GnRH_A和紫萁抑制大黄鱼性腺早熟的机制

应用脑垂体组织生理学和免疫组织化学方法，对GnRH-A和紫萁抑制大黄鱼性早熟的作用机制进行了研究。结果表明，性早熟大黄鱼脑垂体许多促性腺激素分泌细胞的胞质出现空泡，提示性早熟的原因可能是由于GtH细胞提早进入分泌活动所致。长期服用促性腺激素释放激素类似物的养殖大黄鱼（没有性早熟），它的脑垂体GtH细胞对GnRH抗独特型发生弱的免疫阳性反应，而对照组性早熟鱼仍出现强的反应，表明实验组大黄鱼脑垂体GtH细胞对GnRH-A的应答能力下降，出现脱敏效应，这可能与GnRH-A抑制大黄鱼性早熟有关。养殖大黄鱼长期服用紫萁，它的脑垂体GtH细胞膜上GnRH受体则没有出现脱敏现象，提示紫萁抑制大黄鱼性早熟的机制不同于GnRH类似物，确切机制有待进一步研究。     

大黄鱼冷却链用冰量估算系统的设计与评估

为准确评估冰鲜大黄鱼流通过程中的用冰量,应用传热学基本理论对流通过程中泡沫箱与外界间的传热进行分析,建立了环境温度0～25℃范围的大黄鱼流通用冰量估算模型,借助Visual Basic开发平台实现了模型在系统中的应用,增加了模型的实际应用功能。通过不同环境温度下的模拟试验,验证了估算系统的准确性,用冰量估算值和实际值间的相对误差在7.0%～16.2%范围内,平均误差为12.3%,用冰量估算系统的偏差因子和准确性因子分别为0.778和1.285,显示建立的估算系统可以快速可靠地估算冰鲜大黄鱼生产流通实际中的用冰量,是监控大黄鱼流通中用冰量的有效工具。     

东海区大黄鱼渔业资源及资源衰退原因分析

根据近几年东海区渔业资源调查并结合相关历史资料,对东海区大黄鱼Pseudosciaena crocea的渔业状况、种群结构、生殖特性及种群洄游分布规律等进行了研究。结果表明:自20世纪70年代以后,由于东海区大黄鱼渔业投入的捕捞力量和强度过大,已远远超过了大黄鱼资源的承受能力,大黄鱼资源量快速衰减,过度捕捞使东海区在20世纪80年代中期已形不成大黄鱼渔汛,渔业部门虽然制订了许多资源保护措施,但至今大黄鱼仍属东海区资源严重衰退的鱼种;大黄鱼群体组成呈现低龄化、小型化趋势,群体优势年龄组和优势体长组分别由20世纪70年代的4～7龄(220～350 mm),减小到90年代以后的1龄(140～160 mm),且初次生殖年龄提前。     

养殖大黄鱼冷藏过程中细菌菌相的变化

采用感官、挥发性盐基氮(TVBN)、菌落总数对大黄鱼(Pseudosciaena crocea)在0℃、5℃冷藏过程中的品质变化特征进行分析,并对细菌菌相进行定性和定量研究。结果表明,冷藏初期、高品质期和货架期终点菌落总数N(CFU/g)的对数值(lgN)分别为5.40±0.17、6.98±0.17、7.38±0.09,TVBN分别为(7.00±1.82)mg.100-1.g-1、(13.00±1.42)mg.100-1.g-1、(29.92±1.75)mg.100-1.g-1。冷藏初期分离获得211株菌株,84.8%是革兰氏阴性菌,出现少量革兰氏阳性菌(6.2%),优势菌群是肠杆菌科细菌(6.6%)、气单胞菌属(14.2%)、不动杆菌属(13.3%)、摩氏杆菌属(11.8%),并出现了一定比例的假单胞菌属、嗜麦芽窄食单胞菌和其他细菌。冷藏过程中细菌菌相逐渐变得单一,腐败希瓦氏菌上升趋势明显。高品质期时,0℃冷藏大黄鱼优势菌群为腐败希瓦氏菌(45.8%)和缺陷短波胞单胞菌(13.6%);5℃冷藏大黄鱼优势菌群为腐败希瓦氏菌(37.9%)和假单胞菌属(15.6%)。货架期终点时,0℃、5℃冷藏大黄鱼优势菌为腐败希瓦氏菌,比例分别为75.5%和59.6%。     

含盐量对腌制大黄鱼鱼肉品质的影响

为深入探究大黄鱼肌原纤维蛋白(MP)的乳化性,以满足大黄鱼蛋白质高值化开发利用的需求。实验探究了不同pH对大黄鱼MP结构性质及其乳化性的影响。采用pH分别为2、4、6、8、10、12的低盐磷酸缓冲液处理大黄鱼MP,通过SDS-PAGE分析大黄鱼MP降解情况,利用接触角测量仪和荧光分光光度计考察其疏水性变化。将不同pH下大黄鱼MP溶液与大豆油以体积比为1∶1的比例经高速均质制备乳液,并对其乳滴电位、粒径以及乳液的乳析指数进行测定,综合分析在不同pH下乳液的稳定性。SDS-PAGE电泳结果表明,在pH 4时,大黄鱼MP条带颜色较浅,在pH 6~12时,肌球蛋白重链条带基本消失,肌动蛋白条带颜色逐渐加深,且在浓缩胶顶部出现了高分子聚集物。对接触角和荧光光谱的综合分析表明,大黄鱼MP疏水性随pH增加而增加。对不同pH下MP乳液特性分析显示,在pH 8时,乳滴带负电且Zeta电位绝对值大[(49.63±1.52) mV]、粒径较小、乳液稳定性较好,而pH 12条件下容易出现破乳,不利于乳液的稳定。在pH 8时,大黄鱼MP结构更有利于提升乳液稳定性。研究表明,在弱碱性条件下更有利于大黄鱼MP形成稳定的乳液体系。pH对大黄鱼MP结构性质和乳化性的影响探究,有望为大黄鱼MP在食品工业中的开发利用提供理论依据。

     

网箱养殖大黄鱼两种间距分级栅分级效果的比较

对770尾网箱养殖大黄鱼的生物学参数体宽（B）、体长（L）与体重（W）进行测定,运用幂函数拟合方法获得体重与其他两个参数的关系方程。为了达到按重量300 g的分级要求,选择体宽为确定分级栅间距的依据,运用几何形态法、logistic曲线模型方法确定分级栅间距的理论值为34.66 mm,用幂函数拟合方法得理 论值为38.21 mm。分级试验采用平均间距为33.01 mm、37.95 mm二种规格分级栅,对大黄鱼分级,结果表明：经过5～10 min分级,间距33.01 mm分级栅留存的大黄鱼中,达到分级标准的鱼(W≥300 g)的最高比例为50.00%,平均为42.96%,留存下的鱼的平均体 重296 g;间距37.95 mm的分级栅,留存的渔获中,体重高于300 g的最大比例为73.33%,平 均为43.76% ,留存下的鱼的平均体重310 g。使用平均间距37.95 mm的分级栅,在周长为48 m的深水网箱中进行分级操作后,留存的大黄鱼中,最小鱼体重为320 g,分级效果良好。同时也表明用幂函数拟合方法计算分级栅间距比用几何形态法、Logistic曲线模型方法计算出的分级栅间距进行分级的效果要好。     

大黄鱼刺激隐核虫病继发细菌感染致死原因的研究

为明确大黄鱼刺激隐虫病大量死亡的致死原因,从患刺激隐核虫（Cryptocaryon irritans）病的大黄鱼（Pseudosciaena crocea）肝脏中分离细菌,病情程度较轻的鱼未分离到细菌,非常严重的鱼分离到细菌;分离的菌株经纯化后鉴定为创伤弧菌（Vibrio vulnificus）,利用纯化后的菌株作回归感染试验,其感染率为100%,死亡率为80%。研究表明患刺激隐核虫病的大黄鱼体内的细菌为继发性感染,是导致大黄鱼大量死亡的致病菌,其感染途径为水→伤口→体内。     

东海养殖大黄鱼细菌多样性分析

对2004年9月在闽东三都湾4个养殖场取样的大黄鱼进行了细菌多样性定性和定量分析。新捕获大黄鱼细菌总数为1.8×103~6.0×106cfu/g。从养殖密集海区的鱼体分离出135株细菌,对它们形态、生理生化、营养特征等进行系统鉴定,结果显示革兰氏阴性菌占优势。优势菌群为气单胞菌属(Aeromonasspp.)和嗜麦芽寡养单胞菌(Steotromonasmaltophilia),比例为34.1%和21.0%,摩氏杆菌属(Moraxellaspp.)、不动细菌属(Acinetobacterspp.)出现比例较少,均为2.2%,出现了较多数量的弗氏柠檬酸杆菌(Citrobacterfreundii)(5.2%)、阴沟肠杆菌(Enterobactercloacae)(9.6%)。     

Dietary threonine requirement of juvenile large yellow croaker,Larmichthys crocea

A feeding trial was conducted to determine the dietary threonine requirement of juvenile large yellow croaker (Larmichthys crocea). Six diets were formulated containing 45% crude protein with six graded levels of threonine (0.71–2.46% in about 0.35% increment). Each diet was randomly assigned to triplicate groups of 60 juvenile fish (initial body weight 6.00 ± 0.10 g). Fish were fed twice daily (05:00 and 16:30) to apparent satiation for 8 weeks. The result indicated that significant difference was observed in the weight gain among all treatments. Specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and nitrogen retention (NR) increased with increasing levels of threonine up to 1.75% diet (P < 0.05), and thereafter, declined. No significant differences in body dry matter, crude protein, crude lipid or ash content were found among dietary treatments. Theronine contents of fish muscle were significantly affected by dietary threonine levels (P < 0.05). Fish fed the diet with 0.71% threonine showed the lowest threonine content (2.94%) in fish muscle, while fish fed the diet with 1.75% threonine had the highest value (3.16%). Other essential amino acid contents of muscle were not significantly different among the dietary treatments. On the basis of SGR, FE or NR, the optimum dietary threonine requirements of juvenile L. crocea were estimated to be 1.86% of diet (4.13% of dietary protein), 1.90% of diet (4.22% of dietary protein) and 2.06% of diet (4.58% of dietary protein), respectively, using second‐order polynomial regression analysis.     

Antioxidant Efficacy of Protein Hydrolysates from Large Yellow Croaker (Pseudosciaena crocea) in D-galactose-Induced Aging Mice

The antioxidant efficacy of protein hydrolysates prepared from large yellow croaker (Pseudosciaena crocea) by enzymatic hydrolysis using neutral protease was evaluated in D-galactose-induced aging mice. Animals were divided into normal and model control groups, and low-, middle-, and high-dose groups (50, 100, and 300 mg/kg; LYCHs), as well as tocopherol (VE) and antagonistic (LYCHs + VE) groups. The study was carried out for 30 days. Administration of D-galactose induced oxidative damage with a significant rise (p < 0.01) in malondialdehyde and a reduction in several endogenous antioxidant enzymes and glutathione (GSH). Treatment with large yellow croaker protein hydrolysates stimulated an increase in superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase activities, increased levels of reduced glutathione, and decreased malondialdehyde, compared with the model control group. Additionally, hepatocellular damage was evaluated by measuring aspartate aminotransferase and alanine aminotransferase levels. These results demonstrate the protective role of large yellow croaker protein hydrolysates in D-galactose-induced oxidative stress, as well as their potential as nutraceuticals or adjuvant agents for disease prevention.