小肽及其在鱼类营养中的应用

小肽作为蛋白质的主要消化产物,在氨基酸消化、吸收和代谢中起着重要作用。主要对小肽的概念、分类、小肽理论的提出与发展、小肽的吸收机制和特点、小肽在水产养殖中的应用及影响鱼类利用小肽的因素等方面的内容作一概述,并提出一些存在的问题。     

小肽对养殖鱼类的作用

本刊讯：小肽作为质白质的主要消化产物，在氨基酸消化、吸收和代谢中起着重要作用。随着对小肽的研究深入，小肽对养殖鱼类的作用已受到关注，主要表现在以下几个方面：     

神经肽Y系统在硬骨鱼类摄食调控中的作用的研究进展

对硬骨鱼摄食调节机制的研究可以为鱼类养殖中优化饲料配方和养殖方式提供重要的科学指导。在众多参与摄食调节的内分泌因子中,神经肽Y(neuropeptide Y,NPY)家族多肽由于同时参与脑和胃肠道对食欲的调节,备受研究者关注。哺乳动物中存在3种类型的NPY家族多肽,其中NPY是脑中的促摄食因子,而肽YY(peptide YY,PYY)和胰多肽(pancreatic polypeptide,PP)是胃肠道中的抑摄食因子。这3种多肽与其共同的受体——NPY家族受体结合发挥其生理作用。NPY家族多肽和受体被共同称为NPY系统。硬骨鱼经历了第3次基因组复制,其NPY系统的组成更为复杂。目前对于硬骨鱼NPY系统在摄食调节中具体作用的研究还很不完善,尤其是对NPY家族受体的研究尚处于起步阶段。本文论述了硬骨鱼中NPY系统的组成、受体与配体的结合能力以及NPY家族多肽和受体在摄食调节中的作用,以期为该领域未来的研究提供参考。     

鱼类神经肽Y基因及其食欲调控机理研究

下丘脑的神经肽Y(Neuropeptide Y，NPY)是1982年首次从猪脑中分离出来的一种含36个氨基酸的单链多肽，属胰多肽家族。NPY是促进脊椎动物采食量的一个最强有力的诱导因子，所研究过的脊椎动物各物种的NPY存在高度同源性。与哺乳动物相似，鱼类NPY的结合区域也主要位于食欲调节区域。NPY在鱼类摄食活动中也被证实发挥了重要的食欲促进作用。3种鱼类NPY受体在斑马鱼中被成功克隆，为鱼类NPY受体功能及其作用机理研究奠定了基础。     

小肽对水生动物的营养作用探讨

传统的蛋白质营养理论认为,蛋白质必须水解为游离氨基酸后才能被吸收利用。近年来研究发现,蛋白质的水解物小肽可直接被动物机体吸收并在细胞内作为合成蛋白质的底物。小肽是由二个以上的氨基酸彼此以肽键相互连接的化合物,是一种具有多种生物学功能的肽。肽载体吸收能力可能高于各种氨基酸载体吸收能力的总和,在机体内可以传递神经信息（神经激肽）,促进胃肠道消化功能（胃泌素、胃泌素释放肽）,强化养分的消化与吸收（酪蛋白磷酸肽）,调控物质代谢（生长因素释放因子、胰岛素、胰高血糖素）,参与机体的免疫调节（免疫刺激肽）等。此外小肽还有多种生物活性的作用,如抗菌作用、免疫作用、抗氧化作用以及促进矿物质的吸收与利用、调节肉制品风味等特性。进而小肽可以提高饲料转化率,促进鱼类的生长,提高养殖业的经济效益,是一类发展前景广阔的添加剂。     

海洋鱼、虾、贝类的生物活性肽研究进展

肽与蛋白质是海洋生物中含量极其丰富的生理活性物质,近年来的研究表明,海洋生物活性肽具有特殊的生理活性,诸如免疫、抗肿瘤、抗高血压、抗血脂、抗菌和促生长等生理活性。本文就鱼类活性肽中的鲨肝肽、鲨鱼多肽、鱼精蛋白肽、鱼类抗菌肽、鱼类抗高血压肽,虾类活性肽以及贝类中的扇贝多肽和贻贝肽的生物活性研究概况作一简述。为该领域研发海洋保健食品和功能性食品提供参考。     

鱼类内源性生长激素释放肽的研究进展

生长激素释放肽（Ghrelin）是在哺乳动物中发现的第一个生长激素促分泌素受体的内源性配体，部分鱼类的Ghrelin基因和肽链结构已经被确定。与哺乳动物相似，鱼类Ghrelin的主要分泌部位也在消化道，但在脑、肾脏、鳃、心脏等组织中也有少量分泌。鱼类的Ghrelin参与多种生理功能的调节，包括促进摄食以及调节脑垂体内多种激素的分泌，可促进脑垂体分泌LH和GH，某些鱼类Ghrelin可能具有促进脑垂体分泌PRL的功能。本文综述了近年来鱼类Ghrelin结构与生理功能研究概况，旨在为丰富鱼类内分泌生理学研究提供参考资料。[中国水产科学，2008，15（3）：516-522]     

大豆小肽的营养及其在水产养殖中的应用

近年来,小肽作为一种绿色饲料添加剂逐渐成为研究的热点。大豆小肽是大豆蛋白质水解后产生的由几个到几十个氨基酸残基组成的肽混合物,能对动物的生理功能产生直接影响。小肽作为蛋白质的主要消化产物,在氨基酸消化、吸收以及动物营养代谢中起着重要的作用。在水产养殖中,添加适量的小肽可增强水产动物的免疫力,提高养殖成活率、饲料中各种矿物元素的利用率、饲料转换率、体内蛋白质的合成能力以及养殖过程中的增重率,促进鱼类的生长。一、大豆小肽的营养大豆是一种优良的植物蛋白资源,其中含有35%的粗蛋白,经过加工而成的大豆饼粕含有42%左…     

杆菌肽锌对异育银鲫生长影响的初步研究

杆菌肽锌（ＺｉｎｃＢａｃｉｔｒａｃｉｎ）是一种多肽类抗生素，是由地衣型芽孢杆菌发酵而产生多种氨基酸结合而成的。其抗菌谱与青霉素相似。对革兰氏阳性菌，杆菌肽锌在低剂量时可以抑制细菌细胞壁的合成（邱楚武，２００１），因此可以抑制包括梭菌，链球菌、葡萄球菌等有害阳性菌的生长。对部分革兰氏阴性菌、螺旋菌、放线菌也有一定效果。杆菌肽锌的最大优点是在动物体内不吸收，无残留，对环境无污染（吕九琢等，２００１）。杆菌肽锌对水产动物养殖上的应用还少有报道。本试验通过在饵料中添加一定量的杆菌肽锌养殖异育银鲫，旨在探…     

鱼类电感受器的种类、结构与作用模式

鱼类的电感受器,是一种特殊的侧线器官,与机械感受器官同属于侧线感觉系统。电感受器可以感受到生存环境中的弱电场,在鱼类的定位、交流、摄食等行为中发挥着重要的作用。电感受器的种类分为壶腹型电感受器和结节型电感受器,其作用模式分别为主要用于摄食和逃避敌害的"被动模式"和用于电定位与电交流的"主动模式"。研究鱼类电感受器的目的,一方面为了深入了解鱼类的进化意义和生物学特性,并在生态养殖或捕捞中有效地利用鱼类的电感受的特性,以提高增养殖或负责任捕捞技术。另一方面,有利于更好地研究和保护鲟鱼等电觉鱼类资源。     

Mass spectrometry-assisted confirmation of the inability of dipeptidyl peptidase-4 to cleave goldfish peptide YY(1–36) and the lack of anorexigenic effects of peptide YY(3–36) in goldfish (<Emphasis Type="Italic">Carassius auratus</Emphasis>)

Dipeptidyl peptidase-4 (DPP4) is a serine protease of great interest because it has been shown to modulate the activity of several peptidergic factors including peptide YY (PYY) and glucagon-like peptide-1/2. While PYY(1–36) is orexigenic in mammals, PYY(3–36) recently garnered interest as a potent anorexigen. In silico phylogenetic analysis found that the DPP4 cleavage sites are absent in fish PYY sequences. However, no studies were conducted to show that indeed PYY(3–36) is not produced by DPP4 in fish. If DPP4 does not cleave PYY(1–36), is PYY(3–36) an anorexigen in fish? The objectives of this research were to (1) test whether DPP4 cleaves goldfish PYY(1–36) and (2) determine whether PYY(3–36) is an anorexigen in goldfish. First, we identified the highly conserved catalytic region of DPP4 in goldfish. Abundant expression of DPP4 mRNA was found within the gastrointestinal tract. We also report the first MALDI-MS cleavage analysis of DPP4 effects on PYY(1–36) in a non-mammalian vertebrate. Our novel results indicate that DPP4 is unable to cleave goldfish PYY(1–36) to PYY(3–36) in vitro. It also confirms a previously held hypothesis that DPP4 is unable to cleave fish PYY(1–36) that contains N-terminal proline–proline residues. PYY(3–36) had no effects on food intake of goldfish. The appetite inhibitory effects of intraperitoneal and intracerebroventricular injections of 10 ng/g body weight gfPYY(1–36) were abolished by coinjections of BIBP3226, a Y1 receptor antagonist. These results are significant because it shows the lack of generation of endogenous PYY(3–36) and its anorectic effects in goldfish.     

Identification,characterization and feeding response of peptide YYb (PYYb) gene in grass carp (Ctenopharyngodon idellus)

The peptide YYb (PYYb) is a fish-specific peptide belonging to the neuropeptide Y (NPY) family. In the present study, the full-length cDNA sequence and genomic structure of PYYb (gcPYYb) from Ctenopharyngodon idellus have been isolated and characterized. The gcPYYb gene consists of three exons interspaced by two introns, opposing to the typical architecture of most NPY-family genes as well as its paralogs. Alignment of deduced amino acid sequence indicates that the fish PYYb is more variable compared to NPY and PYY as shown by more residue changes in teleosts lineage, suggesting mild selective pressure imposed on the peptide. Real-time quantitative PCR analysis shows the gcPYYb mRNA in developing larvae is increased during the mixed endo- and exogenous-feeding period and is widely distributed throughout the intestine of fully grown individuals. Following a single meal, the gcPYYb mRNA in foregut is increased at 3 h post-feeding and subsequently decreased before the foregut contents are cleared. These results suggest that the gcPYYb has an important role in the early life stages of grass carp and is involved in food intake by transmitting feeding-related signals.     

Growth performance and whole‐body composition of yellow catfish (Pelteobagrus fulvidraco Richardson) under feeding restriction

Fish growth is an important index in aquaculture practice. However, the effect of growth under restricted feeding on quality of fish grown to the same size remains poorly unknown. In this study, yellow catfish were reared by feeding them at three different feeding rates such as low (FR‐L group), medium (FR‐M group) and high (apparent satiation) ration levels for 82, 58 and 34 days to reach the same size, respectively. After this period, the growth performance, whole‐body amino acid composition and fatty acid profile of the fish were evaluated. Feeding restriction led to significant decreases in specific growth rate and feed conversion efficiency. Significant increases in dry matter, protein and energy contents were observed in fish under both restricted feeding treatments. FR‐L‐treated fish had significantly lower whole‐body essential amino acid contents, and significantly higher Ala and non‐essential amino acid contents compared to fish fed to satiation. Fish in restricted feeding treatments had significantly higher n‐3 PUFA and n‐3/n‐6 ratio compared to the fish fed to satiation. The present results indicate that from a quality perspective, there are certain advantages in improvement of whole‐body composition and enrichment of n‐3 PUFA associated with the restricted feeding of yellow catfish at slow growth rate.     

GROWTH OF WHITE STURGEON (Acipenser transmontanus) UNDER HATCHERY CONDITIONS

White sturgeon juveniles were raised for 10 months posthatch under various regimens of feeding, water temperature, and stocking density. Transition to external feeding in larvae occurred 9 to 11 days posthatch and was accompanied by major changes in allometric growth and larval behavior. Condition factor, hepatosomatic index, and survival rate varied significantly throughout the rearing period in the 4 progenies investigated. Growth in body weight for all progenies was largely dependent on water temperature and feeding. On the average, fingerlings raised on natural diets (brine shrimp and tubifex, followed by ground fish) grew 6% of their body weight per day, whereas fingerlings fed artificial pelleted diets (Oregon Moist Pellets) or a mixture of pelleted and natural feeds grew 1–4% per day. Certain individuals (20% of population investigated), however, established a strong feeding performance on artificial diets and exhibited twice the growth rate of fish raised on natural diets; these fish reached a mean body weight of 282 g at 10 months post-hatch. Assuming more efficient procedures are developed for weaning this fish onto artificial diets, the white sturgeon has demonstrated a potential for use in intensive grow-out systems.     

冬季低水温鳜短期饥饿和摄食的生理状态比较

【目的】本试验以我国鳜鱼主产区广东省的冬季水温为参照，在(13±1℃)的水温条件下，进行了鳜鱼短期饥饿与摄食的生理状态比较研究。【方法】选取体重为(84.13±0.14) g的鳜鱼90尾，分为饥饿组(饥饿15 d)和摄食组(摄食15 d)，实验结束后测定各项理化指标。【结果】结果显示：①摄食组鳜鱼的体质量、肝糖原、全鱼与肌肉的粗蛋白、粗脂肪含量均显著高于饥饿组，摄食组增重7.54%，而饥饿组减重8.39%。②摄食组鳜鱼血浆谷丙转氨酶和谷草转氨酶活性显著低于饥饿组，但甘油三酯含量显著高于饥饿组，各类血细胞数量与血糖水平则无明显差异。③摄食组鳜鱼的消化酶活性显著高于饥饿组，肠道组织结构发育更好。④摄食组鳜鱼肝脏抗氧化能力显著高于饥饿组，且饥饿组部分肝细胞有明显的结构损伤，脂滴数量显著少于摄食组。⑤摄食组鳜鱼的血浆溶菌酶活性和血浆、脾脏、肾脏免疫球蛋白M含量显著高于饥饿组。⑥摄食组与饥饿组鳜鱼背肌氨基酸组成无明显差异。但脂肪酸组成有明显差异，摄食组鳜鱼背肌饱和脂肪酸与单不饱和脂肪酸总量显著低于饥饿组，而多不饱和脂肪酸与高不饱和脂肪酸总量显著高于饥饿组。【结论】综上所述，在本试验条件下，摄食组增重而饥饿组减重，两种处理差值达15.93%，且饥饿组存在消化和免疫能力下降，肝脏抗氧化能力减弱，细胞结构损伤的隐形危害，而摄食组的鳜鱼消化、免疫及肝脏功能相对正常，背肌蛋白与脂肪含量更高，脂肪酸组成得到改善，氨基酸组成稳定。     

Economic analysis of overwinter feeding regimens for channel catfish (Ictalurus punctatus)

Abstract

Overwintering is a major source of uncertainty for US catfish farmers, particularly decisions on feeding. To address this issue, economic analysis was undertaken using results from pond experiments. Three overwintering strategies (full‐feed, partial‐feed, and no‐feed) for two year classes of catfish were compared. Year 1 fin‐gerlings were 22 g and year 2 fish were 420 g at stocking. Winter feeding was based on temperature and body weight percentages; (1) full‐feeding followed the regime during the November to April period; (2) partial‐fed treatments followed the temperature/body weight regimen only during the months of November, March and April, with no feeding during the coldest months of December to February; and (3) no‐feeding treatments received no feed during the overwinter period. Cost and returns were estimated for each alternative and each alternative was assessed using: (1) overwinter period experimental results, (2) overwinter period experimental results extended through the grow‐out period, (3) overwinter period experimental results extended to minimally acceptable fish sizes, and (4) adjusted estimates to reflect commercial‐scale practices. Sensitivity analyses on feed conversion ratios, stocking rates and fish selling prices were also conducted on commercial‐scale enterprises. Results consistently showed partial‐fed overwinter practices to be most profitable. Secondly, year 1 fish always had higher returns than year 2 fish due largely to the additional overwintering period and associated variable and fixed costs incurred by the year 2 fish production practices. The data upon which this analysis was based do not include the possibility of having a harvest‐sized fish going into the winter period.     

Optimization of feeding quantity and frequency to rear the cyprinid fish Garra rufa (Heckel, 1843)

Garra rufa has a high commercial value, but their rearing methods are still unknown. Aspects like an adequate daily dose and feeding frequency need to be investigated. This work aimed to establish the optimal feed dose per day to obtain satiation and the optimal frequency of feeding to rear a specific size class of G. rufa. A total of 60 fish were distributed by six aquaria containing 10 fish. First, the fish were fed twice per day, by providing a feed dose correspondent to 1% of their body weight and increasing 0.1 g/fish on the following days, until finding feed leftovers on the next morning. Afterwards, the fish went through a 1 month experimental trial to evaluate the optimal feeding frequency. Fish growth was compared between feeding the optimal daily dose distributed in two or three feeding moments per day. The optimal dose that ensured satiation was 0.042 g fish^?1 day^?1 (3.2% of fish’ body weight). Feeding the fish three times per day promoted higher growth rates, since the fish’ total length was statistically different between feeding frequencies. Statistically significant differences between feeding frequencies were not observed for growth performance parameters. These results contribute to the aquaculture of this target species, allowing fish industry to more efficiently respond to the high demand for G. rufa and, simultaneously, for its preservation in the wild.     

Growth and feeding of white steenbras, Lithognathus lithognathus (Cuvier) (Sparidae), under experimental culture conditions

Growth and feeding of white steenbras, Lithognathus lithognathus (Cuvier). under culture conditions was determined to assess its suitability for mariculture. Ration size ranged from 4.50% to 11.52% and from 1.67% 4.00% dry body weight for small (28 ± 2 g) and large (250 ± 23 g) fish, respectively. Condition factor (K) ranged from 1.19 to 1.35 and from 2.00 to 2.19 for small and large fish, respectively. Specific growth rate (SGR) at 16°C was 0.60% day^?1 for 28-g fish, 0.29% day^?1 for a 74-g fish, and 0.19% day^?1 for a 250-g fish. Gross conversion efficiency (GCE) was inefficient at high feeding levels (21.3%) compared with low feeding levels (32.6%). Proximate body composition in terms of moisture, protein. lipid, ash and energy were not significantly affected by feeding regime or temperature (P > 0.05). The experiments indicate that feeding regimes should be maintained at relatively low levels to obtain optimum K, GCE and SGR, and to avoid over-feeding and food wastage. It was concluded that L. lithognathus could be a suitable candidate for mariculture.     

Effects of feeding frequency and dietary energy level on growth and body composition of juvenile flounder, Paralichthys olivaceus (Temminck & Schlegel)

A two (dietary energy levels; low energy, LE and high energy, HE) × 4 (feeding frequency; one feeding in 2 days, one feeding daily, two times daily and three times daily) factorial experiment was performed to determine the effects of dietary energy level and/or feeding frequency on the growth and body composition of juvenile flounder Paralichthys olivaceus. The survival rate was not significantly different among treatments. Weight gain of fish fed the LE and HE diets significantly increased as feeding frequency increased. The weight gain of fish fed the LE diet was higher at each level of increasing feeding frequency. The weight gain of fish fed the HE diet was higher than that of fish fed the LE diet once in 2 days and once daily, but weight gain of fish fed the HE diet was lower than the LE diet three times daily. Daily feed intake was significantly influenced by feeding frequency, but not by dietary energy level. Feed efficiency of fish fed the HE diet once daily was significantly higher than that of fish fed the LE diet once in 2 days, but no significant difference in feed efficiency was observed among other groups of fish. The protein efficiency ratio of fish fed the LE diet once in 2 days was the lowest. Feeding frequency and dietary energy level had a significant effect on the body lipid content. A feeding frequency of two times or three times daily would be effective, depending on dietary energy level for maximum growth of juvenile flounder grown from 3.5 to 15 g.     

Effects of feeding a high level of D-glucose on liver function in juvenile white sturgeon (Acipenser transmontanus)

Juvenile white sturgeon (Acipenser transmontanus) were fed three isonitrogenous and isoenergetic diets containing either 35% D-glucose (HC), a mixture of 20% dextrin and 10% cellulose (MC), or 23% cellulose (LC), to investigate the effects of dietary carbohydrate on liver function. After 8-week feeding, body weight gain of fish fed the HC diet was consistently higher than that of fish fed the MC and LC diets, but was not significantly different from the MC-fed fish. Fish fed the HC diet had significantly (p < 0.05) higher feed efficiencies and liver glycogen concentrations than fish fed the MC and LC diets. Sturgeon were injected intravenously with 10 mg kg^-1 body weight of sulfobromophthalein (BSP) and post-injection blood taken from the caudal vein at 15, 30, 60, and 120 min. No significant differences in plasma BSP concentrations were found among the treatments at these times. Plasma hemoglobin and activities of aspartate and alanine aminotransferase were not affected by the diets. This study suggests that the HC diet does not adversely affect liver function or weight gain. Inclusion of high dietary levels of digestible and inexpensive carbohydrates in commercial sturgeon feeds seems promising, but long-term feeding trials should be conducted to confirm this assertion.