Diurnal expression of circadian clock genes period 1 and period 3 in Pelteobagrus vachellii

Circadian clock genes are crucial for generating and sustaining most rhythmic daily functions in the animal kingdom,which entrain the rhythms of biochemical,physiological,and behavioural processes.To better understand the molecular oscillations of the circadian rhythms in darkbarbel catfish(Pelteobagrus vachellii),we isolated and characterized two circadian clock genes in P.vachellii,period 1(per1),and period 3(per3).The circadian clock gene per1 was found to encode a 1428-amino acid polypeptide,including PER-ARNT-SIM(PAS)dimerisation domains,a PAS-associated C-terminal motif(PAC),a short mutable domain(S/M),and a nuclear export signal(NES).The 4902-bp per3 cDNA includes an open reading frame encoding a 1292-amino acid residue polypeptide with a PER-ARNT-SIM(PAS)domain,cytoplasmic localisation domain(CLD),interaction site(TIS),and a nuclear localisation signal(NLS).The per1 and per3 gene was constitutively expressed in all examined tissues.Moreover,per1 expression within a light/dark cycles showed rhythmic expression in the diencephalon,brain,liver and intestine,with the acrophase at 15:15,12:52,7:51 and 12:55,respectively.Daily expression of per3 was rhythmic in the diencephalonbrain,liver and intestine,with the acrophase at 8:15,9:54,10:39,and 10:25 h,respectively.These findings expand our understanding of circadian mechanism at the molecular level in this species.

Identification and Biological Characteristics of Edwardsiella tarda Isolated from Pelteobagrus fulvidraco

Over the past five years, an epidemic disease broke out in Pelteobagrus fulvidraco ponds of Zhejiang Province. The diseased fish mainly exhibits head splitting and surface bleeding; dissection results reveal hepatonephromegaly and abdominal bleeding. A bacterial strain HSY201301 was isolated from the liver tissue of P. fulvidraco with typical symptoms. Artificial infection experiment confirmed that the isolated strain had a strong virulence to healthy P. fidvidraco, leading to similar symptoms to naturally infected P. fulvidraco. The isolated strain was identified as an Edwardsiella tarda strain according to conventional morphological, physiological, biochemical characteristics and 16S rRNA gene sequence. Results of drug susceptibility test indicated that the isolated strain was sensitive to cipro- floxacin, doxitard, penicillin, doxycycline, and rocephin. This study laid solid foundation for effective prevention and control of E. tarda.

Effects of feeding time on complement component C7 expression in Pelteobagrus vachellii subject to bacterial challenge

Shifting the feeding time for fish from daytime to nighttime could alter their digestive behavior, disturb their metabolism, and may af fect immune-related genes. This study aimed to clone complement component C7 and analyze the different expression of C7 mRNA in fish fed during either the day or at night and then challenged with Aeromonas hydrophila infection. The P v-C7 cDNA of Pelteobagrus vachellii contained 2 647 bp with an open reading frame encoding a protein of 818 amino acids. Multiple sequences analysis indicated that P v-C7 included eight domains, which was similar to results for other species. Quantitative PCR analysis showed that P v-C7 was mainly expressed in the liver, spleen, intestine and head kidney tissues of healthy P. vachellii. Quantitative PCR analysis showed that C7 mRNA transcript in the liver, spleen and head kidney also increased significantly when the fish were fed at nighttime(20:00). In addition, the expression of Pv-C7 mRNA significantly increased with A. hydrophila challenge in the liver(48–96 h), spleen and head kidney(12–96 h) tissues of P. vachellii. Pv-C7 mRNA expression of the fish fed at nighttime showed significant higher than that in the fish fed at day time at 12–48 h in head kidney and 12–24 h in spleen. This study indicates that altering the feeding time from daytime to nighttime could increase P v-C7 mRNA expression, and feeding time may af fect the immune response involving C7.

Isolation and Pathogenicity Analyses on Yersinia enterocolitica from Pelteobagrus vachelli

Yersinia enterocolitica is an important zoonotic pathogen that can induce disease outbreaks in a wide host range. Strain YER6022 was isolated from Pelteobagrus vachelli and identified using bacterial morphology and 16S rDNA sequence analysis. Five virulence factors were detected, then artificial infection experiment and histopathological method were carried out. These results showed that strain YER6022 was one of Y. enterocolitica family members. In addition, ail, ystb, virF, yadA and HPIint were dectected. In artificial infection experiment, with 80% mortality and 100% morbidity, injected Pelteobagrus vachellis showed red swollen of the anus, abdomen swelling and fim bleeding. There existed serious hyperaemia and edema in kidney, spleen, intestine and liver at the light microscope. Ultrastructural observation indicated that mitochondria of the liver, kidney, spleen and intestine swelled and mitochondrial cristae broke. The data had further shed light on its pathogenicity in Pelteobagrus vachelli. It would benefit for further studies on pathogenesis ofPelteobagrus vachelli infected with Y. enterocolitica.

Artificial induction of androgenetic diploid in Yellow catfish(Pelteobagrus fulvidraco)

Androgenesis was the especial zoogamy that the germ plasma of offspring was from the agnate. In this study the eggs of Yellow catfish （Pelteobagrus fulvidraco） were irradiated by UV suspending in the synthetic ovarian fluid （OF）, and the total dosage of UV irradiation was 220 mJ·cm^-2. Diploid could be induced by heat shock （40℃, 2 min, 3 min） with different time period after fertilization （15-37 min）. The result showed that heat shock with 2 min was better than 3 min; there were two apices of induction in 17-21 min and 27-31 min after fertilization. The highest hatching rate was 3.30% at 29 min after fertilization, and the difference between two apices of induction was unobvious.

Breeding of XX Females( XX ♀),YY Physiological Females( YY♀),YY Super-males( YY♂ ) of Pure-line Yellow Catfish( Pelteobagrus fulvidraco Richardson)

Mature wild-type yellow catfish( Pelteobagrus fulvidraco Richardson) individuals with excellent traits have been screened from the Yangtze River as broodstock to establish the germplasm bank of pure-line yellow catfish by artificial gynogenesis technique and hormonal sex reversal method. Based on pure lines of yellow catfish,super-males and physiological females of yellow catfish were selected by GMT technique,hormonal sex reversal method and test-crossing to establish the germplasm bank of YY physiological females( YY♀). The propagation system of male yellow catfish( XY♂) was established based on the combination of super-males( YY♂) and pure-line female( XX♀) for large-scale production of pure-line yellow catfish males,which effectively overcome the disadvantages in the production of common fingerlings and male fingerlings using low-grade fish with slow growth and small size at the bottom of the fish grader as broodfish,such as progeny germplasm degeneration,loss of growth vigor and reduction of breeding benefits. The technical route of breeding pure-line YY physiological females( YY♀) and YY super-males( YY♂) laid the foundation for large-scale production of environmentally friendly yellow catfish males with pure germplasm and strong stress resistance,and provided an efficient,stable,healthy,environmentally friendly,energy-saving and income-increasing approach for sustainable development of yellow catfish breeding industry.

Study on Early Propagation Technology of Yellow Catfish (Pelteobagrus fulvidraco)

[Objectives] This study was conducted to study early reproduction techniques of yellow catfish(Pelteobagrus fulvidraco) in Jianghan Plain. [Methods] Parents of P. fulvidraco were cultured by the methods of artificial temperature control and nutrition enhancement. [Results] After culture, the body weight, gonad weight, maturity coefficient and egg diameter of P. fulvidraco increased gradually. Up to April 30, the gonad weight of the female parents of P. fulvidraco cultured in greenhouses was significantly higher than that of the parents under natural conditions(P<0.05), 54% higher than that of the parents naturally cultured at the same period;the maturity coefficient of the parents cultured under strengthened conditions was also significantly higher than that of the parents under natural conditions at the same period(P<0.05);and the ovaries of the strengthened parents were orange yellow and full of eggs, and the number of eggs per fish was relatively high. In early May, the parents cultured under strengthened conditions were induced to spawn artificially. The average induced spawning rate and fertilization rate reached 86.7% and 71.6%, respectively, reaching the respective normal level. The gonad maturity of P. fulvidraco cultured under strengthened conditions was 15 d earlier than that under natural conditions, resulting in mass production of early-propagated larvae of P. fulvidraco. [Conclusions] In Jianghan plain area, artificial propagation can be achieved in early May by means of artificial temperature control and strengthened culture, which is 20 d ahead of natural conditions.

不同环境温度下冰藏黄颡鱼品质及微生物菌群变化研究

为研究宰杀后的黄颡鱼(Pelteobagrus fulvidraco)在不同环境温度下冰藏过程的品质变化和保鲜时间,测定了不同环境温度冰藏黄颡鱼肌肉的质构指标、pH、硫代巴比妥酸(TBA)、高铁肌红蛋白(MetMb)、挥发性盐基氮(TVB-N)、营养成分(水分、粗蛋白、粗脂肪、粗灰分)的含量,并通过16S rRNA高通量测序分析了黄颡鱼肌肉微生物菌群的变化。结果显示:15、27、33℃温度下冰藏黄颡鱼肌肉各质构指标均随时间延长而下降。各温度组TBA、TVB-N和MetMb含量随时间延长呈上升趋势,三组的TVB-N和MetMb含量在12 h冰藏期间均没有超过国家标准限值,15℃组TVB-N含量始终处于一级鲜度标准。各温度组肌肉营养成分中粗脂肪、粗灰分和水分含量随冰藏时间延长而有所下降。微生物组分析表明在冰藏期间,三个温度组的黄颡鱼肌肉均未产生有害病原菌微生物。研究表明,宰杀后的黄颡鱼33℃时冰藏保鲜时长为4 h,27℃时冰藏保鲜时长为6 h,15℃时冰藏保鲜时长可达12 h。

Effects of dietary arginine levels on growth performance,body composition, serum biochemical indices and resistance ability against ammonia-nitrogen stress in juvenile yellow catfish(Pelteobagrus fulvidraco)

This experiment was conducted to investigate the effects of dietary arginine levels on growth performance, body composition, serum biochemical indices and resistance ability against ammonia-nitrogen stress in juvenile yellow catfish(Pelteobagrus fulvidraco). Five isonitrogenous and isolipidic diets(42%protein and 9% lipid) were formulated to contain graded levels of arginine(2.44%, 2.64%, 2.81%, 3.01% and3.23% of diet), by supplementing L-Arginine HCI. Seven hundred juvenile yellow catfish with an initial average body weight of 1.13 ± 0.02 g were randomly divided into 5 groups with 4 replicates of 35 fish each and each group was fed one of the diets. After 56 d feeding, fish were exposed to 100 mg/L of ammonia-nitrogen for 72 h. The results showed that weight gain(WG) and specific growth rate(SGR) in2.64% and 2.81% groups were significantly higher than those in 3.23% group(P < 0.05). The feed conversation ratio(FCR) in 2,64%, 2,81% and 3.01% groups was significantly decreased when compared with3,23% group. The protein efficiency ratio(PER) in 2.64% group was significantly higher than that in 2.44%and 3.23% groups(P < 0.05). The condition factor(CF) of fish was significantly higher in 2.81% group than that in 2,44% group(P < 0.05). Dietary arginine levels had no significant effect on hepatosomatic index(HSI), viscerosomatic index(VSI), and whole-body dry matter, crude protein, crude lipid, ash contents, as well as serum total protein(TP), triglyceride(TG), glucose(GLU), urea nitrogen(UN) contents and aspartate aminotransferase(AST), alanine aminotransferase(ALT) activities(P> 0.05). After the fish were challenged to ammonia-nitrogen for 72 h, their cumulative mortality rate in 2.81% group was significantly lower than that in 2.44% group(P < 0.05). The results suggested that dietary arginine level at 2.81%could optimize anti-ammonia-nitrogen stress ability of juvenile yellow catfish and a level of 3.23%arginine seemed to depress the growth performance of fish and decreased their tolerance to the ammonia-nitrogen stress under current study. A quadratic regression analysis based on WG indicated that the optimal dietary arginine requirement of juvenile yellow catfish was estimated to be 2.74% of the diet(6.45% of dietary protein) under current culture conditions.

Identification of three members of the Bmp family from yellow catfish Pelteobagrus fulvidraco and their transcriptional responses to a high fat diet

In this study,three members of the Bmp family were cloned and characterized in yellow catfish Pelteobagrus fulvidraco,including Bmp2a,Bmp4 and Bmp9.The predicted amino acid sequences of P.fulvidraco Bmp2a,Bmp4 and Bmp9 showed the characteristic domains of the Bmp family,including an N-terminal signal peptide,Arg-X-XArg site,TGF-β family signature and seven conserved cysteines,indicating that function is likely to have been conserved during evolution.mRNAs of the three Bmp genes had a variable level of expression in tissues.Compared to the control diet,a high fat diet tended to down-regulate the mRNA expression of Bmp2a,Bmp4 and Bmp9 in mesenteric fat,liver and ovary,while it tended to up-regulate their mRNA levels in muscle and kidney.The responses to dietary lipid status and the potential role in lipid metabolism have not previously been reported and reinforces the idea of their multiple functions.Our findings provide the first data about the potential role of the Bmp family in lipid metabolism in teleost.

黄颡鱼源温和气单胞菌的分离鉴定及中草药体外抑菌效果研究

为探明遵义金鼎镇合江源养殖场患病黄颡鱼(Pelteobagrus fulvidraco)的致病原因,通过对患有腹水、鳍条充血和游动缓慢等症状的黄颡鱼进行了病原菌分离纯化,得到纯培养菌株MLT-1,经过回归感染证实其为黄颡鱼的致病菌,经生理生化和16S rDNA鉴定为温和气单胞菌(Aeromonas sobria)。同时采用乙醇提取法获得30种中草药醇提物,固体培养基打孔测试中药醇提物对MLT-1的抑菌作用,结果显示:诃子、大黄、烟叶、樟叶、桑白皮5种中草药对MLT-1的抑菌效果较好,诃子和大黄的最小抑菌浓度(MIC)及最小杀菌浓度(MBC)均为0.49 mg/mL,烟叶的MIC和MBC均为0.98 mg/mL,樟叶和桑白皮抑杀温和气单胞菌效果相同,MIC和MBC分别为0.195 mg/mL和3.91 mg/mL。结果表明诃子、大黄、烟叶、樟叶、桑白皮5种中草药可用于防治黄颡鱼温和气单胞菌细菌病。

黄颡鱼养殖群体遗传多样性与遗传结构的微卫星分析

为研究14个不同养殖群体的黄颡鱼(Pelteobagrus fulvidraco)遗传多样性及遗传结构,采用8对多态性微卫星引物对14个群体的209尾个体进行遗传多样性和遗传结构分析。结果显示:14个群体的平均等位基因数在8~10之间,平均有效等位基因在5.160~6.882之间,平均观测杂合度在0.633~0.717之间,平均期望杂合度在0.358~0.749之间,平均多态信息含量在0.594~0.681之间,均大于0.5。分子方差分析结果表明:3.69%的遗传变异来自群体间,3.93%来自群体内个体间,92.38%来自所有个体间,变异来源主要来自个体间,其中RB群体和WH群体的遗传分化最大(F_(st)=0.116),ZL群体和XB群体的遗传分化最小(F_(st)=-0.009)。基于遗传距离构建了UPGMA系统树,发现14个群体共分为5个聚类支,HJ、YZ、YH、YB 4个群体聚为一支,HQ和LG单独各自聚为一支,LZ和RB 2个群体聚为一支,DB、ZJ、WH、XH、XB和ZL 6个群体聚为一支。基于贝叶斯的Structure聚类分析同样支持14个黄颡鱼群体可分为5个聚类支,与聚类树的结果吻合。14个黄颡鱼群体的遗传多样性均处于高度多态水平,遗传分化处于低等分化水平。

一株黄颡鱼源迟缓爱德华氏菌弱毒株的分离鉴定及特性分析

为探明湖北荆州市某养殖基地患病黄颡鱼(Pelteobagrus fulvidraco)以烂身、腹水为主要症状且持续性死亡的确切病因,本研究对患病黄颡鱼进行了病原筛查,从患病黄颡鱼组织中分离到一株优势菌,经过形态特征、生理生化鉴定、16S rRNA测序和系统进化分析确定分离菌株为迟缓爱德华氏菌,命名为Et-4。结果显示:分离菌株Et-4具有较强的生物被膜形成能力,不携带esaV、fimA、gadB和katB四种主要的毒力基因。分离菌株Et-4人工感染健康黄颡鱼出现与自然发病类似的症状,并能从病鱼中再次分离出该菌,证实迟缓爱德华氏菌是引起此次黄颡鱼持续性死亡的致病原;分离菌株Et-4对黄颡鱼的LD_(50)为3.9×10^(6)CFU/g,结合毒力基因谱判定其为弱毒株。分离株Et-4携带耐药基因tet A、sulⅠ和add A1,对头孢类药物、庆大霉素、新霉素等敏感;对四环素类、青霉素类、万古菌素等耐药;中药抑菌实验表明乌梅和丁香对迟缓爱德华氏菌Et-4有明显的抑制效果。

基于PacBio平台的黄颡鱼全长转录组测序及分析

为进一步丰富黄颡鱼(Pelteobagrus fulvidraco)信息数据库,采用PacBio测序平台对黄颡鱼的肝脏、肾、背部肌肉、脑、脾、心脏、皮肤、血液、鳃、性腺等组织进行全长转录组混样测序。共获得685574个全长非嵌合(Full-length non-chimeric read,FLNC)序列,通过与黄颡鱼基因组比对分析,共获得72509个非冗余isoforms,平均长度为2918 bp。共鉴定到3169个LncRNA、45872个可变剪接事件、4881个基因存在可变多聚腺苷酸化位点和304个融合基因。将12492个新基因与NR、GO、KEGG、KOG和Swwassprot 5个公共数据库进行比对,成功注释了7233个isoforms。GO分析发现,新基因主要集中于细胞过程(Cellular process)、细胞组分(Cell)和结合功能(Binding)。KEGG pathway分析显示,新基因主要在信号转导(Signal transduction)和免疫系统(Immune system)信号通路中得到富集,此外,涉及黄颡鱼生殖与繁殖相关的内分泌系统代谢途径包括催产素信号通路、雌二醇信号通路、孕酮介导的卵母细胞成熟、促性腺激素释放激素信号通路和卵巢类固醇合成。

天津地区大口黑鲈混合养殖试验

为提高大口黑鲈养殖的经济效益和生态效益,开展了大口黑鲈混养试验,即大口黑鲈与南美白对虾、大口黑鲈与河蟹、大口黑鲈与黄颡鱼的混养模式试验。大口黑鲈与南美白对虾接力混合养殖,南美白对虾投放规格1 cm的苗种,密度45万尾/hm^(2),收获成虾规格42尾/kg,单位产量6318.75 kg/hm^(2),大口黑鲈投放规格150 g/尾,170 m^(3)水槽投放2000尾,收获规格0.79 kg/尾,养殖槽产量1548.4 kg;大口黑鲈与河蟹混养,大口黑鲈投放规格120 g/尾,密度22500尾/hm^(2),单位产量13162.5 kg/hm^(2),投放河蟹苗种规格5.12 g/只,密度7500只/hm^(2),收获河蟹546 kg/hm^(2);大口黑鲈与黄颡鱼混养,大口黑鲈鱼种规格120 g/尾,密度22500尾/hm^(2),收获大口黑鲈13252.5 kg/hm^(2),投放黄颡苗种规格68.25 g/尾,密度3000尾/hm^(2),收获黄颡鱼918 kg/hm^(2)。除接力混养南美白对虾需要投喂,河蟹、黄颡鱼不需投喂。大口黑鲈混养模式在不增加人力物力的情况下既提高了养殖经济效益,同时对水质调控有良好效果。

杂交黄颡鱼池塘高产高效养殖技术

杂交黄颡鱼(Pelteobagrus fulvidraco♀×Pelteobagrus Vachelli♂)是科研人员利用黄颡鱼作母本、瓦氏黄颡鱼作父本杂交获得的新品种,也是受欢迎的水产养殖品种。文章介绍了养殖杂交黄颡鱼的池塘条件、鱼种放养、饲养管理、水质调控、病害防治和捕捞等池塘高产高效养殖技术要点,供养殖者参考。

不同溶氧水平下氨氮和亚硝酸盐对黄颡鱼的急性毒性研究

在高溶氧(10.77±0.40)mg/L、中溶氧(6.89±0.33)mg/L和低溶氧(3.45±0.54)mg/L水平下,研究了氨氮和亚硝酸盐对黄颡鱼急性毒性效应。结果显示:高溶氧水平下,氨氮和亚硝酸盐对黄颡鱼的96 h-LC50值(95%可信区间)分别为148.1 mg/L(125.03～172.37 mg/L)、206.52 mg/L(164.25～246.23 mg/L);在中等溶氧水平下,氨氮和亚硝酸盐对黄颡鱼的96 h-LC50值(95%可信区间)分别为106.69 mg/L(89.92～123.70 mg/L)、145.77 mg/L(116.77～174.77 mg/L);而低溶氧水平下,氨氮和亚硝酸盐对黄颡鱼的96 h-LC50值(95%可信区间)分别为68.03 mg/L(58.32～77.89 mg/L)、81.33 mg/L(64.76～96.70 mg/L)。结果表明,在3种溶氧条件下,氨氮对黄颡鱼的毒性明显大于亚硝酸盐对黄颡鱼的毒性,因而氨氮对黄颡鱼的毒性成为其养殖过程中的重要影响因子。

溶氧水平对黄颡鱼稚鱼摄食、生长及呼吸代谢的影响

在（28±0.5）℃循环水环境中设置4种溶氧水平,分别为2.92 mg/L（G1组）、4.71 mg/L（G2组）、6.77 mg/L（G3组）、9.68 mg/L（G4组）,研究初始体重为（1.62±0.02）g的黄颡鱼（Pelteobagrus fulvidracoR.）稚鱼的生长、摄食及呼吸代谢规律。结果显示：G3组特定生长率（SGR）、饲料效率（FE）均显著高于其它各试验组（P〈0.05）。试验鱼的耗氧率、排氨率与溶氧水平无正相关性,G3组的耗氧率、排氨率始终显著高于其它三组。第6周测定发现：摄食后1-4 h内耗氧率和排氨率均呈现迅速上升,到达最大值后再缓慢下降,二者均在09∶00和21∶00出现高峰,G3组的耗氧率高峰值分别为0.345、0.331 mg/g.h,G3组的排氨率高峰值分别为24.194、17.770μg/g.h。结果表明：不同溶氧条件下,黄颡鱼稚鱼的耗氧率、排氨率变化过程具有类似的特征,二者在能量代谢机制上相互关联;在6.77 mg/L的溶氧水平下,黄颡鱼稚鱼生长最快、呼吸代谢最为旺盛。

黄颡鱼“溃疡综合征”病原的分离鉴定及药敏试验

对湖州地区患"溃疡综合征"的黄颡鱼(Pelteobagrus fulvidraco)开展病原研究,从典型濒死的病样体内分离到优势菌TH0426,对该菌进行了人工感染试验,并进行了形态特征、理化特性及分子生物学等方面的综合分析。结果显示,人工感染试验成功复制"溃疡综合征"症状,证明该优势菌为黄颡鱼"溃疡综合征"病原菌,其半数致死量(LD50)为3.98×104CFU/m L。生理生化及16 Sr DNA序列分析结果表明该菌为维氏气单胞菌(Aeromonas veronii)。药敏试验结果显示头孢曲松、利福平、四环素、多粘菌素B、氟苯尼考、头孢噻吩、强力霉素、头孢西丁、诺氟沙星、头孢拉定、氧氟沙星、环丙沙星、氟罗沙星和恩诺沙星等14种药物对该菌有较好的抑制作用。

不同溶氧条件下黄颡鱼免疫机能及抗病力的研究

研究了水温(28.4±1.0)℃时不同溶氧条件下(A组:(2.28±0.56)mg/L;B组:(4.04±0.38)mg/L;C组:(6.51±0.64)mg/L;D组:(9.11±1.24)mg/L)饲养8周后,黄颡鱼(Pelteobagrus fulvidraco)的免疫机能及对嗜水气单胞菌(Aerom onas hydrophila)的抗病力。结果显示:A组脾脏系数、吞噬百分率极显著低于其他3组(P<0.01),淋巴细胞转化率显著低于其他3组(P<0.05),红细胞数(RBC)显著高于其他3组(P<0.05),白细胞数(WBC)显著高于C、D两组(P<0.05);B组脾脏系数极显著低于C、D两组(P<0.01),吞噬百分率和淋巴细胞转化率显著低于C、D两组(P<0.05),攻毒1周后,A组受试鱼累积死亡率显著高于B组(P<0.05),极显著高于C、D两组(P<0.01)。表明慢性低氧胁迫抑制了黄颡鱼免疫机能。饲养8周后各组黄颡鱼血清皮质醇水平和溶菌酶活力差异均不显著(P>0.05),表明这两个指标不宜作为鱼类慢性胁迫中的应激信号。