Effects of Dietary Carbohydrate To Lipid Ratios On Growth Performance, Body Composition, Serum Biochemical Indexes, Lipid Metabolism And Gene Expression of Central Appetite Regulating Factors In Chinese Perch (Siniperca Chuatsi)

An 8-week feeding trial was conducted to evaluate the effects of dietary carbohydrate to lipid (CHO: L) ratios on growth performance, body composition, serum biochemical indexes, lipid metabolism and gene expression of central appetite regulating factors in Chinese perch (Siniperca chuatsi) (mean initial weight: 12.86 ± 0.10 g). Five isonitrogenous and isoenergetic diets (sh meal, casein as main protein sources) were formulated to contain different graded CHO:L ratio diets ranging from 0.12, 0.86, 1.71, 3.29 and 7.19. Each diet was assigned to triplicate groups of 18 experimental sh for 8 weeks. Our results revealed that nal body weight (FBW), weight gain rate (WGR), specic growth rate (SGR), protein eciency ratio (PER) increased with dietary CHO:L ratio from 0.12 to 1.71, and then decreased with further increases in dietary CHO:L ratio. A two-slope broken-line regression analysis based on WGR showed that the optimal dietary CHO: L level for maximum growth performance of sh was 1.60. Crude lipid and crude protein content in the liver and glycogen concentration in the muscle and liver were signicantly inuenced by the dietary CHO:L ratios (P < 0.05). The lowest crude lipid content in the liver was observed in sh fed the diet with a CHO:L ratio of 1.71(P < 0.05). Dietary CHO:L ratios signicantly induced the Glu contents of serum (P < 0.05). The relative expression levels of genes involved in lipid metabolism, such as srebp1 and fas in the liver showed a trend of rst decreased and then increased with the increase of dietary CHO:L ratios levels. Appropriate CHO:L ratio in the diet can effectively reduce the accumulation of liver fat. We observed in sh fed the 1.71 CHO:L ratio diet showed higher feed intake, up ‐ regulated mRNA expression of neuropeptide Y (NPY) and agouti gene-related protein (AGRP), down ‐ regulated mRNA expression of cocaine-and amphetamine-regulated transcript (CART) and pro ‐ opiomelanocorticoid (POMC) signicantly as compared to control group. Thus, these results provide the theoretical basis for feed formulation to determine the appropriate CHO:L ratio requirement of Chinese perch.


Introduction
Over the past three decades, the growth rate of global aquaculture production is signi cantly higher than that of shing, and it is the fastest growing industry in the global agricultural sector.Fish meal has become an important means to meet the demand for protein of aquatic animals and land animals.
However, the demand for human consumption of sh is also increasing, resulting in high costs and uctuations in shmeal supply(FAO 2018, Montoya-Camachoet al 2019).To address this issue, in addition to constantly seeking high-quality protein sources that can replace sh meal, researchers are also improving feed formulation to save protein and improve feed protein e ciency(Turchiniet al 2009).
Lipids and carbohydrates are one of the most important nutrients for organisms, and carbohydrates are a relatively inexpensive source of energy (Gaoet al 2018).Previous results demonstrate that appropriate lipid and carbohydrate levels in diets can provide energy to organisms and have the effect of saving protein(Hongyanet al 2019, Misraet al 2005, Sehrishet al 2020, Zhaoet al 2020).Lipids provide essential fatty acids for the growth and development of sh, are the main structure of cell membranes, and facilitate the transport and absorption of fat-soluble vitamins in the body(Xuet al 2020, Zhaokunet al 2020).Carbohydrates also have good adhesion and expandability, which can improve the stability of feed in water(Shi-Meiet al 2018).Excessive lipid will cause a series of problems such as physiological metabolic disorders, poor growth and fatty liver (Luet al 2014, Zhouet al 2020).Fish are also born with diabetes, especially carnivorous sh (Wilson 1994), Excessive carbohydrate level will lead to excessive metabolic burden, long-term hyperglycemia, excessive accumulation of liver glycogen, decreased immune function and other obstacles (Kamalamet al 2016, Shi-Meiet al 2018).In sh, glucose is closely related to lipid metabolism.Dihydroxyacetone phosphate produced in the process of glycolysis is then converted into glycerol needed for fat synthesis.Acetyl CoA generated from glucose oxidative decomposition is also a precursor for fatty acid synthesis, which can promote the generation of fat in the body (Liet al 2020).Dietary lipid can also be converted to glucose by gluconeogenesis.(Honoratoet al 2010).Fish appetite is co-regulated by the central system and the peripheral system, through the signal transduction between various appetite regulating factors (including appetite promoting factors and appetite suppressant factors), the "appetite regulating network" of sh is formed(Het al 2005, Yokoboriet al 2012).Food intake is closely related to appetite, and there is evidence in humans, other mammals and sh that the intake of The Chinese perch, which is mainly distributed in China, Russia, Korea, Vietnam and other regions, is one of the unique freshwater aquaculture sh with great economic value in China (Liuet al 2020a).It is a typical carnivorous sh with erce feeding habits.It hunts live prey sh from its mouth-opening and could stably accept arti cial compound feed after domestication (Lianget al 2010, Lianget al 2001).Currently, the protein content in the commercial feed of Chinese perch is extremely high, so changing the CHO:L ratios in the diet to improve the utilization rate of protein of Chinese perch, reduce the content of sh meal, and thus reduce the feed cost is of great signi cance for intensive farming.In fact, there are relatively few studies on nutritional requirements of Chinese perch.This study aims to explore the effects of different dietary CHO:L ratios on growth performance, body composition, liver lipid metabolism, liver histomorphology and appetite of Chinese perch.The results of this study may provide a basis for the development of high e ciency compound feed in the future.

Materials And Methods
All animal care and experimental procedures in the present study were approved by Huazhong Agricultural University and conducted in accordance with the Guidelines for Experimental Animals (Ethical code: HZAUFI-2020-0004).

Experimental diets
The formulation and proximate composition of the experimental diets are provided in Table 1.Five isonitrogenous and isoenergetic experimental diets were formulated to contain different levels of CHO:L ratio (0.12, 0.86, 1.71, 3.29 and 7.19).Experimental diets were compounded with sh meal and casein as main protein sources, sh oil and soybean oil as main lipid sources, and dextrin as a carbohydrate source.All dry ingredients were thoroughly mixed in a mixer before the addition of oil and 40 % water.Then, the mixture was then pelleted (4 mm diameter) by a laboratory pelleting machine (HR 2330 model, PHILIPS, Suzhou, China).The soft pellets were placed in hermetic bags were stored in a freezer at − 20°C until used.The experiment was conducted in an indoor aquarium system at the Chinese Perch Research Center, Huazhong Agricultural University, Wuhan, China.About 500 Chinese perch were purchased from Wuhongshan Breeding Base (Chibi, China).Before the feeding experiment, Chinese perch were trained to accept the arti cial diet according to the method of Liang et al. (2001).After acclimatization, 270 sh (mean initial weight: 12.86 ± 0.10 g) with uniform size, accepts arti cial diet well and health were randomly assigned to 15 tanks with 18 sh per tank.Fish were hand-fed twice (08:00 and 19:00) fed till satiation daily.The amount of feed being consumed by sh in each tank was recorded daily.Uneaten feed was collected by siphoning after 15-min feeding and then oven-dried at 60 •C to calculate feed intake.During the feeding period, the water temperature, pH, and dissolved oxygen (DO) level were 19 − 23 •C, 7.1-7.5, and > 5 mg/L, respectively.Ordinary photoperiod applied throughout the experiment.

Sample collection and analysis
After 8 weeks of feeding trial, all sh were starved for 24 h, and then counted individually and weighed.Six sh were randomly selected from each replicate were anaesthetized with 3-aminobenzoic acid ethyl ester methane sulphonate (MS-222, 50 mg/L water).The blood was obtained from caudal vein of sh by syringe using a 1-mL syringe and pooled into a sterile centrifuge tube to clot overnight at 4 •C, then centrifuged at 4000×g at 4 •C for 20 min to separate the serum and stored at − 80°C until used for analysis.Then these sh were dissected on ice to obtain brain, muscle, liver, intestine, mesentery and visceral adipose, quickly frozen in liquid nitrogen and cryopreserved at − 80 •C for subsequent analysis.
Liver tissues from three shes from each group were collected and immediately xed by 4 % paraformaldehyde for histological evaluation.Another 3 sh were randomly chosen from each tank for whole-body composition.
The data were analysed for Weight Gain Rate (WGR), Speci c Growth Rates (SGR), Hepatosomatic index (HSI), Viscera index (VSI), Mesentery fat index (MFI), Survival Ratio (SR), Feed intake (FI) and Food Conversion Ratio (FCR) using the following formula: Food intake (FI, g sh − 1 days − 1 ) = total amount of the feed consumed /number of sh/days Feed conversion ratio (FCR, %) = amount of feed given /weight gain Crude protein, crude lipid, ash and moisture of diets, whole body, muscle, and liver were measured according to standard Association of O cial Agricultural Chemists methods (International and Technology 1995).Crude protein content was determined by measuring nitrogen (N × 6.25) levels using the Kjeldahl method following acid digestion with an auto Kjeldahl System (Kjel ex K-360; BUCHI Labortechnik AG, Flawil, Switzerland).Moisture content was measured by freeze-drying samples for 48 h in a vacuum freeze dryer (Christ Beta 2-4 LD plus LT, Marin Christ Corporation, Osterode, Germany).Ash level was examined through incineration at 550 •C for 24 h in a mu e furnace.
Total RNA was extracted by RNAiso Plus reagent (Takara, Dalian, China) manually, and the purity and quantity of RNA were determined by agarose gel electrophoresis, protein, and nucleic acid analyser.Then 1 µg of total RNA was used for reverse transcription with HiScript® II Reverse Transcriptase (Code no.R301-01/02; Vazyme, China) in a 20 µL reaction volume to synthesize cDNA.Speci c primers for the candidate genes used for qPCR were designed based on previous published research paper of our laboratory (Table 2).Rpl13a gene was used as an endogenous reference to normalize the template amount.The total volume of the qRT-PCR reaction system was 20 µl, including 10 µl of SYBR Green dye (Code no.Q311-02; Vazyme, China), 0.4 µl of PCR forward/re-verse primers (10 µM), 1 µl of cDNA template and 8.2 µl RNase-free H 2 O.The qRT-PCR ampli cation programme was 95°C for 1 min, followed by 40 cycles consisting of 95°C for 10 s and 57°C for 30 s and a melt curve step (from 95°C, gradually reducing 0.5°C/s to 57°C, with data acquisition every 6 s).The ampli cation e ciencies of control and target genes were approximately equal and ranged from 96.3-104.9%.Gene expression levels were quanti ed relative to the expression of rpl13a using the optimized comparative Ct (2-ΔΔCt) value method.All ampli cations were performed in triplicate for each RNA sample.

Growth performance and feed utilization
As show in Table 3, SR did not show signi cant difference among sh fed the different dietary treatments(P>0.05).Fish fed D3 had the highest FBW, WGR and SGR (P < 0.05).PER in sh fed D3 was signi cantly higher than that in sh fed other diet (P < 0.05).FI was signi cantly affected by the dietary CHO:L ratios (P < 0.05), sh fed D3 was signi cantly higher than D1, D2, D4 groups.HSI and VSI in the D1 was signi cantly higher than that in the other groups (P < 0.05).The IPR of D4, D5 groups were signi cantly higher than that of D1, D2, D3 groups (P < 0.05).FCR exhibited an opposite trend as observed in WGR, with the lowest level in sh fed D3 group (P < 0.05).Values are presented as the means ± SEM (n = 6).Values within a column followed by different superscript letters differ signi cantly (P < 0.05).
Based on broken-line regression analysis of WGR, the dietary CHO:L ratios for optimum growth of Chinese perch was 1.60, corresponding to 15.38% of nitrogen-free extract and 8.97% of crude lipid respectively, belongs to the D3 group (Fig. 1).

Proximate composition and glycogen content in tissues
Effects of dietary CHO:L ratios on whole body, proximate composition and glycogen content of Chinese perch are listed in Table 4.The lipid content of whole body trended downward as dietary CHO:L ratios increased.There were no signi cant differences in moisture, crude protein and crude lipid contents of the muscle among all treatments (P > 0.05).Dietary CHO:L ratios signi cantly affected the contents of crude protein and lipid in liver of Chinese perch (P < 0.05).Fish fed D3 had lower crude lipid content in liver than other groups, and signi cantly lower than D1 and D4 groups (P < 0.05).Values are presented as the means ± SEM (n = 6).Values within a column followed by different superscript letters differ signi cantly (P < 0.05).
The muscle glycogen and liver glycogen had an increase trend with the increasing CHO:L ratios level.The highest muscle glycogen content was observed in D5 group, and signi cantly higher than D1, D2 and D3 groups.There was no signi cant difference in liver glycogen content among D3, D4 and D5 groups (P > 0.05).

Serum biochemical indices
Dietary CHO:L ratios signi cantly induced the contents of GLU (Table 5).TP and ALB were signi cantly in uenced by dietary CHO:L ratios, and it were the lowest in D3 among all groups, and was signi cantly lower than that in D1, D2 and D4 (P < 0.05).The highest concentration of TCHO and TG were found in sh fed a diet with the lowest CHO:L ratio.The activities of AST and ALT both increased with dietary CHO:L ratios, showing a trend of rst decreased and then increased, and reached the lowest in D3 group (P < 0.05).As dietary CHO:L ratio increased, serum HDLC content was signi cantly decreased (P < 0.05).On the contrary, LDLC was not signi cantly in uenced by dietary CHO:L ratio (P>0.05).Values are presented as the means ± SEM (n = 6).Values within a column followed by different superscript letters differ signi cantly (P < 0.05

Relative expression of lipid metabolism-related genes in liver
The expressions of lipid metabolism-related genes in Chinese perch fed different dietary CHO:L ratios levels are presented in Fig. 2. The expression of srebp1 and fas in the liver showed a trend of rst decreased and then increased with the increase of dietary CHO:L ratios.And the expressions of srebp1 and fas in the liver were the lowest in the D3 group, which was signi cantly lower than the other groups (P < 0.05).Compared with the D1 group, the expression of accα in the liver of the other groups was signi cantly reduced, and there was no signi cant difference (P>0.05).The expression level of cpt-1 in the liver of D3 and D5 group was signi cantly higher than that of D1 group (P < 0.05) (Fig. 3).

Relative expression of appetite-related genes in hypothalamus
Concerning appetite regulation-related genes are presented in Fig. 4 and Fig. 5. Compared with the D1 group, the expression of npy in the D2 and D3 groups was signi cantly increased (P < 0.05).The expression of agrp increased with the increase in the level of dietary CHO:L ratios, showing a trend of rst increased and then decreased.The expression levels of npy and agrp were the highest in the D3 group and were signi cantly higher than the other groups (P < 0.05).With the increase of dietary CHO:L ratios, the expression of cart decreased signi cantly compared with the D1 group (P < 0.05).The expression of pomc in the D2 and D3 groups were signi cantly lower than the other groups (P < 0.05).

Histology analyses of liver section and determination of hepatocyte in ammation
Figure 6 shows the oil red O staining and H&E staining of Chinese perch liver tissue fed with different levels of dietary CHO:L ratios diet.The Oil-red O staining con rmed that the number of red dots (lipid droplets) has exhibited no obvious difference among D2 and D4 group, but it increased sharply in D1 and D5 group.The D3 group had the least number of lipid droplets (Fig. 6A).H&E staining con rmed that except for the D3 group, the liver cells of the other treatment groups showed more different numbers of small vacuoles, and the hepatocyte nuclei were squeezed to the edge (Fig. 6B).This means that the liver cells have different degrees of pathological reactions.

Discussion
In the present study, we provided direct evidence that dietary CHO:L ratio of 1.71 advanced the growth performance of Chinese perch.At this point, the WGR, SGR and PER of the Chinese perch reach the maximum.When the dietary CHO:L ratio was 0.12, the WGR, SGR and PER were all lower than those of the other groups.This indicates that a relatively low-or high-CHO:L ratio diet not only depressed Chinese perch growth but also caused their poor feed utilization.Protein utilization e ciency can be improved by adjusting the ratio of carbohydrates to lipids in the feed.(Jobling 2012).Similar results were found in other carnivorous sh.Appropriate CHO:L ratio was helpful for sh to exert synergistic effect in the utilization of carbohydrate and lipid, improve the utilization rate of feed, and thus promote growth.Such as large yellow croaker (Larimichthys crocea) (Zhouet al 2016), juvenile hybrid grouper (epinephelus fuscoguttatus × Epinephelus lanceolatus )(Gaoet al 2018), juvenile cobia (Rachycentron canadum) (Zhaoet al 2020) and juvenile black seabream(Acanthopagrus schlegelii) (Sehrishet al 2020).0.12 CHO:L group showed poor growth, indicating that high-lipid/low-carbohydrate group was not conducive to its growth, and its VSI and HSI were higher than those in other groups, indicating that higher dietary lipid level would affect lipid deposition in viscera and liver.(Zhouet al 2020).Polyline regression analysis based on WGR revealed that the dietary CHO: L requirements of Chinese perch could be satis ed if the CHO:L ratio reached 1.60.Growth, feed e ciency and protein utilization ratio suggest that carbohydrates are a better digestible energy source for Chinese perch compared with lipids and can save protein.
Although the carbohydrate utilization capacity of carnivorous sh is weak, however, the carbohydrate utilization level of sh is a result of interactions with the physical state of dietary starch, molecular complexity, glucose tolerance, environment, temperature, and other nutrient elements in the feed (Braugeet al 1995, Hemreet al 2015, Liet al 2019b).
In this study, dietary CHO:L ratio had no signi cant effect on muscle composition but had signi cant effect on crude lipid content of whole sh and liver.The lipid content of whole sh generally decreases and the lipid content of liver a decreasing trend rst and then increasing trend in response to increasing dietary CHO: L ratio in feed.It indicates that the crude lipid content of whole body is positively correlated with the dietary lipid level, and excessive lipid will be deposited in sh body.However, sh have a poor ability to utilize carbohydrate.When the high-carbohydrate/low-lipid, sh may decompose part of the body lipid for energy supply, such as the lipid in muscle.Similar results were found in large yellow croaker (Larimichthys crocea)(Liet al 2019c) and golden pompano (Trachinotus ovatus)(Donget al 2018).In the liver, both high lipid levels and high carbohydrate levels contribute to fat deposition.These results were similar to those previously reported in largemouth bass (Micropterus salmoides) (Zhouet al 2020) and blunt snout bream (Megalobrama amblycephala) (Wanget al 2017).
The blood index parameters could indicate the physiological and health status of sh and could change dynamically with the nutritional status of sh (Fazio 2019).In this study, TG, TCHO, and HDLC in serum were signi cantly decreased with the increase of CHO: L ratio in the diet, indicating that endogenous lipid transport in sh was also more active under the high lipid diet.Metabolites rich in TG and CHO in liver were transported to other abdominal organs along with blood circulation, resulting in the increase of VSI.
The serum Glu content was signi cantly increased with the dietary CHO: L ratio increasing.Liver glycogen signi cantly increased in the dietary CHO: L of 0.12 to 1.71 and then leveled off.The results show that the Chinese perch could use a certain level of carbohydrate(<15.38%) in feed and store it in liver in the form of liver glycogen.However, the Chinese perch still cannot make good use of carbohydrate.When the dietary carbohydrate level is higher than Feed is the main cost in aquaculture, so the feed intake is considerable important to the aquaculture of economic sh, and the feed intake is controlled by the central and peripheral appetite network system(Liet al 2019a, Marta and L. 2017).In previous studies, sh's appetite was in uenced by the nutritional content of the feed and the proportion of different ingredients added.By Catarina Basto-Silva studies have shown that different dietary protein to energy ratio affects the feeding intake and appetite regulation of gilthead seabream(Sparus aurata)(Catarinaet al 2021).The central system, especially the hypothalamus, can sense the nutritional state of the body, regulate food intake and metabolism through different neural circuits, and maintain the energy homeostasis of the body(Clémence and J 2010).These circuits mainly include npy/agrp, pomc/cart neurons, and central and peripheral endocrine factors that respond to circulating glucose, fatty acid, or amino acid levels, respectively(Blouet and Schwartz 2009, Efeyanet al 2015, Mobbset al 2005).In previous studies based on Chinese perch in our laboratory, central nervous system npy/ agrp was generally used as an appetite promoting factor, while pomc/cart was used as an appetite suppressant factor (Liuet al 2020b).In this study, with the increase of dietary CHO:L ratio, the food intake of Chinese perch in D3 group was signi cantly higher than that in other treatment groups.
The expression of npy/agrp neurons in the hypothalamus of Chinese perch was rstly increased and then decreased in response to increasing CHO:L ratio in feed.However, the expression level of inhibitory appetite factor cart in D1 group was signi cantly higher than that in other treatment groups, and the expression level of pomc in D2 and D3 groups was signi cantly downregulated.These results indicated that high lipid or high carbohydrate diet could inhibit the expression of appetite promoting genes npy and agrp to some extent and promote the expression of appetite suppressing genes cart and pomc.High lipid diets also decrease food intake of sh(Yong-Junet al 2018).Therefore, appropriate CHO:L ratio feed can promote appetite, which has a positive effect on increasing food intake to avoid anorexia in the process of breeding.

Conclusion
In conclusion, through broken line regression analysis, the optimal carbohydrate-to-lipid ratio in the diet of Chinese perch is recommended to be 1.71.The ratio of sugar to lipid in the diet affected the growth and feeding of Chinese perch, the antioxidant indexes in serum and the accumulation of glycogen in body.In addition, the appropriate carbohydrate-to-lipid ratio in the diet up-regulated or down-regulated the expression of lipid metabolism genes in the liver and reduced the lipid deposition in the liver.Appropriate CHO:L ratio affects the transcription level of hypothalamus appetite gene, thus increasing food intake.
The results of this study can provide an important reference for the optimization of compound feed for Chinese perch.

Declarations Figures
Page 21/ a high-fat diet can suppress appetite and reduce sensitivity to the present food (bet al 2017, Liet al 2016, Ortinauet al 2014, Rasmussenet al 2015).In bony sh, fed high carbohydrate diet or injecting glucose intraperitoneally caused rainbow trout (Oncorhynchus mykiss) (Figueiredo-Silvaet al 2013), sea bass (Dicentrarchus labrax) (Castroet al 2015b), and Japanese ounder (Paralichthys olivaceus) (Liuet al 2018) decreased appetite and food intake.In recent years, researchers have made a high number of studies on the effects of dietary CHO:L ratio on growth performance, feed utilization and antioxidant capacity of sh (Gaoet al 2010, Liet al 2012b, Zhouet al 2016).Nevertheless, there are few studies on the effects of different dietary CHO:L ratios on lipid metabolism and appetite of sh.

Figure 1 Broken
Figure 1

Figure 3 The
Figure 3

Figure 4 The
Figure 4

Figure 5 The
Figure 5

Table 1
Formulation and proximate chemical compositions of the tested diets.

Table 2
Primer sequences for the quantitative real-time PCR.

Table 3
Growth parameters of Chinese perch fed the experimental diets.

Table 4
The body composition of whole sh and muscle of Chinese perch fed the experimental diets.

Table 5
Serum biochemical indexes of Chinese perch fed the experimental diets.
(Ferré ande serum Glu content increases continuously, leading to hyperglycemia and partial glycogen storage in the muscle.Similar results have been observed in some carnivorous sh(Mingchunet al 2011, Zhouet al 2016).Serum total protein content is a major indicator of physiological health of sh (Alexanderet al 2011).The albumin and globulin contained in it are generally considered to play an important role in the innate immune response of sh (Liet al 2012a, Wiegertjeset al 1996).ALT and AST are considered sensitive indicators of normal tissue function and are often used to determine whether the liver has been damaged(Xinget al 2020).In this study, when dietary CHO:L ratio was 1.71, TP, ALB, ALT and AST were signi cantly lower than those in other groups.These results indicate that high dietary fat or carbohydrate levels will affect the health of the sh, increase the burden on the liver, and thus activate the non-speci c immunity of the sh.In some previous studies, such as European sea bass (Dicentrarchus labrax L.) (SitjÀ-Bobadilla and PÉRez-SÁNchez 1999), blunt snout bream(Megalobrama amblycephala) (Zhouet al 2013) have been reported.Lipid deposition in the liver is a comprehensive result of lipid uptake, transport, decomposition, and synthesis in hepatocytes(Cet al 2012, Xinget al 2020).srebp-1 is a transcription factor that can activate target genes of its downstream fatty acid synthesis(Kuiperset al 2011).fasandaccαare important enzymes in fat synthesis, which are involved in the synthesis of fatty acids (Castroet al 2016).In this study, srebp-1 and fas showed a trend of decreasing rst and then increasing with the increase of dietary CHO:L ratio, indicating that fatty acid synthesis in liver was more active in the diet of high-lipid/lowcarbohydrate or high-carbohydrate/low-lipid.In addition, the increase of dietary carbohydrate level may also be the reason for the increase of liver srebp-1, which can also mediate the conversion of excess carbohydrates to fatty acids(Ferré and Foufelle 2010, Miriamet al 2008), fatty acids enter the liver and are esteri ed into triglycerides, which are stored in lipid droplets on the one hand and enter liver cells, On the other hand, as TG-rich metabolites, they are secreted into blood for circulation(Yuanet al 2016).However, serum TCHO, TG and LDLC levels did not increase in the high-carbohydrate/low-lipid group (D4 and D5), indicating that fatty acids may mainly exist in liver lipid droplets, which may cause harm to the health of sh.And cpt-1 is the key gene of fatty acid β oxidation.The cpt-1 in liver of Chinese perch was signi cantly up-regulated when the dietary CHO:L ratio is 1.71, indicating that the β-oxidation of fatty acids is more active under this nutritional state.At this time, liver fat was signi cantly lower than that of the other groups, indicating that liver of Chinese perch can effectively alleviate liver fat accumulation by reducing fatty acid synthesis and increasing fatty acid β oxidation when feeding appropriate CHO:L ratio diet.