| Tilapia is one of the most important farmed fish in the world due to its fast growth, euryphage and good taste. The world production of tilapia was 5450 thousand tons in 2014 while 1698 thousand tons in China. With the development of tilapia culture, more feed protein resources are needed. At present, high plant protein resources diets are commonly used in the cultivation of tilapia which the palatability is low and partly results in stunted growth and physiology function. Therefore, it is important to screen the optimal feeding stimulants(FS) in high plant protein resources diets and provide the insight into the mechanisms of FS. In the present study, the effects of seven FS(Dimethylthetin, DMT; Dimethyl-β-propiothetin, DMPT; Betaine, Bet; Taurine, Tau; Tryptophan, Trp; Mixed nucleotides, Mix-NT; Squid liver paste, SQLP) in the diets with high plant protein resources on feed intake, growth performance of juvenile GIFT Oreochromis niloticus were evaluated as well as the effect mechanisms of FS on the feed intake(FI) and growth of tilapia were discussed. The results are as follows.1. The study on the optimal inclusion level of seven feed stimulants in the high plant protein resources tilapia diets.560 fish with initial body weight of 8.59±0.04 g were randomly stocked into seven groups with four replicates of 20 fish, each group tested one FS within an independent circulatory system. The basal diet contained 4% fish meal, 18% soybean meal, 6% canola meal, 20% Pakistan rapeseed meal and 19% cottonseed meal as protein resources and lecithin, soybean oil as lipid sources(protein 354.2 g kg-1, energy 17.95 MJ kg-1). Five inclusion levels were tested for each of the seven FS(0, 0.2, 0.4, 0.6, 0.8 g kg-1 for DMPT; 0, 0.2, 0.4, 0.6, 0.8 g kg-1 for DMPT; 0, 0.6, 1.2, 1.8, 2.4 g kg-1 for Trp; 0, 3, 6, 9, 12 g kg-1 for Bet; 0, 0.4, 0.8, 1.2, 1.6 g kg-1 for Mix-NT; 0, 4, 8, 12, 16 g kg-1 for Tau; 0, 10, 20, 30, 40 g kg-1 for SQLP). The five tested levels of each FS combined with one kind of inert element(Y2O3, La2O3, Sm2O3, Nd2O3, Yb2O3) were added to basal diet to be made into a single diet. Fish of each group were fed mixed diet with equal amount of five single marked diets. Preference for each level of FS was estimated by the relative concentration of single inert element. The results showed that the most effective concentration of each FS were as follows: DMPT, 0.4 g kg-1; DMT, 0.6 g kg-1; Bet, 6 g kg-1; Tau, 16 g kg-1; Trp, 1.8 g kg-1; Mix-NT, 0.4 g kg-1; SQLP, 30 g kg-1.2. The effects of seven FS in high plant protein resources diet on apparent digestibility coefficients of tilapia360 fish with an initial body weight of 62.95±3.54 g were randomly divided into eight groups with three replicates of 15 fish, and fed with basal diet and 7 tested diets. All diets added 300 mg kg-1 Y2O3 as the indicator, and collected the total faeces reach to 10 g(dry weight). The fish were fed to apparent satiation by hand twice daily(9:00 and 16:00). The results showed that, the apparent digestibility coefficients(ADCs) of lipid had no differences between the 8 diets. The ADCs of dry matter, crude protein and energy of SQLP diet were significantly lower than those of other diets. The ADC of dry matter was significantly higher in DMPT diet than that of control diet. The ADC of phosphorus was significantly higher in Bet diet than that of control diet. The ADC of aspartic acid and glutamic acid was significantly lower in SQLP diet than that of other diets, while the ADC of aspartic acid was significantly higher in DMPT diet than those of control, Mix-NT and Tau.3. The effects of seven FS in high plant protein resources diet on feed intake, growth performance, serum biochemical parameters, intestinal morphology and digestive enzyme activities of tilapia.600 fish with initial body weight of 3.34 ± 0.01 g were randomly stocked into eight groups with three replicates of 25 fish, and fed with basal diet and 7 tested diets respectively for 8 weeks. The fish were fed to apparent satiation by hand twice daily(9:00 and 16:00). The seven test diets were prepared by adding DMPT, 0.4 g kg-1; DMT, 0.6 g kg-1; Bet, 6 g kg-1; Tau, 16 g kg-1; Trp, 1.8 g kg-1; Mix-NT, 0.4 g kg-1 and SQLP, 30 g kg-1 to the basal diet, respectively. The results showed that feed intake(FI), final body weight(FBW) and specific growth rate(SGR) in fish fed with SQLP were significantly higher than those of control. FBW, SGR and feed efficiency(FE) in fish fed with Mix-NT were significantly higher than those of control. Protein efficiency rate(PER) and FE in fish fed with Bet were significantly higher than that of control. FS did not have significant influence on whole fish body composition. Viscerosomatic index were significantly increased by Trp, Bet and SQLP. The content of high-density lipoprotein cholesterol(HDL-C) was significantly higher in fish fed with SQLP than that of other FS, meanwhile fish fed with SQLP had significantly higher intestinal amylase activities. Amylase activities in intestine were significantly higher in fish fed with DMPT, Mix-NT and Bet than those in other groups. Protease activities in intestine and lipase activities in hepatopancreas were significantly increased by Bet, meanwhile protease activities in intestine was significantly higher in fish fed with Mix-NT than that of other groups. The length height of intestinal folds was significantly higher in fish fed with Mix-NT and Bet than that of control, meanwhile the muscle thickness was significantly higher in fish fed with Bet than that of control.4. The effects of seven FS in high plant protein resources diet on muscle quality of tilapiaThe test diets, grouping and feeding were the same as(3). After feeding trial, the muscle quality was analyzed. The results showed that, muscle crude protein, collagen, and 15 amino acids, cooking loss of SQLP group were significantly higher than that of control. Muscle inosinic acid, 11 amino acids, and superoxide dismutase(SOD) activities of Bet group were significantly higher than that of control, while muscle malonaldehyde(MDA) content and p H24 h of Bet group were significantly lower than that of control. Muscle p H24 h of Mix-NT group was significantly lower than that of control, while muscle catalase activity was significantly higher than that of control. Muscle malonaldehyde(MDA) content of DMT group was significantly lower than that of control, while muscle threonine and serine content were significantly higher than that of control. Muscle SOD activities and muscle metionine content of DMPT group were significantly higher than that of control. Muscle alanine content of Tau group was significantly higher than that of control. Muscle amino acid contents of Trp and Mix-NT groups had no difference compared to the control group.5. The effects of seven FS in high plant protein resources diet on appetite-related genes expression of tilapiaThe test diets, grouping and feeding were the same as(3). After feeding trial, the appetite-related genes expression in brain, stomach and hepatopancreas were analyzed. The results showed that, the highest gene expression levels of neuropeptide Y(NPY) in brain, agouti-related protein(Ag RP) in brain, cholecystokinin(CCK) in brain and stomach were found in the fish fed with Trp, and NPY expression level was significantly higher than that of the control. The highest gene expression level of ghrelin in stomach was found in fish fed with DMT and had a significant difference in comparison with the control. The highest gene expression level of leptin in hepatopancreas was found in fish fed with Tau and had significant differences compared to the other treatments.6. The effects of seven FS in high plant protein resources diet on serum GH, IGF-I concentrations and growth axis related genes expression of tilapiaThe test diets, grouping and feeding were the same as(3). After feeding trial, the serum growth hormone(GH), insulin-like growth factor-I(IGF-I) concentrations and growth axis related genes expression were analyzed. The results showed that, the gene expression level of GH in brain, serum IGF-I content were significantly improved by SQLP. The gene expression level of GH in brain, growth hormone receptor(GHR), IGF-I and serum IGF-I contents were significantly increased by Mix-NT. The gene expression level of GH in brain was significantly increased by Bet.In conclusion,(1) FI, growth and muscle protein content were significantly improved by SQLP supplement. There were no relationships between SQLP and appetite-related genes. Higher FI and growth axis related factors in SQLP lead to higher growth.(2) Significantly higher SGR and FE were found in fish fed with Mix-NT than that of control due to the improvements of digestive enzymes activities, intestinal morphology and growth axis related factors expression. The promoting effect on FI by Mix-NT was not significant, and there were no relationships between Mix-NT and appetite-related genes.(3) FI was not significantly improved by Bet in long-term trial. There were no relationships between Bet and appetite-related genes. Significantly higher PER, FE and muscle quality were found in fish fed with Bet than that of control due to the improvement of digestive enzymes activities, intestinal morphology, digestibility coefficient of phosphorus and GH m RNA expression.(4) FI and growth were not significantly improved by DMPT, DMT and Trp in long-term trial. Some specific orexigenic and anorexigenic m RNA expressions were enhanced by Trp and DMT. There were no relationships between DMPT and appetite-related genes.(5) FI and growth were slightly decreased by Tau, but had not statistical significance, and it might attribute to significantly higher Leptin m RNA expression in hepatopancreas. |
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