vivo elongation and desaturation activities. The effects were similar after 10 or 36 d of the experimental period, indicating the absence of short-term effects. [ABSTRACT FROM PUBLISHER]

This study on the eggs of the tropical monogenean Neobenedenia girellae presents the first detailed quantitative biochemical information of a marine parasite species’ eggs. Moisture and protein composed the majority of the contents of freshly laid eggs (79.12 ± 0.82 and 11.51 ± 0.49% respectively) followed by lipid (2.50 ± 0.15%). Lipids were composed of approximately equal amounts of saturated, monounsaturated, and polyunsaturated fatty acids and the predominant lipid class was triacylglycerol (33.82 ± 1.20%). This study represents a fundamental step towards a better understanding of the early life biology of this important species of parasite. [ABSTRACT FROM AUTHOR]

The implementation of alternative lipid sources for use in aquaculture is of considerable interest globally. However, the possible benefit of using stearidonic acid (SDA)-rich fish oil (FO) alternatives has led to scientific confusion. Two hundred and forty rainbow trout (Oncorhynchus mykiss) were fed 1 of 4 diets (3 replicate tanks/treatment) containing either FO, linseed oil (LO), echium oil, or mixed vegetable oil (72% LO, 23% sunflower oil, and 6% canola oil) as the dietan/ lipid source (16.5%) for 73 d to investigate the competition and long-chain PUFA (LC-PUFA) biosynthesis between the fatty acid Substrates &agr;-linolenic acid (ALA) and SDA. SDA was more efficiently bioconverted to LC-PUFA compared with ALA. However, when the dietary lipid sources were directly compared, the increased provision of CI 8 PUFA within the LO diet resulted in no significant differences in (n-3) LC-PUFA content compared with fish fed the other diets. This study therefore shows that, rather than the previously speculated substrate competition, the limiting process in the apparent in vivo (n-3) LC-PUFA biosynthesis appears to be substrate availability. Rainbow trout fed the SDA- and ALA-rich dietary lipid sources subsequently had similar significant reductions in (n-3) LC-PUFA compared with fish fed the FO diet, therefore providing no additional dietary benefit on (n-3) LC-PUFA concentrations [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to evaluate the effects of varying total amounts of dietary C18 PUFA on growth performance and tissue fatty acid composition in rainbow trout (Oncorhynchus mykiss). The experimental feeding trial was implemented over an entire grow-out period with a subsequent finishing period up to commercial size. Overall performance was unaffected by the dietary treatments, whilst fillet fatty acid make-up was mirroring that of the diet. The different dietary C18 PUFA levels had different effects on the fillet fatty acid productive value (i.e. fatty acid retention rates) during the grow-out and finishing periods. Specifically, during the grow-out period, diets rich in C18 PUFA resulted in increased n−3 LC-PUFA content in fish fillets. However, from an n−3 LC-PUFA restorative viewpoint, during the subsequent finishing period, the high C18 PUFA content of fillets of fish previously fed with high C18 PUFA diets was detrimental to the success of the finishing strategy. Therefore, depending on the strategy to be implemented (maximal fatty acid bioconversion or a fish oil restorative period), dietary C18 PUFA inclusion can be viewed from both a positive or a negative perspective. [Copyright &y& Elsevier]

The Murray cod (Maccullochella peelii peelii), an iconic Australian freshwater fish, is subject to a small but growing aquaculture sector in Australia. Optimal larviculture techniques for this species have yet to be established, particularly with regard to the nutritional quality of starter diets. As such, optimisation of current Murray cod hatchery practices and feeding regimes is essential to maximize the production of high quality larvae and expand commercial aquaculture prospects. The aim of this investigation was to assess the effects of Artemia nauplii enriched with high levels of long-chain polyunsaturated fatty acids (LC-PUFA; ENR treatment), on the growth and fatty acid composition of larval Murray cod. Using untreated Artemia nauplii as a control treatment (CTL), larvae were fed either treatment to apparent satiation twice daily in triplicate groups of 700 fish with initial mean weights of 0.012 ± 0.06 g for 21 days at 19.85 °C. Survival was not significantly different between treatments (P >.05). Final mean weight and length, as well as specific growth rate, were significantly higher for ENR compared to CTL. Enriched larvae also contained significantly higher total lipid contents and across all three of the major fatty acid groups. Of the individual fatty acids, increases in ARA (20:4n-6) and DHA (22:6n-3) were recorded in the ENR fish, while CTL fish contained high concentrations of 18:4n-3, 20:4n-3 and 22:5n-3, which are intermediate fatty acids along the n-3 conversion pathway, suggesting desaturation and elongation toward EPA (20:5n-3) and DHA. Results demonstrate that enriched Artemia nauplii are vastly superior to untreated Artemia as a starter diet for optimal growth and fatty acid composition of Murray cod larvae. Thus, despite the clear ability of Murray cod larvae to undergo elongation and desaturation of ALA (18:3n-3), the present study demonstrates that this is not sufficient to sustain growth or LC-PUFA tissue levels akin to those possible through high dietary LC-PUFA intake. • Optimal larviculture techniques for Murray cod larvae should include live feed enrichment. • Enrichment of Artemia with long-chain polyunsaturated fatty acids improves the performance of Murray cod larvae • Murray cod larvae showed active elongation and desaturation of 18:3n-3 (α-linolenic acid). • In vivo long chain omega-3 biosynthesis in Murray cod larvae is not sufficient to compensate for limited dietary supply. • DHA content in Murray cod larvae is tightly regulated, and is limiting nutrient. [ABSTRACT FROM AUTHOR]

Abstract To investigate plasticity in biochemical and physiological health attributes of corals, identical colony fragments of the coral Acropora tenuis, from two inshore populations, were exposed to native and novel environmental regimes. Variation in global gene expression (GE) and lipid and fatty acid (FA) composition of surviving colony fragments were quantified after four months. Major FA classes, with the exception of short-chain (C18) polyunsaturated fatty acids (PUFA), decreased in concentration when coral fragments were exposed to lower water quality regardless of their source population. In contrast, a strong effect of source population was detected in the GE profiles of all coral fragments and was enriched with genes associated with translation, ribosome biogenesis and ribosome cellular components. One cluster of co-expressed genes positively correlated with multiple individual FA and included genes involved in developmental processes and cellular pathways. This study demonstrates the strong influence of a source effect defining gene expression relating to basic biological functions, including biosynthetic processing, translation and ribosome biogenesis. However, there is plasticity in FA composition and specific genes relating to elevated health and immunity, which can respond to changes in environmental conditions. These findings suggest hope for future corals, if we can reduce anthropogenic water quality stressors. Highlights • Responses of A. tenuis are a function of source population and transplant environment. • Genes relating to basic biological functions are consistent within source populations. • Plasticity in fatty acids highlights response of corals to changing environments. • Plasticity in health/immunity genes emphasizes response to novel conditions. [ABSTRACT FROM AUTHOR]

Fish are the main source of long-chain polyunsaturated fatty acids (LC-PUFA, >C 18) for human consumption. In general, it has been widely observed that the fatty acid (FA) profiles of farmed fish are reflective of the diet. However, the degree of tissue FA "distortion" based on incorporation of different dietary FA into fish tissues varies greatly depending on FA type, fish species and environmental factors. In terms of fish FA composition, this variation has not been comprehensively reviewed, raising the question: "Are fish what they eat?". To date, this remains unanswered in detail. To this end, the present review quantitatively summarized the 'diet-fish' FA relationship via an analysis of FA composition in diets and fish tissues from 290 articles published between 1998 and 2018. Comparison of this relationship among different fish species, tissue types or individual FA was summarized. Furthermore, the influence of environmental factors such as temperature and salinity, as well as of experimental conditions such as fish size and trophic level, feeding duration, and dietary lipid level on this relationship are discussed herein. Moreover, as a means of restoring LC-PUFA in fish, an emphasis was paid to the fish oil finishing strategy after long-term feeding with alternative lipid sources. It is envisaged that the present review will be beneficial in providing a more comprehensive understanding of the fundamental relationship between the FA composition in diets, and subsequently, in the farmed fish. Such information is integral to maintaining the quality of farmed fish fillets from the perspective of FA composition. • The 'diet-fish' FA relationship was systematically reviewed. • The 'diet-fish' FA relationship was analyzed by quantitative approaches. • Factors influencing the 'diet-fish' FA relationship were analyzed and discussed. • An emphasis was paid to the fish oil finishing strategy in fish farming. • Dietary FA incorporation in fish tissues is affected by many non-dietary factors. [ABSTRACT FROM AUTHOR]

High mortality during larval rearing is a persistent bottleneck in finfish aquaculture and is often caused by inadequate nutrition. Nutritional deficiencies in live feeds are usually overcome by enrichment with commercial lipid emulsions; however, enriching live feeds using microalgae may be more effective. This study investigated the efficacy of the microalga Proteomonas sulcata as a live feed enhancement for rearing larvae of the wide-band anemonefish, Amphiprion latezonatus. We found A. latezonatus larvae fed live feeds enhanced with P. sulcata had higher survival and better growth at 7 days post hatch (dph) compared to fish fed live feeds enriched with a commercial lipid emulsion or left unenriched. At 14 dph, A. latezonatus initially fed rotifers cultured on P. sulcata for several generations had the highest survival overall. These results may be due to the high phospholipid content in rotifers enhanced on P. sulcata compared to other diets. Survival, length, depth, and eye diameter of 7 dph A. latezonatus was also positively correlated with omega-6 docosapentaenoic acid (DPAn-6, 22:5n-6) and high ratios of DPAn-6 to docosahexaenoic acid (DHA, 22:6n-3) in their tissues, highlighting the need to better understand the role of DPAn-6 in larval fish ontogeny. Surprisingly, given their high survival and growth, A. latezonatus larvae fed P. sulcata enhanced live feeds had lower levels of DHA compared to the more poorly performing fish fed the commercial lipid emulsion enriched live feeds; this challenges the paradigm of a positive correlation between DHA and growth and survival that is documented in many other marine fish larvae. This study demonstrates the benefits of using P. sulcata to enhance the nutritional quality of live feeds and highlights the need for a better understanding of the role of n-6 long-chain polyunsaturated fatty acids in the early development of larval fish. • Larval Amphiprion latezonatus survived and grew best when fed live feeds enhanced with the microalga Proteomonas sulcata. • A. latezonatus fed live feeds enriched with a lipid emulsion contained the most DHA, but this did not correlate with survival or growth. • DPAn-6 and the ratio of DPAn-6 to DHA in A. latezonatus tissues was positively correlated with larval survival and growth. • High levels of dietary DHA may be less important for some marine fish larvae than previously thought. [ABSTRACT FROM AUTHOR]

The article focuses on a study on ox desaturase gene sequences from 80 animal species including Cnidaria, Rotifera and Mollusca. The study found that the ability to produce polyunsaturated fatty acids (PUFA) de novo and further biosynthesis of long-chain PUFA are possessed by multiple invertebrates.

Abstract: The complete and successful replacement of fish oil in aquafeed without compromising fillet omega-3 long chain polyunsaturated fatty acid (n−3 LC-PUFA) concentrations has yet to be achieved. As means of overcoming this issue, the potential of in vivo n−3 LC-PUFA biosynthesis in cultured fish has been widely investigated and may permit the future economical and sustainable development of aquaculture. Two of the key enzymes involved in this process include the fatty acid Δ-6 and Δ-5 desaturases, where, in the terminal protein of each complex, iron is present in the active di-iron centres. To the best of authors'' knowledge, no investigations have thus far been attempted to elucidate the potential roles of dietary iron on the fatty acid metabolism of cultured fish. In this study, graded inclusions of dietary iron were tested in rainbow trout fed vegetable oil based diets. This study generated preliminary evidence suggesting that dietary iron concentration can have a positive effect on LC-PUFA biosynthesis in fish and data are herein reported. In particular, dietary iron level was shown to affect the final n−3 LC-PUFA content of fish tissues and also to modulate the activity of fatty acid desaturase enzymes. This activity was insufficient to compensate for a diet lacking in LC-PUFA but does highlight potential strategies to maximise this activity in cultured fish fed fish oil free diets. [Copyright &y& Elsevier]

The fattening of immature female Chinese mitten crab (Eriocheir sinensis) with high quality diets is an effective mechanism for improving ovarian development and nutritional quality. This study investigated the ovarian development and nutritional quality of female E. sinensis during an 80-day fattening period. The results showed that the gonadosomatic index (GSI) and total edible yield of female E. sinensis increased in a stepwise manner over the course of the fattening period, in synchrony with a decrease in feed consumption and feed cost. Crude protein, total lipid and total carbohydrate in ovaries increased significantly over the course of the fattening period, with the highest crude protein content in both the hepatopancreas and meat observed at Day 40. There was a stepwise increased in the content of triacylglycerol (TAG) and cholesterol (CHO) and phospholipid (PL) in ovary and meat, respectively. On the contrary, the content of free fatty acid (FFA) and PL in ovaries and hepatopancreas as well as the meat TAG and FFA decreased significantly over the course of the fattening period. In ovaries, the highest concentration of polyunsaturated fatty acid (∑PUFA) was observed at Day 60, whilst the highest total monounsaturated fatty acid (∑MUFA) in meat was detected at Day 40. The highest content of ∑MUFA in hepatopancreas, and the ∑PUFA and total long chain polyunsaturated fatty acid (∑LC-PUFA) in meat were detected at Day 80, while the highest hepatopancreas ∑PUFA was detected at Day 0. The content of total essential amino acids (∑EAA) and total amino acids (TAA) in ovaries and meat increased significantly during the fattening period of Day 0 to Day 40, while no significant increase was detected on the TAA during the period of Day 40 to Day 80. Essential amino acid scores (EAAS) of ovary and meat were >100 for all essential amino acids (EAA), and fattening culture did not significantly improve EAAS for ovary and meat. In conclusion, the fattening could improve the total edible yield and nutritional values of female E. sinensis. Considering the fattening performance and feed cost, the appropriate fattening period should be 40–60 days for pond-reared female E. sinensis post puberty molting. • Fattening is an effective approach for improving ovarian development and nutritional quality of female E. sinensis. • Gonadosomatic index and total edible yield of female E. sinensis increased significantly during fattening culture. • Appropriate fattening period should be 40–60 days for pond-reared female E. sinensis post pubertal molt. [ABSTRACT FROM AUTHOR]