Lipid And Fatty Acid Quality Of Turbot And Its Nutritional Regulation

This thesis,with turbot,was aimed at exploring the characteristics of lipid and fatty acid nutritional quality of turbot,and the regulatory effects of feed nutritional composition and feeding strategies on it.The results and conclusion are summarized as follows:1.Effects of long-term alternate feeding between fish oil-and terrestrially sourced oil-based diets on fillet quality and fatty acid composition of different tissues of turbotUse of terrestrially sourced oil(TSO)in the diets easily causes adverse effects on fillet quality and reduction in long-chain polyunsaturated fatty acids(LC-PUFA)in farmed fish.The present study,with turbot,was aimed at evaluating the efficacy of alternate feeding between fish oil(FO)-and TSO-based diets in minimizing these adverse effects and comparing the fatty acid regulating effects of the alternate feeding strategy in different tissue types,namely,muscle,liver and subcutaneous tissue around the fin(STF).The control group was fed the FO-based diet continuously for 13 weeks,meanwhile other groups were subjected to weekly alternation between the FO-based diet and diets based on TSO,namely,linseed oil,soybean oil,rapeseed oil,palm oil,and beef tallow,respectively.The feeding trial was conducted in a flow-through seawater system.Each group had triplicate tanks,and each tank was stocked with 35 fishes.Samples were collected at the end of Week9 and 13.At Week 9,no significant difference among groups was observed in growth performance and muscle proximate composition,texture,and odour-active compound profile;however significant differences were observed in the content of long-chain polyunsaturated fatty acids in three tissues,serum malondialdehyde content and somatic indices.At Week 13,the significant difference in the content of long-chain polyunsaturated fatty acids in liver and STF remained,but other differences disappeared.No matter Week 9 or Week 13,STF seemed more like a lipid storage site,with high contents of 18:1n-9 and 18:3n-3,but low LC-PUFA contents.Among all the treatments,alternate feeding between FO-and beef tallowbased diets resulted in the most similar fatty acid profile to the treatment with continuous FO feeding.In conclusion,long-term alternation between FO-and TSO-based diets could mitigate the adverse effects of TSO on farmed turbot.Meanwhile this study added knowledge to the fatty acid composition of fish subcutaneous tissue,as well as to promising application of beef tallow in fish feed.2.Response of lipid and fatty acid composition of turbot to starvation under different dietary lipid levels in the previous feeding periodThe present study was aimed at investigating interactive effects of starvation and dietary lipid level in previous feeding on lipid-related composition and muscle texture of turbot.Juvenile turbot(26.00 ±0.02 g)was firstly fed diets with different lipid levels,namely,8%,12%,and 16%,for 9 weeks,and then subjected to starvation for 30 days.Each diet was fed to sextuplicate tanks of 35 fish in the feeding trial.Tissue samples were collected at the end of the feeding trial(S0)and at10(S10),20(S20),and 30(S30)days after starvation for analysis of lipid and fatty acid-related composition.The results showed that 30-day starvation decreased the lipid content in the liver and subcutaneous tissue around the fin(STF),but increased the lipid content in the muscle.Starvation mobilized different fatty acids among the three tissues,namely,MUFA(16:1n-7 and 18:1n-9)in the muscle,SFA(14:0 and16:0),MUFA(16:1n-7,18:1n-9 and 20:1n-9),and 18C-PUFA(18:2n-6 and 18:3n-3)in the liver,and unexpectedly n-3 PUFA(18:3n-3,EPA,and DHA)in the STF,respectively.Starvation mobilized glycogen in the three tissues,with the content in the liver sharply decreased during the first 7 days.30-day starvation decreased the muscle hardness and resilience,but affected other texture parameters in a starvation time-dependent manner.The lipid and fatty acid composition of fish tissues closely reflected those of the diets.Interactive effects of dietary lipid level and starvation were observed mainly on tissue fatty acid compositions.Results of this study suggested that combined manipulation of dietary lipid level and starvation time could be used as a means of muscle quality regulation.3.The research on the difference of turbot’s lipid and fatty composition compared with other lean marine teleosts having different lipid storage patternsThis study investigated the lipid composition characteristics in turbot(Scophthalmus maximus),tiger puffer(Takifugu rubripes),and Japanese seabass(Lateolabrax japonicus),three important aquaculture species having different lipid storage patterns.All fish were fed the same diet for 9 weeks prior to analysis,in order to minimize the effects of their respective previous diets.Lipid concentration,fatty acid composition,and lipid metabolism-related biochemical parameters in various tissues of these three species was analyzed.Gallbladder bile acid profile and muscle texture were also analyzed.Results of this study evidenced that turbot,tiger puffer,and Japanese seabass used subcutaneous adipose tissue,liver,and intraperitoneal adipose tissue as the predominant lipid storage site,respectively.The lipid contents of turbot liver and muscle were between that of Japanese seabass and tiger puffer,and the Japanese seabass had the highest lipid content in muscle and lowest in liver,respectively.In terms of most fatty acids in muscle,the contents of turbot were between in Japanese seabass and tiger puffer.Low DHA/EPA ratio and high contents of 18:0 and n-6 PUFA were the most distinctive characteristic of muscle fatty acid profile in Japanese seabass and tiger puffer,respectively.High contents of 14:0 in liver and EPA in subcutaneous adipose tissue were the most distinctive characteristic of turbot’s fatty acid profile,respectively.Among some lipid-related hematological parameters,turbot had the lowest content.The analysis of gallbladder bile acid profile provided basic information for lipid physiology in farmed fish having different lipid storage patterns.In conclusion,the lipid storage pattern in marine teleost probably largely determines the lipid composition characteristics.