Determination of hormones inducing oocyte maturation in <Emphasis Type="Italic">Chalcalburnus tarichi</Emphasis> (Pallas, 1811)

Chalcalburnus tarichi is an endemic cyprinid species living in the Lake Van basin, in eastern Anatolia, Turkey. The present study was undertaken to determine which hormones induce oocyte maturation in C. tarichi. The levels of 17α,20β,21-trihydroxyprogesterone (20β-S), progesterone (P), 17α-hydroxyprogesterone (17α-HOP), 11-deoxycortisol (11-DOC), and 17α-hydroxy-20β-dihydroprogesterone (17,20β-P) were measured in fish caught from Lake Van and the Karasu River, and injected with human chorionic hormone (hCG) (1,000 and 1,500 IU/kg). Oocytes of fish caught from the lake were also incubated in vitro with different doses (50, 200, and 1,000 ng/ml) of 20β-S, 17α-HOP, 11-DOC, and 17,20β-P. 11-DOC was found to be the most effective hormone among those measured for inducing oocyte maturation in vivo and in vitro. 17,20β-P could not be determined in the plasma of any fish in vivo (P < 0.05). 1,000 IU/kg dose of hCG given by injection caused a statistically significant increase in all plasma hormone levels (P < 0.05). It was found that there was a significant decrease in the P level only at 1,500 IU/kg dose of hCG injected (P < 0.05), while the level of other hormones increased at this dose (P < 0.05). It was also determined that all the hormones were effective in germinal vesicle breakdown (GVBD) in in vitro oocyte culture (P < 0.05). However, 11-DOC was found to be the most effective hormone in GVBD at a dose of 200 ng/ml (70% GVBD). In conclusion, 11-DOC synthesized during final oocyte maturation in C. tarichi was found to be a potent inducer of GVBD, which shows that 11-DOC may be described as an oocyte maturation steroid in this species.     

The existence of gonadotropin-releasing hormone (GnRH) immunoreactivity in the ovary and the effects of GnRHs on the ovarian maturation in the black tiger shrimp Penaeus monodon

Immunocytochemical localization using antibodies against five isoforms of gonadotropin-releasing hormone (GnRH), namely, luteinizing hormone-releasing hormone (LHRH), salmon (s)GnRH, octopus (oct)GnRH, lamprey (l)GnRH-I, and lGnRH-III, showed that only lGnRH-I immunoreactivity (ir-lGnRH-I) was localized in follicular cells of proliferative, vitellogenic, and mature ovaries. The effects of exogenous GnRHs on the ovarian maturation cycle of Penaeus monodon were compared by treating female broodstocks with LHRH, sGnRH, and lGnRH-I. The cycle of ovarian maturation in both eyestalk-ablated and eyestalk-intact shrimp administered with the three isoforms of GnRH was significantly shorter than that of the control animals. Moreover, administrations of all GnRH isoforms showed similar numbers of spawned eggs and the percentage of successful fertilization as in the control animals. These findings suggest that GnRHs may be highly conserved peptides that play an important role in inducing the ovarian maturation in the shrimp.     

Biological parameters of the bathyal fish black scabbardfish (Aphanopus carbo Lowe, 1839) off the Canary Islands, Central-east Atlantic

The main biological characteristics for black scabbardfish in the Canary Islands waters were established, focusing on its reproductive behaviour and strategy and its growth pattern. The sex proportion differs significantly from the 1:1 ratio, being clearly unbalanced towards the females. The sex ratio according to depth clearly shows the presence of male and female individuals in all the studied layers, thus sex segregation does not happen according to depth. The Canaries can be considered to be a reproduction site for A. carbo, since samples showing all stages of maturity have been observed. The gonadosomatic index (GSI) showed that the mean values were higher in the third and fourth quarters of the year. The index values clearly allow the differentiation of the individuals in resting or in spent (II and V) stages from individuals in ripe or in ripe and running stages, indicating that index levels higher than 2 are typical of maturation followed by spawning process. Up to twelve marks, assumed to be annuli, were visible in the sampled otoliths. Three to five years old were the dominant age classes and only 7.7% of fish were 7 years old or older. Age estimates ranged between 2 and 8 years for males and between 2 and 12 years for females. Estimated growth parameters were: L_∞ = 1477 ± 18.73 mm; k = 0.200 ± 0.016 year⁻¹; and t₀ = −4.58 ± 0.413 year. Biological aspects of the black scabbardfish suggest that this species has a generalist life-history strategy.     

Effects of experimental infection by Caligus rogercresseyi (Copepoda: Caligidae) on the common jollytail, Galaxias maculatus (Osmeriforme: Galaxiidae) (Jenyns, 1842) in Chile

Galaxias maculatus, the common jollytail, is a native smelt fish with a lacustrine or diadromous life cycle. In Chile, the rearing cycle of this fish includes a freshwater and a marine phase. Several diseases and parasites reported for the freshwater phase could be avoided by rearing the fish in salty or brackish water. Nonetheless, this alternative could result in Caligus rogercresseyi infections. The objective of this study was to evaluate experimentally the capacity of C. rogercresseyi to infect the common jollytail and the effects this parasite may cause to the fish. Prevalence and intensity of experimental C. rogercresseyi infections on G. maculatus were estimated and the effects of this parasitosis on the fish were evaluated on fish survival, weight loss, swimming behavior, and skin damage. Two experiments were carried out with adult fish taken from the Maullín Estuary. Fish were acclimatized to a salinity of 32 ppt and divided into two groups of 20 fish each. The experimental group was infected with copepodid stages of C. rogercresseyi and the other was used as a control. The fish were kept in individual tanks until observing ovigerous female copepods. C. rogercresseyi recognizes G. maculatus as a host under experimental conditions and optimal salinity for the parasite. Results show that under experimental condition copepodid stage can successfully infect the fish, developing to the adult stage, mating, and producing eggs (females). C. rogercresseyi caused alterations in fish behavior, superficial body damage, weight loss, and mortality. Rearing the common jollytail in salty water should take into consideration measures to control these infections as they can damage fish and affect surrounding wild fish populations. There are no records of this parasite in natural common jollytail populations; however, our understanding of the ecological role played by the common jollytail in C. rogercresseyi transmissions among sympatric host species could be greatly improved through further research related to host preferences and epidemiological data for different sympatric host species.     

Molecular evidence for the lack of transmission of the monogenean Sparicotyle chrysophrii (Monogenea, Polyopisthocotylea) and isopod Ceratothoa oestroides (Crustacea, Cymothoidae) between wild bogue (Boops boops) and cage-reared sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)

In the Mediterranean area, wild fish have often been suggested as either the reservoirs of the causative agents or at least the carriers of the pathogens responsible for disease outbreaks in cultured fish. However, no epidemiological investigations on actual pathogen/disease interactions between farmed and wild fish have been conducted even for the most important fish pathogens. Only sporadic isolations and identifications of various pathogens in wild fish have been done and real associations with the pathological conditions that exist within the farm environment and vice versa have not been established. Monogenean ectoparasite Sparicotyle chrysophrii and isopod Ceratothoa oestroides are commonly found in the Mediterranean cage-reared sea bream and sea bass and in the surrounding wild fish population. Both species were recognized as pathogens that seasonally inflict serious losses in fingerlings and juveniles of sea bream and sea bass, being potentially propagated and exchanged during wild and caged fish interaction. In order to evaluate the degree of pathogens transfer between wild and farmed fish, we investigated genetic population structures of these two important parasitic pathogens inferred by mtDNA cytochrome oxidase I locus. Parasites isolated from wild and farmed fish on the two most productive Adriatic fish farms showed genetic heterogeneity, contradicting widely accepted hypothesis of cross-contamination, at least in case of S. chrysophrii and C. oestroides. As far as we know, this is the first report that in a study of pathogen transfer molecular evidence was employed to asses the genetic population structure of shared parasites.     

中国鲤育种的主要方法、遗传解析及展望

水产种业是水产养殖业发展的基础,是渔业战略性、基础性核心产业,也是保障未来养殖业绿色、健康发展的核心竞争力。随着水产业全球化、市场化的发展,我国种业正面临着前所未有的机遇与挑战。特别是随着生物技术的快速发展,水产育种也由传统的选择育种和杂交育种,发展至细胞工程育种、分子标记辅助育种、全基因组选择育种、分子设计育种和基因组编辑等精准设计育种。水产动物重要经济性状的基础研究及其遗传改良技术的创建驱动着我国水产种业的蓬勃发展,截止2022年,通过全国水产原种和良种审定委员会审定并由农业农村部公告的水产新品种就有266个,其中鲤新品种数量最多,为31个,表明鲤育种工作卓有成效。本文重点回顾了我国鲤的种质和基因组资源现状,鲤的主要品种及其育种方法;简要介绍了鲤生长、抗病、体色、饲料转化率等经济性状关联的遗传研究进展,并由此提出了新时代背景下鲤种业的发展方向和措施建议,以期为我国鱼类育种提供借鉴。     

长牡蛎第三代选育群体生长性状的选择效应

为了培育长牡蛎的高产抗逆新品种,实验采用群体选育方法构建了中国、日本和韩国3个种群的快速生长选育系,2007年至今已连续进行了6代选育。本实验对长 牡蛎选育F₃代壳高和活体体质量的增长、选择反应和遗传获得等遗传参数进行了分析。结果表明,从第120日龄开始,中国、日本和韩国3个选育群体的壳高和 活体体质量均显著高于对照组,在420日龄时,平均壳高较对照组分别高13.4%、10.1%和10.5%,平均活体体质量较对照组分别重18.5%、13.4%和11.6%;壳高的平均现实遗传力分别为0.447±0.226、0.471±0.297和0.367±0.167,表明适于对壳高的生长速度进行进一步的选育。长牡蛎中国、日本和韩国选育F3代活体 体质量的遗传获得平均值分别为16.01%±3.82%、15.03%±5.21%和11.57%±5.15%,表明对长牡蛎壳高的生长速度进行选育时,活体体质量的生长速度也得到了明显提高。本研究结果可以为长牡蛎快速生长品系的连续选育提供依据。     

长江近口段鳗苗捕捞量的时间格局及其与生态因子的GAM模型分析

为研究长江口鳗苗捕捞量与生态因子的相互关系,于2012年汛期对长江靖江段鳗苗的捕捞量进行了监测,采用广义可加模型(GAM)对日捕捞量与水温、潮差、气压、浑浊度等生态因子之间的相关性作了分析。结果显示,靖江段鳗苗汛期为1月下旬—4月上旬,单船总捕捞量为221~443尾,平均(344.8±83.4)尾。1月均值仅0.4尾/d,且空网率高达90.9%;4月为旺汛期,均值10.4尾/d,空网率仅为10.0%。GAM模型显示,潮汐周期—月份交互项、水温和潮差对鳗苗日捕捞量的影响显著,而气压、浊度和月相周期对鳗苗日捕捞量的影响不显著。潮汐周期—月份交互项、水温和潮差对鳗苗日捕捞量的偏差解释率分别为42.4%、19.1%和13.1%,均呈现正相关关系。统计也显示,日捕捞量表现出上、下弦月较低、新月或满月前后较高的半月周期波动。鳗苗捕获的最低水温为6.3℃,而10~15℃为适宜捕捞水温。高潮期和低潮期分别占总捕捞量的76.8%和23.2%。研究表明,长江口鳗苗在借助潮汐流而快速溯河的过程中,部分在口门水域即被捕获,部分滞留在了长江河口段,而影响鳗苗溯河的重要生态因子是潮汐和水温。     

异育银鲫武汉单极虫病发生、发展、消退和消失的病理变化与PCR分析

为探究武汉单极虫病疾病过程和病理变化等特点,根据患病异育银鲫体表孢囊内有无成熟孢子和成熟孢子的崩溶解程度,将该病划分为发生、发展、消退和消失4个疾病时期,并分别进行病理变化观察和巢式PCR分析。结果发现,发生期的病鱼体表刚形成的孢囊使鳞片和皮肤微微隆起,孢囊乳白色,孢囊内分布着正在繁育逐渐增多的营养体,尚未出现成熟孢子;发展期的病鱼孢囊内已出现成熟孢子,孢囊逐渐增多增大,其表面黑色素细胞增加而呈灰黑色,感染强度高的病鱼出现死亡或畸形;消退期的成熟孢子通过破裂孢囊流入水体或不同步地崩溶解而减少直至全部溶解,孢囊随之逐渐缩小,使得黑色素细胞更为密集,此时期病鱼病情减轻不再出现死亡现象;消失期的病鱼孢囊平坦,内已无成熟孢子,只残留逐渐减少的成熟孢子崩溶解物质,黑色素细胞逐渐减少,最后原孢囊部位被结缔组织取代。巢式PCR分析结果表明,巢式第一轮和第二轮PCR在4个疾病时期都分别能扩增出1 584和853 bp的武汉单极虫目的条带,但在消失期的后期只有巢式第二轮PCR扩增出853 bp目的条带,说明残留的核酸物质含量逐渐减少,10月下旬后原孢囊部位巢式PCR扩增已无条带出现。本研究不仅揭示了武汉单极虫寄生部位在4个疾病时期的病理变化特点,而且明确了疾病消退和消失的2种方式,孢囊内成熟孢子通过破裂孢囊进入水体的方式和首次发现的孢囊内成熟孢子通过崩溶解的方式。     

半滑舌鳎Cs-UBE2D4基因的克隆、表达模式及启动子活性

泛素-蛋白酶体系统作为重要的蛋白质修饰途径,参与多个生物学过程,其中泛素结合酶E2作为关键酶可以决定泛素化对靶蛋白的影响。为了探究泛素结合酶E2在半滑舌鳎雌性性腺发育中的作用,本研究克隆了半滑舌鳎Cs-UBE2D4基因的开放阅读框ORF,检测了该基因在不同组织和不同发育阶段性腺中的表达模式;构建了其启动子报告基因载体(pGL3-Cs-UBE2D4)并进行了启动子活性分析。Cs-UBE2D4开放阅读框为360 bp,编码119个氨基酸,含有保守的泛素结合酶E2结构域。荧光定量PCR结果显示,Cs-UBE2D4在雌鱼的各组织中广泛表达,其中在卵巢和肝脏中表达量较高,而在雄鱼中几乎检测不到表达;在卵巢各发育阶段中,该基因的表达量从90日龄开始上调,6月龄达到峰值,之后开始下调,在1.5龄时表达量最低,在3龄时表达量有所回升,其中6月龄表达量为90日龄表达量的1.97倍。双荧光素酶活性检测结果显示,Cs-UBE2D4启动子具有较强的转录活性。本实验将为进一步开展Cs-UBE2D4基因对半滑舌鳎卵巢发育和性别调控相关机制的研究提供理论依据。     

黄河鲤酪氨酸酶基因的克隆、表达模式及定位分析

为探究Tyrosinase(Tyr)基因在黄河鲤体色形成中的作用,利用生物显微镜对黄河鲤黑色鳞片、银色鳞片、鳍条色素细胞的组成进行观察,并利用RACE克隆黄河鲤Tyr基因全长cDNA序列,荧光定量PCR分析其在不同组织中的表达情况,Western blot印迹和免疫组织化学方法检测其蛋白的表达定位。结果显示,黄河鲤具有黑色素细胞、黄色素细胞和虹彩细胞3种色素细胞,3种色素细胞的数量、种类和分布在不同组织中存在较大差异。黄河鲤Tyr基因cDNA全长1717 bp(GenBank ID:No.KY305667),其中ORF长1605 bp,编码535个氨基酸,5′-UTR区41 bp,3′-UTR区71 bp。蛋白同源分析发现,黄河鲤Tyr与鲤科鱼类相似性最高,与哺乳类及鸟类等脊椎动物相似性最低。系统进化分析显示,黄河鲤Tyr与鲤、瓯江彩鲤、锦鲤和斑马鱼等鲤科鱼类的亲缘关系最近。实时定量PCR分析表明,Tyr基因在黄河鲤不同组织中均有表达,肌肉中的表达量最高,其次是黑色皮肤,另外在黄色皮肤、臀鳍和尾鳍等黑色素细胞存在的组织中也有较高表达。Western blot印迹结果显示,Tyr基因在黑色皮肤中表达最高,其次是臀鳍和尾鳍,银色皮肤中没有表达。免疫组织化学结果显示,Tyr基因在黑色皮肤的黑色素细胞和黏液细胞中有表达。研究表明,Tyr基因表达水平与黑色素细胞数量和分布具有一定相关性,参与黄河鲤体色的形成。     

水体中泼洒复合乳杆菌对尼罗罗非鱼养殖池塘环境、肠道和鳃健康的影响

研究在尼罗罗非鱼养殖池塘中添加复合乳杆菌对养殖池塘环境、尼罗罗非鱼肠道和鳃健康的影响,为乳杆菌在尼罗罗非鱼健康养殖中的应用提供基础。在尼罗罗非鱼养殖池塘水体中泼洒复合乳杆菌(对照组:0;实验组:1.0×104 CFU/mL),实验周期为10周。复合乳杆菌的成分为干酪乳杆菌和酸鱼乳杆菌,比例为1:2.2。监测池塘水质指标、罗非鱼肠道和鳃的免疫及抗氧化指标,并运用高通量测序技术(Illumina MiSeq),比较对照组和实验组水体、底泥、尼罗罗非鱼肠道和鳃黏膜共生菌群落结构差异。结果显示,从第7周开始,实验组水体中的硝酸盐含量始终低于对照组,实验组比对照组降低了72.68%、72.00%、26.27%和21.46%;实验组水体中的总氮含量在从第6周开始低于对照组,分别降低了43.39%、44.64%、15.64%、37.57%和34.49%;实验组水样中的总磷含量从第4周开始低于对照组,分别降低了40.91%、33.33%、50.00%、33.33%、17.39%、39.29%和25.71%。与对照组相比,实验组尼罗罗非鱼肠道的碱性磷酸酶(AKP)活性提高了45.04%,实验组尼罗罗非鱼...     

Genetic variations in survival of rohu carp (Labeo rohita, Hamilton) after Aeromonas hydrophila infection in challenge tests

A challenge test against Aeromonas hydrophila was conducted using 2062 rohu carp (Labeo rohita) fingerlings obtained from 52 dams and 87 sires (87 full-sib families) of two year-classes (2003 and 2004). Attempts to establish a cohabitant challenge model were not successful. Therefore, fish were challenged by intraperitoneal injection with A. hydrophila in two replicate tanks per year-class, and dead fish were collected hourly. The mortality reached its peak at 16–22 h after challenge and had almost completely stopped after 58 h. The test was terminated after 382 h at which the average survival was 43.9 and 48.9% in the two 2003 year-class tanks, and 77.1 and 35.8% in the two 2004 year-class tanks. Heritability estimates for survival were obtained from sire and dam threshold models (THR) and sire and dam linear repeatability models (LINR). For both types of models the heritability estimates based on data from single tanks were not consistent. For both year-classes, data from one of the two challenged tanks demonstrated significant additive genetic variation in survival during the A. hydrophila infection, whereas the heritability estimates were not significantly different from zero for the other tank. Further, genetic correlation between survivals in the two replicate tanks in each year-class was not significantly different from zero. The differential results from the replicate tanks demonstrate that additional challenge test experiments are needed before firm conclusions can be drawn about the magnitude of additive genetic variation for survival to aeromonasis in rohu carp. A cohabitant challenge model that allows the testing of important defence mechanisms in the skin and mucous membranes of the fish might have been more appropriate. To establish a valid cohabitant challenge model for rohu carp should be given high priority.     

The timing of puberty in cultured female yellowtail flounder, Limanda ferruginea (Storer): Oogenesis and sex steroid production in vivo and in vitro

This study examines puberty in female yellowtail flounder, correlating macroscopic, histological and endocrine parameters at the gonadal level. Short-term ovarian tissue incubations were used to study estradiol-17β production in relation to oogenic stage. Examining 2 year classes of young flounder demonstrated that cultured females retain phenotypic plasticity in reproductive age with pubertal onset occurring in one-year, two-year and three-year-olds. Immature ovaries were steroidogenic and capable of responding to gonadotropic stimulation. Endocrine puberty in females was detected by a peak in estradiol-17β production during the cortical alveolar oocyte stage prior to any ovarian evidence of vitellogenesis. Puberty, once initiated, proceeded to ovulation within 8 to 12 months; vitellogenic oocyte development followed the group synchronous pattern. Estradiol-17β was clearly the dominant of the two measured plasma hormones during pubertal onset and throughout vitellogenesis. Plasma testosterone was consistently detectable at low levels by mid-to late-vitellogenesis. Ovaries showed the highest sensitivity to gonadotropic stimulation in vitro during late-vitellogenesis. Variable plasma levels in both estradiol-17β and testosterone occurred in preovulatory and ovulating females during the captive spawning period. Together the results show that yellowtail flounder can mature at a young age and small size when culture conditions permit. In addition, the early sensitivity to gonadotropin by the immature ovaries may be an important physiological determinant for the timing of puberty in this species.     

遗传选育对野生和养殖中华绒螯蟹蟹种形态学特征的影响

以野生和养殖蟹种及其选育后代作为研究对象,实验采用单因素方差分析、判别分析、主成分分析和聚类分析等方法对各组形态特征进行分析。结果显示,(1)野生和养殖群体原代(G0)雌雄个体分别有16和15个形态指标差异显著,而选育2代后36个形态学指标均无显著差异;(2)判别分析中野生和养殖G0的判别准确率高达93%~100%,而2群体G1和G2个体判别准确率仅为56.67%~76.67%,且G2判别率低于G1;(3)主成分散点图显示野生群体G0与G1、G2个体分别可以形成较集中的区域,而主成分分析难以区分养殖群体G0、G1和G2个体;(4)聚类分析将6种群蟹种分为2支,其中养殖群体G0、G1和G2与野生群体G1和G2聚为一支,而野生G0单独聚为一支。研究表明,长江野生和池塘养殖蟹种的形态学差异较大,但在选育过程中逐渐消失,最终与养殖群体趋于一致,因此形态学特征不能作为中华绒螯蟹良种选育的可靠指标。     

不同温度对草鱼C、N、P营养要素收支的影响

模拟草鱼养殖周期内的温度波动范围,研究了温度变化对草鱼C、N、P营养要素收支的影响。实验采用4个温度条件(15、18、24和30 ℃)培养草鱼,测定了不同温 度处理组内草鱼C、N、P营养要素的收支情况。结果表明:温度对草鱼C、N、P营养要素收支具有显著影响。15 ℃处理组中,草鱼摄食率、排氨率、排磷率和排粪 率分别为3.405 7、7.533 4、0.000 8和0.601 3 mg/h,显著低于其他处理组,在24 ℃处理组中,达到最大值,分别为10.442 0、18.995 6、0.001 7和 1.647 0 mg/h。草鱼的耗氧率随温度的升高而增加,耗氧率和温度之间变化规律符合方程OR=0.005 9×T^1.2532(R²=0.84)。15 ℃处 理组中,C、N、P营养要素的生长余力分别为1.064 9、0.126 4和0.018 8 mg/h,显著低于其他处理组,在24 ℃处理组中,达到最大值,分别为3.402 8、0.397 1和 0.071 8 mg/h。15 ℃处理组中,C、N、P营养要素的吸收效率分别为81.38%、83.05%和80.30%,显著低于24和30 ℃处理组。     

虾夷扇贝高品质脂肪酸闭壳肌家系选育

以虾夷扇贝闭壳肌重量与脂肪酸组成为主要筛选指标,通过对不同选育家系的生长性状进行比较,在筛选出闭壳肌高出柱率家系的同时,以EPA、DHA和ω-3/ω-6脂肪酸比值等重要营养性状作为参考指标进行家系筛选。结果显示,在12个选育家系中,B04、B05、B10家系的出柱率优势最显著;各家系闭壳肌的EPA+DHA占总脂肪酸45%以上,ω-3/ω-6脂肪酸比值范围为10.94~12.69,家系B03、B05、B06、B07、B10、B11与B12在闭壳肌脂肪酸含量上具有更高选育价值;综合分析,判定B05和B10为虾夷扇贝闭壳肌高出柱率且高品质脂肪酸家系。研究表明,虾夷扇贝的生长与闭壳肌的主要脂肪酸组成没有显著相关性,以闭壳肌脂肪酸含量与生长性状指标进行虾夷扇贝复合性状选育是可行的,本研究结果可以为扇贝选择育种工作的深入开展提供科学依据。     

2010/2011年夏季南设得兰群岛北部水域南极磷虾的种群组成

为了解中国南极磷虾渔业主要渔场——南设得兰群岛水域南极磷虾种群动态,利用渔业科学观察员收集的生物学数据,在将研究区域划分成10′×10′小尺度单元的基础上,实验分析了南设得兰群岛夏季南极磷虾种群组成的时空特征。结果表明,23个单元中,雌性未成体(F₂)的比例最高(42.1%),其次为雌性成体(F₃,35.6%),雄性个体所占比例不足20%,且均为未成体(M₂),而幼体(I₁)的比例仅占2.7%。12月中旬,I₁阶段的磷虾个体占有一定的比例(9.6%),M₂阶段磷虾个体比例较F₃阶段高。12月下旬的情况与1月上旬较为相似,I₁个体未出现在调查样本中,M₂阶段磷虾个体比例下降,F₃阶段磷虾个体比例明显上升。M₂、F₂和F₃阶段的磷虾个体在各水层中的分布模式较为相似(PSI=90.9～97.7)。I₁阶段磷虾个体主要分布在60～80 m水层(66.9%),而其它3个性成熟度的磷虾个体主要分布在40～60 m水层。     

鳞砗磲的人工繁育和早期发生

基于2015年的预备性试验,于2016年3—6月在三亚开展了鳞砗磲人工繁育技术研究。结果显示,采用五羟色胺催产剂可以有效促使鳞砗磲排放配子,精卵比例为50∶1~100∶1时受精率、孵化率较高,孵化密度控制在15~20个/m L较适宜,经过36 h孵化,获得初孵D形幼虫;优选的D形幼虫经过5 d的微充气培养,即发育至足面盘幼虫,进入附着变态期。利用净水采苗法促使幼虫完成变态,经过7~10 d,幼虫出现鳃、次生壳,并建立完善的虫黄藻系统,即完成变态、形成稚贝。利用一定浓度虫黄藻浸泡足面盘幼虫2 h以内,可以有效地提高变态率。采用微流水+微充气模式和2000~3000 lx光照(白天)进行稚贝培养,稚贝利用体内虫黄藻提供的营养就可以继续完成贝壳生长、器官发育。经过48 d和65 d的培育,分别成功获得壳长×壳高=(1174.0±146.5)μm×(1208.0±135.3)μm的稚贝约3万个,壳长×壳高=(1750.2±224.1)μm×(1816.5±226.5)μm的幼贝约0.5万个。本研究首次在国内人工繁育成功,获得了鳞砗磲苗种,为鳞砗磲人工大规模繁育、增殖放流、移植保育等工作奠定了基础。