Biology of the amphioxus,Branchiostoma belcheri in the Ariake Sea,Japan II. Reproduction

We investigated the reproduction of the amphioxus Branchiostoma belcheri in the southern Ariake Sea, Japan, from 1999 to 2002. Gonads were very small or almost absent from September to December and began to develop in January. Changes in the gonad length index indicated that spawning began in mid June, after the gonads had attained maximum size. Although most gametes were extruded during the first spawning, some remained in the gonads. Shrunken gonads were much smaller but contained gametes, and the second spawning occurred around 10 July. It was unclear whether all adults spawned twice, but a large proportion of individuals did. After the first spawning, both males and females lost 30% of their body weight. Most one-year-old individuals did not spawn, and the minimum size at maturity was ca. 20 mm. We found no termination of reproduction among very large individuals. The average number of gonads was significantly larger on the right side of the body (26.2 in males and 26.1 in females) than on the left side (24.0 in males and 23.5 in females). We found two hermaphrodites in a total of 11,184 specimens examined. Each had four or three ovaries among a total of 45 or 54 gonads.     

铜锈环稜螺繁殖和生长的初步研究

作者于1963年3月至1964年6月间对武昌东湖的铜锈环稜螺的某些生态学问题进行了初步研究:自然种群中铜锈环稜螺的性比为1∶1。成熟雌螺全年怀胚,月平均怀胚数以5月初最高,7、8、9月最低,生活于池塘中的雌螺的怀胚数又高于湖泊中相应壳高组雌螺的怀胚数。生殖季节自4月中旬至11月底,其中以6月份产螺达高峰,其临界水温为16—18℃,最适水温在26℃左右。雌螺生长至壳高15—16毫米开始生殖。在自然种群中,每一雌螺每年平均产螺49.7个。雌螺所产仔螺的大小与年龄有关。对铜锈环稜螺的生长规律,提出了有关方程式。       

Larval development of the oriental lancelet, Branchiostoma belcheri, in laboratory mass culture

We are successfully maintaining a laboratory colony of the lancelet Branchiostoma belcheri bred in the laboratory. Based on living individuals in this mass culture, morphological characteristics from the seven-day larval to benthic juvenile stages have been studied. Most striking was that later larval development of B. belcheri showed great individual variation even in a rather stable culture environment. Metamorphosis first occurred on 60 days post fertilization (dpf) and was continuously observed throughout the present study up to 100 dpf. Morphological traits such as the number of primary gill slits and body size at the start of metamorphosis are apparently affected by culture condition. Body size measured in the largest individuals showed nearly linear growth at 0.087 mm/day. The variability found in larval development calls for caution when developmental stages and chronological ages are compared between populations. However, the developmental flexibility of this animal also raises the possibility that growth and sexual maturation could be controlled artificially in captivity.     

青海沙蜥的两性异型和雌性繁殖

作者研究了青海沙蜥(Phrynocephalus vlangalii)形态特征的两性异形和雌体繁殖特征。蜥蜴于2005年5月初捕自西宁以西约150km的倒淌河,被检形态特征包括体色、体长、腹长、尾长、头长和头宽,新排卵雌体维持在实验室梯度热环境中直至产仔。成体两性异形显著,而性未成熟个体缺乏两性异形。最大的成年雄体和雌体分别为70.2mmSVL(snout-vent length)和82.8mmSVL。雄性成体具有相对较大的头长、头宽和尾长,雌性成体SVL大于雄体且具有相对较大的腹长。对4个形态特征进行主成分分析(特征值≥0.5)区分出2个主成分,共解释83.9%的两性相关形态特征的变异。去除SVL差异的影响后,尾长、头长和头宽在第一主成分有较高的正负载系数(解释57.8%的变异),腹长在第二主成分有较高的负负载系数(解释26.1%的变异)。实验室梯度热环境下的雌体于6月下旬至7月中旬产单窝、2-6个后代。窝仔数和窝仔重与母体SVL呈正相关,幼仔重与母体SVL无关。未在青海沙蜥中检测到后代数量与大小之间的权衡。     

Population dynamics of the date mussel,Lithophaga lithophaga (L., 1758) (Bivalvia: Mytilidae), in the Evoikos Gulf (Greece)

Changes with time in aLithophaga lithophaga population, spatial distribution, size-frequency distribution and recruitment were studied. The population was homogenous, without statistically significant differences, down to a depth of 6 m, the depth to which sampling was carried out. Population density showed periodic variations over the year and changed as the gradient of the substratum increased. Dispersion indices indicated that individuals were distributed randomly in clumps during the period of recruitment at different depths. Juveniles, up to a length of 4 mm, formed the highest percentage of the population. Larvae settled at a length of >260μm, and individuals reached a length of 35 mm by the end of their first year. The appearance of newly settled individuals occurred two months after the maximum occurrence of larvae in the water. High percentages of settled spat were first observed in early winter at a depth of between 0–3 m although, later, higher percentages were found at 3–6 m depth.     

Intra-buccal feeding of young in an undescribed Tanganyikan cichlid Microdontochromis sp.

Synopsis The zooplanktivorous cichlid Microdontochromis sp. formed large stationary schools in midwater consisting of mouthbrooding and nonbrooding individuals. Early young smaller than 6.0 mm in standard length were mouthbrooded solely by females, but large young, up to 17.4 mm, were mouthbrooded by both females and males. Mouthbrooding fish took food as actively as nonbrooding fish to nourish the young and themselves. Eggs were 1.9 mm in maximum diameter, among the smallest known for mouthbrooding cichlid fishes. Young which ate food within the parent's buccal cavity showed a 10-fold increase in dry weight during the mouthbrooding period. Data suggested that parents finally farmed out their young into broods of other cichlid fishes.     

Predation by xanthid crabs on early post-settlement gastropods: the role of prey size, prey density, and habitat complexity

Small predators in marine benthic communities create a hazardous environment for newly settled invertebrates, especially for the smallest individuals. To explore the effects of predation on a newly settled gastropod, queen conch (Strombus gigas Linnaeus), by a xanthid crab (Micropanope sp.), prey size, prey density, and habitat complexity were manipulated in five laboratory experiments. All crabs >3.1 mm CW killed all conch <2 mm SL when individual crabs (<14 mm carapace width (CW)) were offered individual conch that were 2–35 days old after metamorphosis (1.2–8.8 mm shell length (SL)). Only 10% of the crabs >5.0 mm CW, however, killed conch that were >5.0 mm SL, suggesting that conch may reach a size refuge from xanthid crabs at 5 mm SL. Furthermore, when given a choice, crabs (4.8 mm CW) preferred smaller conch (2.0 mm SL) to larger (3.7 mm SL), suggesting that 1 week of additional growth in shell length is advantageous to survivorship. Proportional mortality decreased as conch density increased when crabs were offered conch at seven different densities (two to 96 individuals). Crabs proved to be effective predators regardless of the amount of seagrass structure provided in a microcosm experiment, and could consume two conch in 10 s. The high densities of xanthid crabs that occur in the wild, their effectiveness as predators, and their large appetites point to the important role that small predators may potentially play in structuring the population dynamics of their small prey immediately after settlement.     

Age, growth, reproduction and mortality of the striped seabream, Lithognathus mormyrus (Pisces, Sparidae), off the Canary Islands (Central-east Atlantic)

Striped seabream, Lithognathus mormyrus L. (n=731) caught off the Canary Islands from January 1999 to June 2000 were studied. Fish ranged in size from 113 to 372 mm total length, weighing from 21.1 to 748.2 g total weight. Weight increased allometrically with size (b=2.9071). Fish age was 0–10-years-old. Growth was relatively slow (k=0.88 years⁻¹), with females growing at a slightly faster rate than males. The species displayed protandric hermaphroditism. Male : female ratio was unbalanced in favour of males (1 : 0.85). Males predominated in smaller sizes, females in larger sizes, and intersexual individuals were in intermediate sizes. The reproductive season extended from June to December, with a peak in spawning activity in August–September. Males reached maturity at 207 mm (2 years) and females at 246 mm (3 years). The real value of instantaneous rate of natural mortality was between 0.30 and 0.45 years⁻¹.     

Variations in body size of the lancelet Branchiostoma belcheri at different depths in the Seto Inland Sea: effect of food supply on the growth rate

Variations in body size of the suspension-feeding lancelet Branchiostoma belcheri were examined from April 2001 to December 2001 at different water depths of 10-80 m. The lancelets were abundantly collected (220 indiv./dredge) at water depth of 10 m. The maximum size, ranging from 36.8 to 50.4 mm BL, decreased with increasing water depth. However, the minimum size of 7.4-7.8 mm BL, which corresponds to settling size, did not different with water depth. From seasonal changes in the length-frequency histograms, five cohorts were observed at every water depth. The lancelets grew to 44 mm BL at water depths of 10-20 m and to 34 mm BL at water depth of 80 m with four years of life span. Developmental stages of the gonads at an age of two years showed that no individuals had undeveloped gonads at water depth of 10 m, but 82% of them did at water depth of 80 m. The analysis of the stepwise multiple regressions of monthly growth rate on environmental variables showed that chlorophyll a was the best explanatory variable and showed a significant positive correlation with the growth of 1-2 years age groups. These results suggested that variations in the body length were mainly fluctuated by phytoplankton supply.     

Temporal changes in the reproductive population structures and males’ secondary sexual character of the hermit crab <Emphasis Type="Italic">Diogenes nitidimanus</Emphasis>

We investigated the reproductive ecology of D. nitidimanus in the Waka-River estuary with special reference to temporal change in the relative size of chelae length for males, i.e., secondary sexual character. Ovigerous females were observed from April to October, peaking in June–July with over 90% of females being ovigerous. Adult female carapace size ranged from 3.5 to 8.5 mm, but with the majority of females falling between 5–6 mm. Male carapace length was more evenly distributed between 3.5 and 10 mm. Juvenile settlement occurred mostly in July, during which time the frequency of both large females (over 6.5 mm in carapace length) and large males (over 8.5 mm in carapace length) clearly decreased. The carapace length of precopulatory-guarded females varied from 4.8 to 8.0 mm, while guarding males were almost over 7 mm and always larger than their paired females. The relative growth of the major chelae differed significantly between small and large males during the early months of the year, including the reproductive peak months (April–June). During these early months, large males had relatively larger chelae for their body size than did small crabs. This difference, however, was not evident later in the year (July–September). Large males may grow their chelae relatively long in the early months in order to take advantage of the mating opportunities during April–June. This is the first report in animals, to our knowledge, that relative size of the secondary sexual character for males temporarily change during a single reproductive season.     

Diel feeding rhythms,daily ration,and seasonal changes thereof in marbled flounder Pseudopleuronectes yokohamae

This paper aims to assess the diel feeding pattern and seasonal variation in the daily ration of immature and mature marbled flounder (Pseudopleuronectes yokohamae). A day‐night collection by bottom trawls was conducted in Sendai Bay in July 2014. Marbled flounder (131–493 mm total length; Number of collected individuals = 1830, Number of analyzed individuals = 497) fed mainly on polychaetes during the day. At night, stomach content weight decreased with time, but the weight and proportion of bivalve siphons were consistently higher at night than during the day, suggesting nocturnal feeding by the flounder on bivalve siphons. Daily ration was greater in females (<300 mm: 2.6%–3.2% body weight; ≥300 mm: 1.5%–2.5%) than in males (<300 mm: 1.7%–2.6%; ≥300 mm: 1.3%–1.9%). Seasonal surveys were also carried out, and the greater ration in females than males were consistent throughout the year, suggesting that greater growth in females than males attributes to the greater food intake of females. The ration was highest in June, especially for large individuals, although water temperature in June was lower than that in September. These results indicate that the amount of food intake is related to the annual life cycle of the marbled flounder.     

First report of the presence of Acartia bispinosa Carl, 1907 (Copepoda,Calanoida) in a semi-enclosed Bay (Sharm El-Maya), northern Red Sea with some notes on its seasonal variation in abundance and body size

The calanoid copepod, Acartia bispinosa Carl, 1907, is reported for the first time in the Red Sea, where it is found to be an important copepod in the mesozooplankton community structure of the Sharm El-Maya Bay. Female and male are fully redescribed and illustrated of as the mouthparts of this species have never previously been described and figured. Acartia bispinosa was collected in the plankton samples throughout the year and showed two peaks of abundance, a pronounced one in April (4234 individuals m^-3), and second smaller peak during November (1784 individuals m^-3). The average total length of females varied between 1.32 and 1.53 mm at the end of June and January respectively. For males, the average total length fluctuated between 1.07 and 1.16 mm at end of June and March respectively. Temperature showed an inverse relationship with the body length (P > 0.001) and seemed to be one of the prime factors affecting the body length of both sexes.     

Evidence of sustained populations of a small reef fish on artificial structures. Does depth affect production on artificial reefs?

The length frequencies and age structures of resident Pseudanthias rubrizonatus (n = 407), a small protogynous serranid, were measured at four isolated artificial structures on the continental shelf of north-western Australia between June and August 2008, to determine whether these structures supported full (complete size and age-structured) populations of this species. The artificial structures were located in depths between 82 and 135 m, and growth rates of juveniles and adults, and body condition of adults, were compared among structures to determine the effect of depth on potential production. All life-history stages, including recently settled juveniles, females and terminal males, of P. rubrizonatus were caught, ranging in standard length (L(s)) from 16·9 to 96·5 mm. Presumed ages estimated from whole and sectioned otoliths ranged between 22 days and 5 years, and parameter ±s.e. estimates of the von Bertalanffy growth model were L(∞) = 152 ± 34 mm, k = 0·15(±0·05) and t(0) = -1·15(±0·15). Estimated annual growth rates were similar between shallow and deep artificial structures; however, otolith lengths and recent growth of juveniles differed among individual structures, irrespective of depth. The artificial structures therefore sustained full populations of P. rubrizonatus, from recently settled juveniles through to adults; however, confirmation of the maximum age attainable for the species is required from natural populations. Depth placement of artificial reefs may not affect the production of fish species with naturally wide depth ranges.     

The population dynamics and growth of the mud shrimp <Emphasis Type="Italic">Upogebia major</Emphasis> (De Haan, 1841) (Crustacea: Decapoda) from Peter the Great Bay,Sea of Japan

The dynamics of the size–age composition and growth of the mud shrimp Upogebia major in the upper sublittoral area of Vostok Bay (Peter the Great Bay, the Sea of Japan) were investigated in 2015 and 2016. Ovigerous females were found in April and May after the disappearance of the sea ice cover. Egg laying occurs only once during the breeding season. Hatching of larvae is observed in May, while in July the bottom population is replenished by a cohort of fast-growing young individuals that reach a body length of 43–44 mm during the first season of growth. In the third year of life, the females lay eggs for the first time at a body length of more than 73 mm. The females and males grow at the same rate; their growth can be approximated by a Bertalanffy equation of the form L_t = 118.4 [1–e^{–0.5627 (t + 0.5305)}]. The mud shrimp population consisted of 1–4- and, possibly, 5-year-old individuals 9–117 (females) and 8–116 mm (males) in body length. The specific features of the breeding, growth, and reproduction of the local populations of U. major are indicative of good adaptation of this species to the environmental conditions in Peter the Great Bay, which contributes to sustaining the biodiversity of the coastal zone in the region.     

瘦尾细额溞Oxyurella tenuicaudis(Sars,1862)的若干生物学特征

瘦尾细额溞是一种出现数量极其稀少的枝角类。关于它的生物学特征尚未见诸文献。本文测量了一次采自云南永胜一池塘的本种300个两性个体的体长和怀卵量,就其幼体与成体的数量、体长与怀卵量、雄性以及性比等问题探讨了种群的生物学状况。 详细观察比较了这个种的重要分类特征——雌体后腹部,并描述了变异范围。对卵鞍和雄体也作了描述。     

A skeletochronological study of age and growth in relation to adult size in the water frog Rana epeirotica

The age and growth of individuals in a population of the water frog Rana epeirotica, from northwestern Greece, were studied in 1998 and 1999 using skeletochronology. Analysis of the age structure was based on the enumeration of Lines of Arrested Growth (LAGs) in phalanges. Ages ranged from 1-5 years among 145 males and from 1-5 years among 173 females. The mean snout-vent length was 72.74 +/- 7.96 mm in males and 83.63 +/- 11.73 mm in females. The difference between the sexes in age and size was significant. Endosteal resorption may have eroded away the first LAG in only 9% of the studied individuals and was more frequent in females. Growth of adults was fitted by the Bertalanffy model. The growth coefficient (K) was 0.88 in males and 0.49 in females, reflecting faster male growth between metamorphosis and maturation.     

Sex differences in age structure, growth rate and body size of common frogs Rana temporaria in the subarctic

The thermal environment and length of the activity season are important factors in shaping life-history trait variation in ectotherms. Many ectothermic vertebrates living at high latitudes or altitudes tend to be larger and older than their conspecifics living at lower latitudes or altitudes. However, detailed data on age, body size and growth variation—and how they may differ between males and females—are still scarce, especially from extreme high-latitude environments. We studied growth (body length increment), age and size structure of common frogs (Rana temporaria) in subarctic Finland (69°04′N) by applying skeletochronological methods to individually marked adults (n?=?169) captured and recaptured between 1999 and 2003. We found that breeding males were on average younger (mean?=?8.5?years) than females (11.9?years) and that males started reproducing earlier (≥3–4?years of age) than females (>4–5?years). The oldest encountered individual was an 18-year-old female, which to our knowledge is the oldest wild common frog ever reported. Females were on average larger (mean body length?=?76.6?mm) than males (70.7?mm), and this appeared to be mainly due to their older age as compared to males. While body length increased and growth rate decreased with age in both sexes, growth rate declined significantly faster with age in males than in females. The latter finding provides a proximate explanation for the observation that even after accounting for age differences among sexes (females?>?males), females were longer than males.     

三峡水库秀丽白虾生长与繁殖生物学特征研究

2012 年11 月至2013 年10 月逐月对三峡水库木洞江段秀丽白虾的生长和繁殖生物学特征进行了研究。结果显示秀丽白虾是一年生的虾类, 寿命为1214 个月。雌性个体的平均体长(37.727.92) mm 显著大于雄性(37.086.59) mm, 具有明显的雌雄异形现象。秀丽白虾的渐近体长(L)为59.33 mm, 生长系数(K)是1.6/年, 生长方程为:Lt=59.33-e-1.6(t+0.081)。雌虾繁殖季节从4 月上旬持续至9 月下旬, 繁殖高峰期为4 月中旬至6 月中旬, 由越冬虾和当年虾两个世代的繁殖群体组成。抱卵雌虾的体长为27.0753.71 mm, 平均体长(L50)为37.06 mm。雌雄性比月变化为1.112.36, 平均为1.46, 群体中雌性个体数量显著多于雄性(P 0.001)。绝对繁殖力(FA)为31294 粒, 相对繁殖力(FR)为(11522)粒/g。绝对繁殖力与体长呈幂函数关系(FA=0.0031L2.8632, r=0.72, n=106), 而与体重呈直线关系(FA=104.63W+9.9534, r=0.79, n=106)。卵径(D)平均值为(1215102) m。为合理保护和利用三峡水库秀丽白虾种群资源, 建议加强虾类捕捞管理, 繁殖期间(49 月)禁止捕捞虾类或限制捕捞强度。       

A skeletochronological study of age, growth and longevity in a population of the frog Rana ridibunda from southern Europe

Age at sexual maturity and longevity in a population of Rana ridibunda from north-eastern Greece were studied by skeletochronology performed on the phalanges. Analysis of the age structure was based on counting the lines of arrested growth (LAGs). Sexual maturity for both sexes arises during the first year or after the first hibernation. Ages ranged from 1 to 5 years (mean=2.96) among 52 males and from 1 to 5 years (mean=3.73) among 56 females. The mean snout-vent length was 69.03+/-12.6mm in males and 82.38+/-13.27 mm in females. The difference between the sexes in age and size was significant. Growth of individuals was fitted on? The von Bertalanffy model. The growth coefficient (K) was 0.57 in males and 0.54 in females, mainly due to faster male growth between metamorphosis and maturation.     

Age and growth of manybar goatfish Parupeneus multifasciatus (Mullidae) from the Nha Trang Bay of the South China Sea

The growth of individuals is analyzed in the mass tropical species manybar goatfish Parupeneus multifasciatus from the Nha Trang Bay of the South China Sea. The relationship between the body weight and body length is determined for the females and males. Among the fishes larger 180 mm fork length (FL), the males prevail. Linear growth of the sagitta is characterized by negative allometry in relation to body length, and sagitta growth in length is faster than in width. Age of fish assessed based on the analysis of daily increments on the sagitta does not exceed three years, and the majority of individuals reach the first sexual maturity by the age of one year. The growth rate of the fish is characterized by a large individual variation.