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One of the oldest reservoirs in Peninsular Malaysia, Bukit Merah Reservoir, is a place in which locals participate in fishing activities. Inland fisheries are important to individuals, society and the environment; whereby they generate a source of income and food security. It is essential to gauge the nutrition value of fish caught in this location as food source, especially in terms of fatty acid composition, to better demonstrate its potential towards the betterment of human health and general well-being. From an initial list of 47 fish species available in Bukit Merah Reservoir, a total of seven edible freshwater fish species were identified, namely tinfoil barb (Barbonymus schwanenfeldii), Javanese barb (Barbonymus gonionotus), hampala barb (Hampala macrolepidota), beardless barb (Cyclocheilichthys apogon), glassfish (Oxygaster anomalura), striped snakehead (Channa striata) and horseface loach (Acantopsis dialuzona), and muscle fatty acid content was analysed to determine their nutritional value. Muscle of cyprinid fish contained substantial amount of omega-3 long-chain polyunsaturated fatty acids (LC-PUFA) compared to fish from Channidae and Cobitidae families. Javanese and tinfoil barbs muscle recorded the highest levels of combined eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) indicating the highest nutritional value comparatively. Unexpectedly, the striped snakehead, a predatory carnivore, contained lower levels of LC-PUFA compared to detrivorous/herbivorous fishes. This further justifies that the omega-3 polyunsaturated fatty acids (PUFA) content in fish muscle varies according to their feeding habits. Even though it has been recommended that marine fish be consumed to improve health to a certain extent, there still are benefits of consuming freshwater fish, as there are several species which contain considerable amounts of beneficial omega-3 PUFA.

There is a lack of understanding on how the environment and trophic niche affect the capability of long-chain polyunsaturated fatty acids (LC-PUFA) in freshwater carnivorous teleost. In this present study, we isolated and functionally characterised a fatty acyl desaturase (Fads) from the striped snakehead Channa striata. Sequence comparison and phylogenetic analysis suggested a Fads2 protein that is closely related to previously characterised Fads2 proteins from freshwater carnivorous and marine herbivorous fish species. We further demonstrated the capacity of Δ6 and Δ5 desaturation activities for this particular desaturase, with highest activities towards the conversion of omega-3 (n-3) polyunsaturated fatty acids (PUFA). Low Δ4 desaturation activity was also detected, although the significance of this at a physiological level remains to be studied. The expression of this striped snakehead Δ6/Δ5 fads2 gene was highest in brain, followed by liver and intestine. In liver, diet fortified with high LC-PUFA concentration impeded the expression of Δ6/Δ5 fads2 gene compared to vegetable oil (VO) based diets. The discovery of Δ6/Δ5 Fads2 desaturase here complements the previous discovery of a Δ4 Fads2 desaturase and an Elovl5 elongase, lending proof to the existence of all the required enzymatic machinery to biosynthesise LC-PUFA from C18 PUFA in a freshwater carnivorous species.

Despite the potential of vegetable oils as aquafeed ingredients, a major drawback associated with their utilization is the inferior level of beneficial n-3 long-chain polyunsaturated fatty acids (LC-PUFA). Echium oil (EO), which is rich in stearidonic acid (SDA, 18:4n-3), could potentially improve the deposition of n-3 LC-PUFA as the biosynthesis of LC-PUFA is enhanced through bypassing the rate-limiting ∆6 desaturation step. We report for the first time an attempt to investigate whether the presence of a desaturase (Fads2) capable of ∆4 desaturation activities and an elongase (Elovl5) will leverage the provision of dietary SDA to produce a higher rate of LC-PUFA bioconversion. Experimental diets were designed containing fish oil (FO), EO or linseed oil (LO) (100FO, 100EO, 100LO), and diets which comprised equal mixtures of the designated oils (50EOFO and 50EOLO) were evaluated in a 12-week feeding trial involving striped snakeheads (Channa striata). There was no significant difference in growth and feed conversion efficiency. The hepatic fatty acid composition and higher expression of fads2 and elovl5 genes in fish fed EO-based diets indicate the utilization of dietary SDA for LC-PUFA biosynthesis. Collectively, this resulted in a higher deposition of muscle eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) compared to LO-based diets. Dietary EO improved the ratio of n-3 LC-PUFA to n-6 LC-PUFA in fish muscle, which is desirable for human populations with excessive consumption of n-6 PUFA. This study validates the contribution of SDA in improving the content of n-3 LC-PUFA and the ratio of EPA to arachidonic acid (ARA, 20:4n-6) in a freshwater carnivorous species.

The capacity of crustaceans to biosynthesise long-chain polyunsaturated fatty acids has yet to be fully defined, due to the lack of evidence on the functional activities of enzymes involved in desaturation or elongation of fatty acid substrates. We report here the cloning and in vitro functional analysis of an elongase from the orange mud crab, Scylla olivacea. Sequence and phylogenetic analysis placed the elovl close to the vertebrate Elovl1 and Elovl7 clade, which is distinct from the other remaining five Elovl families. The elongase was also clustered together with several elongases from crustaceans and insects. This elongase showed activities towards 16:1n-7, and at lower rate, linoleic acid (18:2n-6) and linolenic acid (18:3n-3). To our knowledge this is the first description of a functional enzyme involved in biosynthesis of long-chained polyunsaturated fatty acids in a crustacean species. Expression of the S. olivacea elovl7-like mRNA was prominent in stomach, intestine and gill tissues, due to the need to regulate the permeability of epithelial tissue through modification of fatty acid compositions. The implication of our findings, in terms of ability of Crustacea phylum to biosynthesise polyunsaturated fatty acids is discussed.

A high incidence of jaw malformation has hindered the production of quality striped trumpeter Latris lineata juveniles and has been correlated with walling behaviour in Artemia-fed larvae. In this study, striped trumpeter were reared from first feeding to 29 days post-hatching (dph) in different coloured tanks (black or white), culture conditions (clear or greenwater) and fed different diets (enriched or non-enriched rotifers and Artemia), to examine behaviour, retinoid receptor gene expression and jaw malformation. The highest incidence and severity of jaw malformations occurred in clearwater and enriched diet treatments and were significantly more common in white (70 ± 15%, mean ± SD) than in black tanks (26 ± 15%). In black tanks, jaw malformation was significantly more common in larvae fed enriched diets (18 ± 14%) than in those fed non-enriched diets (8 ± 8%) and in clearwater (19 ± 14%) versus greenwater (7 ± 6%). At the end of the rotifer feeding phase, larvae were significantly larger in black than white tanks, and longer in greenwater than in clearwater. In the Artemia feeding phase, larval growth was slowest and mortality was highest in non-enriched diet treatments. Larval length and survival were higher in black tanks and in enriched diet treatments, whilst survival was almost twice as high in greenwater (46 ± 18%) than clearwater (26 ± 13%). The average proportion of larvae walling over the duration of the experiment was higher in white than black tanks, and higher in enriched than non-enriched treatments, with lowest walling in greenwater. There was no consistent relationship between feed intake and jaw malformation. However, there was a significant positive correlation between walling and the incidence of jaw malformation at 29 dph in larvae fed enriched diets. The expression pattern of three retinoid receptor genes indicated that live feed enrichment and stress could potentially perturb retinoic acid-associated pathways leading to skeletal abnormality. We found that the use of greenwater, black tanks and enriched live feeds is required for good growth, development, survival and final yield of striped trumpeter. The study emphasises the importance of reducing walling in the culture of oceanic larvae and may have direct application in the rearing of other marine fish with similar malformations.

There is very little information on the capacity of freshwater carnivorous fish to biosynthesize highly unsaturated fatty acids (HUFA). The striped snakehead fish (Channa striata) is a carnivorous species cultured inland of several Southeast Asian countries due to its pharmaceutical properties in wound healing enhancement. We described here the full-length cDNA cloning of a striped snakehead fatty acid desaturase (fads), which is responsible for desaturation of unsaturated fatty acids in the HUFA biosynthesis. Bioinformatics analysis reveals a protein coding region with length of 445 amino acids containing all characteristic features of desaturase enzyme, including a cytochrome b5-domain with the heme-binding motif, two transmembrane domains and three histidine-rich regions. The striped snakehead fads amino acid sequence shares high similarity with known fads of other teleosts. The mRNA expression of striped snakehead fads also showed an ontogenic-related increase in expression in 0–20 days after hatch larva. Using ISH, we localized the presence of fads in larva brain, liver and intestinal tissues.

Prolactin (PRL) has been shown to directly influence parental-care associated behavior in many vertebrate species. The discus fish (Symphysodon aequifasciata) displays extensive parental care behavior through utilization of epidermal mucosal secretion to raise free-swimming fry. Here, we cloned the full-length cDNA sequence of the S. aequifasciata prolactin receptor (dfPRLR) and investigated the mRNA expression pattern in several adult tissues. Bioinformatic analysis showed the dfPRLR shared rather high identity (79 and 67%) with the Nile tilapia PRLR 1 and black seabream PRLR 1, respectively. The presence of dfPRLR in several osmoregulatory tissues including kidney, gill and intestine is consistent with the known role of PRL in mediating hydromineral balance in teleosts. In addition, upregulated expression of PRLR mRNA was observed in skin of parental fish compared to non-parental fish, indicating possibility of a role of the PRL hormonal signaling in regulation of mucus production in relation to parental care behaviour.

We conducted a study to investigate the effect of different levels of dietary highly unsaturated fatty acids (HUFAs) on tissue fatty acid profiles and reproductive performance in female zebrafish. In addition, the mRNA expression of desaturase and elongase genes in liver, muscle and ovarian tissues were also analysed. Three iso-nitrogenous experimental diets utilizing different ratios of squid oil and linseed oil which were SO (100% squid oil), SLO (1:1 squid oil:linseed oil) and LO (100% linseed oil) as lipid sources were formulated and fed to female zebrafish for 12 weeks. Spawning was carried out twice weekly during the experimental feeding period. Results showed that fatty acid profiles of liver, muscle, ovary and egg reflected profiles of the corresponding dietary treatment. In general, increasing levels of dietary linseed oil lowered deposition of docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (ARA, 20:4n-6) in all tissues. Liver fatty acid profile implied increasing biosynthesis activities during feeding of low dietary HUFA diets, which was supported by increased expression of hepatic desaturase and elongase mRNAs. However, the increased HUFA biosynthesis activities were unable to compensate for the inferior hepatic ARA, EPA and DHA levels of fish fed diet LO. In muscle and ovary tissues, relatively lower concentrations of ARA and EPA were also obtained with diet LO. There was no significant difference in EPA and ARA levels in eggs, which imply accumulation of EPA and ARA in eggs. We also showed an increasing trend of ovarian desaturase and elongase gene expression during low dietary HUFA levels. Highest egg production and hatching rate was obtained with diet SLO, which strongly suggests the need for both inclusion and balanced ratio of dietary n-3 and n-6 unsaturated fatty acids by spawning females. Collectively, this study shows that female zebrafish reproduction benefits from the supply of dietary HUFA during reproductive stages, despite possessing ability to increase transcription of desaturase and elongase in various tissues during low dietary HUFA intake.

The endogenous production of long-chain polyunsaturated fatty acids (LC-PUFA) in carnivorous teleost species inhabiting freshwater environments is poorly understood. Although a predatory lifestyle could potentially supply sufficient LC-PUFA to satisfy the requirements of these species, the nutrient-poor characteristics of the freshwater food web could impede this advantage. In this study, we report the cloning and functional characterisation of an elongase enzyme in the LC-PUFA biosynthesis pathway from striped snakehead (Channa striata), which is a strict freshwater piscivore that shows high deposition of LC-PUFA in its flesh. We also functionally characterised a previously isolated fatty acyl desaturase cDNA from this species. Results showed that the striped snakehead desaturase is capable of Δ4 and Δ5 desaturation activities, while the elongase showed the characteristics of Elovl5 elongases. Collectively, these findings reveal that striped snakehead exhibits the genetic resources to synthesise docosahexaenoic acid (DHA; 22:6n-3) from eicosapentaenoic acid (EPA; 20:5n-3). Both genes are expressed at considerable levels in the brain and the liver. In liver, both genes were up-regulated by dietary C18 PUFA, although this increase did not correspond to a significant rise in the deposition of muscle LC-PUFA. Brain tissue of fish fed with plant oil diets showed higher expression of fads2 gene compared to fish fed with fish oil-based diet, which could ensure DHA levels remain constant under limited dietary DHA intake. This suggests the importance of DHA production from EPA via the ∆4 desaturation step in order to maintain an optimal reserve of DHA in the neuronal tissues of carnivores.

The genus Aureispira consisting of two species, Aureispira marina and Aureispira maritima is an arachidonic acid-producing bacterium and produces secondary metabolites. In this study, we isolated a new Aureispira strain, Aureispira sp. CCB-QB1 from coastal area of Penang, Malaysia and the genome sequence of this strain was determined. The draft genome of this strain is composed of 185 contigs for 7,370,077 bases with 35.6% G + C content and contains 5911 protein-coding genes and 76 RNA genes. Linoleoyl-CoA desaturase, the key gene in arachidonic acid biosynthesis, is present in the genome. It was found that this strain uses mevalonate pathway for the synthesis of geranylgeranyl diphosphate (GGPP), which is precursor of diterpenoid, and novel pathway via futalosine for the synthesis of menaquinones. This is the first draft genome sequence of a member of the genus Aureispira .

Background Although unsaturated fatty acids such as eicosapentaenoic acid (EPA, C20:5n-3), docosahexaenoic acid (DHA, C22:6n-3) and arachidonic acid (ARA, C20:4n-6), collectively known as the highly unsaturated fatty acids (HUFA), play pivotal roles in vertebrate reproduction, very little is known about their synthesis in the ovary. The zebrafish (Danio rerio) display capability to synthesize all three HUFA via pathways involving desaturation and elongation of two precursors, the linoleic acid (LA, C18:2n-6) and linolenic acid (LNA, C18:3n-3). As a prerequisite to gain full understanding on the importance and regulation of ovarian HUFA synthesis, we described here the mRNA expression pattern of two enzymes; desaturase (fadsd6) and elongase (elovl5), involved in HUFA biosynthesis pathway, in different zebrafish ovarian follicle stages. Concurrently, the fatty acid profile of each follicle stage was also analyzed. Methods mRNA levels of fadsd6 and elovl5 in different ovarian follicle stages were determined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) assays. For analysis of the ovarian follicular fatty acid composition, gas chromatography was used. Results Our results have shown that desaturase displayed significant upregulation in expression during the oocyte maturation stage. Expression of elongase was significantly highest in pre-vitellogenic follicles, followed by maturation stage. Fatty acid composition analysis of different ovarian follicle stages also showed that ARA level was significantly highest in pre-vitellogenic and matured follicles. DHA level was highest in both late vitellogenic and maturation stage. Conclusion Collectively, our findings seem to suggest the existence of a HUFA synthesis system, which could be responsible for the synthesis of HUFA to promote oocyte maturation and possibly ovulation processes. The many advantages of zebrafish as model system to understand folliculogenesis will be useful platform to further elucidate the regulatory and mechanism aspects of ovarian HUFA synthesis.