海州湾春季皮氏叫姑鱼摄食习性的空间异质性及其索饵场分布

鱼类通过摄食维持自身的生存、生长和繁殖,对鱼类摄食习性的空间异质性及其索饵场分布进行研究有助于了解鱼类在不同海域间的生长差异。本研究根据2011年及2013―2016年春季在海州湾进行的渔业资源底拖网调查数据,通过胃含物分析研究皮氏叫姑鱼(Johniusbelangerii)的摄食习性,依据胃含物分析结果选择主要饵料生物,结合皮氏叫姑鱼和主要饵料生物的空间分布,研究皮氏叫姑鱼摄食习性的空间异质性,并判别其索饵场。结果表明:皮氏叫姑鱼摄食的饵料生物共有20余种,其中虾类(IRI%=55.54%)和端足类(IRI%=35.94%)为优势饵料类群。基于胃含物分析和底拖网调查,选择海蜇虾(Latreutesanoplonyx)、细巧仿对虾(Parapenaeopsistenella)、鲜明鼓虾(Alpheus distinguendus)、疣背宽额虾(Latreutes planirostris)、细螯虾(Leptochela gracilis)、戴氏赤虾(Metapenaeopsis dalei)、日本鼓虾(Alpheus japonicus)和中华安乐虾(Eualus sinensis) 8种饵料生物研究皮氏叫姑鱼摄食习性的空间异质性及其索饵场。摄食选择性的研究表明,海州湾春季的皮氏叫姑鱼喜食海蜇虾。本研究发现,皮氏叫姑鱼及其主要饵料生物资源丰度重心均位于海州湾中部10～20m深海域;海州湾中南部10～20m海域的饵料生物资源丰度显著高于其他海域(P0.05),而且该海域皮氏叫姑鱼的个体较小,生长速度较快,摄食强度较高,是其主要的索饵场。     

海州湾3种石首鱼的食物组成和生态位重叠

根据2011及2013年在海州湾及其邻近海域进行的渔业资源底拖网调查资料和胃含物分析数据，应用多元统计分析法和生态位重叠指数法等，研究了海州湾皮氏叫姑鱼、小黄鱼和棘头梅童鱼3种石首鱼的食物组成及其营养—空间二维生态位的重叠情况。结果显示，皮氏叫姑鱼属于底栖动物食性，主要摄食虾类、端足类和多毛类；小黄鱼属于底栖动物和游泳动物食性，主要摄食鱼类、虾类、头足类和磷虾；棘头梅童鱼属于底栖动物食性，主要摄食虾类、毛虾类、磷虾和糠虾。这3种石首鱼的营养生态位宽度较为接近，其中小黄鱼的营养生态位宽度(2.69)和空间生态位宽度(2.78)均最高，皮氏叫姑鱼的营养生态位宽度(2.59)最低，而棘头梅童鱼的空间生态位宽度(2.42)最低。3种石首鱼的营养生态位重叠指数为0.24~0.46，其中皮氏叫姑鱼与棘头梅童鱼的营养生态位重叠最高。它们的空间生态位重叠指数为0.19~0.30，表明这3种鱼在空间方面存在一定的分隔。它们的营养—空间二维生态位重叠指数为0.05~0.11，其中皮氏叫姑鱼与棘头梅童鱼的重叠指数最高，因此有可能发生激烈的食物竞争，而小黄鱼与皮氏叫姑鱼和棘头梅童鱼之间则可以通过营养和空间生态位的分化来降低种间竞争。     

南黄海三种石首鱼类的食性

根据2000—2002年秋季和冬季在南黄海进行的定点底拖网调查，利用多元统计分析方法，研究了黑鳃梅童(Collichthys niveatus)、皮氏叫姑鱼(Jobnius belengerii)和小黄鱼(Pseudosciaena polyactis)的食物组成及其差异，摄食随海区、季节和体长的变化，以及3种石首鱼类摄食器官的形态差异对摄食的影响。结果表明：(1)3种鱼的优势饵料生物各不相同，食物组成存在显著差异；(2)3种鱼的食物组成均随海区和季节的不同而有显著的差异；(3)3种鱼的食物组成和饵料多样性都有明显体长变化，黑鳃梅童和皮氏叫姑鱼的饵料多样性随体长的增大而升高，小黄鱼则相反；(4)黑鳃梅童和小黄鱼种内不同体长问的食物重叠指数较高，而皮氏叫姑鱼则较低，3种鱼的种问食物重叠指数位于0．50～0．56；(5)主成分分析(PCA)表明，黑鳃梅童和小黄鱼摄食器官的形态特征与皮氏叫姑鱼存在一定的差异。     

马鞍列岛海域皮氏叫姑鱼渔业生物学初步研究

基于2009年1月—2010年2月渔业资源调查数据,研究了马鞍列岛海域皮氏叫姑鱼的体长组成、体长与体质量关系、性比、繁殖习性和摄食等渔业生物学。结果表明:1)马鞍列岛海域皮氏叫姑鱼群体体长范围30～264 mm,优势体长组为80～100和130～180 mm;2)皮氏叫姑鱼幼鱼和雄性个体的生长呈负异速生长的特性,而雌性个体呈正异速生长的特性;3)雌雄比为1.68∶1(χ2=35.636,P<0.001),雌雄比随月份和体长变化,除8月和9月及体长110～150和160～180 mm外,雌雄个体数差异明显;4)皮氏叫姑鱼的繁殖期从6月持续到9月,其雌性和雄性个体首次性成熟体长分别为124.8和136.4 mm;5)皮氏叫姑鱼的饵料生物随月份和个体生长发生转变,幼鱼主要摄食端足类,而成鱼在繁殖前期主要摄食鱼类和虾类,繁殖期间主要摄食端足类。与其他海域相比,马鞍列岛海域皮氏叫姑鱼群体具有较大的体长范围和优势体长组体长。为持续利用皮氏叫姑鱼资源,建议加强繁殖群体和幼鱼群体的保护。     

长江口外海域龙头鱼营养生态学特征

利用2009年9月至2010年8月在东海北部、黄海南部海域获取的龙头鱼(Harpadon nehereus)样品,采用胃含物分析法,对龙头鱼的摄食习性进行了研究。结果表明,龙头鱼摄食饵料种类有39种,鱼类是其主要饵料类群,所占质量百分比为84.13%。优势饵料种类为龙头鱼(Harpadon nehereus)、小黄鱼(Pseudosciaena polyactis)、细条天竺鱼(Apogonichthys lineatus)、皮氏叫姑鱼(Johnius belengerii)、口虾蛄(Oratosquilla oratoria)等。龙头鱼的摄食强度秋季最高,冬季最低;食物组成季节变化明显,春季主要摄食虾类,其他季节则主要以鱼类为食;不同生长发育阶段的食物组成及摄食强度具有显著差异,体长为100 mm和250 mm处存在食性转换现象,并在体长250 mm时表现为由广食性向狭食性转换的特征,摄食选择性增强。龙头鱼营养级为3.80,在东、黄海食物网中处于较高的营养层次。     

长江口及南黄海水域秋季小黄鱼与皮氏叫姑鱼的食物竞争

根据长江口及邻近南黄海水域多个站位中不同体长小黄鱼(Pseudosciaena polyactis)与皮氏叫姑鱼(Johnius belengerii)及其饵料的碳氮稳定同位索比值,研究了两者的主要食物组成及竞争策略.结果表明:(1)红狼牙鲐虎鱼(Odantamblyopus rubicundus)、六丝矛尾鲐虎鱼(Chaeturichthys hexanema)、中华栉孔鲐虎鱼(Ctenotrypauchen chinensis)、龙头鱼(Harpadon nehereus)、葛氏长臂虾(Palaemon gravieri)、口虾蛄(Squilla oratoria)6种生物饵料为两者的优选食物;(2)小黄鱼与皮氏叫姑鱼的体长与碳氮稳定同位素比值间无显著相关性(P>0.05);(3)小黄鱼、皮氏叫姑鱼及其一些生物饵料的碳氮稳定同位素比值存在站位间的极显著差异(P<0.01);(4)2种鱼采取了栖息地与食物分化的摄食策略来缓和食物竞争.     

东海中北部小眼绿鳍鱼食性的季节变化

根据2008年5月~2009年2月收集到的小眼绿鳍鱼胃含物样品,对其摄食习性的季节变化进行了研究。结果表明,小眼绿鳍鱼全年摄食的饵料种类数共有93种,磷虾类、长尾类和鱼类为其主要饵料类群。其食物组成存在季节差异,春季小眼绿鳍鱼以太平洋磷虾、脊腹褐虾和鳀鱼为主要食物;夏季以细巧仿对虾、脊腹褐虾、口虾姑和葛氏长臂虾为主要食物;秋季以太平洋磷虾、戴氏赤虾、细螯虾和鳀鱼为主要食物;冬季以鳀鱼、细螯虾、褐菖鲉和对虾为主要食物。摄食强度的季节变化呈显著差异(P0.05),春季最高,夏季最低;各个季节的主要饵料类群组成存在差异,但长尾类和鱼类在四个季节都有分布。通过与历史资料进行比较发现,东海小眼绿鳍鱼的食物组成与饵料生物的季节变化息息相关。     

武湖日本沼虾食性的研究

在胃含物分析的基础上 ,1998年 9月～ 1999年 9月对人工养殖湖泊武湖日本沼虾的食性作了研究。结果表明 :日本沼虾是一种广食性、杂食性的动物 ,其主要食物是植物碎片和有机碎屑 ,其次为水生昆虫、水生寡毛类、鱼虾和浮游动物 ,浮游植物仅为日本沼虾摄食时所带入 ;日本沼虾的食物组成具有明显的季节性变化 ;大、中、小三种规格的日本沼虾之间存在明显的食性分化 ;摄食强度存在明显的周年变化     

黄海重要饵料鱼种矢耳石的形态特征

由于鱼类矢耳石的形态结构稳定,具有种的特征,且坚硬不易被消化,其形态特征可用于鱼类胃含物分析中的种类鉴定。本研究选取黄海"简化食物网"中的30种重要饵料鱼种为研究对象,描述了各种类矢耳石的形态特征,并进行了比较分析。结果发现,这30种重要饵料鱼种的矢耳石中形态结构相似的有7组:赤鼻棱鳀和中颌棱鳀,细条天竺鱼和斑鳍天竺鱼,多鳞鱚和少鳞鱚,皮氏叫姑鱼和白姑鱼,黄姑鱼和小黄鱼,黑鳃梅童鱼和棘头梅童鱼,以及矛尾鰕虎鱼和六丝矛尾鰕虎鱼,本研究为胃含物分析等基于耳石形态的种类鉴别提供了基础资料,同时进一步更广泛深入地研究和认知鱼类的耳石形态,近缘种耳石形态特征的量化研究,以及同一种类耳石形态的地理变异等的研究将有助于更准确地进行种类的鉴别,对提高胃含物分析的准确度也有很大帮助。     

浙江南部近海两种石首鱼科鱼类的摄食习性及其食性重叠

对 2020 年 8 月、11 月和 2021 年 1 月在浙江南部近海进行的底拖网调查采集的 287 尾白姑鱼(Pennahia argentata)和 204 尾黑姑鱼(Atrobucca nibe)胃含物样品进行分析, 采用聚类分析等统计方法研究了这两种石首鱼科鱼类(Sciaenidae)的食物组成、摄食习性随体长变化及饵料重叠情况。结果表明, 浙江南部近海白姑鱼摄食饵料生物 48 种, 主要摄食桡足类(Copepoda), 以哲水蚤(Calanus)居多。黑姑鱼摄食饵料生物 43 种, 主要摄食鱼类(Pisces) 和虾类(Decapoda), 优势饵料种类为七星底灯鱼(Benthosema pterotum)。随着体长的增加, 两种石首鱼摄食的主要饵料生物均由浮游动物等小型饵料生物转向鱼类和虾类等大型饵料生物, 摄食强度也随之变化, 白姑鱼的摄食强度随着体长增加而逐渐降低, 而黑姑鱼的摄食强度随着体长增加呈先下降后上升的趋势。两种石首鱼的营养生态位宽度存在较大差异, 其中黑姑鱼的营养生态位宽度(3.06)高于白姑鱼(1.82), 二者间的整体饵料重叠系数为 0.22, 但在部分体长组中存在较大的饵料重叠, 这表明浙江南部近海白姑鱼与黑姑鱼在部分生长阶段有发生食物竞争的可能。     

渤海小黄鱼摄食习性

根据2009年8月至2011年5月4个航次渤海底拖网调查所获得的样品,采用胃含物分析法、K-W检验和聚类分析等方法,对38～218 mm体长范围小黄鱼(Larimichthys polyactis)的摄食习性及其随体长、季节的变化进行了研究,并探讨了小黄鱼摄食随海域和年际的时空变化。结果表明:渤海小黄鱼摄食的饵料有40余种,主要以鱼类、虾类和浮游动物为食,优势饵料种类为六丝钝尾虾虎鱼(Amblychaeturichthys heaema)、日本鼓虾(Alpheus japonicus)、太平洋磷虾(Euphausia pacifia)、长额刺糠虾(Acanthomysis longirostris)和中华哲水蚤(Calanus sinicus)。渤海小黄鱼在春夏秋这三个季节中,春季的摄食强度最低,夏季和秋季的摄食强度都较高,不同的是夏季摄食率更高,而秋季的摄食量更高。随着体长的增大,渤海小黄鱼的摄食策略发生了相应的变化。从摄食强度分析,在体长较小时,胃饱满指数低,小黄鱼通过高摄食率来提高摄食强度;随着体长的增加,通过高胃饱满指数来提高摄食强度。从摄食的饵料个体分析,小黄鱼采取了随着体长增加摄食饵料个数减少,饵料个体增大的摄食策略。从摄食的饵料组成分析,小黄鱼随着体长增加发生了显著的食性转换现象:体长小于60 mm属浮游动物食性;体长60～99 mm时,属混合动物食性;体长100～119 mm时,属虾食性;体长超过120 mm,包括了虾/鱼食性和鱼食性。小黄鱼摄食的时空变化与环境中优势饵料生物的数量波动密切相关。     

Use of a Compound Protein Source as a Replacement for Fish Meal in Diets of Large Yellow Croaker, Pseudosciaena crocea R.

A feeding trial was conducted to evaluate the potential of a compound protein source (CPS) as a replacement of fish meal (FM) in diets for large yellow croaker, Pseudosciaena crocea R. The CPS was made of soybean meal, meat and bone meal, peanut meal, and rapeseed meal (4:3:2:1 in weight) by adding crystalline l ‐methionine (0.77%), l ‐lysine (0.95%), and l ‐isoleucine (0.44%) to ensure the essential amino acid (EAA) contents of CPS diets to reach or exceed those of FM diet. Six isonitrogenous and isoenergetic diets (Diets 1–6) were formulated to contain 0, 9, 18, 27, 36, and 45% CPS replacing 0, 13, 26, 39, 52, and 65% FM protein, respectively. Triplicate groups of 180 fish (initial average 1.88 ± 0.01 g) were fed diets to apparent satiation by hand twice daily for 8 wk in floating sea cages (1.0 × 1.0 × 1.5 m). The water temperature ranged from 26.5 to 29.5 C, the salinity from 25 to 28‰, and the dissolved oxygen content was approximately 7 mg/L during the experimental period. The results showed that specific growth rate (SGR) and feed efficiency ratio (FER) of fish fed Diets 2 and 3 were not significantly different from those of fish fed control diet (Diet 1). However, SGR and FER of fish fed Diets 4–6 were significantly lower compared with control group (P < 0.05). The whole‐body proximate analysis showed that protein significantly decreased with increasing dietary CPS levels (P < 0.05), while the whole‐body lipid, ash, and moisture showed no significant differences among dietary treatments. Methionine, cystine, and lysine contents of the whole body were significantly influenced by dietary CPS level (P < 0.05), while other EAA contents showed no significant differences. Results of the present study indicated that CPS could replace about 26% FM protein in diets for the large yellow croaker on crude protein basis without adverse effect on growth.     

Effects of protein levels on growth,feed utilization,body composition,amino acid composition and physiology indices of juvenile chu's croaker,Nibea coibor

A 49‐day feeding trial was conducted to determine the optimal dietary protein level for juvenile chu's croaker Nibea coibor in sea cages. Five isocaloric diets were formulated to contain graded levels of protein: 360 (D36), 400 (D40), 440 (D44), 480 (D48) and 520 (D52) g kg^?1 diet. Each diet was randomly assigned to triplicate groups of 25 fish (mean 76.0 ± 0.8 g) in a total of 15 floating cages. Specific growth rate (SGR), protein retention efficiency (PRE), feed efficiency and feed intake were significantly higher at D44 and D48. Consumed protein (CP) obtained the maximum at D48, and protein efficiency ratio was significantly higher in fish fed with D44 and D48 compared with fish fed with D36 and D52. Hepatosomatic index and condition factor were not affected. Body protein and moisture content increased with increasing dietary protein, while lipid and ash content were not affected. Individual and total essential amino acids maximized at D44. Digestive enzymes and physiology indices in intestine, liver and plasma were differentially affected. Based on polynomial regression analysis of SGR, PRE and CP, we suggested that the optimum dietary protein level for juvenile chu's croaker was 444–478 g kg^?1 diet.     

Effect of dietary vitamin C on growth performance,body composition and biochemical parameters of juvenile Chu's croaker (Nibea coibor)

Vitamin C is an essential micronutrient for normal physiological and immune functions of fish. However, its requirements and effects in Chu's croaker (Nibea coibor) are currently unknown. A 56‐day feeding trial was conducted to evaluate the optimal dietary vitamin C requirements based on its effects on growth performance, body composition and biochemical parameters in juvenile Chu's croaker (14.17 ± 0.1 g). Six isoproteic (450 g/kg crude protein) and isolipidic (100 g/kg crude lipid) diets were formulated to contain 2.24 (basal diet), 39.03, 85.01, 171.16, 356.49 and 715.46 mg/kg of vitamin C. The results showed that fish fed on 171.16 mg/kg vitamin C diet had the highest growth performance and feed utilization. Fish fed on the basal diet had higher malondialdehyde (MDA) content and lower activities of antioxidant enzymes in the serum and liver as compared with those fed on vitamin C diets. Polynomial analysis indicated that the optimal dietary vitamin C requirements of juvenile Chu's croaker were 102.28, 98.21, 150.26, 165.38, 71.46, 176.19, 84.84 and 103.78 mg/kg based on weight gain, specific growth rate, liver storage, muscle storage, liver MDA content, liver alanine aminotransferase activity, liver alkaline phosphatase activity and liver superoxide dismutase activity, respectively. We recommend an inclusion level in the range of 71.46–150.26 mg/kg vitamin C in the diets of juvenile Chu's croaker for optimum growth performance, liver function, antioxidant capacity and innate immunity functions.     

Species composition and diversity of fish larvae in the Subtropical Convergence Zone of the Sargasso Sea from morphology and DNA barcoding

Specific regions of otherwise oligotrophic oceans seem to attract fish spawning and sustain significant abundances of fish larvae. The Sargasso Sea in the North Atlantic subtropical gyre is known as the spawning area of the Atlantic eels, but numerous other fish species also spawn in the area. In order to evaluate spatial variability of larval fish in the region, we examined species diversity, composition and abundances at eight stations in the Subtropical Convergence Zone (STCZ) using morphological identification and DNA barcoding. From a total of approximately 3500 specimens collected, at least 154 species from 50 families could be identified. The family Myctophidae had the highest species richness, with at least 32 species represented. The myctophids Lepidophanes gaussi, Bolinichthys indicus, Notolychnus valdiviae and Ceratoscopelus warmingii were the four most abundant species. Other common species included the three eels: Nemichthys scolopaceus, Ariosoma balearicum and Anguilla anguilla. Larval fish species composition differed substantially between the relatively closely spaced stations on either side of prominent hydrographic fronts in the study area, presumably because of the strong environmental gradients. Common eel species were concentrated between the fronts whereas common myctophids were of highest abundance at the outer edges of the fronts. The abundances of most species were generally enhanced in the vicinity of the fronts. The use of combined morphological and DNA‐barcoding identification methods facilitated species identification, and we could document substantially higher levels and a larger degree of spatial variability in species diversity of fish larvae than previously shown for oligotrophic ocean areas.     

Visceral granulomas in farmed large yellow croaker,Larimichthys crocea (Richardson), caused by a bacterial pathogen,Pseudomonas plecoglossicida

An enzootic disease characterized by granulomas in internal organs occurred in cage‐farmed large yellow croaker, Larimichthys crocea (Richardson), in April and November 2010, in Ningbo, Zhejiang Province. One bacterial strain, named XSDHY‐P, was isolated from the diseased fish and identified by biochemical characterization, fatty acid methyl ester (FAME) analysis and multilocus sequence analysis (MLSA). According to the results obtained from the biochemical tests, FAME analysis and phylogenetic analysis derived from 16S ribosomal RNA, gyrB, oprF, oprI, oprL and rpoD gene sequencing, the bacterial isolate, XSDHY‐P, was identified as Pseudomonas plecoglossicida. Moreover, lethal dose, 50% trials were carried out to demonstrate the virulence of XSDHY‐P in large yellow croaker when administered at 2.13 × 10⁵ colony‐forming units per fish. Visceral granulomas were found in the experimentally infected fish as well as in the naturally infected fish, indicating that P. plecoglossicida is another bacterial pathogen that causes granulomatosis in L. crocea.     

Replacing fish meal with a blend of poultry by‐product meal and feather meal in diets for giant croaker (Nibea japonica)

An 8‐week feeding trial was conducted to evaluate the potential of replacing fish meal with poultry by‐product meal (PBM) and feather meal (FEM) in giant croaker (Nibea japonica) diet. The control diet (C) contained 400 g/kg fish meal, and 20%, 40%, 60% and 80% of the fish meal in diet C was replaced by a blend of PBM and FEM (PBM: FEM = 7:3) in diets B20, B40, B60 and B80, respectively. The weight gain and feed intake of fish fed diet C did not differ from those of fish fed diets B20 and B40 (p > .05), but were higher than those of fish fed diets B60 and B80 (p < .05). Phosphorus retention efficiency was lower in fish fed diets C, B20 and B40 than in fish fed diets R60 and R80 (p < .05). No significant differences were found in feed conversion ratio, nitrogen retention efficiency, condition factor, hepatosomatic index, body composition and nitrogen waste among the treatments (p > .05). Ratio of fish meal consumption to fish production linearly declined with the decrease in dietary fish meal level. This study indicates that dietary fish meal for giant croaker could be reduced to 240 g/kg by inclusion of the blend of PBM and FEM.     

Effects of dietary animal proteins on growth and body composition of the red drum (Sciaenops ocellatus)

Two experiments were conducted to determine the nutritional value of various dietary proteins for juvenile red drum. In the first 8-week feeding trial, diets containing similar quantities of lipid, carbohydrate, available energy and ash with 35% crude protein from either lyophilized whole-body croaker (Micropogon undulatus), striated beef muscle, red drum processing waste or commercially processed menhaden (Brevoortia tyrannus) fish meal were fed to juvenile red drum in brackish (6 ppt) water along with a control diet containing lyophilized muscle of red drum. The control diet produced significantly (P<0.05) greater weight gain (WG), feed efficiency (FE), and protein efficiency ratio (PER) values than all other diets; intermediate responses were observed for fish fed diets containing protein from red drum waste and whole-body croaker, while diets containing striated beef muscle and menhaden fish meal yielded the lowest values. Some differences in tissue indices and body composition of red drum including hepatosomatic index, whole-body ash and lipid, as well as liver lipid and glycogen were induced by the various diets. In the second 8-week feeding trial, the control diet containing red drum muscle was compared with similar diets containing protein from whole-body croaker and menhaden fish meal. Again the control diet produced the greatest WG, FE, and PER values followed by whole-body croaker and then menhaden fish meal. Effects of the dietary proteins on tissue indices and body composition were limited. The excellent protein quality and low-temperature processing of lyophilized red drum muscle resulted in superior performance of red drum relative to the other evaluated protein products, and lyophilized whole-body croaker provided better performance than commercially processed menhaden fish meal.     

Effects of dietary carbohydrate level on growth and body composition of juvenile giant croaker Nibea japonica

An 8‐week feeding trial was conducted to investigate the effect of dietary carbohydrate level on the growth performance, body composition of giant croaker, Nibea japonica. The six diets were designated as carbohydrate level from 0% to 30%. Each diet was fed to triplicate groups of 18 giant croaker (initially weighing, 7.40 ± 0.15 g fish^?1) in flow‐through sea water system. The weight gain (WG) and special growth ratio (SGR) had tendency to increase with carbohydrate level from 0% to 12% after that decreased, and significantly lower in fish fed diet with 30% carbohydrate level than in other groups. Moreover, fish fed diet with 30% dietary carbohydrate has significantly higher feed conversion ratio (1.48 ± 0.18) and lower protein efficiency ratio (1.69 ± 0.21) than other groups (P < 0.05). The intraperitoneal fat ratio and condition factor had no significant difference in different groups (P > 0.05), hepatosomatic index value increased with dietary carbohydrate increased (P < 0.05). The result of this study also suggested that excess carbohydrate level (30%) led to lower lipid content in whole body. Based on the second‐order polynomial regression analysis of WG and SGR, 12.2–12.7% dietary carbohydrate provided maximum growth of N. japonica.     

Dietary lipid levels affect lipoprotein clearance,fatty acid transport,lipogenesis and lipolysis at the transcriptional level in muscle and adipose tissue of large yellow croaker (Larimichthys crocea)

To investigate the effect of dietary lipid levels on lipid metabolism in muscle and adipose tissue of large yellow croaker (Larimichthys crocea), fish (average body weight 150.0 g) were fed to one of three diets with a low (6%), moderate (12%, the control diet) or high (18%) crude lipid level for 10 weeks. The expression of genes related to lipoprotein clearance (lpl, ldlr, lrp1 and srbi), fatty acid transport (cd36, fatp1, fabp3 and fabp11), lipogenesis (fas and dgat2) and lipolysis (atgl, cpt1 and aco) in muscle and adipose tissue was analysed. In muscle of fish fed the low‐lipid diet, the expression of lpl, lrp1, fas, dgat2 and atgl was significantly downregulated, whereas fabp3 and fabp11 were significantly upregulated compared with those fed the control diet. In muscle of fish fed the high‐lipid diet, the expression of lpl, ldlr, lrp1, cd36, fabp3, fas and dgat2 was significantly decreased, while fabp11 expression was significantly increased compared with those fed the control diet. Compared with the control group, only a significant downregulation of fabp3 expression in adipose tissue was observed in the low‐lipid group. In the high‐lipid group compared with the control group, the expression of ldlr, fabp11, dgat2, atgl and aco in adipose tissue was significantly upregulated, whereas cpt1 expression in adipose tissue was significantly downregulated. These results indicated that the expression of the selected key genes related to lipid metabolism was tissue‐specific regulation by dietary lipid levels in large yellow croaker.