Reproductive biology of the commercially and recreationally important cobia Rachycentron canadum in northeastern Australia

The reproductive biology of 315 cobia, Rachycentron canadum, from northeastern Australia was studied for an 18-month period. Cobia ranged from 181 to 1,470 mm FL (0.06–55 kg). Length–frequency distributions of males and females did not differ significantly. The sex ratio of females to males was 2.18:1. Histological data showed that cobia developed hydrated oocytes during a protracted spawning season between September and June. Gonadosomatic index peaked from October to December, coinciding with the monsoon or “wet” season. Estimated length at first maturity for female cobia was 671 mm FL. Length at 50% maturity (L ₅₀) for females was estimated at 784 mm FL (1–2 years of age). Batch fecundity ranged from 577,468 to 7,372,283 eggs with a mean of 2,877,669 (± SD 1,603,760) eggs. Relative batch fecundity was 249 eggs per g, and no relationship between relative fecundity and fork length was found. There was a significant positive relationship between the total number of eggs produced and fork length. Spawning frequency, estimated by the post-ovulatory follicle method, was 7.6 days. Based on the detection of hydrated oocytes in fish caught at night, cobia most likely spawn at night. Cobia also feed throughout the spawning period. This is the first report on the reproductive biology of cobia in Australian waters, and provides valuable data for future population assessments of cobia throughout the Indo-Pacific.     

Reproductive biology of <Emphasis Type="Italic">Sillago aeolus</Emphasis> in Okinawa Island,Japan

ABSTRACT:   A total of 414 fish (female, 59.3–275.0 mm and male, 61.0–220.0 mm standard length) were collected from December 2000 to March 2002 around Okinawa Island, Japan, for the determination of sex, spawning season, maturity and fecundity. Monthly changes in the gonadosomatic index (GSI) exhibited similar trends for both sexes and the mean GSI maintained a high level between February and May. Furthermore, the percentage frequency of hydrated oocytes and the spermatozoic activity suggested that main spawning occurred between February and May. Some hydrated oocytes were found throughout the year, with a GSI value greater than 1.0, suggesting that sporadic spawning occurred. Length at first maturity was determined for females and males as 120 and 113 mm standard length, respectively. Almost 50% and 100% males were matured at the end of their 0 and 1 year of age group, respectively. In contrast, no females were found to be mature at 0+ age group, and almost 60% of females were mature at 1+ age group. At ages over 2 years, all males and females were found to be mature. Batch fecundity (BF) of 33 females was related to standard length, and the relationship between standard length and BF was expressed by the exponential equation: BF = 269.5e^0.020954SL.     

Reproductive cycle,sexual maturity and diel-reproductive periodicity of white croaker,Pennahia argentata (Sciaenidae), in Ariake Sound,Japan

The white croaker, Pennahia argentata (Houttuyn), is abundant in demersal fish assemblages in Ariake Sound and is a commercially important species. The reproductive biology of white croaker was studied by measurement of gonadosomatic indices (GSI) and histological examination of ovaries. Ovaries were classified into one of five maturity stages based on histological data: (1) immature/resting stage; (2) developing stage; (3) maturing stage; (4) ripe/spawning stage; (5) spent stage. The spawning season lasts from April to September but most activity is observed from May to August. Age at sexual maturity was assumed to be 1 year. Postovulatory follicles coexisted with yolk stage oocytes in histological sections of ovaries indicating that white croaker is a multiple spawner, spawning more than once in a single spawning season. Judging from the diel changes in the proportion of females with ovaries containing postovulatory follicles and oocytes at maturation stage, most females spawned in the evening between 19:00 and 21:30 h.     

Oogenesis and lipids in gonad and liver of daubed shanny (Leptoclinus maculatus) females from Svalbard waters

Oocyte and liver histomorphology of the daubed shanny (Leptoclinus maculatus) from Isfjorden and Kongsfjorden in Svalbard were investigated during three Arctic seasons: summer (July), autumn (October) and winter (April). Three oocyte developmental phases were observed: primary growth phase, secondary growth phase and maturation phase. We observed four different developmental stages: (1) perinucleolus stage with cortical alveolus formation, (2) lipid droplets formation, (3) vitellogenesis stage and (4) maturation. Late maturation stage of oocytes in the ovaries was from the autumn season. Females accumulated lipids in liver (up to 35.2?% dw) and deposited large amounts of lipids into gonads (up to 52.2?% dw) during maturation. Lipid classes in female gonads changed seasonally, with relative increase in cholesterol during summer and depletion of storage lipids (triacylglycerols and wax esters/cholesterol esters) during the winter. Lipid composition in liver changed during oocyte development and spawning, as neutral lipids were transferred to developing oocytes during summer to autumn. During winter, storage lipids were depleted during starvation. Based on the increase in gonadosomatic index (GSI) with length and observed maturation stages, females seem to mature at a length of about 125-130?mm. The GSI and hepatosomatic index of large females sampled in autumn (September-October) were significantly higher than for females in late winter (April) and spring (May). These results indicate that spawning takes place during winter in Isfjorden and that energy reserves stored in the liver are utilized by females during gonadal development and reproduction.     

Maturation and spawning of <Emphasis Type="Italic">Spratelloides gracilis</Emphasis> Clupeidae in temperate waters off Cape Shionomisaki,central Japan

ABSTRACT:   The reproductive ecology of Spratelloides gracilis was investigated in the temperate waters off Cape Shionomisaki, central Japan. Cape Shionomisaki is located at the northern margin of the distribution range of this species. Females of S. gracilis with gonadosomatic index (GSI) ≥ 4.0 were defined as mature based on the relationship between GSI and the histological maturity phases of their ovaries. More than 50% of females greater than 60 mm standard length (SL) were mature. Hatch dates of larvae and juveniles collected in the study area were determined by otolith daily ring counts and found to extend from April to November. The size at maturity of females (60 mm SL) and the spawning season of S. gracilis in the temperate waters off Cape Shionomisaki (April–November) was larger and shorter, respectively, than those in tropical waters in the western Pacific. The reproductive traits observed for S. gracilis off Cape Shionomisaki appear to be adaptive to northern temperate waters with seasonal changes in environmental conditions.     

渤海小黄鱼生长特征的变化

根据1960年、1982年、1993年和2003年各年春季对渤海进行的底拖网调查获得的小黄鱼（Pseudosciaena polyactis Bleeker）生物学数据，对4个不同年代间渤海小黄鱼的群体组成、生长状况等生物学特征的年代间变化进行分析，结果表明，渤海小黄鱼的生物学特征在这4个年代间发生了明显变化。自1982年以来，渤海小黄鱼群体结构呈现个体小型化、低龄化、生长加快、渐近体长和渐近体质量减小、体质量生长拐点提前等现象。小黄鱼生物学特征因子的年代间变化，可能与渔业资源不断衰退以及小黄鱼自身对外界环境因素变化的适应有关。     

Reproductive biology of the common ponyfish <Emphasis Type="Italic">Leiognathus equulus</Emphasis> in the south-western waters off Taiwan

ABSTRACT:   Reproductive biology of the common ponyfish Leiognathus equulus was described based on 958 specimens caught by otter trawlers in the south-western waters off Taiwan and landed at Tungkang and Linuan fishing ports from March 2000 to February 2001. Macroscopic appearance of the ovary, gonad-somatic index, oocyte diameter frequency distribution, and histological examination suggested that the spawning season of the common ponyfish in south-western Taiwan waters is from May to August. Eight stages of oocyte development were determined based on histological examination, and ovarian development can be divided as immature, early maturing, late maturing, mature and spent stages. The sex ratio of 0.52 was not significantly different from 0.5 using χ² test, but females were overwhelmingly more when fork length (FL) was greater than 170 mm. The relations between fecundity (F), batch fecundity (BF), and body weight (BW) were estimated to be F =−5328 + 1.2946 BW ( n  = 132, P  < 0.05) and BF = −11.26 + 0.2748 BW ( n  = 25, P  < 0.05), respectively. Mean fecundity and mean batch fecundity (± standard error) were estimated to be 129 955 ± 79 343 and 28 160 ± 14 698, respectively. Sizes at 50% maturity estimated from the Logistic model were 162 mm FL and 158 mm FL for females and males, respectively.     

Reproductive biology of blue marlin <Emphasis Type="Italic">Makaira nigricans</Emphasis> around Yonaguni Island,southwestern Japan

We studied the spawning seasonality and gonadal development of blue marlin Makaira nigricans using specimens captured around Yonaguni Island in southwestern Japan between February 2003 and February 2006. The mean (±SD) lower jaw–fork length of females (234 ± 24 cm) was greater than that of males (191 ± 12 cm). The smallest mature female and male were 183 and 160 cm, respectively. Most of the 717 females had immature ovaries. However, in March and from May to September, the ovaries of 26 females contained oocytes with yolk globules, hydrated oocytes, or postovulatory follicles. Most males had testes with a large amount of spermatozoa throughout the year. The occurrence of mature blue marlin at Yonaguni Island suggests that spawning occurs here. The mean condition factors (fatness of the fish) of both sexes decreased from March to June or July, presumably as they expended energy to reproduce. We discuss our results in the context of migration theory for blue marlin in the western North Pacific Ocean.     

大黄鱼雌雄性腺长链非编码RNA的挖掘与差异分析

为探究长链非编码RNA在大黄鱼性腺发育与分化中的作用,从雌雄各3尾大黄鱼(Larimichthys crocea)的性腺中提取总RNA,进行去除rRNA的链特异性转录组建库和二代测序。将测序数据比对到大黄鱼参考基因组,经比对、组装共得到来自31675个基因的66088个转录本,严格筛选得到来自3984个基因位点的5162条lncRNA。进一步分析获得了在大黄鱼雌雄性腺中差异表达的mRNA9341个,lncRNA2782个,高度相关的lncRNA-mRNA对1227个;有多个lncRNA靶向已知的性别分化和发育相关基因,其中lncRNA MSTRG.24346与大黄鱼的性别决定候选基因dmrt1距离相近,且相关性极显著。该研究表明lncRNA可能在大黄鱼性别分化中起到重要作用,值得深入研究阐明机制。     

大黄鱼一年两次性成熟发育特征的研究

选择春季产过卵的2^ 龄大黄鱼Pseudosciaena crocea(Richardson)在网箱中进行隔离培育，秋季从中挑选当年再次性成熟的亲鱼进行人工催产，比较春、秋两季的人工繁殖与仔、稚鱼培育效果，并定期观察卵巢及卵细胞的发育情况。实验表明，春季产过卵的同一批大黄鱼雌鱼，有72．1％的个体当年秋季可再次成熟，有58．8％的个体可以再次产卵，证实养殖大黄鱼具有一年“两熟”的性腺发育特征。     

Seasonal changes in oocyte size and maturity of the giant jellyfish, Nemopilema nomurai

To determine the reproductive season of the giant jellyfish Nemopilema nomurai, we investigated gonadal maturity in specimens collected from the East China Sea, Korea Strait, Wakasa Bay, and the Shonai Coast of Yamagata Prefecture. After the sex of the samples was determined, the long axis of at least 256 oocytes from each female was measured. In specimens collected from the coast of Japan in 2005 and in 2006, all gonads were sufficiently developed to determine sex. However, 18 of the 20 specimens from the East China Sea collected in July 2005 were immature, and sex could not be determined. The maximum and third quartile of oocyte length had a significant correlation with days elapsed from 30 June, but they were not related to bell diameter. Observations of gonad tissue sections of specimens collected in Wakasa Bay in 2006 confirmed that oocyte length was a good proxy for female maturity. Male maturity could also be determined. In conclusion, the sex of all of the small-sized medusae collected along the coast of Japan was determinable, and their gonads were at various stages of development up to fully mature. Therefore, the occurrence of small-sized jellyfish during the autumn in Wakasa Bay is not caused by recruitment of young population from the nearby coast.     

繁殖季节长江口斑尾刺虾虎鱼的形态、生殖力与卵巢组织学特征

在繁殖季节研究了斑尾刺虾虎鱼的形态、生殖力与卵巢组织学特征。结果表明,斑尾刺虾虎鱼全长(TL)与体长(SL)、头长(HL)与体长(SL)、体长(SL)与体高(BD)、体重(BW)与空壳重(SW)、体重(BW)与体长(SL)的相关关系分别为:TL=0.779 6SL+1.793 9;HL=0.299 9SL+7.288;SL=0.783 2BD+7.324 9;BW=0.818 4SW-4.979 6;BW=0.062 9SL2.331 5。斑尾刺虾虎鱼个体绝对生殖力(F)为6 328~59 878 egg,与体长(SL)、空壳重(SW)、卵巢重(OW)的相关关系分别为F=94.972SL2-4 832.2SL+833 435;F=83.823SW+14 084;F=507.54OW+13 190。个体绝对生殖力(F)与体长、空壳重、卵巢重、成熟系数(GSI)的多元回归方程为:F=2 375.54+525.67SL-31.44SW+199.43OW+261.74GSI。斑尾刺虾虎鱼体长相对生殖力(FL)平均为88±31 egg/mm,体重相对生殖力(FW)平均为157±54 egg/g。平均卵径为1.22±0.24 mm。斑尾刺虾虎鱼IV期卵巢以第IV时相卵母细胞为主,第IV时相晚期卵母细胞开始出现油球,细胞核偏移和变形,放射带明显;Ⅴ期卵巢的卵细胞游离,卵膜外的二层滤泡膜脱落,卵细胞的外层分别有胶膜、放射带和质膜。     

Gonad development of an anadromous fish <Emphasis Type="Italic">Coilia ectenes</Emphasis> (Engraulidae) in lower reach of Yangtze River,China

ABSTRACT:   Anadromous Coilia ectenes was sampled from the Yangtze estuary at Chongming and two of the primary upstream spawning grounds at Jingjiang and Anqing in April, May, June and August 2006. Gonad development was analyzed for females. In April, fish were collected in the estuary and at Jingjiang, but not at Anqing. No female was mature (gonad at stages IV or V) at either location. In May, 45% of the females were mature in the estuary, 9% at Jingjiang and 5% at Anqing. In June, 86% were mature in the estuary, 83% at Jingjiang and 7% at Anqing. In August, C. ectenes was absent at Jingjiang. No female was mature in the estuary, and all females were mature at Anqing. Absolute fecundity ( AF ) increased significantly with standard length ( SL ) by a power function AF  = 2.27 × 10⁻⁶ ×  SL ^2.67 ( r ² = 0.57, n  = 48, P  < 0.05). Mature females in the estuary were smaller than those at Jingjiang and Anqing. Conservation of spawners in the upstream spawning grounds is important because they have a size-related fecundity advantage over the smaller spawners in the estuary.     

Reproductive biology of female Pacific bluefin tuna Thunnus orientalis from south-western North Pacific Ocean

Pacific bluefin is a highly valuable pelagic species that inhabits a broad range in the North Pacific Ocean. The reproductive biology, especially for the spawning aggregation in the south-western North Pacific Ocean, is not well understood. Thus, a total of 119 paired ovary specimens were collected from the Taiwanese longline fleet during the 1999 fishing season (late April through June) to gain a better understanding of important reproductivity-related stock parameters associated with this species. The following conclusions were made: (i) condition factor decreased from late May to early June; (ii) the sex ratio might be 1∶1 for spawners; (iii) the gonadosomatic index stayed at a relatively high level and markedly increased from late May to early June; (iv) histological examination of oocytes indicated that all specimens were sexually mature; (v) spawning activity appeared to start in May and peak in late May to early June; (vi) batch fecundity incre ased with fork length; and (vii) preliminary estimates of spawning frequency between batches ranged 2–4.5 days based on analysis of postovulatory follicles.     

Reproductive biology of bluefish (Pomatomus saltatrix) along the East Coast of the United States

The reproductive biology of bluefish (Pomatomus saltatrix) along the U.S. East Coast is examined from a collection 1437 females sampled from nearshore to the continental slope and from Florida to New York over a period of 3 years (2001–2003). In most years concurrent sampling along the coast was conducted over spring and summer months to resolve the initiation of spawning. We examined the spawning location, pattern and timing, and calculated the fecundity of fish from 600 to 840 mm in length. Based on macro- and microscopic analysis of female gonads, bluefish are multiple spawners with indeterminate fecundity. The presence of all stages of development in fully mature ovaries further indicates that bluefish have asynchronous oocyte development. Mean age at first maturity for female bluefish was 1.90 years and 480 mm total length. Mean batch fecundity was 402,247 eggs and ranged from 114,513 to 920,746 eggs, depending on age and weight. Direct observation of gonads showed imminent spawning in Florida and North Carolina during March to April, and from April to August from Virginia to New York. Given the progression of oocyte development over the range of space and time we sampled, we suggest that bluefish exhibit continuous spawning during their migration from the South Atlantic Bight (SAB) to Middle Atlantic Bight (MAB).     

Spawning frequency of the Tsushima Current subpopulation of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> off Kyushu,Japan

Female Japanese chub mackerel Scomber japonicus of the Tsushima Current subpopulation were collected during the spawning season from March to May 2001. A total of 137 adult females were caught between midnight and daybreak. A considerable number of fish displayed new postovulatory follicles (POF), whereas there was no evidence of germinal vesicle breakdown or hydrated oocytes in any of the fish collected. This suggests a daily spawning synchronicity toward midnight. To estimate the spawning frequency (S), the female reproductive state was classified into four criteria based on the degenerative stage of the POFs and the developmental stage of the oocytes. To stage the POFs according to age and determine the stage duration, ovaries from S. japonicus were induced to spawn in the laboratory and were sampled 0–72 h after ovulation at appropriate intervals. The average S, which is evaluated from four different indices, was 16.9%, corresponding to the average female chub mackerel spawned every 5.9 days (8.5 times) during the 50 days.     

Colonization,proliferation, and survival of intraperitoneally transplanted yellowtail <Emphasis Type="Italic">Seriola quinqueradiata</Emphasis> spermatogonia in nibe croaker <Emphasis Type="Italic">Nibea mitsukurii</Emphasis> recipient

Recently, we developed an intraspecies spermatogonial transplantation technique in a pelagic egg spawning marine teleost, nibe croaker Nibea mitsukurii. Nibe croaker is an ideal candidate recipient for spermatogonial transplantation since it has a short generation time and small body size. In the present study, yellowtail Seriola quinqueradiata spermatogonia were transplanted into nibe croaker larvae, and the behavior of transplanted spermatogonia in recipient gonads was observed. Three weeks post-transplantation, yellowtail spermatogonia were incorporated into the gonads of 72 out of 88 recipients. An antiproliferating cell nuclear antigen was detected in incorporated yellowtail spermatogonia, suggesting that the xenogenic germ cells were proliferating in recipient gonads. Yellowtail vasa-positive spermatogonia survived for 11 months after transplantation in the gonads of recipient fish. Thus, we showed that the microenvironment in nibe croaker gonads can support the colonization, proliferation, and survival of germ cells derived from a different taxonomic family.     

Gonadal development in early life stages of <Emphasis Type="Italic">Spratelloides gracilis</Emphasis>

ABSTRACT:   The gonad of Spratelloides gracilis was not sexually differentiated in the yolk-sac, preflexion, flexion and postflexion stages. Sexual differentiation and development of the ovary and testis started in the transition stage from larva to juvenile. In juveniles at the fin ray completion stage, the ovary and testis could be distinguished because the ovary contained germ cells initiating meiosis and the testis had blood vessels and a high density of somatic cells. The ovary further developed in larger juveniles to have oocytes of perinucleolus stage together with those of the chromatin nucleolus stage, and oogonium. However, in the testis of larger juveniles, primary spermatogonium began proliferation by meiosis. Sexual differentiation may be regarded as one of morphological and functional changes accompanying metamorphosis in S. gracilis . Some fish larger than the mature size of 60 mm standard length had advanced germ cells and functional gonads, others did not have functional gonads. The distal end of the immature gonads did not connect with a genital duct near the anus. These observations indicate that S. gracilis has large variability in size-at-maturity. The variability in size-at-maturity in S. gracilis , together with large variability in age-at-maturity, may constitute an ecological basis for an extended spawning season in S. gracilis .     

中国主要海洋底层鱼类生物学研究的回顾与展望

回顾了中国海洋主要底层经济鱼类资源生物学的研究历史和科研成果,并重点叙述了带鱼、小黄鱼、大黄鱼和绿鳍马面鲀等重要经济鱼类资源生物学研究概况.概述的内容包括地理种群及其产卵群体的鉴别和划分、生活史型的演变、种群和群体结构、种群数量变动、年龄组成和生长特性、摄食习性、性成熟周期、性腺成熟指数(GSI)、产卵群体生殖力、产卵场、索饵场、越冬场及洄游路线、资源量和渔获量、各种作业渔船的调整及其捕捞力量的限制措施等,并展望了中国海洋底层经济鱼类资源生物学研究的前景.     

Histological observations of seasonal reproductive and lunar-related spawning cycles in the female honeycomb grouper Epinephelus merra in Okinawan waters

Seasonal reproductive and lunar-related spawning cycles of the female honeycomb grouper Epinephelus merra inhabiting Okinawan waters were examined by histological observation of ovaries. Gonadosomatic index (GSI) increased beginning in May and peaked in June. Histological observations revealed that many oocytes laden with yolk were present in the ovaries from May to August. From September to October, ovaries were occupied by immature oocytes. These results suggest that the reproductive season of E.   merra lasts for 4 months from May through August in Okinawan waters. When the fish were collected according to the lunar cycle, GSI increased with the approach of the full moon. Oocytes at various development stages were observed from the first quarter to the full moon. Fresh ovulatory follicles were present in the ovaries around the last quarter moon. These results suggest that E.   merra has a lunar spawning cycle and spawns between the full moon and the last quarter moon. Ovarian features of the fish collected around the last quarter moon were different among individuals; some fish had many oocytes at the tertiary yolk stage in the ovaries, while the ovaries of the others were occupied by the oocytes at the peri-nucleolus and the oil droplet stages. This observation suggests that a minor release of eggs occurs in this species before or after a major spawning lunar day. Oocytes at the migratory nucleus and the maturation stages were not observed in any ovarian samples. This may mean that maturation of oocytes is related to the spawning behavior of this species and makes rapid progress in the process of aggregation at the spawning sites.