Optimum Dietary Protein Level and Protein-to-Energy Ratio for Growth of Juvenile Korean Rockfish Sebastes schlegeli

An 8-wk feeding trial was conducted to estimate the optimum dietary protein level and protein-to-energy (P/E) ratio in juvenile Korean rockfish Sebastes schlegeli. Twenty experimental diets were formulated with four energy levels and five protein levels at each energy level. Four gross energy levels of 14.2, 16.5, 18.6, and 20.9 kJ/g diet were included at various crude protein (CP) levels. Diets containing CP at 30, 40, 45, 50, and 55% had either 14.2 or 16.5 kJ/g energy; those with CP levels of 35, 40, 45, 50, and 60% had either 18.6 or 20.9 kJ/ g energy. After 2 wk of conditioning, fish initially averaging 7.3 ± 0.04 g (means ± SD) were randomly distributed into net cages as groups of 20 fish. Each diet was fed to fish in three randomly selected net cages for 8 wk. After 8 wk of the feeding trial, weight gain (WG) of fish fed 50% and 55% CP with 14.2 kJ/g diet was significantly higher than those of fish fed 30% and 40% CP diets (P 0.05). WG of fish fed 45, 50, and 55% CP with 16.5 kJ/g diet was significantly higher than those of fish fed 30% and 40% CP diets (P < 0.05). WG of fish fed 60% CP with 18.6 kJ/g diet was significantly higher than those of fish fed 35, 40, and 45% CP diets. WG of fish fed 45% CP with 20.9 kJ/g diet was significantly higher than those of fish fed 35, 40, and 60% CP diets. Generally, feed efficiency (FE) and specific growth rate (SGR) showed a similar trend as WG. However, protein efficiency ratio (PER) was negatively related to dietary protein levels. WG of fish did not always increase with increasing dietary protein and energy levels. Comprehensive comparison among diets containing 40, 45, and 50% CP with different energy levels indicated that the increase in protein from 40 to 45% significantly increased WG (P < 0.05), but such effect was not significant when protein increased from 45 to 50% at all energy levels. Increasing dietary energy significantly increased WG of fish fed 40% and 45% CP at each energy level; however, there was no difference in WG of fish fed 50% CP with energy levels of 18.6 and 2.9 kJ/g diet. There was no significant difference in WG of fish fed 50% CP with 18.6 kJ/g or 45 and 50% CP with 20.9 kJ/g diet. Broken-line analysis of weight gain indicated that the optimum dietary protein level was 50.9 ± 1.1% and PIE ratio was 35.4 ± 0.8 mg/kJ with 14.2 kJ/g diet; the optimum dietary protein level was 49.3 ± 5.0% and P/E ratio was 30.2 ± 1.0 mg/kJ with 16.5 kJ/g diet; the optimum dietary protein level was 46.2 ± 9.2% and P/E ratio was 24.7 ± 4.9 mg/kJ with 18.6 kJ/g diet; and the optimum dietary protein level was 45.1 ± 1.8% and P/E ratio was 21.5 ±0.7 with 20.9 kJ/g diet. Therefore, these data indicated that the concept of P/E ratio must be restricted to diets containing adequate protein and energy levels. Based on WG, the optimum P/E ratio was between 21.5 and 35.4 mg protein/kJ gross energy in juvenile Korean rockfish when gross energy ranged from 14.2 to 20.9 kJ/g diet.     

芦荟粉对血鹦鹉幼鱼体色与生长的影响

在水温27.2~28.5℃下,将初始体长为(3.6±0.2)cm的血鹦鹉幼鱼饲养在0.4m×0.5m×0.4m的水族箱中,投喂添加0%、0.25%、0.50%、0.75%和1.00%芦荟粉的饲料42d,研究芦荟粉含量对血鹦鹉幼鱼体色、生长性能、消化酶活力与免疫酶活力的影响。试验结果表明,饲料中芦荟粉含量显著影响血鹦鹉幼鱼的褪色率(P0.05),0.75%芦荟粉组血鹦鹉幼鱼平均褪色率比例最大(63.83%)。饲料芦荟粉抑制血鹦鹉幼鱼生长,随芦荟粉含量增加血鹦鹉幼鱼特定生长率下降,当芦荟粉含量为1.00%,血鹦鹉幼鱼特定生长率最小(1.55%/d);芦荟粉含量低于0.75%时,各组血鹦鹉幼鱼特定生长率差异不显著(P0.05)。饲料芦荟粉水平对血鹦鹉幼鱼消化酶与免疫酶活力影响不显著(P0.05)。芦荟粉能提高血鹦鹉幼鱼的褪色率,饲料中芦荟粉的适宜含量为0.75%。     

卵形鲳鲹幼鱼饲料中适宜蛋白能量比的研究

以鱼粉、豆粕为蛋白源,豆油、鱼油为脂肪源,配制9种不同蛋白能量水平的饲料,蛋白质3个水平(38%、43%、49%),每个蛋白水平设3个脂肪梯度(6%、10%、14%),其蛋白能量比为19.3～27.4mg/kJ。卵形鲳鲹初始质量为(25.02±0.16)g,每个处理设3个重复,每个网箱(1.5 m×1.0 m×2.0m)放养卵形鲳鲹苗20尾,养殖试验持续8周。结果显示,卵形鲳鲹特定生长率随饲料蛋白水平的升高而显著升高(P<0.05)。投喂含43%或49%蛋白质、6%脂肪饲料的卵形鲳鲹表现出较好的特定生长率。饲料中不同的脂肪水平未表现出蛋白质节约效应,较高的脂肪水平反而抑制了卵形鲳鲹的特定生长率、饲料效率和蛋白质效率。卵形鲳鲹鱼体蛋白和脂肪含量分别随饲料蛋白质和脂肪水平的上升而显著升高(P<0.05)。在该试验条件下,卵形鲳鲹幼鱼饲料中最适蛋白质、脂肪水平和蛋白能量比分别为43%、6%和24.4 mg/kJ。     

Effect of Dietary Carbohydrate‐to‐Lipid Ratio on Growth and Carcass Composition of Juvenile Abalone,Haliotis discus,Reeve 1846

The optimal dietary carbohydrate (C) : lipid (L) ratio on growth and carcass composition of juvenile abalone, Haliotis discus, was determined. A total of 1260 juveniles were randomly distributed into 18 containers. Six experimental diets containing different ratios of C to L (49:1, 48:2, 47:3, 45:5, 43:7, and 41:9) were prepared and referred to as the C49:L1, C48:L2, C47:L3, C45:L5, C43:L7, and C41:L9 diets, respectively. Water stability of the experimental diets was measured 12, 24, and 48 h after seawater immersion. Crude protein, L and ash content of the experimental diets decreased with time. Survival of abalone fed the C48:L2 diet was higher than that of abalone fed the C49:L1 and C41:L9 diets. Weight gain and specific growth rate (SGR) of abalone fed the C49:L1, C48:L2, and C47:L3 diets were higher than that of abalone fed the C45:L5, C43:L7, and C41:L9 diets. Crude L content of the soft body of abalone was directly reflected from dietary crude L content. In conclusion, the optimal dietary C : L ratio was estimated to be 48:2 and 47:3 based on survival, weight gain, and SGR of juvenile abalone, respectively. Greater than 3% L content in the diet deteriorated performance of this species of abalone.     

Optimum Level of Dietary n‐3 Highly Unsaturated Fatty Acids for Juvenile Sea Cucumber,Apostichopus japonicus

A feeding trial was conducted to estimate the optimum level of dietary n‐3 highly unsaturated fatty acids (HUFAs) for juvenile sea cucumber, Apostichopus japonicas, based on growth performance and fatty acid compositions. Diets with five n‐3 HUFAs levels (0.15, 0.22, 0.33, 0.38, and 0.46%) were fed to sea cucumber juveniles (1.97 ± 0.01 g) once a day for 60 d. The sea cucumbers fed diets containing 0.22% n‐3 HUFAs showed significantly (P < 0.05) higher body weight gain, feed efficiency, and protein efficiency ratio than the sea cucumbers fed diets containing 0.15% n‐3 HUFAs, but not significantly different (P > 0.05) from those of sea cucumbers fed diets containing 0.33, 0.38, and 0.46% n‐3 HUFAs. The sea cucumbers fed diets containing 0.46% n‐3 HUFAs showed significantly (P < 0.05) higher eicosapentaenoic acid and saturated fatty acid than the sea cucumber fed diets containing 0.15% n‐3 HUFAs, but not significantly different (P > 0.05) from those of sea cucumbers fed diets containing 0.22, 0.33, and 0.38% n‐3 HUFAs. The results of growth performance and n‐3 HUFA compositions of body wall indicated that the optimum level of dietary n‐3 HUFAs for juvenile sea cucumber is between 0.22 and 0.46%.     

Effects of Dietary Protein and Lipid Levels with Different Protein‐to‐Energy Ratios on Growth,Feed Utilization,and Plasma Biochemical Parameters of Dianchi Golden‐line Barbell,Sinocyclocheilus grahami

An 8‐wk feeding trial was conducted to evaluate the effects of varying dietary protein and lipid levels with different protein‐to‐energy (P/E) ratios on growth, feed utilization, and plasma biochemical parameters of Sinocyclocheilus graham. Nine experimental diets were formulated to contain three protein levels (35, 40, and 45%), and each with three lipid levels (4, 8, and 12%), to produce a range of P/E ratios from 71.31 to 98.64 mg protein/kcal. Each diet was randomly assigned to triplicate groups of 25 fish. Fish grew best when fed the diet containing 45% protein and 12% lipid. However, fish fed the diet with 40% protein and 8% lipid had similar weight gain and specific growth rate as those fed the above diet but showed relatively better feed conversion ratio, protein efficiency ratio, and protein and energy retentions. Additionally, plasma total amino acids and blood urea nitrogen contents and γ‐glutamyltransferase, aspartate aminotransferase, and alanine aminotransferase activities in fish fed the diet containing 40% protein and 8% lipid were relatively low among the dietary treatments. These results may indicate that a diet containing 40% protein and 8% lipid with P/E ratio of 84.05 mg protein/kcal would be suitable for the optimal growth, feed utilization, and health of S. graham.     

Effects of Dietary Carbohydrate‐to‐lipid Ratio on Growth Performance,Body Composition,Digestive Enzyme Activities,and Hepatic Enzyme Activities in Juvenile Large Yellow Croaker,Larimichthys crocea

An 8‐wk feeding trial was conducted to investigate the effects of dietary carbohydrate‐to‐lipid ratios (CHO : L) on growth performance, body composition, digestive enzyme activities, and hepatic enzyme activities of juvenile large yellow croaker, Larimichthys crocea. Six isonitrogenous (45% crude protein) and isoenergetic (18 kJ/g gross energy) diets with varying CHO : L ratios (0.07, 0.48, 1.20, 2.19, 4.81, and 10.48) were fed to triplicate groups of large yellow croaker in floating sea cages. Results showed that the highest specific growth rate (SGR) was found in fish fed diets with CHO : L ratio of 2.19. Fish fed the lower (0.07 and 0.48) CHO : L ratios tended to produce lower growth (P < 0.05). The whole‐body lipid content significantly decreased, while hepatosomatic index, liver glycogen content, and plasma glucose concentration significantly increased as dietary CHO : L ratios increased (P < 0.05). Plasma total cholesterol, triglyceride, and low‐density lipoprotein cholesterol concentrations significantly decreased with elevated dietary CHO : L ratios (P < 0.05). The increasing dietary CHO : L ratios significantly stimulated the activities of intestinal amylase and hepatic pyruvate kinase and depressed the activity of hepatic phosphoenolpyruvate carboxykinase (P < 0.05). Based on a second‐order polynomial regression analysis of SGR, 2.38 was determined as the optimal dietary CHO : L ratio for juvenile large yellow croaker.     

Optimum Dietary Level of Chlorella Powder as a Feed Additive for Growth Performance of Juvenile Olive Flounder,Paralichthys olivaceus

ABSTRACT

The present study was conducted toestimate the optimum dietary supplementation level of Chlorella powder as a feed additive to optimize growth of juvenile olive flounder, Paralichthys olivaceus. Four experimental diets supplemented with Chlorella powder (CHP) at 0, 1, 2 and 4% (CHP₀, CHP₁, CHP₂, and CHP₄, respectively) of diet as a dry-matter (DM) basis were prepared. Three replicate groups of fish averaging 1.1±0.02 g were fed one of the four experimental diets for 12 weeks. After the feeding trial, fish fed the CHP₂ diet had a higher (P < 0.05) weight gain (819%) than did fish fed CHP₀ (707%) and CHP₁(712%); however, there was no significant difference between fish fed CHP₂ (8197%) and CHP₄ (7559%) as among fish fed CHP₀, CHP₁, and CHP₄ (P > 0.05). Fish fed CHP₂ had a higher (P < 0.05) feed efficiency (134%) than did fish fed CHP₀ (123%); however, there was no significant difference (P > 0.05) among fish fed CHP₀ (123%), CHP₁ (125%), and CHP₄ (125%) as among fish fed CHP1 (125%), CHP₂ (134%), and CHP₄ (125%). Fish fed CHP₂ and CHP₄ had a lower (P < 0.05) serum glucose level (average 32.9 mg/dL) than did fish fed CHP₀ and CHP1 (average 34.8 mg/dL). Fish fed CHP1 and CHP₂ had a lower (P < 0.05) serum glutamic oxaloacetic transaminase (GOT) level than did fish fed CHP0 and CHP₄. Glutamic pyruvic transaminase (GPT) levels significantly (P < 0.05) deceased as dietary CHP increased. Fish fed CHP₂ and CHP₄ had a less (P < 0.05) whole-body fat than did fish fed CHP₀. These results indicate that the optimum dietary supplementation level of Chlorella powder as a feed additive in juvenile olive flounder could be approximately 2% of diet.     

Optimum Dietary Protein and Lipid Levels in Juvenile Filefish,Stephanolepis cirrhifer,Feed

A feeding trial was designed to assess the effects of dietary protein and lipid content on growth, feed utilization efficiency, body composition, and hematological indices of juvenile filefish, Stephanolepis cirrhifer. Eight experimental diets were formulated with a combination of four protein (35, 40, 45, and 50%) and two dietary lipid levels (7 and 14%). Each diet was fed to triplicate groups of fish (3.2 ± 0.06 g) to apparent satiation for 8 wk. Fish growth performance and feed utilization were significantly affected by increasing dietary protein and lipid levels, with no significant interactions between factors. The highest growth performance value, in terms of weight gain, was observed in groups fed the diets with 50% protein (399%). However, fish fed the diet containing 45% protein had comparable growth (357%) while achieving relatively higher protein efficiency ratio. Hepatosomatic index was significantly affected by interaction of dietary lipid and protein with the highest values observed in those fish fed the highest protein (45–50%) and lipid (14%) diets. There was a significant increase in body lipid content (5.1 to 6.6%) and a decrease in body protein (15.8 to 14.8%) and ash (2.47 to 2.16%) with increasing dietary lipid levels from 7 to 14%. Muscle lipid content was significantly affected by both dietary protein and lipid levels and tended to increase with increasing dietary protein and lipid levels, ranging from 0.13 to 1.20%. Liver lipid content (65.9 to 68.7%) was significantly increased with the increase in dietary lipid levels while liver moisture content (28.9 to 25.9%) showed a clear decreasing trend. Hematological values were also altered with the increase in either dietary protein or lipid levels. These findings may suggest that a diet containing 45% protein and 7% lipid, with a protein to energy ratio of 23.8 mg/kJ, could deliver sufficient nutrient and energy to support acceptable growth and feed utilization and avoid excessive fat deposition in juvenile filefish.     

饲料蛋白水平对眼斑双锯鱼幼鱼生长性能和体成分的影响

为确定眼斑双锯鱼幼鱼人工配合饲料中合适蛋白水平,试验研究了饲料蛋白水平对眼斑双锯鱼幼鱼生长、饲料转化率和体成分的影响。养殖试验在循环水系统中进行,初始体质量为(0.085±0.002)g的幼鱼随机分配到6个处理组(每组3个平行,每个平行40尾),分别投喂蛋白水平38.11%、40.91%、44.16%、47.21%、50.02%和53.16%的人工饲料,试验持续56d。不同蛋白水平饲料对眼斑双锯鱼幼鱼质量增加率、特定生长率、饲料系数、蛋白质效率以及全鱼的体成分等均有显著影响。饲料蛋白水平为38.11%~50.02%时,随着饲料蛋白水平的增加,眼斑双锯鱼幼鱼的质量增加率和特定生长率呈增加的趋势,饲料蛋白水平为53.16%时略有下降。经回归分析,当饲料蛋白水平为51.8%时,质量增加率最大;蛋白水平为51.1%时,特定生长率最大。饲料系数也随着饲料蛋白水平增加而呈现先降后升的趋势,饲料系数谷值出现在蛋白水平为47.21%试验组,而蛋白质效率则相反。经回归分析,当饲料蛋白水平为47.5%时,饲料系数最小;饲料蛋白水平为47.8%时,蛋白质效率最大。全鱼粗蛋白随饲料蛋白水平升高呈增加趋势,但到一定水平后维持该水平不再增加,而粗脂肪则随饲料蛋白水平升高呈先降后升的趋势。综合生长、饲料转化率和体成分等指标,本试验条件下眼斑双锯鱼幼鱼适宜的饲料蛋白水平为47.5%~51.8%。     

Dietary Protein Requirement of Juvenile Dianchi Golden‐line Barbell,Sinocyclocheilus grahami

A 10‐wk feeding trial was conducted to estimate the dietary protein requirements of juvenile Dianchi golden‐line barbell, Sinocyclocheilus grahami (initial average weight 7.55 g). Five isocaloric diets were formulated to contain graded levels of protein (29, 34, 39, 44, and 49%). Each diet was fed to triplicate groups of fish in a recirculating rearing system maintained at 18–22 C. Feed intake of fish fed the diet with 39% protein was significantly higher than those fed the diet with 29, 34, and 49% protein (P < 0.05). Weight gain, specific growth rate (SGR), and protein gain significantly increased with increasing dietary protein levels up to 39% (P < 0.05), whereas no significant differences were observed among fish fed the diet with 39, 44, and 49% protein (P > 0.05). In contrast, feed conversion ratio was significantly decreased with increasing dietary protein levels up to 39%. Maximum protein retention and protein efficiency ratio were observed in fish fed the diet with 39% protein. The regression analysis based on SGR and protein gain showed that the dietary protein requirements of juvenile S. grahami were 38.57% or 41.09% (equivalent to ca. 32.94% or 35.42% estimated digestible protein) of diet with a calculated digestible energy of 3.6 kcal/g.     

Effects of Dietary Protein Level on Nitrogen and Energy Budget of Juvenile Chinese Soft‐shelled Turtle,Pelodiscus sinensis,Wiegmann

The effects of dietary protein level on nutrient digestibility and utilization of protein and energy of juvenile Chinese soft‐shelled turtle, Pelodiscus sinensis, were investigated. Seven isoenergetic diets containing graded levels of protein (25, 27, 29, 31, 33, 35, and 43%) were fed to turtles initially averaging 4.8 ± 0.7 g for 8 wk at 30 ± 0.5 C. The apparent digestibilities of dry matter, protein, and energy were generally increased with dietary protein level. Proportions of nitrogen intake (CN) allocated to excretory nitrogen (UN) were higher in 25 and 43% protein diets than the other diets. UN proportion was lowest in the 33% protein diet, whereas retained (growth) nitrogen (RN) followed an inverse pattern with UN. Percentages of gross energy intake (IE) used for excretory energy (UE) generally increased when dietary protein levels increased. Turtles fed 25–29% protein diets showed a markedly higher proportion of metabolizable energy (ME) than those fed 31–43% protein diets. Analysis by second‐order polynomial regression using RN as the indicator indicated that the estimated optimal dietary protein level was 34.6%. The lowest and highest percentages of retained (growth) energy (RE) were observed in the 25 and 33% protein groups. Nitrogen and energy budget equations of turtles fed 33% protein diet were 100 CN = 8.22 FN + 37.48 UN + 54.30 RN and 100 IE = 10.88 FE + 2.82 UE + 65.60 ME + 20.69 RE, respectively. Diets with excessive protein resulted in high proportions of protein and energy used for excretion.     

Optimum dietary protein‐to‐energy ratio for juvenile whiteleg shrimp,Litopenaeus vannamei,reared in a biofloc system

An 8‐week feeding trial was conducted to evaluate the optimum dietary protein‐to‐energy (P/E) ratio in juvenile whiteleg shrimp, Litopenaeus vannamei. Six diets were formulated with two protein levels (30% and 35%) and three digestible energy levels (16, 17.5 and 19 kJ/g diet) at each protein level (₃₀P₁₆, ₃₀P_17.5, ₃₀P₁₉, ₃₅P₁₆, ₃₅P_17.5 and ₃₅P₁₉). Fifty shrimp averaging 0.97 ± 0.03g (Mean ± SD) were randomly distributed in biofloc tanks and fed one of the experimental diets. Weight gain (WG), specific growth rate (SGR) and feed efficiency (FE) of shrimp fed the ₃₅P_17.5 diet were significantly higher than those of shrimp fed ₃₀P₁₆, ₃₀P_17.5 and ₃₀P₁₉ diets (p < .05). Results for non‐specific immune responses showed that diet ₃₅P_17.5 caused higher lysozyme activity in shrimp comparing to lower protein diets. Thiobarbituric acid reactive substances (TBARS) of plasma were lower for shrimp fed on diets consisting of higher protein and energy levels than shrimp fed on the ₃₀P₁₉ diet. Analyses of digestive enzyme activities showed higher trypsin activities for shrimp fed on ₃₅P_17.5 and ₃₅P₁₉ diets comparing to ₃₀P₁₆ and ₃₀P_17.5 diets. Also, hepatopancreatic lipase activity of shrimp fed ₃₅P₁₆, ₃₅P_17.5 and ₃₅P₁₉ diets were significantly higher than those of shrimp fed the other diets. In conclusion, based on the results for growth performance, biochemical parameters, immune responses, oxidative stress and enzyme activities, 35% protein and 17.5 kJ/g digestible energy (₃₅P_17.5) could be considered as the optimum protein‐to‐energy ratio in the diet of juvenile whiteleg shrimp reared in a biofloc system.     

Effect of Dietary Lipid Level and Protein Energy Ratio on Growth and Body Composition of Largemouth Bass Micropterus salmoides

A feeding trial was conducted in aquaria with juvenile largemouth bass Micropterus salmoides to examine the effects of increasing dietary lipid levels on growth and body composition. Feed‐trained largemouth bass fingerlings were graded to a similar size (16.3 ± 2.4 g) and randomly stocked into 15 113.6‐L glass aquaria at 25 fish/aquarium. Fingerlings were fed twice daily to apparent satiation with one of five isonitrogenous extruded experimental diets based on practical ingredients. Diets contained approximately 40% crude protein and either 0, 5, 10, 15, or 20% added lipid. Due to background lipids in the ingredients, this equated to total lipid levels of 7, 10, 16, 20, and 23%, respectively. These diets had protein to energy ratios of 137, 120, 106, 95, and 86 mg/kcal, respectively. There were three replicate aquaria per dietary treatment. After 12 wk, there were no statistically significant differences (P > 0.05) in average weight (g), specific growth rate (% body weight/d), survival (%), or protein efficiency ratio (PER, %) among fish fed the five diets, which averaged 79.3 ± 5.6, 1.9 ± 0.1, 99.5 ± 1.5, and 2.11 ± 0.19, respectively. Juvenile largemouth bass fed diets containing 15 and 20% added lipid had significantly lower (P± 0.05) feed conversion ratios (FCR) (1.1 ± 0.0 and 1.1 ± 0. 1, respectively) than fish fed diets containing 0, 5, and 10% added lipid (1.4 ± 0.1, 1.3 ± 0. 1, and 1.3 ± 0.2, respectively). Proximate analysis of whole body samples indicated a significantly higher (P ± 0.05) lipid content in fish fed 15 and 20% added lipid compared to fish fed lower lipid levels. While FCR was lowest in fish fed the 15 and 20% added lipid diets, increased whole body lipid deposition may indicate that these levels are above optimal levels for juvenile largemouth bass. It appears that 7–16% total dietary lipid (P/E:137–106 mg/kcal) is sufficient to support efficient growth without impacting body composition in juvenile largemouth bass when fed a diet containing 40% crude protein.     

Dietary Protein and Lipid Requirements for Juvenile Largemouth Bass,Micropterus salmoides

A feeding trial was conducted to evaluate dietary protein and lipid requirements for juvenile largemouth bass, Micropterus salmoides. A 4 × 2‐factorial layout included four protein (420, 450, 480, and 510 g/kg) and two lipid (80 and 120 g/kg) levels. Fish (initial weight 8.7 g) were fed the test diets for 8 wk. Weight gain, feed intake, feed conversion ratio, hepatosomatic index, and body composition were dependent on dietary protein level. Nitrogen retention efficiency was independent of dietary protein level, lipid level, and their interaction. Weight gain was higher in fish fed the diet containing 480–510 g/kg crude protein than in fish fed the diet containing 420–450 g/kg crude protein at two dietary lipid levels. The feed intake and weight gain were higher in fish fed the diet containing 484 g/kg crude protein and 115 g/kg crude lipid than in fish fed the diet containing 478 g/kg crude protein and 77 g/kg crude lipid. This study indicated that the suitable dietary protein and lipid levels for largemouth bass are 480–510 g/kg and 120 g/kg, respectively.     

饲料蛋白水平对宝石鲈增重和体成分的影响

用5种不同蛋白质水平(分别为30.89%、36.67%、40.08%、44.90%、49.14%)的饲料分别饲喂宝石鲈(Scortum bacoo)幼鱼25 d,每组3重复(每重复30尾鱼),室内网箱饲养试验结果表明:40.08%组的日增重、特定生长率显著高于30.89%组(P<0.05),饲料转化率极显著高于30.89%组(P<0.01);不同组间的肝体指数、脏体指数和肥满度无显著差异(P>0.05);饲料蛋白水平对宝石鲈幼鱼肌肉水分、粗蛋白、粗脂肪、灰分及肝脏的水分、粗脂肪无显著影响(P>0.05)。     

零换水条件下饲料蛋白水平对团头鲂幼鱼生长、消化酶活力和血清生化指标的影响

为探究零换水养殖水体中饲料蛋白水平对团头鲂(Megalobrama amblycephala)幼鱼生长、消化酶活力和血清生化指标的影响,实验设计投喂4个不同蛋白水平的生物絮团试验组(BF-20%、BF-25%、BF-30%、BF-35%)以及1个投喂35%蛋白的循环水对照组,每个处理组设置3重复,每个养殖桶放养初始体重为(6.06±0.01)g团头鲂幼鱼25尾,养殖周期为6周。结果表明:(1)形成的生物絮团可以有效地调节水质,降低水体中的氨氮、硝酸盐氮和亚硝酸盐氮水平;(2)BF-30%和BF-35%组和对照组的终末体重、增重率和饲料系数差异不显著(P0.05),但其显著高于BF-20%组(P0.05),各处理组间的存活率没有显著性差异(P0.05);(3)BF-25%组、BF-30%组和BF-35%组的肠道、肝脏超氧化物歧化酶和谷胱甘肽过氧化物酶活性显著高于对照组和BF-20%组(P0.05),而BF-20%组的肝脏丙二醛含量显著高于其他处理组(P0.05);BF-25%组、BF-30%组和BF-35%组的血清碱性磷酸酶和溶菌酶活性显著高于对照组和BF-20%组(P0.05),而其血清中总蛋白含量、白蛋白含量、谷丙转氨酶和谷草转氨酶活力差异不显著(P0.05)。研究表明,零换水条件下饲料中35%蛋白水平减少至25%并不影响团头鲂幼鱼的生长和非特异性免疫力。     

Effect of Dietary Essential Oils Supplementation on Growth Performance,Nutrient Utilization,and Protein Digestibility of Juvenile Gilthead Seabream Fed a Low‐Fishmeal Diet

The present study aimed to assess the efficacy of supplemental plant essential oils (PEOs) on the growth performance and digestive processes of juvenile gilthead seabream. Three experimental diets were tested: (1) a control (CTRL) diet formulated with low marine‐derived protein level (19%); (2) CTRL diet supplemented with a blend of anise, citrus, and oregano essential oils at 1.2 g/kg (diet Phyto C); and (3) CTRL diet supplemented with a similar blend at 0.2 g/kg, but in encapsulated form (diet Phyto E). Triplicate groups of 20 fish (mean initial body weight = 27.9 ± 2.1 g) were fed the experimental diets over 63 d. Results showed that specific growth rate, voluntary feed intake, feed conversion ratio, and protein efficiency ratio were not significantly affected by the two dietary supplements. The commercial blend of PEOs tested here can be successfully incorporated into a low‐fishmeal diet to maximize protein and fat retention and to minimize nitrogenous losses in seabream juveniles. Phyto E presented a decrease in nitrogenous metabolic and fecal losses. The practical implications of including this plant‐based blend in aquafeeds can potentially include faster fish growth and improved production time, but these remain to be tested in a longer experimental trial.