Effects Of Dietary Lipid Levels Research Articles

Effects of Dietary Lipid Levels on the Growth, Muscle Fatty Acid and Amino Acid Composition, Antioxidant Capacity, and Lipid Deposition in Mirror Carp (Cyprinus carpio).

In fish, increasing the crude lipid level of feed can save protein and improve feed utilization. Mirror carp (Cyprinus carpio) is one of the most widely farmed fish species in the world. In this study, mirror carp larvae were fed isonitrogenous diets with different lipid levels (3%, 5%, 7%, 9%, 11%, and 13%). The rearing trial lasted for eight weeks. The results revealed that when the fat content was 9%, the AWGR, WGR, and FCR were highest, whereas FCR was lowest. The AWGR was correlated with the dietary lipid level, and the regression equation was y = -2.312x2 + 45.01x + 214.49. Compared with those in the control group, the T-CHO and TG contents were significantly greater in the 13% lipid content groups and significantly lower in the 9% lipid content groups (p < 0.05). In terms of muscle quality, the contents of MUFAs, PUFAs, and DHA + EPA were significantly greater than those in the other experimental groups (p < 0.05). Oil red O staining revealed a lipid content of 13% with severe fat deposition. In addition, the results of the analysis of antioxidant enzyme activity revealed that the activities of GSH, CAT and T-AOC were significantly greater at the 9% lipid content, and that the MDA content was significantly greater at the 13% lipid content (p < 0.05). Similarly, the mRNA levels of GH, IGF-I, FAS, and LPL were significantly highest at a lipid level of 9% (p < 0.05). The above results revealed that the optimal dietary lipid requirement for the fast growth of mirror carp (6.86 ± 0.95 g) was 9.74% on the basis of nonlinear regression analysis of the AWGR. The dietary lipid level (9%) improved the growth, stress resistance, and lipid utilization of mirror carp to a certain extent.

Effects of dietary lipid levels on growth, lipid metabolism, fatty acid composition and antioxidant capacity of juvenile greasyback shrimp (Metapenaeus ensis)

The optimal dietary lipid requirement and underlying lipid metabolic mechanisms remain elusive in greasyback shrimp (Metapenaeus ensis), presenting significant obstacles to the advancement of their culture development. Five isonitrogenous diets (38.39% crude protein) containing lipid levels of 2.25%, 4.72%, 7.50%, 10.18%, and 12.71% were formulated to evaluate the effects of dietary lipid levels on growth, lipid metabolism, fatty acid composition and antioxidant capacity of juvenile greasyback shrimp. The results indicated that shrimps fed a diet with 7.50% lipid exhibited significantly higher percent weight gain (161.36%) and specific growth rate (1.72%/d) than those fed other diets (P < 0.05). As the dietary fat content increased, the lipid levels of the whole shrimp, muscle, hepatopancreas, and serum exhibited similar elevations. Concurrently, H&E staining clearly revealed the occurrence of hepatocyte swelling and hepatocyte vacuolization in the 10.18% and 12.71% groups, and hepatic lipid accumulation was further observed in these groups by Oil red O staining. In addition, with the increase in dietary fat levels, saturated fatty acids (SFA) decreased and polyunsaturated fatty acids (PUFA) increased in both hepatopancreas and muscle. The expression of genes involved in lipogenesis (fas, acc and dgat) was initially up-regulated and subsequently down-regulated with increasing dietary lipid levels, whereas the expression trends of lipolysis genes (hsl, atgl) remained similar. The mRNA levels of genes associated with long-chain PUFA biosynthesis (elovl5, lxrβ, srebp1) and fatty acid oxidation (cpt1, acox1) in the hepatopancreas of shrimp fed a diet with 7.50% lipid were significantly elevated compared to those in other dietary groups (P < 0.05). With the increase in dietary fat levels, the expression of fatty acid transport genes fatp4 and fabp1 was up-regulated. Antioxidant enzyme activities in the hepatopancreas initially increased with dietary lipid levels, peaking in shrimp fed the 7.50% lipid diet, but subsequently declined. In conclusion, optimal dietary fat levels enhance growth performance, while high lipid levels impede growth, decrease antioxidant enzyme activities, and regulate lipid deposition in greasyback shrimp by modulating lipid metabolic pathways.

Epigenetic changes in pyloric caeca of Atlantic salmon fed diets containing increasing levels of lipids and choline

ABSTRACT An earlier study of ours investigating the effect of dietary lipid levels on the choline requirement of Atlantic salmon showed increasing severity of intestinal steatosis with increasing lipid levels. As choline is involved in epigenetic regulation by being the key methyl donor, pyloric caeca samples from the study were analysed for epigenetic effects of dietary lipid and choline levels. The diets varied in lipid levels between 16% and 28%, and choline levels between 1.9 and 2.3 g/kg. The diets were fed for 8 weeks to Atlantic salmon of 25 g of initial weight. Using reduced representation bisulfite sequencing (RRBS), this study revealed that increasing dietary lipid levels induced methylation differences in genes involved in membrane transport and signalling pathways, and in microRNAs important for the regulation of lipid homoeostasis. Increasing choline levels also affected genes involved in fatty acid biosynthesis and transport, lipolysis, and lipogenesis, as well as important immune genes. Our observations confirmed that choline is involved in epigenetic regulation in Atlantic salmon, as has been reported for higher vertebrates. This study showed the need for the inclusion of biomarkers of epigenetic processes in studies that must be conducted to define optimal choline levels in diets for Atlantic salmon.

Evaluation of the effects of diets containing different lipid levels for juvenile yellowfin seabream Acanthopagrus latus

This study evaluated the effect of dietary lipid levels on growth, body composition, amino acid and fatty acid profile, and nutrient utilization of juvenile yellowfin seabream (Acanthopagrus latus). Six diets with different crude lipid levels at 7% (CL7), 9% (CL9), 11% (CL11), 13% (CL13), 15% (CL15), and 17% (CL17) were designed, and each diet was fed to 4 cages (50 fish per cage; 19.00 ± 0.01 g per fish) for sixteen weeks. Results indicated that weight gain (WG) and specific growth rate (SGR) were highest at 13% dietary lipid level, while feed conversion ratio (FCR) was lowest (P < 0.05). Intraperitoneal fat ratio (IPF) increased with increasing dietary lipid level from 7% to 17%. The lipid efficiency ratio (LER), lipid retention (LR), and nitrogen excretion (NE) decreased significantly with increasing dietary lipid level (P < 0.05). Crude protein and lipid of the whole body decreased or increased with increasing dietary lipid level, respectively (P < 0.05). The dorsal muscle and liver lipid content significantly increased with increasing dietary lipid (P < 0.05). With the dietary lipid increasing, total fatty acid content was significantly increased (P < 0.05). Results about the fatty acid profile of the whole body indicated that the proportions of C14:0, C16:1, C20:4, C20:5, and C20:6 were significantly decreased with increased dietary lipid level (P < 0.05). In contrast, the proportions of C18:0, C18:1, and C22:1 were increased with increased dietary lipid level (P < 0.05). The retention of fatty acids was decreased with increasing dietary lipid (P < 0.05). Form a nutritional, environmental, and economic point of view, 13% dietary crude lipid was recommended. Excess dietary lipid levels in diets negatively affect the structure of the liver, leading to lipid accumulation and inflammation development.

Effects of dietary lipid levels on fiber quality, lipidomic profiles, antioxidant and inflammation responses in muscle of yellow catfish Pelteobagrus fulvidraco

The present study explore the impacts of dietary lipid levels on fiber quality, lipidomic profiles, antioxidant and inflammation responses in muscle of yellow catfish. For this purpose, yellow catfish were fed with low-fat (LF), medium-fat (MF) and high-fat (HF) three different lipid levels diets for 8 weeks, and at the end of the feeding trial, muscle tissues were taken for analysis. We found that HF diet increased lipid deposition, lipogenesis and decreased fatty acid oxidation in muscle of yellow catfish. HF diet induced oxidative stress and inflammatory response in muscle therefore suppressed the proliferation and differentiation of myofibril. Lipidomic analysis detected 229 differentially abundant lipids (DALs) among three groups, and PCs, TGs/DGs and PEs as the predominant lipid species. Moreover, HF diet significantly decreased the abundance of SHP, LPE, PC, PE, PI, PG and PS species. Overall, these findings revealed that dietary lipid levels influence lipid metabolism and muscle quality by affecting lipid profile and oxidative stress status in muscle of yellow catfish, which provided novel insight into the lipid nutrition of freshwater fish.

Dietary lipid levels affect growth performance, lipid metabolism, antioxidant and immune status of Amur sturgeon, Acipenser schrenckii

The proper lipid content in the diets is crucial for fish growth and health. However, the appropriate lipid requirement of Amur sturgeon has not been systematically studied. This study was aimed to explore the effects of dietary lipid levels on growth performance, lipid metabolism, antioxidant and immune status of juvenile Amur sturgeon (Acipenser schrenckii). Six isonitrogenous diets containing 5.11% (L5), 8.87% (L9), 12.96% (L13), 16.93% (L17), 20.84% (L21) and 24.88% (L25) lipid were fed to Amur sturgeon (4.16 ± 0.07 g) for 10 weeks. The fish in L21 group had the highest growth, feed utilization and survival rate. Based on the broken-line regression analysis of WGR, the lipid requirement for juvenile Amur sturgeon was 20.31%. HSI, hepatic crude lipid content and serum TG, TC and LDL-C contents elevated significantly with the increase of dietary lipid. Higher hepatic SOD, Anti-O2.- were found in L21 group, while MDA in both serum and liver maintained an upward trend with dietary lipid increase. The expression levels of fasn and lpl were suppressed when dietary lipid levels reached or exceeded 16.93%. While cpt1α and pparα were up-regulated, and peaked in L21 group, but down-regulated in L25 group. The expression level of il1β was on the rise as dietary lipid increased, but il10 and tgfβ1 showed a downward trend in high lipid groups. In conclusion, based on WGR, a lipid level of 20.31% in the diet was optimal for juvenile Amur sturgeon. Low (5.11%−12.96%) or high lipid (24.88%) diet decreased growth, feed utilization and survival rate. High lipid (24.88%) diet induced excessive lipid deposition, leading to intense oxidative stress, lipid metabolism disorder and inflammation.

Effects of dietary lipid levels on lipid accumulation and health status of adult Onychostomamacrolepis

The effects of different dietary lipid levels on lipid accumulation, inflammatory response, serum bio-chemical index and histological features of intestine and hepatopancreas of O.macrolepis was experimentally evaluated in an eight-weeks study. Fish (initial weight 50.11 ± 2.86 g) were fed with five iso-nitrogenous diets (around 390 g/kg protein) varying with lipid level (5%, 7%, 9%, 11%, 13%, being LL5, LL7, LL9, LL11, and LL13 respectively) in triplicates. Results showed that the content of crude lipid in carcass and hepatopancreas were not affected by dietary lipid levels (P > 0.05). Serum ALT, TP, HDL-c and MDA, etc., were not significantly affected by diets (P > 0.05), while serum total antioxidant capacity in LL9 and LL11 groups were significantly higher than the other groups (P < 0.05). Histological features of hepatopancreas and intestine showed no significant difference among the five diets (P > 0.05), while the height of intestine villus showed the higher trend in LL9 compared with other groups. The relative expression of lipid metabolism related genes (ppar α, cpt-1α, fas, and hsl) and immune response related genes (tlr 22, nrf 2, tnfα, and il-γ) in the hepatopancreas of fish fed diets differing in their crude lipid levels were not significantly different (P > 0.05). The results suggested that a proper dietary lipid level of 9%–11% could maintain higher antioxidant and health status of adult O.macrolepis.

Effects of dietary lipid level on growth, digestive physiology and disease resistance in lumpfish (Cyclopterus lumpus)

Effects of dietary lipid level on growth, digestive physiology and disease resistance in lumpfish (Cyclopterus lumpus)

Differential regulatory effects of dietary lipid level on growth, antioxidant capacity and expression of genes involved in lipid and glucose metabolism of juvenile mud crab Scylla paramamosain

Three isonitrogenous diets (41% crude protein) with 4.87%, 10.75% and 16.10% lipid were designed to evaluate the effects of dietary lipid levels growth, antioxidant capacity, expression levels of genes related to lipid and glucose metabolism of juvenile Scylla paramamosain. Each diet was fed to four replicates of 32 crabs with initial weight 5.10 ± 0.05 g for 6 weeks. The results indicated that crabs fed diet with 10.75% lipid exhibited significantly higher percent weight gain (PWG) and specific growth rate (SGR) than those fed diet with 4.87% lipid (P < 0.05), and crabs fed diets with 10.75% and 16.10% lipid had significantly higher protein efficiency ratio (PER) and feed efficiency (FE) than those fed diet with 4.87% lipid (P < 0.05). Crabs fed diet with 4.87% lipid had the lowest concentrations of lipid and glycogen in muscle, lipid content in hepatopancreas and hemolymph glucose among all treatments (P < 0.05). The concentrations of free fatty acid (FFA), triglyceride (TG), total cholesterol (TCHO) and pyruvate in hemolymph and hepatopancreas increased significantly with the dietary lipid levels increasing from 4.87% to 16.10% (P < 0.05), while the concentration of crustacean insulin-like (INS) in hemolymph and crustacean hyperglycemic hormone (CHH) in hepatopancreas significantly decreased with the increase of dietary lipid levels (P < 0.05). In the hepatopancreas, The Oil Red-positive area significantly increased with increase of dietary lipid levels (P < 0.05). Crabs fed diet with 16.10% lipid showed the lowest concentration of glutathione peroxidase (GSH-Px) (P < 0.05). On the contrary, the highest concentration of malondialdehyde (MDA) was observed at crabs fed diet with 16.10% lipid (P < 0.05). Crabs fed diets with 10.75% and 16.10% lipid down-regulated expression of genes related to long-chain-PUFA biosynthesis and lipid synthesis in hepatopancreas than those fed diet with 4.87% lipid (P < 0.05). The mRNA level of cpt1 significantly up-regulated with the increase of dietary lipid levels, while the mRNA expression level cpt2, acox1 and fabp4 in hepatopancreas significantly down-regulated in crabs fed diets with 10.75% and 16.10% lipid (P < 0.05). The expression of gk and pfk in crabs fed diet with 16.10% lipid significantly down-regulated than those in other groups (P < 0.05). The expressions level of genes related to gluconeogenesis significantly down-regulated in crabs fed diets with 10.75% and 16.10% lipid (P < 0.05). The lowest mRNA expression of glucose transporter 4 (glut4) was occurred in crabs fed diet with 16.10% lipid (P < 0.05). Overall, the results of present study demonstrated that the dietary 10.75% lipid can improve the growth and feed utilization for juvenile mud crab, in addition, dietary lipid can affect the antioxidant capacity, lipid metabolism, glucose metabolism and insulin signaling pathway, dietary excessive lipid resulted in lipid deposition of hepatopancreas for juvenile mud crab.

Effects of dietary lipid level and environmental temperature on lipid metabolism in the intestine and liver, and choline requirement in Atlantic salmon (Salmo salar L) parr.

Choline was recently established as an essential nutrient for Atlantic salmon at all life stages. Choline deficiency is manifested as an excessive accumulation of dietary fat within the intestinal enterocytes, a condition known as steatosis. Most of today's plant-based salmon feeds will be choline-deficient unless choline is supplemented. Choline's role in lipid transport suggests that choline requirement may depend on factors such as dietary lipid level and environmental temperature. The present study was therefore conducted to investigate whether lipid level and water temperature can affect steatosis symptoms, and thereby choline requirement in Atlantic salmon. Four choline-deficient plant-based diets were formulated differing in lipid level of 16, 20, 25 and 28 % and fed to salmon of 25 g initial weight in duplicate tanks per diet at two different environmental temperatures: 8 and 15 °C. After 8 weeks of feeding, samples of blood, tissue and gut content from six fish per tank were collected, for analyses of histomorphological, biochemical and molecular biomarkers of steatosis and choline requirement. Increasing lipid level did not affect growth rate but increased relative weight and lipid content of the pyloric caeca and histological symptoms of intestinal steatosis and decreased fish yield. Elevation of the water temperature from 8 to 15 °C, increased growth rate, relative weight of the pyloric caeca, and the histological symptoms of steatosis seemed to become more severe. We conclude that dietary lipid level, as well as environmental temperature, affect choline requirement to a magnitude of importance for fish biology and health, and for fish yield.

Does Dietary Lipid Level Affect the Quality of Triploid Rainbow Trout and How Should It Be Assessed?

Organoleptic properties and nutritional value are the most important characteristics of fish fillet quality, which can be determined by a series of quality evaluation indexes and closely related to fish nutrition. Systematic organoleptic and nutritional quality evaluation indexes consisting of 139 indexes for physical properties and chemical compositions of triploid rainbow trout were established. Besides, effects of dietary lipid levels (6.6%, 14.8%, 22.8% and 29.4%) on the quality of triploid rainbow trout were analyzed in the study. The main results showed that, for fillet appearance quality, fish fed diets with lipid levels above 22.8% had higher fillet thickness and redness but lower gutted yield and fillet yield (p &lt; 0.05). For fillet texture, fish fed the diet with a 6.6% lipid level had the highest fillet hardness (5.59 N) and lowest adhesiveness (1.98 mJ) (p &lt; 0.05), which could be related to lipid, glycogen, water soluble protein and collagen contents of the fish fillet. For fillet odor, the odor intensity of "green, fatty and fishy" significantly increased with the increase of the dietary lipid level (from 1400 to 2773 ng/g muscle; p &lt; 0.05), which was related to the degradation of n-6 and n-9 fatty acids. For fillet taste, a high lipid diet (≥22.8%) could increase the umami taste compounds contents (from 114 to 261 mg/100 g muscle) but decrease the bitterness and sourness taste compounds contents (from 127 to 106 mg/100 g muscle and from 1468 to 1075 mg/100 g muscle, respectively) (p &lt; 0.05). For nutritional value, a high lipid diet could increase the lipid nutrition level (such as the content of long chain polyunsaturated fatty acids increased from 3.47 to 4.41 g/kg muscle) but decease tryptophan and selenium content (from 2.48 to 1.60 g/kg muscle and from 0.17 to 0.11 g/kg muscle, respectively). In total, a high lipid diet could improve the quality of triploid rainbow trout. The minimum dietary lipid level for triploid rainbow trout should be 22.8% to keep the better organoleptic and nutritional quality.

Effect of Dietary Lipid Level on Growth Performance, Body Composition, and Physiometabolic Responses of Genetically Improved Farmed Tilapia (GIFT) Juveniles Reared in Inland Ground Saline Water.

A 60-day feeding trial was carried out to determine the effect of dietary lipid levels on growth and physiometabolic responses to optimize the dietary lipid requirement for maximizing the growth of Genetically Improved FarmedTilapia (GIFT) juveniles reared in inland ground saline water (IGSW) of medium salinity (15 ppt). Formulation and preparation of seven heterocaloric (389.56-449.02 Kcal digestible energy/100 g), heterolipidic (40-160 g/kg), and isonitrogenous (410 g/kg crude protein) purified diets were done for conducting the feeding trial. Random distribution of 315 acclimatized fish (mean weight 1.90 ± 0.01 g) was made in seven experimental groups such as CL4 (40 g/kg lipid), CL6 (60 g/kg lipid), CL8 (80 g/kg lipid), CL10 (100 g/kg lipid), CL12 (120 g/kg lipid), CP14 (140 g/kg lipid), and CL16 (160 g/kg lipid) with 15 fish per triplicate tank (fish density, 0.21 kg/m3). Respective diets were used for feeding the fish at satiation level three times daily. Results indicated that weight gain percentage (WG%), specific growth rate (SGR), protein efficiency ratio, and protease activity significantly increased up to 100 g lipid/kg fed group, and then the values significantly decreased. Muscle ribonucleic acid (RNA) content and lipase activity were highest in 120 g/kg lipid-fed group. RNA/DNA (deoxyribonucleic acid) and serum high-density lipoproteins levels of 100 g/kg lipid-fed group were significantly higher than 140, and 160 g/kg lipid-fed groups. The lowest feed conversion ratio was found in the 100 g/kg lipid-fed group. The amylase activity was significantly higher in 40 and 60 g lipid/kg fed groups. The whole-body lipid level was increased with increasing the dietary lipid levels, whereas, there was no significant difference in whole-body moisture, crude protein, and crude ash contents of all groups. Highest serum glucose, total protein and albumin, and albumin to globulin ratio and lowest low-density lipoproteins level were found in 140 and 160 g/kg lipid-fed groups. Serum osmolality and osmoregulatory capacity did not vary significantly, whereas carnitine palmitoyltransferase-I and glucose-6-phosphate dehydrogenase showed an increased and decreased trend, respectively, with the increasing dietary lipid levels. According to second-order polynomial regression analysis based on WG% and SGR, the optimum dietary lipid for GIFT juveniles in IGSW of 15 ppt salinity was found to be 99.1 and 100.1 g/kg, respectively.

Transcriptome analysis reveals the effects of dietary lipid level on growth performance and immune response in golden pompano (Trachinotus ovatus)

Present study was conducted to accurately evaluate the optimal dietary lipid level in golden pompano (Trachinotus ovatus) diets combining phenotypic responses and transcriptomics analysis. Fish with initial body weight 27.65 g ± 0.17 g were fed diets with six lipid levels (9.13%, 10.59%, 12.12%, 14.98%, 16.25%, 19.26%), respectively. Results showed that dietary lipid levels significantly altered the weight gain rate, specific growth rate protein efficiency ratio and reached the maximum when fish fed diet with 12.12% lipid. Proximate composition analysis indicated that body nutrients content were significantly improved by dietary lipid levels. Moreover, total glucose, triglycerides and high-density lipoprotein were also elevated by dietary lipid level. Transcriptomic analysis suggested that muscle growth regulation, hormone response, nutrient metabolism and immune response were more sensitive to dietary lipid levels. Further analyzed mechanisms, data demonstrated that dietary lipid levels could through nutrient sensing signaling pathways to regulate lipid metabolism. Meanwhile, Diet 3 (lipid level: 12.12%) had lower level mRNA expression of the key regulators in immune responses and antioxidant defense. Either too lower or too higher lipid in diet could trigger oxidative stress and immune responses. In conclusion, according to broken-line regression on WGR and SGR, the optimal lipid level for golden pompano were 11.28% and 11.20%, respectively. Present study provided the optimal requirement of dietary lipid level based on a comprehensive method.

Effects of Dietary Lipid Levels on Growth and Gonad Development of Onychostoma macrolepis Broodfish

To assess the lipid requirements of O. macrolepis broodstock, five iso-nitrogenous diets (39 g kg−1) with five lipid levels, 50 (5 L), 70 (7 L), 90 (9 L),110 (11 L), and 130 (13 L; g kg−1), were made. A total of 105 three-year-old individuals (50.11 ± 2.86 g per fish) were divided into five groups (triplicate per group) and were fed with the diets, respectively, for eight weeks. Then, the fish were sampled, and items were determined. The results showed that growth rate and feed efficiency ratio were not significantly affected by diets (p &gt; 0.05). A clear dose–response effect of dietary lipid was observed on somatic indexes of gonad indexes of the O. macrolepis brookstock, with the highest values corresponding to fish fed 9 and 11 g kg−1 lipids, in contrast, gonad indexes were reduced as dietary lipid moved away from this level. The other somatic indexes, such as viscerosomatic index, perivisceral fat index, etc., were not significantly affected by diets (p &gt; 0.05). The content of crude lipid and crude protein in carcass, hepatopancreas, and gonad were not significantly affected by dietary lipid levels (p &gt; 0.05). The gonad fatty acids of 16:0 and 22:6n-3 decreased and 18:2n-6 increased with the increasing lipid level, being significantly altered by diets (p &lt; 0.05). The histological features of the gonad showed no significant difference among the five diets (p &gt; 0.05). The relative expression of sex steroid-synthesizing proteins (fshr, 3β-hsd, 17β-hsd, aro., and star.) in the gonad of fish was most significantly highly expressed in the 9 L and 11 L groups (p &lt; 0.05). The results suggested that a proper dietary lipid level of 90–110 g kg−1 could maintain gonad development of O. macrolepis broodstock without affecting growth performance.

The Benefit of Optimal Dietary Lipid Level for Black Seabream Acanthopagrus schlegelii Juveniles under Low-Salinity Environment.

The present study was aimed at evaluating the regulatory effects of dietary lipid levels on growth performance, osmoregulation, fatty acid composition, lipid metabolism, and physiological response in Acanthopagrus schlegelii under low salinity (5 psu). An 8-week feeding trial was conducted in juvenile A. schlegelii with an initial weight of 2.27 ± 0.05 g, and six isonitrogenous experimental diets were formulated with graded levels of lipid: 68.7 g/kg (D1), 111.7 g/kg (D2), 143.5 g/kg (D3), 188.9 g/kg (D4), 239.3 g/kg (D5), and 269.4 g/kg (D6), respectively. Results indicated that fish fed with diet containing 188.9 g/kg lipid significantly improved growth performance. Dietary D4 improved ion reabsorption and osmoregulation by increasing the concentrations of Na+, K+, and cortisol in serum and activities of Na+/K+-ATPase as well as expression levels of osmoregulation related to gene expression levels in the gill and intestine. The expression levels of long chain polyunsaturated fatty acid biosynthesis-related genes were dramatically upregulated when dietary lipid levels increased from 68.7 g/kg to 189.9 g/kg with levels of docosahexaenoic (DHA), eicosapentaenoic (EPA), and DHA/EPA ratio being highest in the D4 group. When fish fed dietary lipid levels from 68.7 g/kg to 188.9 g/kg, lipid homeostasis could be maintained by upregulating sirt1 and pparα expression levels, whereas lipid accumulation was observed in dietary lipid levels of 239.3 g/kg and over. Fish fed with high dietary lipid levels resulted in physiological stress related to oxidative stress and endoplasmic reticulum stress. In conclusion, based on weight gain, the optimal dietary lipid requirement of juvenile A. schlegelii reared at low-salinity water is 196.0 g/kg. These findings indicate that the optimal dietary lipid level can improve growth performance, n-3 LC-PUFA accumulation, and osmoregulatory ability and maintain lipid homeostasis and normal physiological functions of juvenile A. schlegelii.

Effects of Dietary Lipid Levels on Growth, Digestive Enzyme Activities, Antioxidant Capacity, and Lipid Metabolism in Turbot (Scophthalmus maximus L.) at Three Different Stages

Three 56-day feeding trials were conducted to evaluate dietary lipid requirements and effects of dietary lipid levels on growth, digestive enzyme activities, antioxidant capacity, and lipid metabolism in turbot (Scophthalmus maximus L.) at three growth stages. The initial mean body weight of turbot was 9.13 ± 0.17 g, 50.10 ± 0.38 g, and 80.05 ± 0.76 g (small, medium, and large turbot), respectively. Five practical diets were formulated to contain 68.4, 93.9, 120.7, 147.8, and 171.2 g/kg lipid (L68.4, L93.9, L120.7, L147.8, and L171.2), respectively. Results of three trials showed that the weight gain rate and specific growth rate of turbot fed with L120.7, L147.8, and L171.2 diets were all significantly higher compared with turbot fed with L68.4 and L93.9 diets except for large turbot fed with the L147.8 diet. Activities of intestinal trypsin, lipase and hepatic catalase, superoxide dismutase, and total antioxidant capacity firstly increased and then decreased as dietary lipids increased. Meanwhile, malondialdehyde content decreased firstly but then increased with the elevation of dietary lipids in small and medium turbot, and it was significantly higher in the L171.2 group than the rest in large turbot. With increasing levels of dietary lipid, contents of whole-body lipid, liver lipid, serum total cholesterol, triglyceride, and low-density lipoprotein cholesterol were markedly increased at three stages. In addition, serum high-density lipoprotein cholesterol contents increased firstly and then decreased over the L120.7 group. Transcriptional levels of lipolysis-related genes lipin1 and lpl were significantly upregulated firstly and subsequently downregulated with increasing dietary lipid levels except lipin1 in medium fish. Meanwhile, a significant increase in lipogenesis-related genes lxr and pparγ expressions was detected in all fish. Based on the specific growth rate, the dietary lipid level of 130.1, 120.1, and 107.7 g/kg was optimal for the growth performance of turbot cultured at three phases, respectively. Additionally, the results indicated that high lipid diets may lead to abnormal lipid deposition and affect the physiological health of turbot.

Effects of Dietary Lipid Levels on the Lipid Deposition and Metabolism of Subadult Triploid Rainbow Trout (Oncorhynchus mykiss)

A growth trial was conducted to evaluate the effects of dietary lipid levels on the lipid deposition and metabolism of subadult triploid rainbow trout. Diets with low (148 g lipid kg-1 diet), moderate (228 g lipid kg-1 diet), and high (294 g lipid kg-1 diet) crude lipid contents were fed to quadruplicated groups of fish ( 233 g ± 0.2 g ) for 80 days, and they were named as LL, ML, and HL, respectively. Results showed that the lowest and highest values of condition factor and hepatosomatic index were shown in the LL group, respectively, while the HL group obtained the highest liver redness value, plasma total cholesterol, high-density lipoprotein-cholesterol, and low-density lipoprotein-cholesterol contents ( P &lt; 0.05 ). The viscerosomatic index and plasm glucose, nonesterified fatty acids, and triglyceride contents were comparable among groups ( P &gt; 0.05 ). As for lipid deposition, viscera and muscle were the main lipid storage place for triploid rainbow trout when tissues’ weight is taken into consideration. Overall quantitative PCR showed that the lipid uptake, triglyceride, and fatty acid catabolism were upregulated, but glycolysis was downregulated as dietary lipid increased. The expression of genes involved in lipogenesis, lipoprotein clearance, very low-density lipoprotein assembly, and glycogenesis was not affected by dietary lipid levels ( P &gt; 0.05 ). In summary, subadult triploid rainbow trout store lipid mainly in viscera and muscle; it could maintain hepatic lipid homeostasis when fed with dietary lipid levels ranging from 150 to 300 g kg-1 by regulating lipid uptake and switching energy supply between glycolysis and fatty acids β-oxidation.

Effect of dietary lipid levels on the anti-oxidant responses, initial immunity, and mTOR signaling in the liver of coho salmon (Oncorhynchus kisutch)

In the present study, we evaluated the effects of dietary lipid levels on the anti-oxidant responses, initial immunity, and mTOR signaling in the liver of coho salmon Oncorhynchus kisutch. The post-larval coho salmon were fed four isonitrogenous experimental diets with crude lipid levels of 6.6%, 10.56%, 18.91%, and 26.91% for 12 weeks, respectively. Compared to the control group (6.6% dietary lipid level), the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), peroxidase (POD), glutathione peroxidase (GSH-PX), and total antioxidant capacity (TAC) were enhanced by 10.56% and 18.91% dietary lipid levels in the liver of coho salmon. However, no significant difference was observed on these anti-oxidant enzyme activities when the fish were fed 26.91% lipid level diet. Compared to the control group (6.6% dietary lipid level), the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA) as well as the generation of hydroxy radical (·OH) and superoxide anion (O2·-) were decreased by 10.56% and 18.91% dietary lipid levels. In addition, the gene and protein expression level of PI3K, Akt, and mTOR was induced by 10.56%, 18.91%, and 26.91% dietary lipid levels. The gene expression level of IL-1β, IL-6, and TNFα was also increased with the increase of dietary lipid levels. The result of hepatic tissue sections showed that the cellular morphology of liver was affected by the higher dietary lipid levels. In conclusion, the dietary lipid levels affected the anti-oxidant responses, initial immunity, and mTOR signaling in the liver of post-larval coho salmon.

Effects of dietary lipid levels on growth, feed utilization, RNA/DNA ratio, digestive tract enzyme activity, non-specific immune response and optimum inclusion in feeds for fingerlings of rohu, Labeo rohita (Hamilton)

The current investigation was conducted to assess the effects of different levels of dietary lipid on growth performance, feed utilization, digestive tract enzyme activity, lipid deposition, and non-specific immune response of fingerling Labeo rohita (2.23 ± 0.06 g). Six isonitrogenous (400 g kg−1) purified diets with increasing levels of lipid (20, 40, 60, 80, 100, 120 g kg−1 diet) were fed to triplicate groups of 30 fish per tank at 08:00, 12:00, and 16:00 h to apparent satiety for 8 weeks. Absolute weight gain (AWG), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), protein retention efficiency (PRE) and RNA:DNA ratio improved significantly (P < 0.05) up to 100 g kg−1 lipid in diet. Somatic indices and whole body lipid positively correlated with the increase in dietary lipid. Dietary lipid levels significantly affected hepatic antioxidant activities. Liver superoxide dismutase (SOD) and catalase (CAT) activities improved significantly up to 100 g kg−1 lipid in diet. However, liver thiobarbituric acid reactive substances activity (TBARS), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities showed a negative correlation with the increase in levels of lipid in the diets. Highest intestinal protease and lipase activity was also noted in fish received 100 g kg−1 lipid in diet. Second-order polynomial analysis of AWG, FCR, RNA/DNA ratio, SOD and serum lysozyme activity against varying levels of dietary lipid reflected the requirement in the range of 94.77–98.35 g kg−1 dietary lipid for optimum growth of L. rohita.

Effects of dietary lipid levels on growth, lipid deposition, oxidative stress and hepatic morphological changes in giant grouper, Epinephelus lanceolatus

The present study examined the effects of dietary lipid levels on growth performance, lipid deposition, oxidative stress and liver morphological changes in giant grouper, Epinephelus lanceolatus. Five isonitrogenous diets containing graded lipid levels (100, 125, 150, 175 and 200 g/kg diet) were applied to triplicate groups of grouper (mean weight: 17.59 ± 0.14 g) in a seawater recirculation system for 56 days. Dietary lipid levels from 100 to 200 g/kg exhibited no influence on weight gain, specific growth rate, protein efficiency ratio and feed efficiency of the fish. Grouper whole-body and hepatic total lipid content, intraperitoneal fat ratio and oxidative stress (malondialdehyde content) increased linearly (p < 0.05) with escalating dietary lipid levels, reaching the highest values for a fish fed diet with 200 g/kg lipid content. In comparison with the observations in the liver of 100–125 g/kg lipid groups, the liver sections from the 175–200 g/kg lipid groups showed more numerous and larger vacuoles and the presence of round or elliptical hepatocytes. The results indicated that giant grouper could tolerate dietary lipid levels of up to 200 g/kg without exhibiting any negative impacts on growth performance in the 56-day feeding trial. According to the results of intraperitoneal fat, hepatic lipid content, oxidative stress and liver morphology, a dietary lipid level no higher than 150 g/kg is recommended for this species.