The Research On The Plant Protein Utilization By Marine Fish And Shrimp——antinutritional Factors And Methionine

The present studies were conducted to do basic research on how to improve plant meal utilization by fish and shrimp. Atlantic salmon (Salmo salar) and turbot (Scophthalmus maximus L) were used as experimental subjects to investigate the effects of anti-nutrients in plant meal on the health of these two carnivorous fish species. Studies were also conducted to investigate the effects of supplementation of different forms of essential amino acids on growth and feed utilization in white shrimp (Litopenaeus vannanei) and turbot fed with high levels of plant meal. The studies are summarized as follows:1. Dietary saponin dose response in Atlantic salmon (Salmo salar):. Effects on growth, digestive enzyme, and gut health.The goal of the current work was to examine the dose response of purified soya-saponins on growth, digestive physiology and gut health in Atlantic salmon (Salmo salar, L). Two basal diets were formulated:a fish meal based diet (FM) and a plant meal based diet (PM). Each basal diet was produced without or with soya-saponin supplementation (2,4,6or10g kg-1). Each diet was fed to duplicate tanks of Atlantic salmon (initial weight442±33g; mean±SD). The feeding trial lasted10weeks. At termination fish were sampled to analyze growth and intestinal responses, including chyme trypsin activity, tissue brush border enzyme activity and histology. Fish fed the PM based diets had lower final weights compared to fish fed the FM based diets. Saponins significantly influenced the growth performance of FM fed fish, showing higher growth at low (2-4g kg-1) saponin levels but lower growth at high (6-1Og kg-1) levels (R2=0.953,.P＜0.001). Increasing dietary soya-saponin concentration caused:1) Decreased enterocyte brush border enzyme activity in the distal intestine;2) Increased trypsin activity in digesta from the distal intestine;3) Increased enterocyte proliferation in distal intestine. Inflammation was observed in the distal intestine associated with high levels (6-10g kg-1) of dietary soya-saponin, regardless of the basal diet formulation.2. Effects of dietary plant meal and soya-saponin supplementation on intestinal and hepatic lipid droplet accumulation, lipoprotein and sterol metabolism in Atlantic salmon (Salmo salar L.).Altered lipid metabolism has been shown in fish fed with plant protein sources. This study aimed at gaining further insight into how intestinal and hepatic lipid absorption and metabolism are modulated by plant meal and soya-saponin inclusion in salmon feed. Post-smolt Atlantic salmon (initial weight442±24g; mean±SD) were fed one of four diets based on fish meal or plant meal, with or without1.0%soya-saponin for10weeks. Plant meal inclusion resulted in decreased growth performance, excessive accumulation of lipid droplets in pyloric caeca and liver and reduced plasma levels of cholesterol. Intestinal and hepatic gene expression profiling revealed up-regulation of genes involved in lipid absorption and lipoprotein synthesis (apolipoproteins, fatty acid transporters, microsomal triglyceride transfer protein, acyl-coA cholesterol acyltransferase, choline kinase, choline-phosphate cytidylyltransferase A), cholesterol synthesis (3-hydroxy-3-methylglutaryl-coenzyme A reductase) and associated transcription factors (sterol regulatory element binding protein2and peroxisome proliferator activated receptor gamma). Soya-saponin inclusion resulted in reduced body pools of cholesterol and bile salts. Hepatic gene expression of the rate-limiting enzyme in bile acid biosynthesis (cyp7a1) as well as the transcription factor liver X receptor and the bile acid transporter (abcb11) were down-regulated by soya-saponin inclusion. Significant interaction was observed between plant meal and soya-saponin inclusion in plasma cholesterol level. In conclusion, gene expression profiling suggested that the capacity for lipoprotein assembly and cholesterol synthesis were up-regulated by plant meal exposure, probably as a compensatory mechanism for excessive lipid accumulation and reduced plasma cholesterol levels. Soya-saponin inclusion had hypocholesterolemic effects on Atlantic salmon, accompanied by decreased bile salt metabolism.3. Effects of diet supplementation of soya-saponins, isoflavones and phytosterols on Atlantic salmon(Salmo salar, L) at early growth stage. A14-week trial was conducted to investigate the effects of antinutritional factors (ANFs) commonly present in soybean ingredients, singly and in combination, on Atlantic salmon (Salmo salar L.). Fry performance, including growth, digestive enzyme activities, intestinal and liver histology, and skeletogenesis were evaluated. The experimental diets consisted of a reference control fish meal diet (FM), and four diets based on the FM diet supplemented with2g kg-1soya-saponins (SAP),1.5g kg-1isoflavones (IFL),0.3g kg-1phytosterols (PHS) or a mixture of these (MIX). Each diet was randomly allocated to triplicate groups of fish fry (approximately0.18g) from start-feeding. Fish fed the SAP diet showed significantly higher growth performance than those fed FM, while the IFL treatment significantly decreased final body weight and specific growth rate (P<0.05). For digestive enzyme activities, fish fed the IFL diet had significantly lower maltase activity and higher trypsin activity in proximal intestine than fish fed the FM diet (P<0.05). No significant difference among the treatment groups was observed either in intestinal bile acids concentration or in activities of leucine aminopeptidase or amylase. Nor was intestinal histomorphology affected. Histological differences were observed in the liver of fish fed the IFL diet, characterized by reduced size of the hepatocytes due mainly to reduction in glycogen content. Dietary treatments tended to change the incidence of skeletal deformities in salmon fry (P＜0.10). Fish fed the PHS and IFL diets showed the highest frequencies (5.1and4.3%, respectively) of deformities among the five treatments, In conclusion, the results indicate that purified isoflavones may negatively affect growth performance, intestinal function, liver metabolism and bone formation of salmon fry.4. Effects of β-conglycinin and glycinin on growth, digestive enzymes and immune responses in juvenile turbot (Scophthalmus maximus L).The study was conducted to investigate the effects of β-conglycinin and glycinin on growth, digestive enzymes and immune responses in turbot (Scophthalmus maximus L). The basal diet was formulated to contain48%crude protein and12%crude lipid, and was used as the control. The other four diets were supplemented with6.0%β-conglycinin (diet7S),6.0%heat treated β-conglycinin (diet H7S),6.0% glycinin (diet11S) and6.0%heat treated glycinin (diet H11S), respectively. Each diet was randomly allocated to triplicate groups of fish (initial average weight of6.80g) for4weeks. Fish fed7S diet showed significantly lower specific growth rate (SGR) and higher feed conversion rate (FCR) than the others (P<0.05). Furthermore, it had reduced digestive enzyme activities (amylase activity, lipase activity, maltase activity and alkaline phosphatase activity) in different gastrointestinal (GI) sections (pyloric caeca, mid-intestine and distal intestine). Additionally, fish fed7S diet showed significantly higher acid phosphatase activity and lysozyme activity in distal intestine compared with fish fed the other diets (P<0.05). In conclusion, P-conglycinin (7S) significantly decreased the growth, feeding efficiency, digestive enzyme activities and induced the immunological responses in distal intestine of turbot. These changes were not observed in the fish fed heat treated7S diet. Glycinin (11S) had no significant influence on the health of turbot. Immunogenicity of β-conglycinin (7S) in turbot may be relative to its heat processing.5. Effects of dietary crystalline methionine or oligo-methionine on growth performance and feed utilization of white shrimp(Litopenaeus vannanei) fed high plant protein diets.An eight-week feeding experiment was conducted to investigate the effects of dietary crystalline methionine (CMet) or oligo-methionine (OMet) on growth performance and feed utilization of white shrimp, Litopenaeus vannanei. A practical diet was used as control diet. The other four isonitrogenous and isolipid diets replacing30%and60%fish meal by a mixture of soybean meal and peanut meal (SPP) were formulated. To balance the methionine content,0.1%CMet (SPP30-CMet) or0.1%OMet (SPP30-OMet) was added in30%fish meal replacing diets and0.2%CMet (SPP60-CMet) or0.2%OMet (SPP60-OMet) was added in60%fish meal replacing diets. Methionine source significantly affected growth performance, body compositions and hepatosomatic indices (HSI) of white shrimps (P＜0.05). Shrimps in SPP60-CMet treatment showed significantly lower weight gain, crude protein content in whole body and significantly higher HSI than those in control (P<0.05). However, no significant difference in these indices was observed between control and OMet supplemented treatments (P>0.05), Shrimps in SPP30-OMet treatment showed significantly higher feed efficiency ratio and protein efficiency ratio than those in SPP30-CMet treatment (P＜0.05). The present study indicated that compared with the CMet, dietary OMet resulted in better growth and feed efficiency of L. vannanei fed high plant protein diets.6. Effects of dietary crystalline methionine or oligo-methionine on postprandial plasma free amino acid level, growth performance and feed utilization of turbot (Scophthalmus maximus L) fed high plant protein diets.Two experiments were conducted to investigate the effects of dietary crystalline methionine (CMet) or oligo-methionine (OMet) on postprandial plasma free amino acid level (experimental I), growth performance and feed utilization of turbot (Scophthalmus maximus L) fed high plant protein diets (experimental Ⅱ). In experimental I, a methionine deficient diet (1.0%methionine) was formulated and used as basal diet. To balance the methionine content,0.5%crystalline methionine (CMet-0.5) or0.5%oligo-methionine (OMet-0.5) was added. Each diet was fed to triplicate groups of turbot (approximately35.8g) for a week. Plasma samples were collected3h,6h,9h and12h postprandially to analyze free amino acid concentration. The plasma methionine level of fish fed the OMet-0.5diet showed similar postprandial change pattern with most of the other assayed amino acids. However, in CMet-0.5treatment, the time observed for peak level of plasma methionine was earlier than that of any other assayed amino acids. In experimental II, exclusive of two diets used in Experimental I, another four isonitrogenous and isoenergetic diets with0.25%and1.0%of crystalline methionine (named as CMet-0.25and CMet-1.0) or oligo-methionine (named as OMet-0.25and OMet-1.0) were prepared. Each diet was fed to triplicate groups of turbot (approximately6.8g) for8weeks. The results showed that oligo-methionine could improve the growth performance and feed utilization of turbot compared with crystalline methionine. High supplementation of methionine showed negative effect on the growth performance of turbot.