Leptin and lipid metabolism in fish

The aim of this chapter is to highlight potential links between leptin and the lipid metabolism in fish, within the context of current research interests of the fish nutrition amd aquaculture sector. In fact, it is envisaged that the whole aquacuture and fish biology sector will significantly benefit from an increased knowledge of such a powerful hormone, and it is believed this will contribute in transforming current aquaculture industry into an environmental and economical means of producing nourishing fish and seafood for the growing global population. The context is framed by a brief introduction on the current challenges in aquaculture and fish nutrition, and susequently the chapter focuses on the potential roles of leptin on voluntary food intake and lipid digestion and absorption in fish. Following this, the possible roles of leptin on lipid deposition and utilisation and the fatty acid metabolism in fish are presented and discussed. Eventually the possible interrelationships between dietary lipids and leptin are analysed underlining how knowledge gained from human nutrition could be extremely useful to tentatively address current constraints and obstacles found in the aquaculture nutrition sector. The present analysis suggests that we are likely only able to see the tip of the iceberg, and great and significant breakthrough discoveries will be likely by fathoming such fascinating area of research

Fish oil replacement in starter, grow-out, and finishing feeds for farmed aquatic animals

As aquaculture production continues to grow, there will be an increased use of lipid resources (oils and fats) alternative to fish oil for feed production. The potential for the use of these alternatives varies depending on the feeds in which they are included according to the production phase of the animals to which they are being fed. In starter feeds, where rapid growth, high survival, and normal development are critical priorities, there will remain a need for the use of lipid resources high in omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). Fish in this starter phase have a critical requirement for the n-3 LC-PUFA docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), and fish oils remain the only cost-effective source of these nutrients in the volumes required. However, the greatest demand for lipids is in those diets for the grow-out phase. Most studies on alternative lipid use with animals in this part of the production phase show positive outcomes, in that there are few studies where all the added fish oil cannot be replaced. There are some species, however, where potential replacement levels are suggested to be more conservative, and a general substitution level in this production phase of 75% has been suggested. One of the key effects noted across the grow-out phase is that all alternatives affect the flesh fatty acid characteristics by reducing the level of n-3 LC-PUFA. This issue has provoked the concept of finisher diets, whereby a high n-3 LC-PUFA content diet is fed in order to restore the desired meat fatty acid profiles. Studies examining this concept have found that the tissue triacylglycerol fatty acids were greatly modified and responded in a simple dilution process to the added oil fatty acid composition, whereas the fatty acids of tissue phospholipids were less influenced by dietary fatty acid makeup.<br /

Effect of dietary saturated and monounsaturated fatty acids in juvenile barramundi Lates calcarifer

Barramundi (Lates calcarifer), a catadromous teleost of commercial interest, perform well when fed a wide range of dietary oils. However, the range of alternative oils now being explored is typically rich in saturated and monounsaturated fatty acids (SFA and MUFA). In this study, the response of juvenile barramundi (47.0 g per fish initial weight) fed isolipidic and isoenergetic diets with 82 g kg-1 added oil was tested. The experimental test diets had a 2 : 1 or 1 : 2 ratio of SFA to MUFA (SFA-D and MUFA-D, respectively) compared to a control diet (CTRL-D) fed for 8 weeks. The diets containing mostly olive oil (dietary MUFA-D) and mostly refined palm oil (dietary SFA-D) did not impact the growth performance or feed utilization parameters of the barramundi. The in vivo beta-oxidation activity was consistent with the dietary fatty acid composition, with the most dominant FA being heavily beta-oxidized. Together, the in vivo whole-body mass balance of fatty acids showed that n-3 long-chain polyunsaturated fatty acids (LC-PUFA) were most efficiently utilized in the SFA-D- and MUFA-D-fed fish. This study provides evidence that additional dietary MUFA and SFA are suitable lipid classes for juvenile barramundi and they are both equally efficient at sparing LC-PUFA from an oxidative fate.

Alternative Lipid Sources in Aquafeeds

The global aquaculture industry is one of the fastest growing food production sectors with farmed seafood currently accounting for about 50% of all fish consumed in the world. It is estimated that aquaculture produces about 65 million tonnes of seafood valued at more than US$78 billion annually. Aquaculture is anticipated to play an increasingly important role in meeting the seafood demand of a growing human population. The rapid increase in aquaculture production worldwide has been fueled by the use of industrially manufactured aquafeeds. Conventionally, marine fish meal and fish oil are used as the major feed ingredients in the formulation of commercial aquafeeds to supply dietary protein and lipid, respectively. It is estimated that aquafeeds currently consume about 90% of the global supply of fish oil and many have predicted that the demand for fish oil from the aquaculture industry will imminently out strip supply. Marine fish oil production has not increased beyond 1.5 million tonnes for the past quarter of a century and in order to further expand, the global aquaculture industry cannot continue to rely solely on this source of lipid. The high demand, impending short supply and often times high prices makes dietary fish oil a bottle-neck in the farming of aquatic animals, and there is currently great urgency within the global aquafeed industry in finding suitable alternatives to replace marine fish oils. This article will give an overview of the various alternative lipid sources, grouped according to their main chemical characteristics. Their unique potential advantages and challenges for use in aquafeeds will be highlighted. The physiological effects of various lipid sources and their components on growth, lipid metabolism, health and post-harvest qualities of the farmed fish are briefly discussed

Thoughts for the Future of Aquaculture Nutrition: Realigning Perspectives to Reflect Contemporary Issues Related to Judicious Use of Marine Resources in Aquafeeds

In recent decades, aquaculture nutrition research has made major strides in identifying alternatives to the use of traditional marine‐origin resources. Feed manufacturers worldwide have used this information to replace increasing amounts of fish meal and fish oil in aquafeeds. However, reliance on marine resources remains an ongoing constraint, and the progress yielded by continued unidimensional research into alternative raw materials is becoming increasingly marginal. Feed formulation is not an exercise in identifying "substitutes" or "alternatives" but rather is a process of identifying different combinations of "complementary" raw materials—including fish meal, fish oil, and others—that collectively meet established nutrient requirements and other criteria for the aquafeed in question. Nutrient‐based formulation is the day‐to‐day reality of formulating industrially compounded aquafeeds, but this approach is less formally and explicitly addressed in aquaculture research and training programs. Here, we (re)introduce these topics and explore the reasons that marine‐origin ingredients have long been considered the "gold standards" of aquafeed formulation. We highlight a number of ways in which this approach is flawed and constrains innovation before delving into the need to assess raw materials based on their influence on aquafeed manufacturing techniques. We conclude with a brief commentary regarding the future funding and research landscape. Incremental progress may continue through the accumulation of small insights, but a more holistic research strategy—aligned with industry needs and focused on nutrient composition and ingredient complementarity—is what will spur future advancement in aquaculture nutrition.This article also appears in: World Fisheries Da

Rapid effects of essential fatty acid deficiency on growth and development parameters and transcription of key fatty acid metabolism genes in juvenile barramundi (Lates calcarifer)

Barramundi (Lates calcarifer), a catadromous teleost of significant and growing commercial importance, are reported to have limited fatty acid bioconversion capability and therefore require preformed long-chain PUFA (LC-PUFA) as dietary essential fatty acid (EFA). In this study, the response of juvenile barramundi (47&middot;0 g/fish initial weight) fed isolipidic and isoenergetic diets with 8&middot;2 % added oil was tested. The experimental test diets were either devoid of fish oil (FO), and thus with no n-3 LC-PUFA (FO FREE diet), or with a low inclusion of FO (FO LOW diet). These were compared against a control diet containing only FO (FO CTRL diet) as the added lipid source, over an 8-week period. Interim samples and measurements were taken fortnightly during the trial in order to define the aetiology of the onset and progression of EFA deficiency. After 2 weeks, the fish fed the FO FREE and FO LOW diets had significantly lower live-weights, and after 8 weeks significant differences were detected for all performance parameters. The fish fed the FO FREE diet also had a significantly higher incidence of external abnormalities. The transcription of several genes involved in fatty acid metabolism was affected after 2 weeks of feeding, showing a rapid nutritional regulation. This experiment documents the aetiology of the onset and the progression of EFA deficiency in juvenile barramundi and demonstrates that such deficiencies can be detected within 2 weeks in juvenile fish

Defining the allometric relationship between size and individual fatty acid turnover in barramundi Lates calcarifer

An experiment was conducted with barramundi (Asian seabass; Lates calcarifer) to examine the allometric scaling effect of individual fatty acids. Six treatment size classes of fish were deprived of food for 21 days (Treatment A, 10.5 &plusmn; 0.13 g; Treatment B, 19.2 &plusmn; 0.11 g; Treatment C, 28.3 &plusmn; 0.05 g; Treatment D, 122.4 &plusmn; 0.10 g; Treatment E, 217.6 &plusmn; 0.36 g; Treatment F, 443.7 &plusmn; 1.48 g; mean&plusmn; SD) with each treatment comprising of fifteen fish, in triplicate. The assessment of somatic losses of whole-body energy and lipidwere consistentwith previous studies, validating themethodology to be extended to individual fatty acids. Live-weight (LW)exponent values were determined to be 0.817 &plusmn; 0.010 for energy and 0.895 &plusmn; 0.007 for lipid. There were significant differences among the fatty acids ranging from 0.687 &plusmn; 0.005 for 20:5n-3 (eicosapentaenoic acid) and 0.954 &plusmn; 0.008 for 18:1n-9 (oleic acid). The LW exponent values were applied to existing fatty acid intake and deposition data of barramundi fed with either 100% fish oil or 100% poultry oil. From this the maintenance requirement for each fatty acid was determined. The metabolic demands for maintenance and growth were then iteratively determined for fish over a range of size classes. Application of these exponent values to varying levels of fatty acid intake demonstrated that the biggest driver in the utilisation of fatty acids in this species is deposition demand and despite their reputed importance, the long-chain polyunsaturated fatty acids had nominal to no maintenance requirement

The effect of marine and non-marine phospholipid rich oils when fed to juvenile barramundi (Lates calcarifer)

An experiment was conducted to assess the response of juvenile barramundi (Lates calcarifer) to four diets containing either marine- or non-marine derived neutral lipid (NL) or polar lipid (PL) sources for eight weeks in a 2 &times; 2 factorial design. The four diets contained 8.2% added lipid composed of a 1% fish oil base with 7.2% test lipid (n - 3 NL: Fish oil, n - 3 PL: Krill oil, n - 6 NL: Soybean oil, n - 6 PL: Soybean lecithin). The results demonstrated that the different lipid sources (either n - 3 or n - 6 omega series from either NL or PL class) had significant effects on growth performance and feed utilisation with some interaction terms noted. Growth was negatively affected in the n - 6 NL fish and the feed conversion (FCR) was highest in the n - 6 PL fish. Digestibility of total lipid and some specific fatty acids (notably 18:2n - 6 and 18:3n - 3) were also negatively affected in the n - 6 PL fish. Analysis of the whole body neutral lipid fatty acid composition showed that these mirrored those of the diets and significant interaction terms were noted. However, the whole body polar lipid fatty acids appeared to be more tightly regulated in comparison. The blood plasma biochemistry and hepatic transcription of several fatty acid metabolism genes in the n - 6 PL fed and to a lesser extent in the n - 6 NL fed fish demonstrated a pattern consistent with modified metabolic function. These results support that there are potential advantages in using phospholipid-rich oils however there are clear differences in terms of their origin. Statement of relevance: Juvenile barramundi may benefit from dietary phospholipid. &copy; 2016 Elsevier B.V

What is the most effective way of increasing the bioavailability of dietary long chain omega-3 fatty acids-daily vs. weekly administration of fish oil?

The recommendations on the intake of long chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFA) vary from eating oily fish (&quot;once to twice per week&quot;) to consuming specified daily amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (&quot;250-500 mg per day&quot;). It is not known if there is a difference in the uptake/bioavailability between regular daily consumption of supplementsvs. consuming fish once or twice per week. In this study, the bioavailability of a daily dose of n-3 LC-PUFA (Constant treatment), representing supplements, vs. a large weekly dose of n-3 LC-PUFA (Spike treatment), representing consuming once or twice per week, was assessed. Six-week old healthy male Sprague-Dawley rats were fed either a Constant treatment, a Spike treatment or Control treatment (no n-3 LC-PUFA), for six weeks. The whole body, tissues and faeces were analysed for fatty acid content. The results showed that the major metabolic fate of the n-3 LC-PUFA (EPA+docosapentaenoic acid (DPA) + DHA) was towards catabolism (&beta;-oxidation) accounting for over 70% of total dietary intake, whereas deposition accounted less than 25% of total dietary intake. It was found that significantly more n-3 LC-PUFA were &beta;-oxidised when originating from the Constant treatment (84% of dose), compared with the Spike treatment (75% of dose). Conversely, it was found that significantly more n-3 LC-PUFA were deposited when originating from the Spike treatment (23% of dose), than from the Constant treatment (15% of dose). These unexpected findings show that a large dose of n-3 LC-PUFA once per week is more effective in increasing whole body n-3 LC-PUFA content in rats compared with a smaller dose delivered daily