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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., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Ocean warming (OW) and ocean acidification (OA) are threatening coral reef ecosystems, with a bleak future forecast for reef-building corals, which are already experiencing global declines in abundance. In contrast, many coral reef sponge species are able to tolerate climate change conditions projected for 2100. To increase our understanding of the mechanisms underpinning this tolerance, we explored the lipid and fatty acid (FA) composition of four sponge species with differing sensitivities to climate change, experimentally exposed to OW and OA levels predicted for 2100, under two CO 2 Representative Concentration Pathways. Sponges with greater concentrations of storage lipid, phospholipids, sterols and elevated concentrations of n-3 and n-6 long-chain polyunsaturated FA (LC PUFA), were more resistant to OW. Such biochemical constituents likely contribute to the ability of these sponges to maintain membrane function and cell homeostasis in the face of environmental change. Our results suggest that n-3 and n-6 LC PUFA are important components of the sponge stress response potentially via chain elongation and the eicosanoid stress-signalling pathways. The capacity for sponges to compositionally alter their membrane lipids in response to stress was also explored using a number of specific homeoviscous adaptation (HVA) indicators. This revealed a potential mechanism via which additional CO 2 could facilitate the resistance of phototrophic sponges to thermal stress through an increased synthesis of membrane-stabilizing sterols. Finally, OW induced an increase in FA unsaturation in phototrophic sponges but a decrease in heterotrophic species, providing support for a difference in the thermal response pathway between the sponge host and the associated photosymbionts. Here we have shown that sponge lipids and FA are likely to be an important component of the sponge stress response and may play a role in facilitating sponge survival under future climate conditions., (© 2018 John Wiley & Sons Ltd.)

Fish oil replacement in aquaculture feeds results in major modifications to the fatty acid makeup of cultured fish. Therefore, in vivo fatty acid biosynthesis has been a topic of considerable research interest. Evidence suggests that pyridoxine (vitamin B(6)) plays a role in fatty acid metabolism, and in particular, the biosynthesis of LC-PUFA has been demonstrated in mammals. However, there is little information on the effects of dietary pyridoxine availability in fish fed diets lacking LC-PUFA. This study demonstrates a relationship between dietary pyridoxine supplementation and fatty acid metabolism in rainbow trout. In particular, the dietary pyridoxine level was shown to modulate and positively stimulate the activity of the fatty acid elongase and Δ-6 and Δ-5 desaturase enzymes, deduced by the whole-body fatty acid balance method. This activity was insufficient to compensate for a diet lacking in LC-PUFA but does highlight potential strategies to maximize this activity in cultured fish, especially when fish oil is replaced with vegetable oils.

Global shortages in fish oil are forcing the aquaculture feed industry to use alternative oil sources, the use of which negatively affects the final fatty acid makeup of cultured fish. Thus, the modulation of fatty acid metabolism in cultured fish is the core of an intensive global research effort. The present study aimed to evaluate the effects of various dietary α-linolenic acid (ALA, 18:3n-3)/linoleic acid (LA, 18:2n-6) ratios in cultured fish. A feeding trial was implemented on the freshwater finfish Murray cod, in which fish were fed either a fish oil-based control diet or one of five fish oil-deprived experimental diets formulated to contain an ALA/LA ratio ranging from 0.3 to 2.9, but with a constant total C₁₈ PUFA (ALA+LA) content. The whole-body fatty acid balance method was used to evaluate fish in vivo fatty acid metabolism. The results indicate that dietary ALA was more actively β-oxidized and bioconverted, whereas LA appears to be more efficiently deposited. LA was β-oxidized at a constant level (~36% of net intake) independent of dietary availability, whereas ALA was oxidized proportionally to dietary supply. The in vivo apparent Δ-6 desaturase activity on n-3 and n-6 PUFA exhibited an increasing and decreasing trend, respectively, in conjunction with the increasing dietary ALA/LA ratio, clearly indicating that this enzymatic activity is substrate dependent. However, the maximum Δ-6 desaturase activity acting on ALA peaked at the substrate level of 3.2186 (μmol g fish⁻¹ day⁻¹), suggesting that additional inclusion of ALA is not only wasteful but counterproductive in terms of n-3 LC-PUFA production. Despite a constant total supply of ALA+LA, the recorded total in vivo apparent Δ-6 desaturase activity on both substrates (ALA and LA) increased in synchrony with the ALA/LA ratio, peaking at 1.54, and a 3.2-fold greater Δ-6 desaturase affinity toward ALA over LA was recorded.

Currently there are several contrasting methods utilized for estimating elongation and desaturation of fatty acids and their general metabolism. The majority of these methods involve an ex vivo approach, requiring expensive and sophisticated equipment, likely to result in considerable variation in enzyme activity between and within species. In the present paper we introduce a further development of the whole-body fatty acid balance method for the estimation of the elongation and desaturation of fatty acids. This method though receiving considerable attention because of its simplicity and reliability has yet to be presented in detail. Theoretically, the whole-body fatty acid balance method can potentially be applied to any organism and requires little more than a gas chromatography unit for fatty acid analysis and elementary calculations. As such in this paper we attempt to spell out in detail the theoretical basis and the methods of application drawing specific examples. Using the present method it is possible to measure the fate of individual fatty acids towards desaturation, elongation and oxidation and calculate the elongase, Delta-6 desaturase and Delta-5 desaturase activities.

The aim of the present investigation was to quantify the fate of C18 and long chain polyunsaturated dietary fatty acids in the freshwater fish, Murray cod, using the in vivo, whole-body fatty acid balance method. Juvenile Murray cod were fed one of five iso-nitrogenous, iso-energetic, semipurified experimental diets in which the dietary fish oil (FO) was replaced (0, 25, 50, 75, and 100%) with a blended vegetable oil (VO), specifically formulated to match the major fatty acid classes [saturated fatty acids, monounsaturated fatty acids, n-3 polyunsaturated fatty acids (PUFA), and n-6 PUFA] of cod liver oil (FO). However, the PUFA fraction of the VO was dominated by C18 fatty acids, while C20/22 fatty acids were prevalent in the FO PUFA fraction. Generally, there was a clear reflection of the dietary fatty acid composition across each of the five treatments in the carcass, fillet, and liver. Lipid metabolism was affected by the modification of the dietary lipid source. The desaturation and elongation of C18 PUFAs increased with vegetable oil substitution, supported by the occurrence of longer and higher desaturated homologous fatty acids. However, increased elongase and desaturase activity is unlikely to fulfill the gap observed in fatty acid composition resulting from decreased highly unsaturated fatty acids intake.

The whole-body fatty acid balance method was used to investigate the fatty acid metabolism in Murray cod (Maccullochella peelii peelii) fed diets containing canola (CO) or linseed oil (LO). Murray cod were able to elongate and desaturate both 18:2n-6 and 18:3n-3. In fish fed the CO diet, 54.4% of the 18:2n-6 consumed was accumulated, 38.5% oxidized and 6.4% elongated and desaturated to higher homologs. Fish fed the LO diet accumulated 52.9%, oxidized 37% and elongated and desaturated 8.6% of the consumed 18:3n-3. The overall roles of n-6 fatty acids appeared more important in Murray cod compared to other freshwater species. Murray cod also showed a preferential order of utilization of C18 fatty acid for energy production (18:3n-3 > 18:2n-6 > 18:1n-9). Moreover, it is demonstrated that an increase in dietary 18:3n-3 is directly responsible of increased desaturase activity and augmented saturated fatty acid accumulation in the fish body. The present study also suggests that, in the context of the possible maximization of the natural ability of fish to produce long chain polyunsaturated fatty acids, the whole-body approach can be considered well suited and informative and Murray cod is a suited candidate to fish oil replacement for its diets.

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]

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 A common strategy for aquafeed manufacturers has been the utilisation of relatively large amounts of terrestrial, both animal and plant, oil sources to produce diets with a high energy content. The provision of high fat diets is aimed at promoting the utilisation of energy from lipid, thus increasing the amount of dietary protein used for tissue synthesis. However, in recent years the cost of marine sourced dietary lipids has risen, at the same time, farming operations are under increasing pressure to limit environmental degradation associated with nitrogenous waste effluent. Currently there is limited information available regarding the environmental and economic impacts of an altered dietary protein: lipid ratio in diets for large Atlantic salmon (Salmo salar) reared in seawater, presenting a potential impediment for nutritional based solutions. Accordingly the present study compared two isoenergetic diets with varied protein: lipid ratios via an assessment of growth, fatty acid utilisation, human nutritional quality, nitrogenous waste output and economic considerations. The trial diets were fed to the fish for the final 150 days of an on-farm grow-out period and resulted in minimal differences in fish growth, fatty acid utilisation and fillet quality. A decreased dietary protein: lipid ratio resulted in a more efficient protein utilisation both in terms of digestibility and assimilation into fish and, therefore, nitrogenous waste output was reduced. However, due to small differences in feed utilisation, the cost of fish production was numerically higher. Highlights • An altered dietary protein: lipid ratio had virtually no effect on fillet fatty acid composition and fatty acid metabolism. • A reduction in the dietary protein:lipid ratio resulted in lower nitrogenous waste output emanating from undigested protein. • Differences in growth were shown to equate to considerable differences in terms of the cost of fish production. [ABSTRACT FROM AUTHOR]

Developing an optimal heterotrophic feeding regime has the potential to improve captive coral growth and health. This study evaluated the efficacy of three exogenous diets: Artemia nauplii (ART), a commercially available coral diet (Reef Roids) (RR), and a novel, micro-bound diet (ATF), against a comparatively natural, unfiltered seawater treatment (RAW), and an unfed, ultra-filtered seawater treatment (CTL), in adult Acropora millepora and Pocillopora acuta nubbins. After 90 days, both species showed significantly positive weight gain in response to one treatment (A. millepora–RAW, P. acuta–ART), and comparatively low growth in response to another (A. millepora–ATF, P. acuta–RR). The results highlighted substantial differences in the nutritional requirements between species. The nutritional composition of A. millepora in the best performing treatment was dominated by high-energy materials such as storage lipids and saturated and monounsaturated fatty acids. In contrast, the P. acuta nutritional profile in the superior treatment showed a predominance of structural materials, including protein, phospholipids, and polyunsaturated fatty acids. This study demonstrates that Artemia nauplii can successfully replace a natural feeding regime for captive P. acuta, yet highlights the considerable work still required to optimise supplementary feeding regimes for A. millepora. [ABSTRACT FROM AUTHOR]

Scleractinian corals are colonial organisms comprising multiple physiologically integrated polyps and branches. Colonialism in corals is highly beneficial, and allows a single colony to undergo several life processes at once through physiological integra- tion and compartmentalised functioning. Elucidating differences in the biochemical composition of intra-colonial branch positions will provide valuable insight into the nutritional reserves underlying different regions in individual coral colonies. This will also ascertain prudent harvesting strategies of wild donor-colonies to generate coral stock with high survival and vigour prospects for reef-rehabilitation efforts and captive husbandry. This study examined the effects of colony branch position on the nutritional profile of two different colony sizes of the common scleractinian, Acropora millepora. For smaller colonies, branches were sampled at three locations: the colony centre (S-centre), 50% of the longitudinal radius length (LRL) (S-50), and the colony edge (S-edge). For larger colonies, four locations were sampled: the colony centre (L-centre), 33.3% of the LRL (L-33), 66.6% of the LRL (L-66), and the edge (L-edge). Results demonstrate significant branch position effects, with the edge regions containing higher protein, likely due to increased tissue synthesis and calcification. Meanwhile, storage lipid and total fatty acid concentrations were lower at the edges, possibly reflecting catabolism of high-energy nutrients to support proliferating cells. Results also showed a significant effect of colony size in the two classes examined. While the major protein and structural lipid sink was exhibited at the edge for both sizes, the major sink for high-energy lipids and fatty acids appeared to be the L-66 position of the larger colonies and the S-centre and S-50 positions for the smaller colonies. These results confirm that the scleractinian coral colony is not nutritionally homogeneous, and while different regions of the coral colony are functionally specialised, so too are their nutritional profiles geared toward meeting specific energetic demands. [ABSTRACT FROM AUTHOR]

Heterotrophic feeding in newly-settled coral planulae can potentially improve survivorship and accelerate early development in some species; however, an optimal diet to facilitate this does not currently exist. This study evaluated the efficacy of three heterotrophic feeding regimes (enriched rotifers, unfiltered seawater, and a novel, particulate diet), against a wholly-phototrophic treatment on Acropora hyacinthus, A. loripes, A. millepora, and A. tenuis recruits, over 93 days post-settlement. The unfiltered seawater treatment recorded maximum survival for all species (A. hyacinthus 95.9±8.0%, A. loripes: 74.3±11.5%, A. millepora: 67±12.7%, A. tenuis: 53.2±11.3%), although not significant. Growth (% surface area gain) was also greatest in the unfiltered seawater, and this was significant for A. millepora (870±307%) and A. tenuis (693±91.8%) (p<0.05). Although total lipid concentration was relatively stable across treatments, the lipid class composition exhibited species-specific responses to each treatment. Lower saturated and higher polyunsaturated fatty acids appeared beneficial to recruit performance, particularly in the unfiltered seawater, which generally contained the highest levels of 20:5n-3 (EPA), 22:6n-3 (DHA), and 20:4n-6 (ARA). The present study demonstrates the capacity of a nutritionally adequate and readily accepted heterotrophic feeding regime to increase coral recruit survival, growth, and health, which can greatly reduce the time required in cost- and labour-intensive culture. [ABSTRACT FROM AUTHOR]

Abstract: This study aimed to gain a better understanding of the metabolic fate of dietary fatty acids in rainbow trout, with a specific focus on the effect of varying total C18 PUFA level. Fish were fed a control fish oil based diet or one of five experimental fish oil deprived diets formulated with a constant 1/1 ratio of 18:3n-3/18:2n-6 and varying total C18 PUFA levels for a period of 7weeks. The transcriptional changes of the Δ-6 desaturase and elongase enzymes in direct comparison to in vivo fatty acid bioconversion, estimated using the whole-body fatty acid balance method, were analysed. The main findings were that i) the efficiency of Δ-6 desaturase was negatively affected by C18 PUFA availability, but the total apparent in vivo enzyme activity was directly proportional to C18 PUFA substrate availability; ii) Δ-6 desaturase had a greater affinity towards n-3PUFA than n-6PUFA; iii) excessive C18 PUFA substrate availability could limit the availability of Δ-6 desaturase to act on C24 fatty acid; iv) the elimination of dietary n-3LC-PUFA (enzyme products) up-regulated the transcription rate of Δ-6 desaturase; but v) the total apparent in vivo enzyme activity was directly and positively affected by substrate availability, and not product presence/absence nor the extent of the enzyme transcription rate. [Copyright &y& Elsevier]

Fish oil (FO)- and canola oil (CO)-based diets were regularly alternated in a daily cycle (amCO: alternation of CO in the morning and FO in the afternoon, and pmCO: alternation of FO in the morning and CO in the afternoon) or in a series of weekly cycles (2W: alternation of 2 weeks on CO and 2 weeks on FO, 4W: alternation of 4 weeks on CO and 4 weeks on FO), over a 16-week period in juvenile Murray cod ( Maccullochella peelii peelii). No significant differences were observed between any of the treatments in relation to the final weight. However, fish subjected to the 2W schedule were larger ( P>0.05) than all other treatments (37.2 ± 0.30 vs. 34.3 ± 0.58 in the control treatment). Fish receiving the 2W treatment had a significantly lower total net disappearance of eicosapentaenoic acid 20:5n-3 (EPA) and docosahexaenoic acid 22:6n-3 (62.1% and 24.0% respectively) compared with the control treatment (fish continuously fed a blend of 50% FO and 50% CO). Likewise, Murray cod receiving the amCO daily schedule had a significantly lower total net disappearance of EPA in comparison with the CD and pmCO treatments. These data point towards the existence of cyclical mechanisms relative to fatty acid utilization/retention. [ABSTRACT FROM AUTHOR]

The dynamics of fatty acid composition modifications were examined in tissues of Murray cod fed diets containing fish oil (FO), canola oil (CO) and linseed oil (LO) for a 25-week period and subsequently transferred to a FO (finishing/wash-out) diet for a further 16 weeks. At the commencement of the wash-out period, following 25 weeks of vegetable oil substitution diets, the fatty acid compositions of Murray cod fillets were reflective of the respective diets. After transfer to the FO diet, differences decreased in quantity and in numerousness, resulting in a revert to the FO fatty acid composition. Changes in percentages of the fatty acids and total accumulation in the fillet could be described by exponential equations and demonstrated that major modifications occurred in the first days of the finishing period. A dilution model was tested to predict fatty acid composition. In spite of a general reliability of the model ( Y=0.9234 X+0.4260, R2=0.957, P<0.001, where X is the predicted percentage of fatty acid; Y the observed percentage of fatty acid), in some instances the regression comparing observed and predicted values was markedly different from the line of equity, indicating that the rate of change was higher than predicted (i.e. Y=0.4205 X+1.191, R2=0.974, P<0.001, where X is the predicted percentage of α-linolenic acid; Y the observed percentage of α-linolenic acid). Ultimately, using the coefficient of distance ( D), it was shown that the fatty acid composition of fish previously fed the vegetable oil diets returned to the average variability of the fillet fatty acid composition of Murray cod after 70 or 97 days (LO and CO respectively). [ABSTRACT FROM AUTHOR]

Abstract: The Murray cod, an Australian native freshwater fish, supports a relatively small but increasing aquaculture industry in Australia. Presently, there are no dedicated commercial diets available for Murray cod; instead, nutritionally sub-standard feeds formulated for other species are commonly used. The aim of the present investigation was to assess the suitability of two plant based lipid sources, canola oil (CO) and linseed oil (LO), as alternatives to fish oil for juvenile Murray cod. Five iso-nitrogenous, iso-calorific, iso-lipidic semi-purified experimental diets were formulated with 17% lipid originating from 100% cod liver oil (FO), 100% canola oil, 100% linseed oil and 1:1 blends of canola and cod liver oil (CFO) and 1:1 blends of linseed and cod liver oil (LFO). Each of the diets was fed to apparent satiation twice daily to triplicate groups of 50 Murray cod with initial mean weights of 6.45±1.59 g for 84 days at 22 °C. Final mean weight, specific growth rate and daily feed consumption were significantly higher for the FO and LFO treatments compared to the LO treatment. Feed conversion and protein efficiency ratios were not significantly different amongst treatments. Experimental diets containing vegetable oil and vegetable oil blend(s) had significantly higher concentrations of n-6 fatty acids, predominantly in the form of linoleic acid (LA), while n-3 fatty acids were present in significantly higher concentrations in LO and LFO treatments. The fatty acid composition of Murray cod fillet was reflective of the dietary lipid source. Fillet of fish fed the FO was highest in EPA (20:5n-3), ArA (20:4n-6) and DHA (22:6n-3). Fish fed the CO diet had high concentrations of oleic acid (OlA) (192.2±10.5 mg g lipid−1), while the fillet of Murray cod fed the LO diet was high in α-linolenic acid (LnA) (107.1±6.7 mg g lipid−1). The present study suggests that fish oil can be replaced by up to 100% with canola oil and by up to 50% with linseed oil in Murray cod diets with no significant effect on growth. [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]

[Display omitted] • Biomarkers to identify and quantify carbon contributors to sequestration are needed. • Use of complete sets of fatty acid (FA) profiles are novel to biomarker discovery. • XGBoost models of FA profiles discriminated seaweed carbon from other sources. • High predictive accuracies of this biomarker approach may facilitate quantification. • Quantifying seaweed contributions to blue carbon sequestration may soon be feasible. Differentiating between carbon contributors in marine environments is crucial to gaining a deeper understanding of marine carbon sequestration, and some efforts have been made through the application of various approaches. This study proposed a new approach through the use of fatty acid (FA) profiles of six marine macrophytes within three macroalgal lineages, and three coastal angiosperms (mangrove, saltmarsh, and seagrass). We compiled FA profiles (consisting of 84 individuals and 9 classes/groups of FAs) of 544 Australian coastal macrophyte species identified in published reports. The data were gradually screened into three different datasets (full-84FA, reduced-57FA, and reduced-48FA) for analysis to minimise the effects of imbalanced distributions of data on analysis. XGBoost (eXtreme Gradient Boosting) multiclass classification modelling with hyperparameter tuning was applied to reveal the specific FA signatures of each macrophyte lineage. The XGBoost models run across the three datasets generated high model-performance metrics including precision, recall, F-score, and multiclass-AUC, indicating similar performance between the three models with predictive accuracies of 94%, 85%, and 95%, respectively. At the class level, the three models also demonstrated high performance with precision, recall, and F-score values for each lineage above 0.95, except for Rhodophyta, which ranged from around 0.80 to 0.89. Overall, our findings suggest that the XGBoost classifier can reveal the lineage-specific patterns of FAs (carbon-based molecules) that can be implemented to predict and potentially quantify the carbon contributors to marine sediments, and more specifically, to discern macroalgal carbon contributions from those of other coastal macrophytes. [ABSTRACT FROM AUTHOR]

A considerable body of literature exists concerning the use of marine-derived raw materials in aquaculture feed formulations and the resulting modifications of the health promoting qualities of farmed fish. However, these investigations and reports are fundamentally limited to fatty acids and little is known regarding the other nutritional characteristics of cultured fish and seafood products. This knowledge gap, often coupled with inaccurate or incomplete media reports, generates consumer confusion and mistrust in relation to farmed fish quality. The aim of the present study was therefore to characterise not only the fatty acid composition, but also the resulting protein, amino acid and micronutrient composition of rainbow trout fed diets containing fish oil or vegetable oils. To achieve this, triplicate groups of rainbow trout ( Oncorhynchus mykiss ) were subjected to two distinct vegetable oil- based diets (one rich in alpha-linolenic acid, 18:3n-3, ALA and the other rich in linoleic acid, 18:2n-6, LNA) and a traditional n-3 long chain polyunsaturated fatty acid (LC-PUFA) rich, fish oil-based diet over a 126 day period. Growth performance and feed utilisation parameters as well as tissue fatty acid composition, amino acid composition, vitamin, mineral and trace element concentration in fish fillets were subsequently assessed. Expectedly, major differences were evident between treatments in relation to fatty acid composition, where for the most part fillet composition reflected that of the diet. Notably, no differences were observed regarding fillet amino acid composition, as was also the case for the vast majority of vitamins, minerals and trace elements. Therefore, with the exception of the fatty acid profile and vitamin A concentration, other beneficial nutritional qualities of fish are fundamentally maintained and unaffected when alternative oil sources are implemented in aquaculture feed formulations, maintaining cultured rainbow trout a nutritious and nourishing product for human consumption. [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]

Current research on lipid nutrition in farmed fish has primarily focused on the nutritional, biochemical, biomolecular, and physiological aspects of n-3 LC-PUFA, with limited knowledge available on the interrelationships amongst different dietary fatty acids. This study aimed to evaluate the effects of individual dietary fatty acids (FA) on the metabolism of omega-3 fatty acids in juvenile Atlantic salmon. Specifically, the study investigated the relationships between omega-3 fatty acids and other individual dietary fatty acids characterised by different chain lengths but the same level of unsaturation (lauric acid, 12:0; palmitic acid, 16:0; and stearic acid, 18:0), and different degrees of unsaturation but the same chain length (stearic acid, 18:0; oleic acid, 18:1n-9; and linoleic acid, 18:2n-6). Diets rich in n-3 LC-PUFA or alpha-linolenic acid (ALA, 18:3n-3) were used to explore possible interactions and nutritional relationships. The experiment followed a five by two factorial design, with a total of 10 experimental dietary treatments fed to triplicate groups of fish (n = 3, N = 30). Five diets were formulated with minimal n-3 LC-PUFA content and abundant ALA content (referred to as "ALA diets"), while the other five diets had minimal ALA content and abundant n-3 LC-PUFA content (referred to as "n-3 LC-PUFA diets"). Within each dietary group, the five experimental diets were isoproteic, isolipidic, and isoenergetic. They were formulated to spike the concentration of a single FA while maintaining a constant supply of all other FA across all diets. The selected FA used to formulate the experimental diets were 12:0, 16:0, 18:0, 18:1n-9, or 18:2n-6. The feeding trial lasted 92 days, during which all treatments resulted in fish growth exceeding 300% of their initial body weight. Chemical composition analysis, fatty acid apparent metabolism, and selected gene transcription were performed on the samples to monitor the main nutritional, biochemical, biomolecular, and physiological outcomes. The most interesting and unexpected finding was the identification of a direct link between the physical properties of dietary fatty acids, particularly their melting point, and the resulting changes in omega-3 fatty acid metabolic patterns. This study demonstrated, for the first time, that the melting point of dietary fatty acids plays a crucial role in regulating omega-3 fatty acid metabolism in Atlantic salmon. It is envisioned that this discovery could open new possibilities for future advancements in lipid nutrition for aquaculture species. • Further optimizing omega-3 metabolism in salmon nutrition is crucial for long-term sustainability of the sector. • Here, it was described how different dietary fatty acids affect the metabolism of dietary omega-3. • First-time discovery: Dietary fatty acid melting point regulates omega-3 metabolism. [ABSTRACT FROM AUTHOR]

Elucidation of the key nutritional requirements for complete larval development of the tropical spiny rock lobster, Panulirus ornatus , presents a major challenge for the development of robust commercial aquaculture for this crustacean. As a foundation study in this area, the chemical composition of early–mid stage P. ornatus phyllosoma (Stages I–VI) receiving a novel formulated diet was analysed immediately prior and post-ecdysis to provide insight into the crude nutritional trends during the larval development cycle. From the onset of moulting, cyclical patterns were evident in the proximate composition of phyllosoma, resulting in substantial restructuring between the pre- and post-moult stages of the moult cycle. Proportions of protein, lipid and ash were high at the premoult stage, reflecting growth and nutrient accumulation over the intermoult period, and reduced at the post-moult stage, reflecting the large uptake of water to facilitate subsequent growth. Polar lipid was the dominant lipid class, accounting for > 90% of the total lipid content. Conversely, triacylglycerol concentrations were low (< 5%), despite being the principal lipid class available in the formulated diet. Likewise, despite receiving high concentrations of eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) (9.2 and 7.6% of the dietary lipid source, respectively), levels of these fatty acids were comparatively low in phyllosoma (3.4 and 4.7%, respectively). In contrast, there is selective deposition of these fatty acids in wild caught phyllosoma. This finding suggests a poor assimilation of triacylglycerols by captive larvae and highlights the importance of future investigations into alternative sources of EPA and DHA. Ultimately, this study provides insight into the nutritional requirements of phyllosoma, providing valuable knowledge on diet formulation for commercially viable hatchery production of spiny rock lobsters. [ABSTRACT FROM AUTHOR]

• Adult female P. trituberculatus has four grades based on visible ovarian fullness. • Higher-graded females are richer of high value nutrients in their edible tissues. • Differences in tissue nutrients are largely correlated with crab ovarian maturity. Ovary is an important edible component of female crabs in many countries, and ovarian fullness (maturity) had become an important quality indicator used for crab marketing. Adult females Portunus trituberculatus are typically divided into four grades (Grade I - Ⅳ) based on ovarian fullness in the carapace during the marketing. This study investigated the chemical composition and nutritional quality of market size female P. trituberculatus. The gonadosomatic index (GSI), hepatosomatic index (HSI) and total edible yield (TEY) showed a stepwise increase from Grade Ⅰ to Ⅳ (P < 0.05). Crude protein and total lipid content in both ovaries and muscle significantly increased with fullness, where Grade Ⅱ - Ⅳ had significantly higher lipid contents in the hepatopancreas compared to Grade Ⅰ. Redness (a *) of carapace and ovaries was consistent with the total carotenoid contents in tissues. Σ MUFA in both ovaries and muscle increased with crab grade, while Σ PUFA in ovaries and muscle, as well as Σ MUFA in the hepatopancreas decreased. For most amino acids in ovaries and muscle were also found to increase with grade. Higher-graded females generally had higher TEY, color parameters and better nutritional quality in edible tissues than the Grade I and II, which appears related to their different ovary stages of P. trituberculatus. [ABSTRACT FROM AUTHOR]