Effects Of Dietary Fatty Acids On Growth Performance, Health And Accumulation Of Lipids And Fatty Acids In Juvenile Japanese Seabass (Lateolabrax Japonicus)

Feeding experiments were conducted to investigate the effects of dietary fattyacids on growth performance, health and fatty acids accumulation in juvenileJapanese seabass (Lateolabrax japonicus), one of wildly cultured as an importantcommercial carnivorous species in China. The results are summarized as follows:1. Effects of dietary ratio of docosahexaenoic acid to eicosapentaenoic acid(DHA/EPA) on growth performance, immune response and tissue fatty acidcomposition of juvenile Japanese seabass, Lateolabrax japonicusA10-week feeding experiment was conducted to investigate the effects of dietarydocosahexaenoic acid to eicosapentaenoic acid (DHA/EPA) ratio on growthperformance, immune response, stress resistance and tissue fatty acid composition ofjuvenile Japanese seabass (mean initial weight9.48±0.09g) in seawater floating netcages. DHA enriched oil and EPA enriched oil were supplemented into the basal dietto formulate six practical diets with different DHA/EPA ratios (0.55,1.04,1.53,2.08,2.44and2.93, respectively). All diets had the same total n-3long chainpolyunsaturated fatty acid (LC-PUFA) level. Triplicate groups of30fish were fed toapparent satiation twice daily. The results showed that final weight (FW) and specificgrowth rate (SGR) significantly increased with increasing dietary DHA/EPA ratiofrom0.55to2.08(P<0.01) and thereafter declined. The feed efficiency ratio (FER)had the similar pattern with SGR. No significant differences were found in survivalrate, hepatosomatic index (HSI), viscerosomatic index (VSI), and condition factoramong dietary treatments. Activities of serum lysozyme (LYZ)(P<0.01) andsuperoxide dismutase (SOD)(P<0.01) in treatment with low DHA/EPA (0.55) wassignificantly lower than those in treatments with higher DHA/EPA (1.53~2.93), respectively. The activity of serum alternative complement pathway (ACP) in fish feddiet with1.53DHA/EPA was significantly higher than that in fish fed diet with2.93DHA/EPA (P<0.05). However, no differences were observed in activities of bothrespiratory burst (RPB) of head kidney macrophage and serum catalase (CAT) amongdietary treatments. The survival rate after air exposure in treatments with intermediateand higher DHA/EPA (1.53,2.08and2.93) was significantly higher than that intreatments with low DHA/EPA (0.55)(P<0.01). The fatty acid composition of wholebody and tissues reflected closely those of diets, while fish accumulated much moreDHA than EPA in fish tissues, especially in muscle. These results suggested that basedon growth performance, immune response, stress resistance and tissue fatty acidcomposition, the recommended dietary DHA/EPA ratio for juvenile Japanese seabasswas1.53~2.44. On basis of SGR, the optimum DHA/EPA ratio in diets of juvenileJapanese seabass was estimated to be2.05.2. Effects of dietary arachidonic acid (ARA) on growth performance,immune response and tissue fatty acid composition of juvenile Japaneseseabass, Lateolabrax japonicusA12-week feeding experiment was conducted to investigate the effects of dietaryarachidonic acid (ARA) on growth performance, immune response and tissue fattyacid composition of juvenile Japanese seabass (Lateolabrax japonicus)(mean initialweight9.48±0.09g) in seawater floating net cages (1.5×1.5×2.0m). An ARAenriched oil was supplemented into the basal diet to formulate six isonitrogenous andisoenergetic practical diets containing0.08%(the control group),0.22%,0.36%,0.56%,1.33%and2.12%ARA of dry weight, respectively. All diets had the sametotal n-3long chain polyunsaturated fatty acid (LC-PUFA) level and22:6n-3/20:5n-3ratio. Triplicate groups of30fish were fed to apparent satiation twice daily for12weeks. The water temperature ranged from22.5to31.5°C, the salinity from28‰to33‰and the dissolved oxygen content was approximately6mg l1during theexperimental period. The results showed that final weight (FW) and specific growth rate (SGR) significantly increased with increasing dietary ARA from0.08%to0.36%(P<0.01) and thereafter declined. The feed efficiency ratio (FER) had the similarpattern with SGR, and fish fed the diet with0.36%ARA showed significantly higherFER than the control (P<0.05). No significant differences were found in survival rateamong dietary treatments (P>0.05). The hepatosomatic index (HSI) decreasedsignificantly with the increase of dietary ARA, and HSI in fish fed the diets with morethan0.22%ARA content were significantly lower than the control group (P<0.01).The serum lysozyme (LYZ), alternative complement pathway (ACP) and superoxidedismutase (SOD) activity were significantly enhanced by the supplementation of ARA,especially in moderate supplementation (0.36-0.56%). However, there were nodifferences in both respiratory burst activity of head kidney macrophage and serumcatalase (CAT) activity among dietary treatments. The body composition analysisshowed that whole-body protein first increased, then decreased with increasingdietary ARA, while whole-body lipid content followed the opposite pattern. The fattyacid composition of whole body and liver reflected closely those of the diets, whileliver EPA levels were inversely related to dietary ARA. These results suggested thatdietary ARA, especially moderate ARA level (0.22-0.56%d.w.), significantlyenhanced growth and immune response and modified the chemical composition ofwhole body and liver of Japanese seabass juvenile.3. Effects of dietary α-linonlenic acid (LNA) and linoleic acid (LA) ongrowth performance, survival, immune responses and tissue fatty acidcomposition of juvenile Japanese seabass, Lateolabrax japonicusA66-day feeding experiment was conducted to investigate the effects ofreplacement of fish oil (FO) with linseed oil (LO) or soybean oil (SO) on growthperformance, immune response, and tissue fatty acid composition in Japanese seabass(mean initial weight10.09±0.70g) in seawater floating net cages. LO or SO wasincluded in the isonitrogenous and isoenergetic diets to substitute1/3,2/3or3/3fishoil (Diet F2L1, F1L2, LO, respectively, or Diet F2S1, F1S2, and SO, respectively). A diet with9%fish oil (Diet FO) and a diet with combined oil (FO:LO:SO=1:1:1)(DietF1L1S1) were added as the control. Triplicate groups of30fish were fed to apparentsatiation twice daily. The results showed that the replacement of FO by LO or SO didnot significantly influenced the specific growth rate (SGR) and final weight (FW), butSGR and FW in F2L1group was significantly higher compared to SO group (P<0.05).The feed efficiency ratio (FER) followed a similar trend with SGR and FW.Hepatosomatic index (HSI) in LO treatment was significantly higher than that inF1L1S1treatment (P<0.05). The survival rate among dietary treatments was notsignificantly different (P>0.05). Fish fed Diet LO and SO showed significantly lowerphagocytic index of head kidney macrophage compared to the FO control group(P<0.01). Diet LO and SO also significantly reduced the lysozyme activity (P<0.05)and Serum superoxide dismutase (SOD)(P<0.01) in serum, respectively, compared tothe FO control group. Serum catalase activity showed a similar trend with SOD,however, no significant differences were observed in Respiratory burst (RPB) activityof head kidney macrophage and serum alternative complement pathway (ACP)activity among dietary treatments. Replacement of FO by LO significantly decreasedthe whole body moisture content but increased the lipid content compared to the FOcontrol group (P<0.05). The fatty acid composition of whole body and tissuesreflected closely those of the diets, while tissue C22:5n-3concentration negativelycorrelated to dietary C22:5n-3, but positively correlated to tissue EPA content. DietaryLO or SO supplement reduced tissue LC-PUFA concentrations, whereas fishselectively accumulated more DHA than EPA in fish tissues and the DHA content inmuscle was significantly higher than that in liver and whole body. These resultssuggested that linseed oil and soybean oil were both potential alternative lipid sourcesfor juvenile Japanese seabass though sole supplement of LO or SO could causereduction in tissue LC-PUFA concentration and certain innate immune parameters.Linseed oil performed better than soybean oil in enhancing the growth performanceand innate immune responses. 4. Molecular cloning, characterization and mRNA expression of Δ6fatty aciddesaturase (FAD6) from Japanese seabass Lateolabrax japonycus in responseto dietary fatty acidsIn the present study, the cDNA of Δ6fatty acid desaturase (FAD6) from Japaneseseabass Lateolabrax japonycus was cloned by homology cloning withdegenerate primer and RACE techniques. The full-length cDNA of FAD6was of1920bp, including an open reading frame (ORF) of1338bp encoding a polypeptide445amino acids with predicted molecular weight of51.8kDa and theoreticalisoelectric point of8.86. BLAST analysis revealed that FAD6of Japanses seabassshared high similarity with known FAD6in other aquatic vertebrates. The real-timePCR assay showed that the expression of FAD6in brain, eye, liver and intestine wassignificantly higher compared to other tissues. The expression levels of FAD6in liverwere measured by real-time PCR after Japanese seabass were fed diets with fattyacids of different carbon chain length and desaturation (midium-chain fatty acid,C8:0+C10:0; saturated fatty acid, C16:0; saturated fatty acid, C18:0; monounsaturatedfatty acid, C18:1n-9; n-318-carbon polyunsaturated fatty acid, C18:3n-3; n-3longchain polyunsaturated fatty acid (n-3LC-PUFA), DHA+EPA; Fish oil). The resultsshowed that the expression levels of FAD6transcript were significantly up-regulatedin liver of Japanese seabass fed the diet with C16:0compared with that of fish feddiets with midium-chain fatty acids, C18:3n-3, n-3LC-PUFA and fish oil (p<0.01)and the levels in liver of fish fed diets with midium-chain fatty acids, n-3LC-PUFAand fish oil were significantly lower compared to fish fed other diets (p<0.01). Theseresults indicated that dietary long carbon chain polyunsaturated fatty acids couldinhibit the mRNA expression of FAD6, while the dietary palmitic acid couldstimulate the mRNA expression of FAD6in liver of Japanese seabass.5. Effects of dietary fatty acids of different carbon chain length and desaturationon growth performance, body composition, tissue accumulation of lipidand fatty acids, liver health and fillet quality of juvenile Japanese seabass,Lateolabrax japonicus A70-day feeding experiment was conducted to investigate the effects of dietaryfatty acids of different carbon chain length and desaturation on growth performance,body composition, tissue accumulation of lipid and fatty acids, liver health and filletquality of juvenile Japanese seabass (Lateolabrax japonicus)(mean initial weight29.53g) in seawater floating net cages (1.5×1.5×2.0m). Caprylic/capric triglyceride,Tripalmitin, Tristearin, Rapeseed oil, Blended oil of linseed oil and perilla oil (3:1),n-3LC-PUFA enriched oil and fish oil was supplemented into the basal diet to formulateseven isonitrogenous and isoenergetic practical diets, containing C8:0+C10:0, C16:0,C18:0, C18:1n-9, C18:3n-3, DHA+EPA and fish oil fatty acid profile as representativefatty acid, respectively. The seven treatments were named as follows:①MCA,midium-chain fatty acid, C8:0+C10:0;②PA, palmitic acid, C16:0;③SA, stearicacid, C18:0;④OA, oleic acid, C18:1n-9;⑤LNA, α-linolenic acid, C18:3n-3;⑥n-3LC-PUFA, n-3long chain polyunsaturated fatty acids, DHA+EPA;⑦FO, fish oil.The results showed that fish fed diet MCA showed significantly lower final weight(FW) compared to other treatments and fish fed diet PA and SA showed significantlylower FW than fish fed diet OA, LNA, n-3LC-PUFA and FO. FW in fish fed FO wassignificantly higher than that in other treatments except LNA and n-3LC-PUFA groupand no significant differences were observed in FW between fish fed OA and LNA,and between fish fed LNA and n-3LC-PUFA. The specific growth rate (SGR) of fishshowed a similar trend with FW. Fish fed FO showed significantly higher feedefficiency ratio (FER) than fish fed MCA and PA, and fish fed MCA showedsignificantly lower FER than fish fed LNA, n-3LC-PUFA and FO. The feeding rate infish fed MCA was significantly lower compared to other treatments. Thehepatosomatic index (HSI) and viscerosomatic Index (VSI) in fish fed MCA weresignificantly lower than fish fed OA and LNA. Lower moisture and ash content ofwhole body, while higher lipid content was observed in fish fed OA, LNA and n-3LC-PUFA, compared to fish fed MCA, PA and SA. With the increase of dietarycarbon chain length and desaturation, the lipid content in serum, gut and muscle ofexperimental fish increased significantly. However, fish fed SA, OA and LNA havethe highest liver lipid content. The fatty acid composition of experimental fish reflected closely those of diets. With the increase of dietary carbon chain length anddesaturation, the activity of liver glutamic-pyruvic transaminase (GPT),glutamic-oxalacetic transaminease (GOT) and lactic dehydrogenase (LDH) decreasedsignificantly while alkaline phosphatase (AKP) activity and albumin contentsignificantly increased. The assay of histological structure of liver showed that theintegrity of hepacytes in fish fed MCA was destroyed and cell enlargement, nuclearmigration and fatty degeneration were observed in fish fed PA, SA and OA. Fish fedn-3LC-PUFA and FO showed normal hepatic morphology and structure. Comparedto fish fed MCA, PA and SA, fish fed LNA, n-3LC-PUFA and FO showed increasedmuscle malondialdehyde (MDA), muscle protein carbonyl level, liver superoxidedismutase (SOD) activity, liver catalase (CAT) activity and liver glutathion peroxidase(GPX), and decreased liver glutathione reductase (GR) and glutathione transferase(GST). The increase of fietary fatty acid carbon chain length and desaturationdecreased the hardness, fracturability, springiness, chewiness and gumminess of thefillet. In conclusion, carbon chain length of dietary fatty acid significantly influencedthe growth performance, body composition, tissue accumulation of lipid and fattyacids, liver health and fillet quality of juvenile Japanese seabass. Midium-chain fattyacids in the diet led poor palatability, and subsequently inhibited the growth. Saturatedand monosaturated fatty acids in the diet could cause alteration to liver health, lipidaccumulation and fillet quality.