Program

Marine ecosystems are responsible for virtually all global production of long-chain (≥ C20) polyunsaturated fatty acids (LC-PUFA), particularly the so-called “omega-3” (n-3) including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Such n-3 LC-PUFA are health-promoting compounds in a variety of human conditions. Production of n-3 LC-PUFA and their shorter chain (C18) PUFA precursors in the marine environment occurs primarily by the action of photosynthetic microalgae, heterotrophic protists and bacteria. Higher trophic level organisms such as marine invertebrates and fish accumulate n-3 LC-PUFA and thus fish and seafood become primary sources of the healthy omega-3 fatty acids for humans. Additionally to dietary input, endogenous production (biosynthesis) of LC-PUFA can partly explain the abundance of n-3 LC-PUFA in aquatic animals. Particularly in farmed fish, the LC-PUFA biosynthetic pathways have been extensively investigated for determining the specific dietary essential fatty acids that guarantee normal growth and development in captivity, and also for maintaining high nutritional value (i.e. high EPA and DHA) in farmed fish products. It is now well established that the capacity for LC-PUFA biosynthesis of a particular fish species depends upon the repertoire of the key enzymes required, namely the fatty acyl desaturases (Fads) and elongases of very long-chain fatty acids (Elovl). Interestingly, it has become clear that the ability for LC-PUFA biosynthesis in fish is more diverse than in other vertebrates, this hypothesised to be the result of a combination of factors that interact along the evolutionary history of fish linages. Recently, remarkable progress has been made on elucidating the LC-PUFA biosynthetic pathways that operate in marine invertebrates, confirming that this animal group possess active and specialised pathways. This paper reviews the current knowledge on the complement and function of Fads and Elovl enzymes involved in LC-PUFA biosynthesis in aquatic animals, with particular attention to species with interest in aquaculture.

Sustainability of aquaculture requires feeds to be based on plant-based ingredients rather than traditional marine-derived raw materials, fishmeal (FM) and fish oil (FO) that are finite and limited. However, plant-based diets can affect fish growth performance and reduce nutritional quality by lowering levels of the key omega-3 fatty acids, EPA and DHA. The concept of nutritional programming involves the application of a dietary stimulus during early development that can induce long-term changes in animal biochemistry and physiology. The present study investigated the use of this concept to adapt Atlantic salmon to sustainable plant-based feeds and thus improve their utilisation. At first exogenous feeding, fry were fed either a marine diet (Diet M, 80%FM/4%FO) or a vegetable diet (Diet V, 10%FM/0%FO) for 3 weeks. All fish were then fed with Diet M for 15 weeks and thereafter challenged with Diet V for 6 weeks. Growth performance, feed intake, nutrient utilisation, and liver transcriptome were investigated. The early nutritional stimulus significantly improved performance when the fish were challenged later in life with the V diet, with fish initially given the V diet stimulus (V-fish) showing higher growth rate and increased feed efficiency compared to M-fish. There was no difference in feed intake between nutritional histories, but increased nutrient retentions, including greatly increased retentions of EPA and DHA, highlighted the improved utilisation of the V diet in V-fish. Microarray analysis of liver transcriptome revealed that key pathways of intermediary metabolism were up-regulated in V-fish, including oxidative phosphorylation, pyruvate metabolism, TCA cycle and glycolysis, as well as fatty acid biosynthesis pathways. Overall, the data suggested that the early dietary stimulus improved the utilisation of plant-based feeds when fed later in life, including enhancing EPA and DHA metabolism, and these effects can be attributed to physiological and/or metabolic changes induced by the stimulus.

Elovl6 is a rate-limiting enzyme catalyzing elongation of saturated and monounsaturated long-chain fatty acid. Although functional characteristics of elovl6 have been demonstrated in mammal, the role of elovl6 in fish remains unclear. In this study, we firstly cloned three isoforms of elovl6 (elovl6a, elovl6b and elovl6l) from loach (Misgurnus anguillicaudatus). Molecular characterizations of three elovl6 isoforms in the loach and their expressions of early life stages and different tissues were determined. We also functionally characterized the three elovl6 isoforms using heterologous expression in baker's yeast. Results obtained here showed three elovl6 proteins in the loach can elongate C16:0 and C16:1 to C18:0 and C18:1, respectively. At last, to confirm the role of three loach elovl6 isoforms for elongation of fatty acids in adaption to cold stress, differences in skin histological structures, body fatty acid compositions, expressions of four hepatic lipogenesis and lipolysis related genes, and expressions of the three elovl6 isoforms and their related gene UCP1 in different tissues were investigated in the loach reared in two different water temperatures (28°C and 4°C) for ten days. Cold stress increased ratios of C18/C16 and C20:5n-3/C18:3n-3 in loach body, and induced expressions of hepatic SCD1, SREBP1, CPT1 and FAS. Meanwhile, significant differences were found in expressions of the three elovl6 isoforms in different tissues between 28°C and 4°C groups. Overall, this study suggests three elovl6 isoforms in the loach have ability to elongate C16 to C18, and elovl6 proteins in loach play an important role in adaptation to cold stress.

Apolipoprotein (Apo) is the major bounded protein component that classically binds and transports lipid through the blood circulatory system. Apo-14 is a specific lipoprotein in fish which has no homologous protein with other vertebrate. However, the mechanisms underlying the lipid metabolism in fish has been scarcely dedicated. For a better understanding of fish Apo-14 and its function on lipid metabolism under nutritional regulation, we cloned a cDNA encoding Apo-14 from the liver of Mekong giant catfish, Pangasianodon gigas. The Apo-14 cDNA obtained by a combination of 3' and 5' rapid amplification of cDNA ends from Mekong giant catfish was 744 pb, with an open reading from of 432 bp encoding 143 amino acids. This sequence showed high identities with those Apo-14 genes of Asian seabass and yellow perch with 98 and 82 % identity, respectively. The alignments of multiple amino acid sequences shown Apo-14 sequence also processes the common features of the Apo-14 family including; signaling peptide sequence and conserved serine residues. The real-time PCR revealed that Apo-14 was ubiquitous distributed, with high levels in the adipose fin, liver, and inclinator muscle of fin and the lowest level in the heart. During feed deprivation, the Apo-14 mRNA were suppressed by starvation up to 7 days in adipose tissue and liver but not in skeletal muscle. Fasting 20 days, expression levels of Apo-14 mRNA were reduced in all tissue examined. The decreased Apo-14 mRNA levels were 4 times higher than Apo-14 mRNA in adipose tissue. While re-feeding 30 days, fish continuously reduced the expression levels of Apo-14 mRNAs. The results of the present study revealed that Apo-14 expression composes of diverse lipid metabolism. Apo-14 transcripts were independently regulated under nutritional deprivation with tissue-specific. Moreover, skeletal muscle is a potential organ that contributed lipid transport during short-term fasting in Mekong giant catfish.

The fact that high amount of taurine in the body of common carp even if the expression of CSD was low suggesting the possibility that common carp is utilizing another pathway than cysteine sulfinic acid pathway for taurine synthesis. In addition, cysteine and cysteamine could be toxic when present at high amount. However, the negative impact on carp has been little studied. Therefore, this study aims to determine the effect of dietary cysteamine on growth, the conversion efficacy of sulfur amino acid into taurine and gene expression of taurine synthesizing enzymes.
A total of eight diets with different level of taurine, methionine, cysteine, and cysteamine was fed to juvenile common carp for 30 days. Results indicate that supplementation with dietary cysteamine caused growth retardation, myopathy and body deformity in common carp. All sulfur amino acids increased taurine deposition in the carcass, and 1.5% cysteamine increased taurine deposition at 1.8 to 5.5 folds than methionine and cysteine treatments. Both CDO1 and CDO2 tend to be down-regulated by cysteine and by low dose of taurine but is up-regulated by high dose of cysteamine. The CSD on the other hand was down-regulated by addition of sulfur amino acid. While ADO was down-regulated by methionine and cysteine and low dose of taurine but is up-regulated by cysteamine. Growth related genes SST14 was up-regulated by cysteamine. While IGF-1 was up-regulated by high dose of taurine and cysteine but down-regulated by high dose of cysteamine.
These results suggest that cysteine sulfinic pathway plays a role in taurine synthesis in common carp and ADO involved in cysteamine pathway. It was also suggested that cysteamine pathway is another major taurine synthesizing pathway in common carp.

Two cycles of mass scale feeding trial were performed to describe the effects of recombinant growth hormone (rGH) in growth (Total Biomass), survival rate (SR) and feed conversion ratio (FCR) performance of Indonesian Saline Tilapia (SALINA) within dry (1#cycle) and rainy season (2nd cycle) condition. About 25.000 of 5-8 cm seeds of Saline tilapia (Oreochromis niloticus) are cultured in 4.000 m² of 3 (three) brackish water ponds during dry and rainy season, respectively. The first diet (rGH) is commercial diet (26% crude protein) mixed with 2 mg/kg of rGH. The second diet (rGH-Vaccine) is commercial diet (26% crude protein) mixed with 2 mg/kg of rGH and 5 mg/kg Streptococcus DNA-Vaccine. The third diet (control) is commercial diet (26% crude protein) only. The fish were fed 3 times daily with feeding rate of 3-5% of body weight per day. During grow out culture, high water level of ponds has maintained by adding some new water, while at last 3 months of feeding trial, 5-10% of pond water volume has changed to maintain rearing water condition. The results of two cycles culture shows that total biomass (6.548 kg and 3.875 kg) and SR (93.78% and 73.24%) of fish fed with rGH diet higher than both in control diet biomass (6.139 kg and 3.190 kg) and survival rate (85.61% and 62.34%), also in rGH-Vaccine diet biomass (4.582 kg and 3.098 kg) and survival rate (81.27% and 64.64%). While feed efficiency (FCR) observed in fish fed with rGH diet (1.46 and 1.32) higher than both in rGH-Vaccine diet (1.49 and 1.96), also control diet (1.56 and 1.96). The study described that diet with 2 mg/kg rGH provides better productivity performance and is economically viable for Indonesian saline tilapia grow in brackish water pond.