Dietary methionine requirement of pre‐adult blunt snout bream, (Megalobrama amblycephala Yih, 1955)

A nine‐week feeding trial was conducted to test the hypothesis that an adequate methionine diet might improve growth, feed utilization, body composition and physiology, and biochemical parameters in pre‐adult blunt snout bream Megalobrama amblycephala, whereas a methionine deficiency might have adverse effects on these parameters. Six isonitrogenous and isoenergetics semi‐purified diets (33.0% crude protein, 7.0% crude lipid) were formulated to contain graded methionine levels (0.39–1.54% of dry weight) at 0.25% increments replaced by equal proportions of glycine. Results show that the survival rate (SR) was not significantly affected by the dietary methionine level. Final weight (FW), feed efficiency ratios (FER), weight gain (WG), and specific growth rate (SGR) increased with increasing dietary methionine levels up to 1.00% and then showed a declining trend. Using quadratic regression analysis of FER and SGR, the dietary methionine requirement was estimated to be 0.74% (2.24% of dietary protein) and 0.76% of the diet (2.30% of dietary protein), respectively. Fish fed the 0.39% methionine diet showed significantly lower whole body protein content compared to those fed with 0.85, 1.00 and 1.24% methionine diets (P < 0.05). Whole body moisture, lipid, and ash contents in pre‐adult adult blunt snout bream were not significantly affected. The urea content in fish fed the 0.85% methionine diet was significantly higher than those of fish fed a 0.39, 0.56, 1.24, 1.54% methionine diet (P < 0.05), but not significantly different in fish fed the 1.00% methionine diet (P > 0.05). No significant differences were found in other indexes such as the hepatosomatic index (HSI), viscerosomatic index (VSI), condition factor (CF), albumin (ALB), total protein (TP), alanine aminotransferase (ALT), and spartate transaminase (AST) (P > 0.05). Most important, the optimal dietary methionine level of pre‐adult blunt snout bream should be 0.74–0.76% of the diet (2.24–2.30% of dietary protein).     

Dietary protein requirement of juvenile triangular bream Megalobrama terminalis (Richardson, 1846)

A 10‐week feeding trial was conducted to determine the dietary protein requirement of juvenile triangular bream (Megalobrama terminalis). Five semi‐purified diets (white fishmeal as a protein source) were formulated with five crude protein (CP) levels (26.30%, 32.94%, 38.33%, 44.18% and 50.09%; diets P1–P5). Each diet was fed to triplicate groups (20 per fish replicate, initially weighing 1.30 ± 0.02 g). The following parameters were measured to evaluate the effects of different CP levels: weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), daily feed intake (DFI), viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat ratio (IPF), lipid retention (LR), liver glycogen content and plasma triglyceride level. The results of the feeding trial showed that WG, SGR and FE were significantly enhanced by an increasing dietary protein level of up to 44.18%, but there were no significant differences in protein levels from 44.18% to 50.09%. The PER and DFI showed a decreasing trend with increasing dietary CP levels. The VSI and HSI were not significantly affected by the different treatments, whereas the IPF increased significantly with decreasing CP levels. The highest LR value, liver glycogen value and triglyceride level in plasma were observed in fish fed the lowest CP diet (P1). Based on the WG and FE, this study suggests an optimum dietary protein level for M. terminalis of 44.18%.     

Effect of dietary protein and carbohydrate levels on growth,nutrient utilization and body composition in fingerling rohu,Labeo rohita (Hamilton)

Twelve experimental diets (D‐1 to D‐12) in a 4 × 3 factorial design having four protein levels (25, 35, 40 and 45%) and three carbohydrate levels (15, 25 and 35%) were formulated and fed to fingerling rohu, Labeo rohita (5.48 ± 0.02 g) for 60 days in three replicates at 2% BW per day. The best performance of fish in terms of weight gain (%), specific growth rate (SGR; % per day), feed conversion ratio (FCR) and protein efficiency ratio (PER) was recorded with diet D‐9 containing 40% protein and 35% dextrin as a source of dietary carbohydrate. In general, lower protein consumption per kilogram BW was observed at all protein levels with the rise of the dextrin level. The apparent digestibilities of protein and lipid were not affected by the dietary treatments. At the end of the experiment the body composition of animals from all treatments showed lower percentages of moisture and higher percentages of protein as compared to the initial values. A consistent rise in protein retention efficiency was noted in fish fed diets with increasing dextrin levels. The highest protein sparing effect was found in fish fed the diet containing 40% protein and 35% dextrin.     

Dietary protein requirement for juvenile Chinese sucker (Myxocyprinus asiaticus)

This study was conducted to determine the dietary protein requirement for juvenile Chinese sucker, Myxocyprinus asiaticus. Six fishmeal‐based experimental diets containing various crude protein levels ranging from 300 to 500 g kg^?1 were fed to triplicate groups of 20 fish each (initial weight 13.5 ± 1.1 g) for 56 days at a temperature of 28 ± 1°C (tank size 400 × 45 × 40 cm, linked to a recirculation system). Survival was not affected by dietary protein level (overall survival 71 to 90%). Weight gain (WG) and specific growth rate (SGR) increased with an increasing dietary protein level up to 460 g kg^?1. The feed conversion rate (FCR) generally showed a decline at higher protein levels (from 1.62 in 300 g protein kg^?1 to 1.13 in 500 g protein kg^?1 feed). Protein efficiency ratio (PER) showed gradual improvements with increasing dietary protein up to 460 g kg^?1. A similar trend was found for the protein productive value (PPV). Among the proximate compositions of the fish, crude protein content increased significantly with increasing dietary protein levels. Based on broken‐line regression analysis of SGR against dietary protein levels, the optimal dietary protein requirement for juvenile Chinese sucker was estimated to be close to 465 g kg^?1.     

Effect of dietary fish oil replacement with palm oil on growth performance,hematology and liver anti‐oxidative enzymes of juvenile Japanese flounder Paralichthys olivaceus (Temminck & Schlegel, 1846)

A 60‐day feeding trial was conducted to evaluate the effects of dietary palm oil supplements on growth performances, hematology, liver anti‐oxidative enzymes and air exposure resistance of Japanese flounder, Paralichthys olivaceus (initial weights 2.56 ± 0.01 g). Five diets were tested wherein the dietary fish oil was replaced by palm oil at: 0% (Control), 20% (20%), 40% (40%), 50% (50%) and 60% (60%). After the feeding trial, the 20% dietary palm oil was shown to provide similar growth rates and feed efficiency with no negative effects compared to the control group (P > 0.05). Significantly lower growth rates and feed utilization were found in fish fed higher than 40% palm oil in the diet (P < 0.05). Except for total serum protein, the blood parameters, liver anti‐oxidative enzymes, stress resistance and proximate compositions of Japanese flounder were not altered, even with dietary palm oil up to 60% of the lipid source (P > 0.05). According to the present results, palm oil is a valuable lipid source substitute in Japanese flounder diets; around 20–40% fish oil can be replaced with palm oil with no negative effects.     

Growth performance and body composition of sub-yearling Persian sturgeon, (Acipenser persicus, Borodin, 1897), fed different dietary protein and lipid levels

In order to evaluate the protein and energy requirement of Persian sturgeon (Acipenser persicus) sub‐yearlings, eight experimental diets containing two protein levels (40% and 45%) and four lipid levels (10%, 15%, 20% and 25%) were tested. Sturgeons (W₀ = 136.8 g) were fed the experimental diets to satiation four times daily for 150 days, resulting in a final mean weight of 375.8 g. Growth was significantly affected by lipid content of the diets. At 40% protein level, weight gain and specific growth rate (% per day) were significantly improved (P < 0.05) by increasing the dietary lipid (energy) content. Protein efficiency ratio (PER) was significantly affected by different dietary treatments for each dietary protein level tested, reaching a mean value of 3.58 in fish fed high lipid diets and a PER of 2.77 in low lipid diets. Results obtained in the present study suggest that the optimum dietary protein content for Persian sturgeon is 40%, with an estimated optimum protein‐to‐energy ratio of 18–20 mg kJ⁻¹.     

Effect of dietary carbohydrate on the growth performance,immune response,hepatic antioxidant abilities and heat shock protein 70 expression of Wuchang bream,Megalobrama amblycephala

To investigate the effects of different carbohydrate (CHO) levels in the diet of Wuchang bream Megalobrama amblycephala, the fish were randomly divided into six treatment groups. Five groups were fed 19, 25, 31, 38 and 47% CHO, respectively, for 8 weeks, and a control group was fed a diet with no CHO. Growth performance and feed utilization were significantly (P < 0.05) affected by the dietary carbohydrate level. Maximum weight gain and specific growth rate occurred at the 31% dietary carbohydrate level. Compared to the control, the 31% CHO group had a significantly increased serum total protein content, respiratory burst activity of leucocytes, serum complement 3 (C3) levels, serum lysozyme activity, serum alkaline phosphatase (AKP) activity and hepatic total antioxidative capacity (T‐AOC), as well as a decrease in serum glutamic‐oxaloacetic transaminase (GOT) activity. Compared to the control, the 47% CHO group had significantly increased serum GOT activity, and a tendency toward an increase in serum cortisol content and a decrease in serum lysozyme activity, hepatic superoxide dismutase (SOD) activity and T‐AOC. The relative level of hepatic heat shock protein 70 (HSP70) mRNA in fish fed the 38% CHO diet was significantly higher than those of fish fed the 19, 25 and 31% CHO diets, respectively (P < 0.05). After challenge with Aeromonas hydrophila, fish fed the 47% CHO had the significantly lowest post‐challenge survival, and fish fed the 31% CHO had the significantly highest post‐challenge survival (P < 0.05). The results of this study suggest that ingestion of excessive dietary CHO can impact the non‐specific immune responses, decrease the hepatic antioxidant abilities, and thus affect the health status of M. amblycephala.     

Effect of dietary carbohydrate-to-lipid ratios on growth and feed utilization in Chinese longsnout catfish (Leiocassis longirostris Günther)

An 8‐week growth trial was carried out in a semi‐recirculation system at 26 ± 0.5°C to investigate the optimal dietary carbohydrate‐to‐lipid (CHO:L) ratio for carnivorous Chinese longsnout catfish (Leiocassis longirostris Günther). Triplicate tanks of fish were assigned to each of five isocaloric and isonitrogenous diets with different carbohydrate‐to‐lipid ratios (0.75, 1.48, 1.98, 2.99 and 5.07). The results showed that a higher specific growth rate (SGR) and feed rate (FR) were observed in the fish fed diet ratios of 1.98 CHO:L (P < 0.05). Overloading dietary carbohydrate (5.07 CHO:L ratio) caused skeletal malformations. Apparent digestibility of dry matter (ADC_d) significantly increased with dietary CHO:L ratio (P < 0.05), while significantly higher apparent digestibility of protein (ADC_p) and apparent digestibility of energy (ACD_e) was observed only in the 1.98 CHO:L group (P < 0.05). Whole body contents of dry matter, lipid and energy significantly increased as the CHO:L ratio decreased (P < 0.05). The hepatosomatic index (HSI) was highest at 1.98 CHO:L ratio (P < 0.05). Highest dietary CHO:L ratio resulted in lower liver glycogen, liver lipid, plasma glucose and plasma triacylglycerol (P < 0.05), whereas there was no significant difference in plasma total cholesterol (P > 0.05). High dietary CHO:L ratio caused pathological changes in fish morphology and liver histology. Based on maximum growth, the optimal carbohydrate‐to‐lipid ratio was 1.98 for Chinese longsnout catfish.     

Dietary inclusion of mussel meal enhances performance and improves feed and protein utilization in common sole (Solea solea,Linnaeus, 1758) juveniles

The present study was carried out to test different mussel meal (MM) dietary levels in combination with fishmeal (FM) on the growth performance, fatty acid composition and liver histology of common sole, Solea solea juveniles to highlight the growth potential of this species. Four isoproteic (53%) and isolipidic (11%) pelletized diets were formulated to contain graded levels of mussel meal, MM0 (0%), MM25 (25%), MM50 (50%) and MM75 (75%), up to 75%. Sole juveniles (initial individual mean body weight 13.1 ± 2.3 g, n = 840) were fed to satiation for 91 days. Seventy fish per tank (500‐L, 0.64 m² bottom surface) were reared in 12 tanks (3 tanks per treatment) at 20 ± 1°C. Diets containing MM (MM25, MM50 and MM75) gave a significantly higher specific growth rate (SGR, 1.27 ± 0.01, 1.38 ± 0.06 and 1.40 ± 0.05, respectively), higher feed intake and lower feed conversion rate (FCR, 1.09 ± 0.01, 1.00 ± 0.04 and 0.98 ± 0.02, respectively) when compared to the FM‐based diet (MM0, SGR, 0.98 ± 0.11, FCR, 1.52 ± 0.13). Carcass proximate composition was not influenced by dietary treatments, with the exception of the significantly lower lipid content in the MM75 group. Protein efficiency ratio (PER) and gross protein efficiency (GPE) were significantly improved by the mussel meal inclusion (PER, 1.29 ± 0.12, 1.76 ± 0.01, 1.89 ± 0.06, 1.95 ± 0.08; GPE, 25.29 ± 1.85, 33.38 ± 0.89, 35.96 ± 1.36, 36.59 ± 1.05 in MM0, MM25, MM50 and MM75, respectively). A significant decrease in the viscerosomatic index was observed in fish fed with MM50 and MM75 in comparison to MM0. The hepatosomatic index of fish fed with MM0 and MM25 was higher than that of fish fed with MM75, although the histological examination of liver parenchyma in all experimental groups showed a uniformly abundant accumulation of lipid droplets. Carcass fatty acid composition was significantly affected by dietary treatments, reflecting the dietary fatty acid profile. According to these results, the inclusion of MM in experimental FM‐based diets improved the performance and feed utilization of common sole juveniles. The inclusion of MM in the present trial allowed a higher SGR than that registered in previous growth trials on common sole. This study could provide useful information to detect effective ingredients for practical diets in Solea solea. It also seems advisable to consider an inclusion of at least 25% MM in the experimental reference diet to be used for further application towards the development of specific diets for this species.     

饲料糖水平对大黄鱼生长和糖代谢的影响

以初始体重为（137.5±0.4）g的大黄鱼Larimichthys crocea为实验对象,在海水浮式网箱中进行为期8周的摄食生长实验,研究饲料中糖水平对其生长、饲料利用、血液生化指标和糖代谢酶活力等的影响,以确定大黄鱼的饲料糖需求量。实验饲料按等氮（粗蛋白质45%）等能（18 kJ/g）设计,糖含量分别为1.75%、6.67%、13.64%、21.15%、26.69%和32.25%。结果表明随着饲料糖水平的升高,大黄鱼特定生长率（SGR）先升高后降低,当糖含量为26.69%时,SGR达最大值,显著高于糖含量为1.75%、6.67%、13.64%和32.25%处理组（P < 0.05）。饲料效率（FER）和蛋白质效率（PER）均在糖含量为13.64%-21.15%时显著高于其他处理组（P < 0.05）。随饲料中糖水平的升高,全鱼粗脂肪含量显著降低,在糖含量为32.25%时降至最低（10.56%）,显著低于其他处理组（P < 0.05）。肝体比和肝糖原含量均随饲料糖水平的升高而显著升高（P < 0.05）,在糖含量为32.25%时达到最大值,显著高于糖含量为1.75%和6.67%处理组（P < 0.05）。随饲料糖水平的升高,血浆甘油三酯和胆固醇水平均显著降低（P < 0.05）,而血糖水平不受饲料糖含量的影响（P>0.05）。大黄鱼血清溶菌酶、脂蛋白脂酶和肝脂酶活性均随饲料糖水平的升高显著降低（P < 0.05）,而肠淀粉酶活性表现为先升高后降低,在糖含量为26.69%时,酶活力达到最大值。随饲料糖水平的升高,大黄鱼肝脏己糖激酶活性先上升后下降,在糖含量为21.15%时达到最大值,显著高于糖含量为32.25%处理组（P < 0.05）,而丙酮酸激酶活力在糖水平为32.25%时达到最大值,显著高于糖含量为1.75%和6.67%处理组（P < 0.05）。用二次多项回归模型拟合特定生长率和饲料糖水平的关系,得到大黄鱼饲料中最适糖含量为22.7%。     

Growth performance,antioxidant and immune status of Siberian sturgeon (Acipenser baeri) fed diets containing green tea extract and oxidized fish oil

The present study was conducted to determine the effects of dietary oxidized fish oil (OFO) and green tea extract (GTE) on growth performance, antioxidant status and immunological parameters in Siberian sturgeon (Acipenser baeri). Fish weighing about 108 g were randomly assigned to one of nine dietary treatments (control diet without OFO and GTE; diets containing only 25 or 50 mg/kg of GTE; diets containing 50 mg/kg of OFO combined with 0, 25 or 50 mg/kg of GTE; diets containing 100 mg/kg of OFO combined with 0, 25 or 50 mg/kg of GTE) with three replicates of 15 fish stocked in fiberglass tanks using a completely randomized design. Growth performance indices, immunological parameters and antioxidant status of all treatment groups were determined using appropriate assays and compared. Results showed that GTE could enhance growth performance. Feeding GTE alone or combined with the OFO could decrease the hepatosomatic index (HSI) and viscerosomatic index (VSI). Serum lysozyme activity and antibody level were increased significantly by GTE alone or combined with OFO compared to the oxidized diets (p < 0.05). Conversely, lipid peroxidation products and antioxidant enzyme activity were significantly lower in GTE treatment groups and those that received combination of GTE and OFO compared to the oxidized diets. Low‐density lipoprotein (LDL) level in GTE groups was lower than other treatment groups (p < 0.05) however, in OFO treatment groups the LDL level in fish serum was significantly increased in comparison with the other treatment groups (p < 0.05). GTE and OFO alone or combined together significantly decreased the levels of triglyceride and cholesterol compared to the control group (p < 0.05). In conclusion, immunological and biochemical parameters were improved by inclusion of GTE into Siberian sturgeon rancid diets which can protect fish from the oxidative damage challenged by dietary oil oxidation.     

Growth performance and body composition in response to dietary protein and lipid levels in Nile tilapia (Oreochromis niloticus Linnaeus, 1758) subjected to normal and temporally restricted feeding regimes

A factorial experiment was designed to examine the effect on compensatory growth (CG) of Nile tilapia Oreochromis niloticus fed diets containing different protein and lipid levels under normal and temporally restricted feeding regimes. Four diets were formulated to contain either 30% or 36% crude protein, and 5% or 11% crude lipid. Triplicate replicates of each treatment were assigned to 24 150‐L tanks (20 fish/tank density). Fish (mean initial weight ± SD = 8.79 ± 0.34 g) were then fed either the normal feeding regime (thrice daily to apparent satiation) or the restricted regime (1 day feed deprivation followed by 3 days of feeding to apparent satiation) over a 44‐days study period. Fish receiving a diet under the restricted regime achieved weight gains (WG) comparable to fish consuming the diet containing 30% protein and 5% lipids under the normal feeding regime. Fish maintained on the restricted feeding regime exhibited reduced feed intake (FI), WG, feed efficiency ratio (FE), protein efficiency rate (PER) and hepatosomatic index versus fish on the normal feeding regime, except WG in fish fed the diet with 30% protein and 5% lipids. However, the resultant FI (85%~94%) was higher than the excepted 75% intake when fish were subjected to the restricted regime. Feeding 11% lipid diets led to improved FI, WG, FE, and PER compared to feeding the 5% lipid diets. Increased FI, WG, and FE, but reduced PER were observed in fish fed with 36% protein versus fish fed 30% protein. Fish receiving the 36% protein diets had lower whole‐body moisture and ash contents, but elevated whole‐body protein and lipid contents compared to those receiving the 30% protein diets. Whole‐body moisture contents were lower, but whole‐body protein, lipid and ash contents were higher in fish fed 11% lipid diets than in fish fed 5% lipid diets. There was an increase in whole‐body moisture content, but a decrease in protein and lipid content in response to the restricted feeding regime. Ash content was not affected by the feeding regime. The present study shows that Nile tilapia fed diets subjected to a restricted feeding regime exhibited growth comparable to those fed the diet at 30% protein and 5% lipid levels under a normal feeding regime. This positive effect was more pronounced in diets at a high protein level or in a combination of high protein and lipid levels.     

Phytase can reduce theneedfor monocalcium phosphate supplementation in soybean and rapeseed meal‐based diets of black sea bream,Acanthopagrus schlegelii (Bleeker, 1854)

A feeding trial was conducted to study the effect of partial replacement of dietary monocalcium phosphate (MCP) with phytase on growth performance, feed utilization and phosphorus discharge in black sea bream, Acanthopagrus schlegelii. In the feeding trial, the control diet (designated as P1.5) was prepared with 1.5% MCP but without phytase, and the three other diets (designated as PP1.0, PP0.5 and PP0, respectively) were supplemented with 1.0%, 0.5% and 0% MCP, respectively, along with 200 mg (400 U) phytase/kg diet in each. Each diet was tested in triplicate tanks and fish were fed twice daily to satiation. After an 8‐week feeding trial in indoor flow‐through cylindrical fibreglass tanks (25 fish per tank, initial body weight: 11.5 ± 0.12 g), fish fed with PP1.0 and PP0.5 had no significant change in weight gain (WG), specific growth rate (SGR), protein efficiency rate (PER) or feed conversion ratio (FCR) compared to the control (p > .05), whereas fish fed with PP0 showed a significantly lower growth performance in the above parameters (p < .05). The addition of phytase did not affect the body composition or muscle composition. The apparent digestibility coefficients (ADCs) of crude protein and phosphorus increased when fish were fed diets in which MCP was replaced by phytase. Phosphorus discharge was also significantly reduced in fish fed diets in which MCP was replaced by phytase (10.2 ± 0.50 to 8.01 ± 0.47 g/kg weight gain). The present study suggests that dietary MCP can be reduced when phytase is added to the black sea bream diet, with a maximum MCP reduction level of up to 1% when phytase is supplemented at 200 mg (400 U)/kg diet. Thus, phytase in the diet of black sea bream is economically and ecologically beneficial.     

Modulation of blackspot seabream (Pagellus bogaraveo) intermediary metabolic pathways by dispensable amino acids

The objective of the present work is to investigate the main metabolic pathways by which dispensable amino acids (DAA) are diverted towards lipid formation in blackspot seabream. For that purpose, a control diet was formulated to contain 45% of crude protein (7.2 g N/100 g dry matter) mainly supplied by fish meal (45P). In two other diets, 22.2% of the dietary nitrogen (1.6 g N/100 g dry matter) was replaced by an equivalent amount of nitrogen provided by two different mixtures of DAA: alanine and serine (diet AS) or aspartic and glutamic acid (diet AG). A fourth diet (diet 35P) only containing 35% of crude protein (5.6 g N/100 g dry matter) was included in order to analyze the possible additive effects of DAA. Compared to fish fed diet 35P, blackspot seabream appear to make a more efficient use of the nitrogen provided by alanine and serine than that provided by aspartic and glutamic acids in terms of growth. Contrary to fish fed AG, fish fed AS attained similar specific FAS activities as 45P fed fish, suggesting a further role of alanine and serine on this lipogenic pathway. Dietary nitrogen reduction (45P vs. 35P) or its replacement by a mixture of aspartic and glutamic acids (diet AG) were shown to up-regulate phosphoenolpyruvate carboxykinase (PEPCK) but without, however, any effect on plasma glucose levels. Dietary nitrogen level and nature seems to exert a complex regulation on energetic pathways through the gluconeogenesis/tricarboxylic acids cycle interaction.     

Effect of dietary fiber of “Rihane” barley grains and azoxymethane on serum and liver lipid variables in Wistar rats

The aim of the present study is to evaluate the effects of diet enriched with dietary fiber of barley variety “Rihane” and azoxymethane on serum and liver lipid variables in male rats. Forty male rats were divided into four groups and fed on control diet or experimental diet that contained control enriched with dietary fiber of barley variety “Rihane”. Animals were injected with saline (controls) or azoxymethane (20 mg/kg body weight s.c.) at 7 and 8 weeks of age. The experimental diet significantly decreased cholesterol level compared with the control diet. Rats fed with BR diet significantly increased the serum high-density lipoprotein (HDL) cholesterol and significantly decreased low-density lipoprotein (LDL) cholesterol concentrations. The experimental diet decreased the atherogenic index (p < 0.05) compared with the control diet. Whereas the azoxymethane induced a significant increase of liver lipid, serum LDL and triglyceride concentrations, but it caused a significant reduction of HDL. Consequently, the ratio of HDL/TC decreased significantly compared with the control (p < 0.05). Accordingly, these results indicated that the diet enriched with dietary fiber of barley variety “Rihane” could be effective in decreasing the atherogenic risk factors in rats whereas the use of the azoxymethane as colon-specific carcinogen substance altered the lipid metabolism.     

Adequate dietary protein level enhances stress resistance and immune status of blunt snout bream (Megalobrama amblycephala Yih, 1955)

This study hypothesized that an optimum dietary protein level might play an important role in improving stress tolerance, enhancing an immune function, and ultimately minimizing temperature stress. For this purpose, the present study conducted a 10‐week feeding trial followed by a 7‐day stress experiment to evaluate the effects of dietary protein levels (28%–36%) on the physiological performances and hepatic Hsp70 gene expression in blunt snout bream Megalobrama amblycephala fry under a high temperature challenge. Fish fry (initial weight, 16.08 ± 0.03 g, n = 25) were fed with their respective diets to apparent satiation, and samples taken once before stress and four times during high temperature stress days (0.125, 0.5, 2 and 7 days). Serum total protein and cholesterol contents before stress were affected by dietary protein levels; during stress these parameters showed no significant changes up until day 2, showing some changes thereafter. Regardless of 0.125, 0.5, 2 or 7 days during stress, cortisol and aspartate aminotransferase levels in the group fed 32% dietary protein were significantly lower than in the other groups. At 0.125, 0.5 or 2 days during stress, the complement component 3 (C3) and 4 (C4) levels increased significantly up to certain levels, declining thereafter. The expression level of Hsp70 mRNA before stress was not affected by dietary protein levels, but increased significantly from 0.125 to 0.5 days during stress, and was reduced thereafter. Overall, low cortisol and high C3, C4 and Hsp70 mRNA levels were found in the group fed 32% protein throughout the stress experiment, which indicated that an adequate protein level enhances stress resistance and immunity in fish.     

饲料脂肪水平对瓦氏黄颡鱼生长及脂蛋白脂酶基因表达的影响

研究采用脂肪水平分别为4.7%、7.9%、10.9%、15.4%、18.9%的五种等氮配合饲料饲喂瓦氏黄颡鱼早期幼鱼,进行了为期30d的生长实验,探讨了瓦氏黄颡鱼早期幼鱼的脂肪需求。并克隆了瓦氏黄颡鱼脂蛋白脂酶(LPL)cDNA序列片段,采用实时荧光定量PCR研究了饲料脂肪水平对肝脏LPL基因表达水平的影响。结果表明,饲料脂肪水平从4.7%增加到10.9%显著促进了瓦氏黄颡鱼早期幼鱼的生长(P<0.05)。饲料脂肪水平显著影响了实验鱼的鱼体体成分,随着饲料脂肪水平的升高,鱼体干物质和脂肪含量显著增加而蛋白含量显著下降(P<0.05)。高脂诱导了瓦氏黄颡鱼肝脏LPL基因表达,摄食15.4%、18.9%这两组较高脂肪水平的实验鱼肝脏LPLmRNA表达水平显著升高(P<0.05)。根据特定生长率通过折线回归分析得出瓦氏黄颡鱼早期幼鱼最适脂肪水平为11.2%。       

饲料蛋白质水平与投喂频率对大黄鱼生长、体组成及蛋白质代谢的影响

以初始体重为(13.640.18)g的大黄鱼( Pseudosciaena crocea R.) 幼鱼为实验对象, 采用32双因子实验, 研究饲料蛋白质水平(40%、45%、50%)和投喂频率(2次/d、1次/d)及其交互作用对其生长、体组成和蛋白质代谢的影响。养殖实验在海水浮式网箱中进行, 养殖周期为8周。结果表明: 饲料蛋白质水平和投喂频率对大黄鱼幼鱼的增重率(WGR)、特定生长率(SGR)和饲料转化率(FCR)均影响显著(P0.05)。在40%和45%蛋白质组, 1次/d投喂的大黄鱼幼鱼的WGR和SGR均显著低于2次/d投喂组, 而FCR则相反。在2次/d投喂时, 45%蛋白质组的大黄鱼幼鱼SGR显著高于40%蛋白质组, 但与50%蛋白质组差异不显著(P0.05)。而在1次/d投喂时, 50%蛋白质组的大黄鱼幼鱼SGR显著高于40%和45%蛋白质组。在两种投喂频率下, 随着饲料蛋白质水平提高, 鱼体水分含量均有升高趋势, 蛋白质含量显著升高而脂肪含量显著下降(P0.05)。饲料的蛋白质水平和投喂频率分别对大黄鱼幼鱼的肝脏指数(HSI)、内脏指数(VSI)和血清中的谷丙转氨酶(ALT)及谷草转氨酶(AST)均影响不显著(P0.05)。投喂频率对肝脏的ALT和AST的影响不显著(P0.05)。在同一投喂频率下, 肝脏ALT和AST均随着饲料蛋白质水平的增加而显著提高(P0.05)。饲料中的蛋白质水平和投喂频率对大黄鱼幼鱼的生长和FCR的影响存在显著的交互作用(P0.05), 而对血清和肝脏中的ALT和AST、HSI、VSI、肥满度(CF)以及体组成的影响均无交互作用。       

Cold storage effects on flesh quality of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) fed diets containing different vegetable oils

The intention of this experiment was to assess the effects of different sources of dietary lipid on the fatty acid composition of the fillet and liver and the flesh quality traits of rainbow trout (Oncorhynchus mykiss) after a 70‐day feeding period. Four iso‐nitrogenous (approx. 51% crude protein) and iso‐lipidic (approx. 14% crude lipid) experimental diets were formulated. The control diet contained only fish oil (FO) as the primary lipid source. In the other three dietary treatments, fish oil was replaced by 100% (LO30/SO35/SFO35) and 70% (FO30/LO35/SO35 or FO30/SO35/SFO35) sesame oil (SO), linseed oil (LO), or sunflower oil (SFO). Triplicate groups of 40 rainbow trout (~46 g) held under similar culture conditions were hand‐fed daily to apparent satiation for 70 days. At the end of the feeding trials, no difference in growth performance among experimental groups was noted (P > 0.05). There were some differences in the proximate composition of fish fillets (P < 0.05): the eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels were highest in fish fed the control diet (P < 0.05); and EPA and DHA levels in fish fed the FO30/LO35/SO35 diet were closest to the control diet (P < 0.05). In contrast, fish fed the diet containing 100% plant oils (LO30/SO35/SFO35) had the highest level of total n‐6 fatty acids in the fillet and liver. In a 12‐day refrigerated storage at 1°C the thiobarbituric acid (TBA), trimethylamin nitrogen (TMA‐N) and pH values gradually increased in all dietary groups (P < 0.05). The chemical indicators of spoilage, TBA, TMA‐N, and pH values were within the limit of acceptability for human consumption.     

Effects of dietary protein intake on the oxidation of glutamate,glutamine, glucose and palmitate in tissues of largemouth bass (Micropterus salmoides)

Largemouth bass (Micropterus salmoides, a carnivorous fish native to North America) prefers to utilize amino acids as energy sources rather than glucose and fatty acids. However, little is known about the nutritional regulation of substrate oxidation in the fish. Therefore, this study was conducted to determine whether the oxidation of glutamate, glutamine, glucose and palmitate in its tissues might be influenced by dietary protein intake. Juvenile largemouth bass (initial weight 18.3 ± 0.1 g) were fed three isocaloric diets containing 40%, 45% and 50% protein for 8 weeks. The growth performance, energy retention, and lipid retention of juvenile fish increased with increasing dietary protein levels. The rate of oxidation of glutamate by the intestine was much greater than that of glutamine, explaining why increasing the dietary protein content from 40% to 50% had no effect on the serum concentration of glutamate but increased that of glutamine in the fish. The liver of fish fed the 50% protein diet had a higher (P < 0.05) rate of glutamine oxidation than that in the 40% and 45% protein groups. In contrast, augmenting dietary protein content from 40% to 45% increased (P < 0.05) both glutamine and glutamate oxidation in the proximal intestine of the fish and renal glutamine oxidation, without changes in intestinal or renal AA oxidation between the 45% and 50% protein groups. Furthermore, the rates of glucose oxidation in the liver, kidney, and intestine of largemouth bass were decreased in response to an  increase in dietary  protein content   from 40% to 45% and a concomitant decrease in dietary starch content from 22.3% to 15.78%, but did not differ between the 45% and 50% protein groups.   The rates of oxidation of glucose in skeletal muscle and those of palmitate in all tissues (except for the  kidney) were not affected by the diets. Collectively, these results indicate that the largemouth bass can regulate substrate metabolism in a  tissue-specific manner to favor protein and lipid gains as dietary protein content increases from 40% to 50% and have a lower ability to oxidize fatty acids and glucose than amino acids regardless of the dietary protein intake.