Effects of vitamin E supplementation on growth,lipid peroxidation and fatty acid composition of Dojo loach (Misgurnus anguillicaudatus Cantor) fingerlings

A high mortality of cultured loach during their early development has constrained loach aquaculture industry in China. The objective of this study was to evaluate the effects of dietary vitamin E (VE) supplementation on growth performance, lipid peroxidation and fatty acid composition of loach Misgurnus anguillicaudatus fingerlings. Six test diets supplemented with 0 (0E), 50 (50E), 100 (100E), 150 (150E), 200 (200E) and 500 mg kg^?1 (500E) of dl‐α‐tocopheryl acetate were fed loach fingerlings (mean initial weight 24.0 ± 0.2 mg) in triplicate for 40 days. Results showed that the fish fed diet 100E and 200E had significantly higher body weight gains and specific growth ratios and significantly lower feed conversion ratios compared with fish fed diet 0E. With the increase in dietary VE level, whole‐body VE content was significantly increased (except 500E) and thiobarbituric acid reactive substances value was significantly reduced. Increasing dietary VE level increased the percentages of 20:4n‐6 and 20:5n‐3 in neutral lipid fraction, but decreased the percentages of 20:4n‐6 and 20:5n‐3 in polar lipid fraction. In conclusion, VE requirement of loach fingerlings for optimum growth and functionally preventing lipid peroxidation was 136.1 mg kg^?1 of dry diet under the present experimental conditions.     

Effects of dietary highly unsaturated fatty acid levels on growth,fatty acid profiles,antioxidant activities,mucus immune responses and hepatic lipid metabolism related gene expressions in loach (Misgurnus anguillicaudatus) juveniles

A 9‐week rearing trail was conducted to examine the effects of different dietary highly unsaturated fatty acid (HUFA) levels on the growth performance, fatty acid profiles, antioxidant activities, mucus immune responses and lipid metabolism‐related gene expressions of loach (Misgurnus anguillicaudatus) juveniles. Five test diets supplemented with 0%, 0.32%, 0.64%, 0.96% and 1.28% HUFA were used here. The loaches fed no HUFA diets had the lowest specific growth rate and survival rate. The loaches fed 0.32% HUFA diets had the lowest feed conversion rate and while no significant differences were found among the other four diet groups. Contents of hepatic eicosapentaenoic acid, docosahexaenoic acid and total polyunsaturated fatty acids were significantly increased with incremental dietary HUFA levels. Activities of hepatic superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) in 0% HUFA group were lowest, while malondialdehyde was just the opposite. The lysozyme activity was significantly increased with incremental dietary HUFA levels. However, the activities of alkaline phosphatase and acid phosphatase reached a peak in 0.32% HUFA group. Loaches fed diets with HUFA significantly up‐regulated expressions of SOD, GPx, CAT and two lipid metabolism related genes. In conclusion, the optimal dietary HUFA level for loach juveniles was 0.64%–0.96%.     

Effects of different dietary vitamin C supplementations on growth performance,mucus immune responses and antioxidant status of loach (Misgurnus anguillicaudatus Cantor) juveniles

A 60‐day feeding trial was conducted to determine the effects of different dietary vitamin C levels on growth performance, immune response and antioxidant capacity of loach juveniles. Six isonitrogenous (58.6% of crude protein), isoenergetic (17.5 kJ g^?1) practical diets supplemented with 0 (VC0), 100 (VC100), 200 (VC200), 500 (VC500), 1000 (VC1000) and 5000 mg kg^?1 (VC5000) of VC (35% ascorbic acid equivalent) were fed to fish (mean initial weight 0.11 ± 0.02 g) in triplicate. Results showed that fish fed VC0 diet had significantly lower body weight gain (BWG) and survival rate (SR). However, BWG and SR improved significantly in fish fed VC100 and VC200 diet respectively. Whole body ascorbic acid concentration increased with incremental dietary VC levels from 0 to 100 mg kg^?1. The activity of mucus alkaline phophatase was significantly increased by the dietary VC level. Incremental levels of VC significantly reduced activities of glutathione peroxidase (GPx) and catalase. Moreover, fish fed diets containing more than 100 mg kg^?1 VC significantly down‐regulated the superoxide dismutase and GPx mRNA expression in liver. Meanwhile, the expressions of liver heat shock protein (HSP70) and nuclear factor‐erythroid 2‐related‐2 (Nrf2) were affected by fish fed diets containing VC from 100 to 5000 mg kg^?1. In conclusion, VC requirement of loach juveniles for optimum growth and functionally preventing lipid peroxidation was more than 200 mg kg^?1 of diet. Moreover, high dose of VC supplementation did not show any detrimental effects on loach growth performance.     

Optimum dietary protein and lipid levels for juvenile rockfish (Sebastes schlegeli,Hilgendorf 1880)

Optimum dietary protein and lipid levels for juvenile rockfish were determined. Eight hundred and ten juvenile fish averaging 3.22 g were randomly chosen and distributed into 27 flow‐through tanks of 50 L (30 fish per tank). Nine experimental diets were prepared according to a 3 × 3 factorial experimental design: three crude protein levels (45%, 50% and 55%) × three crude lipid levels (11%, 15% and 19%). Crude protein and crude lipid levels increased at the expense of dextrin and cellulose in the experimental diets. Survival of fish was not affected by either dietary protein or lipid level. Weight gain of fish was affected by dietary protein level, but not by dietary lipid level. Weight gain of fish fed the 50P‐15L (50% protein and 15% lipid) diet was higher than that of fish fed the 45% protein diets regardless of lipid level, but not different from that of fish fed the 50P‐11L (50% protein and 11% lipid), 50P‐19L (50% protein and 19% lipid), 55P‐11L (55% protein and 11% lipid), 55P‐15L (55% protein and 15% lipid) and 55P‐19L (55% protein and 19% lipid) diets. Feed consumption of fish was affected by dietary protein level, but not by dietary lipid levels. Feed efficiency ratio (FER) of fish was affected by dietary protein level, but not by dietary lipid level. Protein efficiency ratio (PER) of fish was affected by dietary protein level, but not by dietary lipid level. Nitrogen retention efficiency (NRE) of fish fed the 45P‐19L diet was higher than that of fish fed the 45P‐11L, 50P‐11L, 50P‐15L, 50P‐19L, 55P‐11L, 55P‐15L and 55P‐19L diets, but not different from that of fish fed the 45P‐15L diet. Moisture, crude protein and crude lipid contents of fish was affected by dietary protein and/or lipid level. Plasma triglyceride of fish was affected by dietary lipid level, but not by dietary protein level. In conclusion, optimum protein and lipid levels for growth and feed utilization (PER and NRE) for juvenile rockfish were 50% and 15%, and 45% and 19%, respectively, and the optimum dietary protein‐to‐energy ratio of 27.4 and 23.9 mg protein kJ^?1.     

Effects of dietary protein and lipid levels on growth,feed utilization and body composition in Pseudobagrus ussuriensis fingerlings

An 8‐week feeding trial was conducted to investigate the optimum dietary protein and lipid levels for growth, feed utilization and body composition of Pseudobagrus ussuriensis fingerlings (initial weight: 3.40 ± 0.01 g). Twelve diets containing four protein levels (350, 400, 450 and 500 g kg^?1 crude protein) and three lipid levels (50, 100 and 150 g kg^?1 crude lipid) were formulated. Fish were randomly allotted to 36 aquaria (1.0 × 0.5 × 0.8 m) with 25 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. The results showed that weight gain and specific growth rate (SGR) decreased with increasing dietary lipid level from 50 to 150 g kg^?1 at the same dietary protein level. Fish fed the diets containing 150 g kg^?1 lipid exhibited higher feed conversion ratio (P < 0.05), lower protein efficiency ratio (PER) and nitrogen retention efficiency (NRE) relative to fish fed the diet containing 50 and 100 g kg^?1 lipid. Weight gain and SGR significantly increased with increasing dietary protein from 350 to 450 g kg^?1 at the same dietary lipid level, and even a little decline in growth with the further increase in dietary protein to 500 g kg^?1. Daily feed intake, NRE and PER were significantly affected by both dietary protein and lipid levels (P < 0.05) and tended to decrease with increasing dietary protein and lipid levels. Whole‐body protein content increased as protein levels increased and lipid levels decreased. Whole‐body lipid and muscle lipid content increased with increasing dietary lipid level, and decreased with increasing dietary protein at each lipid level. There was no significant difference in condition factor and viscerosomatic index among fish fed the diets. Hepatosomatic index was affected by dietary lipid level (P < 0.05), and increased with increasing dietary lipid level at the same protein level. These results suggest that the diet containing 450 g kg^?1 protein and 50 g kg^?1 lipid with a P/E ratio of 29.1 mg protein kJ^?1 is optimal for growth and feed utilization of P. ussuriensis fingerlings under the experimental conditions used in the study.     

Effect of Dietary Protein and Lipid Levels on Growth and Body Composition of Spotted Halibut,Verasper variegatus

A 83‐d feeding experiment was undertaken to evaluate the effects of dietary protein and lipid levels on growth and body composition of spotted halibut, Verasper variegatus (initial average weight of 93.0 ± 1.0 g). Nine diets were formulated to contain three protein levels (40, 45, and 50%), each with three lipid levels (8, 12% and 16%). Each diet was randomly fed to triplicate groups of 20 fish per tank in the indoor culture system. Results showed that the survival rate of fish was not significantly affected by protein and lipid levels (P > 0.05). Weight gain, specific growth rate (SGR), and feed intake (FI) significantly decreased with the increasing dietary lipid levels (P < 0.05). Feed efficiency significantly increased while the feed conversion ration significantly decreased with increasing dietary protein levels (P < 0.05). Weight gain, SGR, FI, and feed efficiency of fish fed 50% protein and 8% lipid were significantly higher than that of the other groups. For each level of dietary lipid, the increase in dietary protein resulted in significant increases in whole‐body crude protein (CP) contents (P < 0.05); the increase in dietary lipid caused significant increases in whole‐body crude lipid content and gross energy at each protein level (P < 0.05). The muscle CP, lipid, and gross energy had the same tendency. The results of this study indicated that increasing dietary lipid levels did not result in a protein‐sparing effect. It could be recommended that the proper dietary protein and lipid levels of spotted halibut were 50 and 8%, respectively.     

The effects of dietary protein and lipid on growth and body composition of juvenile and sub-adult red snapper, Lutjanus campechanus (Poey, 1860)

To allow for the initial identification of practical diet formulations for red snapper culture, the present study was conducted to evaluate the effects of feeding varying levels of dietary protein and lipid on growth and body composition of juvenile and sub‐adult red snapper. Twelve diets were formulated to contain varying levels of dietary protein and lipid. In trial 1, juvenile red snapper (initial mean weight 5.9 g) were offered diets with graded levels of dietary protein (32%, 36%, 40%, 44%) and practical energy to protein ratios. In trial 2, juvenile red snapper (initial mean weight 8.64 g) were offered isonitrogenous diets (44% protein) containing graded levels of dietary lipid (8%, 10%, 12%, 14%). Sub‐adult fish (initial mean weight 151.5 g) were used in trial 3 and maintained on diets similar to those of trial 1 (32–44% protein). Sub‐adult fish (initial mean weight 178.3 g) in trial 4 were offered isonitrogenous diets containing 32% dietary protein and graded levels of dietary lipid (6%, 8%, 10%, 12%). There were no significant differences in growth, feed efficiency ratio (FER) or survival in juvenile fish. Juvenile fish offered 32% dietary protein exhibited a significantly greater (P=0.0497) protein conversion efficiency (PCE) than fish offered a diet containing 44% dietary protein. Juvenile fish in trial 2 also had significantly higher (P=0.005) intraperitoneal fat ratios (IPFRs) at 14% dietary lipid than fish offered diets containing 8–10% dietary lipid, and displayed trends towards greater protein as a percent of whole‐body composition at 8–10% dietary lipid. Sub‐adult snapper in trials 3 and 4 showed no significant differences in growth, FER or survival. However, in trial 4 there was a general trend towards increased % weight gain (P=0.0615), FER (P=0.0601) and final mean weight (P=0.0596) with increasing levels of dietary lipid. Fish in trial 4 offered 6% dietary lipid also had significantly lower (P=0.0439) IPFR and PCE (P=0.0188) than fish offered 12% dietary lipid. Based on data obtained from these trials, inclusion of dietary protein at levels of 32–36% appears sufficient to support growth. For this level of protein, dietary lipid should be ～10% in order to meet the energetic demands of the fish and to spare dietary protein for growth.     

Dietary protein requirement of juvenile obscure puffer,Takifugu obscurus

A 10‐week feeding experiment was conducted to determine the optimum dietary protein requirement of juvenile obscure puffer (Takifugu obscurus). Six isoenergetic (20 MJ kg^?1 gross energy) diets were formulated to contain graded levels of 34%, 38%, 42%, 46%, 50% or 54% crude protein (as dry matter basis). The results showed final body weight, weight gain and specific growth rate (SGR) increased significantly with increasing protein levels up to 42% and then decreased thereafer. Second‐order polynomial regression analysis (y = ?0.0024x² + 0.1788x ? 1.3196, R² = 0.9032) indicated a maximum SGR at protein level of 37%. Feed conversion ratio (FCR) decreased with increasing levels of dietary protein up to 42% and increased thereafter. Second‐order polynomial regression analysis (y = 0.0054x² ? 0.4351x + 10.391, R² = 0.753) indicated a minimum FCR at protein level of 40%. Protein efficiency ratio (PER) of fish fed the 34%, 38% and 42% diets was significantly higher than that of fish fed the 46%, 50% and 54% diets, and broken‐line analysis indicated PER tended to decrease when dietary protein level was higher than 40%. Generally, whole body lipid content, total cholesterol, low‐density lipoprotein cholesterol and triacylglycerol decreased with increasing levels of dietary protein. Fish fed the 42% protein diet showed the highest essential amino acids (histidine, isoleucine, leucine, lysine and threonine) and non‐essential amino acids (aspartic acid and glutamic acid) in muscle. Based on the second‐degree polynomial regression analysis of SGR and FCR and broken‐line analysis of PER, the optimal dietary protein level of obscure puffer is estimated to be between 37% and 40% (% as dry matter basis).     

Effect of Dietary Lipid Level and Feeding Frequency on the Growth,Feed Utilization,and Body Composition of Juvenile Spotted Seabass,Lateolabrax maculatus

A 6‐wk feeding trial was conducted to evaluate the effects of different dietary lipid levels and feeding frequencies on the growth performance, feed utilization, and body composition of juvenile spotted seabass, Lateolabrax maculatus. Two experimental diets were prepared with two different dietary lipid contents, low lipid (7%; LL) and high lipid (14%; HL). Each diet was fed to triplicate groups of fish (5.5 ± 0.01 g) to apparent satiation at three meals per day, two meals per day, one meal per day, and one meal every 2 d, respectively, for 6 wk. Fish growth performance in terms of weight gain (WG) and specific growth rate (SGR) was significantly affected by frequency of feeding, with increasing values as feeding frequency increased up to twice daily, regardless of dietary lipid content. In addition, fish fed the diet with the HL level (14%) showed significantly higher WG and SGR than those fed the LL diet (7%) at all the feeding frequencies tested. Feed efficiency (FE) and protein efficiency ratio (PER) were affected by both dietary lipid level and feeding frequency. FE and PER values were significantly higher in fish fed the HL diet and/or when fish were fed twice or thrice a day. However, daily feed intake and daily energy intake were significantly affected only by feeding frequency and were significantly reduced when the fish were fed only once every 2 d compared with those fed more frequently. Whole‐body moisture content of fish tended to decrease with increasing dietary lipid level and frequency of feeding. In contrast, whole‐body lipid content increased in fish as dietary lipid level and feeding frequency increased. Consequently, we can conclude that feeding spotted seabass twice daily to apparent satiation is acceptable and sufficient to achieve good growth and FE, as fish performance was not significantly enhanced when feeding was increased from two to three times daily.     

Effects of dietary protein levels on the growth,survival, amylase and trypsin activities in large yellow croaker,Pseudosciaena Crocea R., larvae

A feeding trial was conducted to investigate the effects of dietary graded protein levels on the growth, survival, amylase and trypsin activities of large yellow croaker (Pseudosciaena crocea R.) larvae from 12 to 42 days after hatching (DAH). Five approximately isoenergetic microbound diets (16.65 MJ/kg diet) were formulated to contain different protein (47.1%, 52.0%, 57.1%, 62.2% and 67.5%) levels. Frozen copepods, containing 54.5% crude protein (CP), 6.0% crude lipid, 27.2% ash and 6.7% glycogen, were used as a control. Each diet was randomly fed to triplicate groups of larvae with an initial mean body weight of 1.76 ± 0.09 mg (mean ± SD) in 180 L white plastic tanks, and each tank was stocked initially with 3500 larvae. Both the survival and the specific growth rate (SGR) of large yellow croaker larvae significantly increased with increasing dietary protein level up to 57.1%, and decreased thereafter. Frozen copepods resulted in intermediate survival and low SGR compared with the other diets. Whole‐body moisture and protein of larvae were not significantly affected by the dietary protein level. In contrast, whole‐body lipid of larvae fed diet with 47.1% CP was significantly higher (P<0.05) than those from fish fed the diets containing more than 57.1% CP. Additionally, fish fed the frozen copepods had the lowest whole‐body protein and lipid. The amylase‐specific activity increased with increasing dietary carbohydrate level during the period of this experiment. However, trypsin activity was not significantly affected by the dietary protein content before 42 DAH, indicating a later onset of trypsin than amylase in the regulation of enzymatic synthesis induced by a dietary substrate.     

Optimum dietary protein to lipid ratio for Starry flounder (Platichthys stellatus)

An 8‐week feeding trial was conducted to evaluate the optimum dietary protein to lipid ratio (P/L) for Starry flounder Platichthys stellatus (30.7 ± 0.7 g initial weight). Nine fishmeal‐based diets with three protein levels (40%, 45% and 50%) and three lipid levels (8%, 11% and 14%) were fed to 30 fish in triplicate. Results showed that the growth performance was affected by dietary P/L ratio significantly, and the best weight gain rate, specific growth rate and feed conversion ratio were appeared at fish fed P45L14 and P50L11 diets. Apparent digestibility coefficient of protein was increased with increasing dietary lipid, but lipid digestibility was decreased by dietary lipid. Lipid deposition in tissues was increased with increasing dietary lipid at each protein level and was higher for the lower protein diets. In liver, the per cent of both eicosapentaenoic acid and docosahexaenoic acid were increased by dietary protein. High dietary protein level (50%) at high lipid level (14%) increased arachidonic acid significantly. Aspartate aminotransferase and alanine aminotransferase were affected significantly by dietary P/L ratios. High density lipoprotein cholesterol and total cholesterol of 45% protein groups were significantly higher than others. The study revealed that the optimum dietary protein to lipid ratio for starry flounder was P45L14 or P50L11, or P/E ratios were 25.49 and 27.70 mg protein kJ^?1 gross energy respectively.     

Growth performance and body composition of white seabream (Diplodus sargus) juveniles fed diets with different protein and lipid levels

An 83‐day feeding trial was carried out to determine the effect of different dietary protein and lipid levels on the growth performances and carcass composition of white seabream. Juveniles (10.7±0.2 g) were fed to satiation on four diets, varying in protein (15% and 28%) and lipid (12% and 16%) levels. The best growth performance was observed in fish fed on diets with higher protein level. Dietary lipids did not affect growth performance. Voluntary feed intake decreased with a increasing dietary protein level at both dietary lipid levels. Feed conversion ratio improved with the increase in dietary protein and lipid levels. Carcass composition remained unaltered by dietary protein levels (P>0.05). Carcass protein content tended to decrease, while lipid content tended to increase in groups fed on 16% lipid, compared with the 12% lipid groups. Additionally, protein retention was higher in fish fed on low‐protein and low‐lipid levels, compared with the high‐protein and high‐lipid group (29% vs. 19%). Lipid retention increased significantly with dietary protein level (P<0.001). Energy retention improved with dietary protein, but was not affected by dietary lipid levels. On the basis of our results, feeding white seabream on 15% dietary protein had a negative effect on growth and feed utilization. Dietary lipid did not induce a protein‐sparing action in Diplodus sargus juveniles.     

Influence of dietary lipid on growth performance and some lipogenesis‐related gene expression of tongue sole (Cynoglossus semilaevis) larvae

A 30‐day feeding trial was conducted to investigate the effects of dietary lipid levels on growth performance, activities of digestive enzymes, fatty acid composition and some lipogenesis‐related gene expression of half‐smooth tongue sole (Cynoglossus semilaevis) larvae. Five isoproteic diets were formulated with graded lipid levels (6.68%, 9.84%, 13.47%, 17.89% and 21.88% dry weight) using fish oil as the main lipid source. Each diet was randomly allocated to triplicate groups of 150 larval tongue sole (35 DAH, 54 ± 1 mg). Fish were fed five times daily to apparent satiation during the feeding experiment. Results showed that, the survival rate (SR) of larvae increased significantly firstly, and thereafter decreased significantly. The specific growth rates (SGR) of larvae fed the diet with 13.47% lipid were significantly higher than other treatments. Larvae fed 9.84% or 13.47% dietary lipid showed higher trypsin, lipase, leucine aminopeptidase and alkaline phosphatase (AP) activities than other treatments, whereas amylase activity nearly showed reverse trend with them. The fatty acid composition of the tongue sole larvae was well correlated with dietary fatty acid profile. Expression of acetyl‐CoA carboxylase alpha (ACC1) was found to be slightly negatively correlated with dietary lipid level, and high dietary lipid level depressed the expressions of acetyl‐CoA carboxylase beta (ACC2) and fatty acid synthase (FAS) mRNA expression significantly, implying that larvae may cope with high dietary lipid mainly through down‐regulating lipogenesis‐related gene expression of FAS and ACC2. Besides, on the basis of SGR, the optimal dietary lipid level for larval tongue sole was estimated to be 13.56% using second‐order polynomial curve.     

Effects of Protein and Lipid Levels in Practical Diets on Growth and Body Composition of Tongue Sole,Cynoglossus semilaevis Gunther

A 9‐wk feeding experiment was conducted to estimate the optimal dietary protein and lipid levels for tongue sole, Cynoglossus semilaevis Gunther (initial average weight of 43.8 ± 0.18 g). Six practical test diets were formulated to contain three protein levels (45, 50, and 55%, respectively) at two lipid levels (12 and 16%, respectively) with P/E ratios ranging from 87.1 to 110.5 mg protein/kcal. Each diet was randomly fed to triplicate groups of 20 fish per tank (1000 L). The results showed that fish fed the diet with 55% protein and 12% lipid (P/E ratio of 110.5 mg protein/kcal) had the highest thermal‐unit growth coefficient (TGC), feed efficiency ratio, protein productive value, and energy retention. TGC was significantly increased with increasing dietary protein levels irrespective of dietary lipid levels (P < 0.05). However, fish fed the diet with 16% lipid showed significant lower growth than fish fed the diet with 12% lipid. These results suggest that the diet containing 55% protein and 12% lipid with P/E of 110.5 mg protein/kcal is optimal for tongue sole and the increase of dietary lipid level has no effective protein‐sparing effect.     

Effects of dietary fish oil replacement by microalgae raw materials on growth performance,body composition and fatty acid profile of juvenile olive flounder,Paralichthys olivaceus

Replacing dietary fish oil with DHA‐rich microalgae Schizochytrium sp. and EPA‐rich microalgae Nannochloropsis sp. for olive flounder (Paralichthys olivaceus) was examined. Three experimental isonitrogenous and isolipidic diets with lipid source provided by 50% fish oil (F50S50), 50% (M50F25S25) and 100% microalgae raw material (M100) respectively were compared with a soybean oil (S100) diet as control. Triplicate groups of olive flounder juveniles (16.5 ± 0.91 g) were fed the experimental diets, and a group was fed the control diets for 8 weeks in a recirculation system. Results showed feed efficiency and growth performance were not significantly changed when fish oil (FO) was totally substituted by soybean oil (SO) or microalgae raw material (MRM). The whole‐body composition, lipid content of liver and muscle, and lipid composition of plasma were not significantly influenced by the total substitution of FO by MRM. The polyunsaturated fatty acids (PUFA) content of muscle and liver declined in fish fed S100 diet, whereas it was not significantly reduced in fish fed M50F25S25 and M100 diets. The total substitution of FO by MRM not only maintained the levels of arachidonic acid, EPA or DHA but also increased n‐3/n‐6 ratio. In conclusion, MRM as the sole lipid source is sufficient to obtain good feed efficiency, growth performance and human health value in olive flounder juveniles.     

Effects of dietary protein levels on the growth,body composition,serum biochemistry and digestive enzyme activity in Chinese rice field eel (Monopterus albus) fingerlings

A 12‐week feeding trial was conducted to determine the influence of dietary protein levels on growth performance, body composition, haematological parameters and digestive enzyme activity of Chinese rice field eel (Monopterus albus) fingerlings. Six isolipidic experimental diets (27.89%, 32.23%, 35.95%, 40.06%, 43.31% and 46.53%) were formulated to randomly assign to triplicate groups of 50 rice field eel fingerlings (5.0 ± 0.5 g) cultured in plastic cages. Results indicated that the best growth performance of fish with the highest WG (158.68 ± 31.59%) and SGR (2.28 ± 0.21%) was obtained at 40.06% group. Significant alterations were demonstrated on whole‐body crude protein, crude lipid and amino acid profile by different dietary protein levels. Besides, haematological parameters including triacylglycerol, aspartate aminotransferase and alkaline phosphatase decreased with various levels by the increasing of dietary protein levels. The lowest pepsin activity was observed in 27.89% protein group, which suggested lower availability of protein as substrate for protease activity. Meanwhile, the highest amylase activity in fish of 27.89% group indicated higher carbohydrate level in this group. Based on the polynomial regression analysis of WG and SGR, the dietary protein requirement for fingerlings of Monopterus albus was estimated to be 386.4–390.8 g/kg, respectively, with the lipid level of 10.08%.     

Effects of dietary protein at two lipid levels on growth,gonadal development,body composition and liver metabolic enzymes of brown trout (Salmo trutta fario) broodstock

This study was conducted to estimate the effects of dietary protein and lipid levels on the growth, body composition, gonadal development and activity of liver metabolic enzymes of the brown trout Salmo trutta fario broodstock. Ten diets were formulated containing five different protein levels (360, 390, 420, 450 and 480 g/kg) and two different lipid levels (90 and 180 g/kg). The experiment was a completely randomized 5 × 2 factorial design. The fish with an initial body weight of 462.53 ± 45.40 g were cultured in a spring water flow‐through system for 77 days. The growth performance was affected by dietary protein and lipid levels. Increase in the dietary protein and lipid resulted in increase in the body lipid and protein contents. The male gonadosomatic index decreased in the groups treated with relatively high levels of protein (390–480 g/kg). The activities of the hepatic amino acid‐catabolizing enzymes—alanine aminotransferase and aspartate aminotransferase—increased significantly with the increase in the dietary protein level. The activities of the lipogenic enzymes (fatty acid synthetase and glucose‐6‐phosphate dehydrogenase) and gluconeogenic enzyme (fructose‐1,6‐bisphosphatase) increased with the increase in the dietary protein level. Further, an increase in the activities of glycolytic enzyme in liver with an increase in the dietary lipid was observed. The variation in some intermediary metabolizing enzymes due to dietary components supports the high‐metabolic adaptability of this species to dietary protein and lipid levels. A diet with 450 g/kg protein and 90 g/kg lipid with 24.56 mg/kJ protein/energy ratio maximizes the growth, feed efficiency and gonadal development.     

The effects of dietary lipid levels on performance and heat‐shock protein response of juvenile white seabass,Atractoscion nobilis

A feeding trial was conducted to study the effect of dietary lipid on growth performance and heat‐shock protein (HSP70 and HSP60) response of white seabass (WSB), Atractoscion nobilis. Five diets were formulated to contain 440 g kg^?1 protein from 300 g kg^?1 fish meal, 240 g kg^?1 soybean meal and 100 g kg^?1 soy protein concentrate with different levels of lipid: 100, 120, 140, 160 or 180 g kg^?1. At the end of the trial, heat shock response based on HSP70 and HSP60 was measured in liver and white muscle from fish at ambient temperature and temperature shock conditions. Final weight and percent gain were significantly higher for fish fed the 100 g kg^?1 lipid diet than for fish fed the rest of the diets (P ≤ 0.05). Feed conversion ratio was lowest for fish fed the 100 g kg^?1 lipid diet. The HSP70 and HSP60 responses were positively correlated to dietary lipid levels following temperature shock. At ambient temperature, HSP60 and HSP70 responses in muscle and HSP60 response in liver increased with dietary lipid level. Temperature shock significantly increased the HSP response of fish in all treatments. Results of this study demonstrated that a moderate (110–120 g kg^?1) level of dietary lipids would be recommended for production diets but a higher dietary lipid level may be required for optimal stress tolerance.     

Growth Performance and Proximate and Fatty Acid Compositions of Channel Catfish, Ictalurus punctatus, Fed for Different Duration with a Commercial Diet Supplemented with Various Levels of Menhaden Fish Oil

A 15‐wk study was conducted to evaluate the effect of supplemental menhaden fish oil levels and feeding duration on growth performance and tissue proximate and fatty acid (FA) compositions of juvenile channel catfish, Ictalurus punctatus. Dietary fish oil levels had no effect on final weight gain, feed efficiency, and survival of channel catfish. Tissue lipid contents were directly correlated to dietary lipid levels, while moisture contents were inversely related to dietary lipid levels. Fillet moisture contents progressively decreased, whereas fillet lipid increased with increasing feeding duration. Significant increase in saturated and total n‐3 FAs and decrease in monoenoic and total n‐6 FA in whole body and fillet were observed at each incremental level of dietary fish oil. Percentages of n‐3 and n‐3 highly unsaturated fatty acids in fillet of fish fed the control and 3% fish oil diets decreased with increasing feeding periods, whereas those of fish fed 6 or 9% added fish oil diets remained stable or increased. Ratios of n‐3/n‐6 were statistically comparable throughout the 15‐wk feeding. When expressed in terms of mg/g of fillet, the highest concentration of n‐3 was obtained in fillets of fish fed the 9% added fish oil diet for 15 wk.