Dietary Lipid Levels Research Articles

Effects of Varying Quantities of Dietary Protein and Lipid on Growth Performance, Blood Biochemical Parameters, Digestive Histology and Enzyme Activity in Juvenile Gold Fish (Carassius auratus)

Background: Goldfishes are used as an ideal model for nutritional studies in larval and juvenile cyprinids. However, of the limited published data that is available on goldfish, protein requirements have varied from 29% to 53% for goldfish larvae. So the present study was undertaken to determine growth performance of goldfish, C. auratus fed with different dietary protein and lipid levels to develop nutritionally balanced diets. Methods: In this study, Carassius auratus juveniles were fed with six diets containing two protein levels (300 and 400 g/kg) and three lipid levels (40, 80 and 120 g/kg) to evaluate the optimal dietary protein and lipid levels to determine growth performance, blood biochemical parameters, digestive enzyme activity and intestinal and liver histology. Result: According to the findings, gold fish juveniles when fed a casein-dextrin based semi-purified diet containing 400 g/kg dietary protein and 80 g/kg dietary lipid content, maximum development and feed utilisation are seen. Second-order polynomial regression also suggests that a diet with 400 g/kg protein and 80 g/kg lipid is best for juvenile goldfish growth and feed utilisation.

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 > 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 > 0.05). The content of crude lipid and crude protein in carcass, hepatopancreas, and gonad were not significantly affected by dietary lipid levels (p > 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 < 0.05). The histological features of the gonad showed no significant difference among the five diets (p > 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 < 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.

Lipid metabolism disorders of hybrid grouper (♀Epinephelus fuscointestinestatus × ♂E. lanceolatu) induced by high-lipid diet

This study investigated the effect of lipid levels on growth, body composition, lipid metabolism enzymes activity and related genes expression in hybrid grouper (♀Epinephelus fuscointestinestatus× ♂E. lanceolatu). Three diets with different lipid levels of 6% (low-lipid feed, LF), 11% (medium-lipid feed, MF) and 16% (high-lipid feed, HF) were designed and each diet was fed to triplicate groups of 30 fish each (6.73 ± 0.00g) for eight weeks. The results revealed the following. 1) The maximum weight gain rate (WGR), specific growth rate (SGR), protein efficiency ratio (PER) and the lowest feed conversion ratio (FCR) values were found in the HF group. There was no significant difference in the survival rate (SR) among the groups (P> 0.05). 2) Condition factor (CF), hepatosomatic index (HSI) and visceralsomatic index (VSI) increased with increasing dietary lipid. 3) Crude lipid content in the whole-body and muscle increased significantly as the dietary lipid level increased (P< 0.05). 4) Principal component analysis of fatty acids showed that sum n-3 polyunsaturated fatty acids (∑n-3PUFA)/sum n-6 polyunsaturated fatty acids (∑n-6PUFA) was significantly higher in the HF group than in the other two groups (P< 0.05). 5) Biochemical serum indexes showed higher triglycerides (TG), total cholesterol (TC), alkaline phosphatase (AKP) and low-density lipoprotein-cholesterol (LDL-C) levels but lower high-density lipoprotein-cholesterol (HDL-C) level in the HF group. 6) Liver lipid metabolism enzymes activity and biochemical indicators showed that fish fed the MF diet had higher lipoprotein lipase (LPL), hepatic lipase (HL) and triglyceride lipase (ATGL) activity but lower fatty acid synthase (FAS) activity and very-low density lipoprotein-cholesterol (VLDL-C) level. 7) The relative expression levels of lipoprotein lipase (lpl), adipocyte-type fatty acid-binding protein (a-fabp), liver-type fatty acid-binding protein (l-fabp), heart-type fatty acid-binding protein (h-fabp) and hormone-sensitive lipase (hsl) genes in the fish liver were higher in the MF group with increasing dietary lipid (P< 0.05), while the fatty acid synthase (fas) gene was expressed at lower relative level (P< 0.05). 8) Histological oil-red sections of the liver showed that fish in the HF group had larger and more hepatic lipid droplets than those fed the other diets. It was concluded that fish fed the HF diet had better growth performance but this diet was not conducive to the progress of lipid metabolism, resulting in lipid accumulation and affecting the quality of the fish. This study provides useful information for the formulation of environmentally friendly and cost-effective diets for hybrid grouper.

The effect of dietary carbohydrate to lipid ratios on growth performance in juvenile California yellowtail Seriola dorsalis

Two eight-week feeding trials were conducted to evaluate the effect of dietary carbohydrate to lipid ratios on growth performance on juvenile California yellowtail Seriola dorsalis. In Trial 1, groups of twenty California yellowtail (ca. 6.8 g) were fed five iso‑nitrogenous diets that were formulated to contain decreasing levels of crude lipid from 21% to 6% by replacing menhaden fish oil with corn starch on a weight basis In Trial 2, groups of twenty fish (ca. 5.2 g) were fed five iso‑nitrogenous diets that were formulated using a similar matrix, corn starch 0–24% was used to replace lipids (11.3 to 1.3%) at approximately 2:1 ratio to maintain the diets with similar energy content and the nitrogen free extract (carbohydrates) from 10% to 30% of the diet Fish were fed 5–11% body weight per day over the course of both trials. Growth performance metrics including thermal-unit growth coefficients and protein retention efficiencies were measured and compared using a quadratic regression model. Fish that were fed diets containing high levels of dietary lipids (15% or higher) exhibited decreased growth performance in Trial 1. In Trial 2, fish that received diets containing the highest level of carbohydrates exhibited improved feed efficiency and overall performance. The results from both trials demonstrate that juvenile California yellowtail with a starting size of 5–7 g have an energy fraction preference and display increased growth when fed diets containing a carbohydrate to lipid ratio of up to 5.8.

Adiponectin and adiponectin receptors in common carp (Cyprinus carpio): Tissue distribution and their expressions in response to high-carbohydrate and high-lipid diets

In order to investigate the roles of adiponectin in glucose and lipid metabolism in common carp, the tissue distribution of adiponectin and its receptor genes in common carp were firstly detected in this study, and then the effects of high-carbohydrate (45%) and high-lipid (11%) diets on their expressions were studied in the feeding trial. The results showed that adipoqa and adipoqb mRNA levels were highest in the red muscle, followed by the heart and white muscle. Adiponectin receptor genes were widely expressed in all tested tissues. Two subtypes of adiponectin receptor 1 genes (adipor1a and adipor1b) were expressed at the highest level in the brain, while adipor2 mRNA was highly expressed in the heart and red muscle. The high-carbohydrate diet significantly up-regulated adipoqa and adipoqb mRNA level in the heart of common carp, while the high-lipid diet significantly promoted adipoqa mRNA expression in the red muscle and heart, compared to the control diet. For adiponectin receptor gene expression, a high-carbohydrate diet up-regulated adipor2 mRNA level in the hepatopancreas, while a high-lipid diet significantly promoted adipor1a, adipor1b and adipor2 mRNA expression in the red muscle and hepatopancreas. The results showed that both high-carbohydrate and high-lipid diets could induce adiponectin genes expression in common carp, and AdipoRs expression was more likely to be increased by the high-lipid diet than the high-carbohydrate diet. This study suggested that adiponectin and its receptors were involved in the metabolic regulation of fish under high dietary carbohydrate and lipid levels.

The Optimum Lipid Level for the Juvenile Redclaw Crayfish Cherax quadricarinatus: Practical Diets with Soybean Oil as the Lipid Source.

As a new species in aquaculture, the lipid nutrition requirement for the juvenile redclaw crayfish Cherax quadricarinatus on a dietary basis on a practical formula needs to be evaluated accurately. In this study, the optimum dietary lipid level was explained by analyzing the growth performance, antioxidant state, lipid metabolism, and gut microbiota of C. quadricarinatus after an eight-week cultivation trial. Six diets with different soybean oil levels (named L0, L2, L4, L6, L8, and L10) were fed to C. quadricarinatus (11.39 ± 0.28 g). The results indicated that the specific growth rate and weight gain of crayfish fed the L4 and L6 diets were significantly higher than those of the other groups (P < 0.05). By the analysis of a second-order polynomial regression model according to growth performance (weight gain rate), the optimum lipid level in a practical diet for juvenile C. quadricarinatus was 9.67%. The survival, condition factor, and hepatosomatic index of crayfish were not significantly affected by dietary oil levels (P > 0.05). As the level of dietary lipids increased, the total antioxidant capacity and glutathione peroxidase activity in serum showed a tendency to rise and then fall and the enzyme activity was highest in crayfish fed the L6 diet. Gut lipase and pepsin activities showed the highest value in crayfish fed the L6 diet. There was no significant difference in acetyl-CoA carboxylase and carnitine palmitoyltransferase-1 contents in crayfish among all the groups (P > 0.05). The relative abundance of Proteobacteria in the phylum and Citrobacter in the genus showed a significant decrease in crayfish of the L10 diet, while the relative abundance of Firmicutes in the phylum markedly increased compared to that of the other groups (P < 0.05). In summary, the results indicated that the 10.39% (L6 diet) dietary lipid level could induce better growth performance, antioxidant ability, and digestive enzyme activity. Most of the fatty acid composition of muscle is not closely related to the fatty acid composition of the diet. Moreover, the composition and diversity of the gut microbiota of C. quadricarinatus were changed by high dietary lipid levels.

Effects of dietary protein and lipid levels on growth performance, feed utilization and body composition of juvenile giant trevally ( Caranx ignobilis Forsskal, 1775)

An 8-week feeding study was carried out to assess the effects of dietary protein and lipid levels on growth, feed utilization and body composition of juvenile giant trevally (Caranx ignobilis Forsskal, 1775). Six diets were produced with three crude protein levels of 42%, 47%, 52% and two crude lipid levels of 10% and 18% in a 3 × 2 factorial design. Treatments were named by their protein and lipid levels, viz. P42:L10, P42:L18, P47:L10, P47:L18, P52:L10 and P52:L18, corresponding P/E of 20.23, 18.73, 22.31, 20.81, 24.63 and 22.12 g/MJ respectively. Growth performance in terms of length, final body weight and specific growth rate were the highest (p < 0.05) when juveniles were fed P52:L10 with P/E of 24.63 g/MJ. The same diet also resulted in the highest effective feed utilization in terms of feed intake and feed conversion ratio. Crude protein in whole body increased when dietary protein or dietary lipid increased from 42% to 52% and 10% to 18% respectively. Significantly increased levels of amino acids in fish's body, including alanine, aspartic acid, glutamine, serine, leucine, threonine, valanine and arginine, were observed in fish fed 52% protein. Increasing dietary lipid from 10% to 18% led to reduced levels of alanine, glutamine, leucine, threonine, valine and arginine in fish. The result suggests that P52:L10 diet with P/E ratio of 24.63 g/MJ subjects the growth requirement of juvenile giant trevally.

Estimation of the Optimum Dietary Protein to Lipid Ratio in Juvenile Pengze Crucian Carp (Carassius auratus Var. Pengze)

An 8-week feeding experiment was conducted to evaluate the effect of dietary protein to lipid ratio on fish growth performance, digestive enzyme activity, body composition, serum biochemistry, immunity, and antioxidant capacity of Carassius auratus var. Pengze juveniles. Nine experimental diets were formulated in a 3 × 3 factorial design to contain three protein levels (30%, 35%, and 40%) and three lipid levels (5%, 8%, and 11%), with protein-to-energy (P/E) ratios ranging 19.2–27.1 mg/kJ and named as Diet 1 (30/5), Diet 2 (30/8), Diet 3 (30/11), Diet 4 (35/5), Diet 5 (35/8), Diet 6 (35/11), Diet 7 (40/5), Diet 8 (40/8), and Diet 9 (40/11), respectively. Each diet was randomly assigned to triplicate groups of 20 fish per cylindrical fiberglass tank. The fish fed with Diet 4 had the highest specific growth rate (SGR) among the 9 groups. The whole-body lipid content increased significantly with increasing dietary lipid levels regardless of dietary protein content ( P &lt; 0.05 ), whereas moisture content showed an opposite trend ( P &lt; 0.05 ). The highest values of activities of serum lysozyme (LZM) and alkaline phosphatase (AKP) were detected in the fish fed Diet 4 (35/5), whereas malondialdehyde (MDA) was lowest in the fish fed Diet 4. In addition, serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) were the lowest, while high-density lipoprotein (HDL-C) and high-density lipoprotein to total cholesterol ratio (HDL-C/TC) were the highest in the Diet 4 group. The results indicate that a combination of 35.1% protein and 5.1% lipid with dietary CP/GE (mg/kJ) ratio of 24.0 is optimal for the culture of Carassius auratus var. Pengze juveniles.

Feeding restriction unalters physiological responses to dietary lipid and carbohydrate levels in juvenile gibel carp (Carassius gibelio)

To investigate the physiological responses to different energy sources under feeding restriction in fish, gibel carp were fed a high lipid, low carbohydrate diet (HL diet, 12% lipid, 16% carbohydrate) or a high carbohydrate, low lipid diet (HC diet, 34% carbohydrate, 4% lipid) to satiation or 70% satiation (restriction) for 56 d; then, growth performance, nutrient metabolism, endoplasmic reticulum (ER) stress, autophagy, and apoptosis were determined. Fish that were fed the HL diet had higher final body weight, specific growth rate, and feed efficiency, lower phosphorylation levels of AKT and mTOR proteins and lower mRNA levels of gk than the HC group. When fed to 70% satiation, fish had lower feed intake, feeding rate, final body weight, and specific growth rate, and lower plasma glucose and nonesterified fatty acid levels. Feeding restriction induced the transcript level of gk and suppressed the mRNA level of acly, acc, fas. There were no significant differences in ER stress, autophagy and apoptosis between feeding levels or diets. Interactions between feeding level and diet were observed in plasma triglyceride level and the gene expression levels of fbpase and srebp1. Thus, gibel carp utilized HL diet better than HC diet, which was unalerted by feeding restriction.

Tissue distribution and nutritional regulation of peroxisomal fatty acid β‐oxidation genes: A preliminary study in two marine teleosts, turbot ( Scophthalmus maximus ) and tiger puffer ( Takifugu rubripes )

Peroxisome plays an important role in the modulation of lipid catabolism in fish. The present study investigated the tissue distribution of five peroxisomal fatty acid β-oxidation genes, including vlcs, acox1, acox3, ehhadh and acaa1, in turbot and tiger puffer. Their expressions in response to different nutritional status (starvation and change in dietary lipid levels) were also studied. Both fish were fed diets with graded lipid levels (8%, 12% and 16%) for 9 weeks, followed by 1-month of starvation. The five genes were highly expressed in the liver, intestine and pyloric caecum of turbot, and tiger puffer intestine. High-lipid diets up-regulated the expression of vlcs and acox3 in tiger puffer liver, whereas did not affect the expression of all genes investigated in turbot. During the starvation, expression of acox1, acox3 and acaa1 in turbot liver was increased firstly from day 0 to day 10, and then was decreased, while expression of vlcs in muscle, and acaa1 in muscle and subcutaneous adipose tissue was linearly increased. In tiger puffer liver, the expression of peroxisomal β-oxidation genes increased linearly with starvation time, but the expression of acox3, ehhadh and acaa1 in the muscle firstly increased from day 0 to day 4–9, and thereafter decreased. In conclusion, the peroxisomal fatty acid β-oxidation genes were highly expressed in the liver and intestine of both turbot and tiger puffer, and starvation could stimulate and high dietary lipid levels have less impact on their expression.

A Screening Study on Effects Varying Dietary Macronutrient Composition on Gut Functions in Lumpfish (Cyclopterus lumpus)

Cultivation of lumpfish (Cyclopterus lumpus) as lice cleaner fish for salmon is now expanding. For successful cultivation of a new species, understanding the basic biology of digestive functions is vital to facilitate and optimize diet formulation. This paper presents results from two experiments conducted to deepen our knowledge on lumpfish intestine physiology. Experiment 1 was a 42-day feeding trial in which lumpfish were fed twelve different diets in the following ranges of macronutrients: Protein 43-68%, lipid 4-17%, and carbohydrate 6-17%. Intestinal tissue, gut content and liver were sampled from 6 fish per tank. The results showed that with increasing lipid level and corresponding decrease in protein level, there was a linear decrease in several of the observed biomarkers, including activity of brush border membrane digestive enzymes, expression of genes related to nutrient digestion and transport, ion exchange, immune regulation, and cell remodeling. Increased intracellular accumulation of lipid (steatosis) was observed in gut and liver with increasing dietary lipid level. Fewer effects were observed for increased dietary carbohydrate and corresponding decreased protein level. Experiment 2 was a two-week feeding trial for estimation of macronutrient digestibility in which lumpfish were fed three diets, all containing 55% crude protein, with lipid to carbohydrate ratio of the low lipid diet of 7.5%/18.3%, the medium lipid diet of 13.8%/14.6%, and high lipid diet of 18.1%/9.5%. Fecal samples were collected as pooled samples per tank. These results showed that fatty acid digestibility’s increased as dietary lipid level increased. Of note, starch digestibility decreased greatly as starch level increased, whereas protein digestibility did not change as lipid or starch level varied. Taken together, the present studies indicated that increasing lipid level in the diet with corresponding decrease in protein level affects digestion, absorption, and immune responses in the lumpfish intestine. Variation in dietary carbohydrate to protein level showed less effects, possibly due to low starch digestibility which makes the variation in available carbohydrates much less than the variation in the analysed level of dietary carbohydrates.

Modulation of dietary protein to lipid ratios for gilthead seabream on-growing during summer temperature conditions

Gilthead seabream (Sparus aurata) tend to increase fat deposition during summer farming conditions in the Mediterranean, which may negatively affect productive performance and consumers’ quality perception of the final product. Therefore, this study evaluated the impacts of protein to lipid ratios in low fishmeal/fish oil diets on growth performance, body composition, feed conversion and nutrient utilization of seabream on-grown during summer temperature conditions. The experimental diets contained low levels of fishmeal, fish oil, and crude protein (39%), differing in crude lipid content: 16% (MF diet) or 12% (LF diet). A growth trial was performed with seabream (initial weight: 100 ± 7 g) from August to October (water temperature: 23.1 ± 2.2 ºC). A digestibility trial was also performed (at 23 ºC). Key performance indicators, whole-body composition and activities of digestive enzymes were evaluated at the end of the experiment (64 days). Low dietary lipid levels negatively affected lipid, energy, and amino acid digestibility, and as a result, fish fed the LF diet presented higher nitrogen faecal losses. Still, the decrease in nutrient digestibility was not related to dietary effects on the digestive enzyme activities. The experimental diets did not compromise the activity of pancreatic, gastric, and intestinal digestive enzymes nor feed utilization, but a slight growth impairment was observed in fish fed the LF diet, probably due to the lower amino acid and lipid digestibility. However, a potential benefit of this dietary treatment towards reducing fat accumulation in seabream during summer was observed. Nevertheless, the environmental impact of the nitrogen losses during seabream on-growing should be considered when estimating the sustainability of the production. This study demonstrated that the optimisation of diet formulations should account for the environmental conditions, especially in Mediterranean aquaculture, so the economic and environmental impacts may be correctly evaluated towards a more sustainable fish production.

Dietary lipid and protein levels influence the growth and feed utilisation of large yellowtail kingfish (Seriola lalandi) at summer water temperatures

Yellowtail Kingfish (Seriola lalandi; YTK) have a fast growth rate, and as a result, a high energy demand that could be satisfied by dietary lipids. The aim of this experiment was to determine the optimum dietary protein and lipid levels for large YTK maintained during a summer growing season. In this 84-day experiment (2 × 3 factorial design), the growth, feed utilisation and health of YTK (initial weight 2.13 ± 0.02 kg, mean ± SE) fed two nominal lipid levels 25% crude lipid (CL) (20 MJ kg−1 energy) and 30% CL (21 MJ kg−1 energy) and three nominal crude protein (CP) levels (40, 44 and 48%) were investigated. The specific growth rate of fish was significantly affected by the interaction between dietary CP and CL level. The results indicate that fish fed the 25% CL diets grew better than those fed the 30% CL diets. The interaction effect was primarily driven by the significant increase in growth for fish fed diet 1 (40% CP × 25% CL) and diet 2 (44% CP × 25% CL) compared to their respective 30% CL diets, diet 4 (40% CP × 30% CL) and diet 5 (44% CP × 30% CL). The growth of fish fed diet 3 (48% CP × 25% CL) and diet 6 (48% CP× 30% CL) was not significantly different. Feed conversion ratio (FCR) was not significantly influenced by diet however, the fish fed the 25% CL diet series and 40% protein series consumed the most feed. Fish fed the 25% CL series increased their feed intake with decreasing dietary CP level, to potentially compensate for reduced dietary protein. In contrast, fish fed the 30% CL series did not. Crude protein intake was higher when fish were fed the 48% CP diets and was reduced when fed the 40% and 44% CP diets. This response was more pronounced in the 30% CL diet series. There were no negative health effects noted during the study for various analyses including blood biochemistry and haematology, and gastrointestinal tract morphology. Numerically, the highest final weight, biomass gain, SGR, and FCR were consistently observed in the fish fed diet 2, however these were not significantly different to diet 1. Based on the combined results for 2.1–3.5 kg YTK raised during summer, the diet should contain at least 42.9% CP and 25.3% CL (equivalent to diet 2) corresponding to 19.9 MJ kg−1 GE diet with and a CP: GE ratio of 21.6 g MJ−1. In terms of actual protein and energy intake required this corresponds to 5.2 g CP−1 kg BW−1 d−1 (4.5 g DP−1 kg BW−1 d−1) and 242 KJ−1 GE kg BW−1 d−1 (207 KJ−1 DE kg BW−1 d−1) which appears to be optimal. We do not recommend diet lipid levels of approximately 30% over summer periods, as demonstrated in this experiment.

Effects of dietary protein and lipid levels on growth, feed utilization and meat quality of clown knifefish (Chitala chitala)

Effects of dietary protein and lipid levels on growth, feed utilization and fillet quality of clown knifefish (Chitala chitala) were implemented to determine the protein and energy requirements of this species at 400 g stage. A 4 x 3 factorial design with four dietary protein levels (25%, 30%, 35% and 40%) and three dietary lipid levels (6, 9, and 12%) corresponded to 3 energies levels 18, 19 and 20 MJ/kg. Clown knifefish (407 ± 5.0 g) was stocked at a density of 10 fish/m2. The experiment was arranged in a completely randomized design in triplicate tanks for 8 weeks. There was a significant interaction effect (P&lt;0.05) between protein and lipid levels on weight gain and specific growth rate with the fish growth being highest in the 35 CP-9% lipid treatment. The survival rate of fish was not affected (P&gt;0.05) by dietary protein and lipid levels and ranged from 93.3 to 100%. The feed efficiency of fish was influenced by dietary protein or lipid content as well as the interaction between these two factors. Protein utilization efficiency increased as protein content increased, and diet contained t 35% protein and 9% lipid, enhanced chewiness and hardness of fish paste. These results showed that clown knifefish fed 32.8% dietary protein and 19 MJ energy with a P/E ratio of 18.6 had the optimal growth and the best quality of fish meat.

Differential regulatory effects of optimal or excessive dietary lipid levels on growth, lipid metabolism and physiological response in black seabream (Acanthopagrus schlegelii)

This study was conducted to obtain the optimal dietary lipid requirement and evaluate the differential regulatory effects of optimal or excessive dietary lipid levels on growth performance, lipid metabolism and physiological responses including oxidative stress (OS) and endoplasmic reticulum stress (ERS) of juvenile black seabream (Acanthopagrus schlegelii) (initial weight 2.08 ± 0.01 g). Six isonitrogenous experimental diets were formulated with graded levels of lipid: 6.87% (D1), 11.17% (D2), 14.35% (D3), 18.89% (D4), 23.93% (D5) and 26.94% (D6), respectively. Results indicated that fish fed with the D2 diet showed significantly higher values of final weight (FW), weight gain (WG) and specific growth rate (SGR) than those fed with the other diets, except for D3 group. In fish fed with the diets containing 11.17% and 14.35% (D2 and D3 groups) had the significantly higher contents of high density lipoprotein cholesterol (HDL-C) than other treatments, but showed markedly low concentrations of low density lipoprotein cholesterol (LDL-C). The contents of cholesterol (TC), triglyceride (TG), aspartate aminotransferase (AST) and alanine transaminase (ALT) in serum increased with the increasing of dietary lipid levels, except for the contents of AST and ALT in D1 group. Likewise, the results of hepatic paraffin section indicated that fish fed the dietary lipid levels of 18.89% or beyond (D4, D5 and D6) increased vacuolar fat drops and induced hepatic fat pathological changes. The mRNA expression level and protein concentration of sterol regulatory element-binding protein-1(srebp-1) were significantly up-regulated with the increasing of dietary lipid levels. However, the mRNA expression levels and protein concentrations of peroxisome proliferator-activated receptor alpha (pparα) and silent information regulator 1 (sirt1) significantly activated by fish fed with the D2 diet. Additionally, when fish fed with excessive dietary lipid (over 18.89%) could result in various responses related to OS and ERS. The key marker of OS malonaldehyde (MDA) was significantly increased with the increasing of dietary lipid levels being highest in the D6 group. A contrary pattern was found for total antioxidant capacity, which showed significantly higher activity in the D2 group. All parameters related to ERS increased with the increasing of dietary lipid levels and, hence, triggering inflammation and apoptosis by up-regulating the expression levels of key genes including nuclear factor kappa B (nf-κb) and c-Jun N-terminal kinase (jnk). Overall, based on WG, the optimal dietary lipid requirement of juvenile A. schlegelii is 12.82% by quadratic curve model analysis. When dietary lipid level exceeded 18.89%, excessive lipid could reduce growth performance, cause hepatic fat pathological changes, induce lipid deposition by modulating Sirt1/Srebp-1/Pparɑ pathways, lead to OS and ERS and, hence, triggering hepatic inflammation and apoptosis. These findings provide further insight and understanding of the regulatory effects on growth, lipid metabolism, physiological stress response (including OS and ERS) of A. schlegelii fed with optimal or excessive dietary lipid levels

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.