Gonad Length Research Articles

Use of ultrasonography to determine the structural and functional state of ovaries of donor embryo cows

Purpose: Assessment of the possibility of using ultrasonography for early prediction of the response of the functional activity of the ovaries to the introduction of some hormonal drugs at ET.Materials and methods. The study was conducted on 42 cows of various breeds (Holstein, Ayrshire, Black-and-white breed of cows) — potential donors of egg and embryos in several farms of various organizational and legal forms of ownership of the Saratov and Volgograd regions of the Russian Federation. Cow donors are selected taking into account anamnestic data. To assess the full response of the ovaries, two experiments were produced to carry out the stimulation of supersuvulation: the first study was introduced on the 10th day of the estrous cycle, 9 animals of follitropine on the developed protocol, and 7-animals — «plus» and the second study — for 11 days of the estrous cycle 8 — animals injected follitropine, and 6 cows — «plus» in the 4-day protocol. The synchronization of the estrus was carried out according to the generally accepted protocol. For morphological studies, the donor cows were extracted by ovaries and studied their physical characteristics, such as volume, weight, thickness, width, gonad length, the size of yellow bodies and follicles. For a more detailed study, ultrasonography was carried out using a Mindray DP 10 VET portable scanner with a rectilinear rectal sensor 7.5 MHz by 10-11 (before the administration of the drug) and zero (after the introduction of the follicularity of the hormonal preparation) of the estrous cycle days.Results. The average rate of ovaries before the introduction of drugs, on the 10th day of the estrous cycle, was 11.103±2.275 cm3, the volume of yellow bodies — 7,122±3.435 cm3. The average volume of yellow bodies to the ovary was 48.7±1.3%. The level of supervision reaction depends on the quality of the yellow body in the middle of the L-phase, at the time preceding the beginning of the gonadotropic stimulation from donor cows.Conclusion. Based on the data obtained, it can be concluded that the visual analysis of sleepograms is an acceptable method for predicting the suitability of donor cows prior to the beginning of animal treatment with gonadotropic drugs and can be used as the animal selection criterion into a group of potential donors. Using ultrasound echography, relevant data reflecting the morphological and functional state of cows ovaries were obtained.

Reproductive aspects of <i>Chiton virgulatus</i> in Bahía de La Paz, Gulf of California, Mexico

This study analyzed the reproductive cycle of Chiton virgulatus and its relationship with air temperature (AT) sea and surface temperature (SST), photoperiod, and tidal cycle (TC) in Bahía de La Paz, in the coast of the Gulf of California. Monthly samples were collected from September 2008 to September 2009. The parameters recorded included total length, total weight, and gonad weight of each organism; the gonad was processed using a histological technique, and the gonadal index and length at first maturity (L50) were estimated. C. virgulatus displays partial spawning with a reproductive peak in summer and autumn (July to December). The frequency of ripe organisms was associated with rises in SST (30.6 ºC), AT (29.9 ºC), and TC (68 cm, high tidal), while photoperiod (longer days) regulated the frequency of developing organisms. The length at first maturity was 29.7 mm. Chiton virgulatus is a polyplacophoran species in which high temperatures and high tides influence reproductive timing, while an increase in daylight boosts gonad development.

Role of intraspecific competition in intrinsic growth rate regulation in an Oikopleura dioica (Tunicata) population

Planktonic Oikopleura dioica respond almost instantly to opportunistic algal blooms, but it is unknown whether the population increase can change from an exponential to a logistic model to avoid a final sudden collapse. To test the hypothesis that intraspecific competition regulates the intrinsic rate of natural increase (r), density-dependent effects on growth and reproduction performance were investigated in O. dioica via laboratory incubations. Over a large food concentration range, batch maturation was observed above the per capita food supply (PFS) of 8.1 µgC/ind. in 4.5 d. Somatic growth was saturated beyond this PFS value, whereas gonad length increased continuously. Below this threshold, individuals reached small body and gonad lengths, and maturation was rarely observed during the incubation period. The gonad/body volume and maturation ratios also increased with the PFS. Instead of the food concentration, the r values were regulated by competition pressure via variability in maturation duration and the proportion of mature individuals in the cohorts. When the minimum food demand was satisfied in the designated generation time, the r value tended to be regulated by the spawning proportion in the population. Otherwise, prolonged development duration and decreased r values were expected.

Growth performance of Oikopleura dioica during flood seasons in Jiaozhou Bay: Implications on early maturation favored rapid response to environmental fluctuation

Gelatinous tunicates with rapid bloom capability are ubiquitous and important in marine ecosystems. To evaluate the rapid response of a most common appendicularian species, Oikopleura dioica, to fluctuating environmental conditions, spatio-temporal abundance, chlorophyll a concentration and body size was investigated twice a week at 5 stations in Jiaozhou Bay, a eutrophic and semi-closed embayment of China. The highest recorded O. dioica abundance was 28107 ind. m−3. Mature individuals attained body lengths ranging from 114.92 to 619.11μm. Compared with the body/gonad length relationship established in laboratory studies, the natural population in Jiaozhou Bay had greater gonad length at the same body length. The difference of gonad length between natural and laboratory specimens was -1.04–6.03μm for matures and 24.93–30.63μm for immatures at various food regimes. Body size in this study showed a significant positive correlation with chlorophyll a concentration of the size range 0.2–20μm. Considering that maturation at smaller body size and shorter generation time arising therefrom can result in higher intrinsic rates of natural population increase, it suggests that early maturation favors a rapid response of O. dioica to fleeting phytoplankton blooms. Although such response was limited to blooms of small size phytoplankton, it may help on recovery of micro-phytoplankton dominance in natural environments.

Macroscopic characteristics of the gonad maturity stages of dusky parrotfish Scarus niger

The dusky parrotfish Scarus niger is an important economic fish. Like other reef fish that have good taste, white and thick meat, and don’t have a lot of tiny bones, the dusky parrotfish is a fine food fish. The dusky parrotfish has a very wide distribution in tropical and subtropical sea waters. This study aimed to validate the maturity stage descriptions based on macroscopic characters. The results of this study are expected to be a reference in the study of the reproductive biology of dusky parrotfish and other parrotfishes, such as first maturity and the reproductive cycle. The samplings were done monthly at Makassar Fisheries Port from January 2018 to May 2019. The parameters measured were total length, body weight, gonad weight, gonad length and width, and liver weight. The observed aspect was the gonad colour and condition for both male and female fishes. Five stages of gonad maturity used to identify the gonad maturity stages were quite accurate. The accuracy was indicated by the gonadosomatic index (GSI) and hepatosomatic index (HSI) values that increased progressively from Stage I to IV. This accuracy validates macroscopic characters used for identifying the maturity stage of dusky parrotfish

Maturity stages of the redbreasted wrasse Cheilinus fasciatus

The redbreasted wrasse Cheilinus fasciatus is an ornamental fish exploited for the marine aquarium trade. Even though it has white flesh, the redbreasted wrasse is not popular as a food fish because the flesh is quite thin. The redbreasted wrasse is widely distributed in the Indian and Pacific Oceans. It lives in tropical waters at depths of 4 to 60 m and at temperatures of 23 to 27°C. The objective of this study was to describe the gonad maturity stages of this fish using macroscopic characteristics. Sampling was carried out at Makassar Fishing Port from January 2018 to May 2019. The parameters observed in both male and female specimens were gonad length, width, weight, and gonad colour. Each specimen was also weighed and measured. Five gonad maturity stages were identified and described: Stage I (Immature or transition), Stage II (Early maturation), Stage III (maturation), stage IV (mature) and Stage V (post spawning or spent). These stages were described based on macroscopic structure and morphometric parameters of the gonads. The five stages coincided with changes in the Gonadosomatic Index (GSI), indicating that the five stages were valid. These stages could be used as a practical reference for identifying gonad maturity and describing the reproductive cycle of the redbreasted wrasse C. fasciatus.

Influence of Xenorhabdus (Gamma-Proteobacteria: Enterobacteriaceae) symbionts on gonad postembryonic development in Steinernema (Nematoda: Steinernematidae) nematodes.

Steinernema nematodes and their Xenorhabdus partners form an obligate mutualistic association. This partnership is insecticidal to a wide range of insects. Steinernema rely on their Xenorhabdus partner to produce toxins inside the insect cadaver to liberate nutrients from the insect, as well as antimicrobials to sterilize the cadaver, thus creating a suitable environment for reproduction. In return, Steinernema vector their Xenorhabdus between insect hosts. Disruption of this partnership may affect the success of both partners. For instance, when Steinernema associates with non-cognate symbionts, their virulence and reproductive fitness are affected. In this study, we examined the effect of symbiotic (cognate and non-cognate) and non-symbiotic bacteria on maturation time, gonad postembryonic development, and sex ratio of first-generation Steinernema adults. Two Steinernema spp. were considered: S. feltiae SN and S. carpocapsae All. In vitro assays were carried out by pairing each nematode sp. with symbiotic (cognate and non-cognate) Xenorhabdus, and with non-symbiotic bacteria (Serratia proteamaculans). Additionally, for comparative purposes, we also considered adult nematodes reared in vivo in Galleria mellonella larvae to assess nematode development under natural conditions. Results from this study showed non-symbiotic Serratia proteamaculans did not support adult development of S. feltiae but it allowed development of S. carpocapsae adults. Sex ratio decreased from 2:1 to 1:1 (female: male) when S. carpocapsae adults were reared with the non-symbiotic S. proteamaculans. Cognate or non-cognate Xenorhabdus spp. and/or strains did not change the sex ratio of any of either Steinernema spp. tested. Morphometric analysis also revealed that bacterial conditions influenced adult size and gonad postembryonic development in both Steinernema species. Body size (length and width), and gonad length in both S. feltiae males and females, were significantly reduced when reared with a non-cognate Xenorhabdus species. In S. carpocapsae, males exhibited an enhanced body size (length and width) and gonad length when reared with a non-cognate X. nematophila strain. S. carpocapsae females also exhibited an enhanced gonad length when reared with a non-cognate X. nematophila strain. S. carpocapsae males and females were underdeveloped when reared with the non-symbiotic S. proteamaculans, and exhibited reduced body sizes and gonad lengths. We conclude that development of first-generation adults of both Steinernema spp. tested, in particular time to adult maturation as well as body and gonad size were directly influenced by the bacterial symbionts they were cultured with. However, response to the culture conditions was species specific.

Maturation and Reproductive Biology of Reba Carp Cirrhinus Reba (Hamilton) in Lower Anicut Reservoir, Tamil Nadu, India

Examine the reproductive biology of Cirrhinus reba at Lower Anicut reservoir and analyses of gonads assessed by ovarian cycles. Sex ratio, size at first maturity, GSI, macroscopic appearance ovary, fecundity, oocyte diameter and histological examination suggested as a result of spawning season. Males were 59.4% and females 40.6% suggested the ratio significantly deviated from expected 1:1. Size at 50% maturity estimated from logistic model curve 132 mm in males and 148 mm for females. GSI was represented increasing the development of gonads in both sexes until it was ripe and spent. During spawning, increasing the length and weight of gonads from immature to ripe, maximum values of GSI for both sexes (3.43%-3.49% to 4.09%- 6.01%) were obtained during April to August with peak in July. Size-frequency distribution of ova diameter were clearly indicate maximum values of diameter enclosed during July to corresponding microscopic stages of gonads. Five stages of oocyte development were determined through histological examination can be divided immature, maturing, matured, ripe and spent. Total length, weight, gonad length and weight were significantly related to fecundity. Stocks of C. reba were enclosing females spawn once a year during spawning season. Following, the implications for management and controlled feral carp stocks were discussed in detail.

Masculinization of silver perch (Bidyanus bidyanus Mitchell 1838) by dietary supplementation of 17α-methyltestosterone

The aim of this research was to assess the possible use of dietary supplementation of 17α-methyltestosterone (MT), to produce all-male population of silver perch, Bidyanus bidyanus Mitchell 1838, as a step forward in producing neomales, which later can be used to produce an all-female population. Larvae were fed 17α-MT at various concentrations, viz. 0 (control), 9 and 18mg/kg diet for the period of 30days from 31 to 60days post hatching (dph). Phenotypic sex ratios at 225dph identified through histological examination revealed that MT significantly (P<0.05) increases the male percentage from 59% to 100%. Testes of MT-fed fish were well developed, had a normal appearance at the same developmental stages to that of the control group. No significant differences (P>0.05) in gonad weight (GW), gonad length (GL) and gonadosomatic index (GSI) among treatments which may indicate that the resulting neomales were viable. The MT supplementation did not influence the mortality rate, but significantly (P<0.05) increased the final weight and specific growth rate (SGR). The study suggests that the dietary supplementation of MT at 9–18mg/kg of the diet from 31 to 60dph larvae is effectively in inducing masculinization in silver perch.

Effect of Dietary Estradiol‐17β on the Feminization of Silver Perch, Bidyanus bidyanus (Mitchell, 1838)

AbstractThe silver perch, Bidyanus bidyanus (Mitchell 1838), displays sexual dimorphism in size, with females reaching larger maximum size than males. In an attempt to produce all‐female populations, larvae at 30 d posthatching were fed an estradiol‐17β (E2) diet at dosages of 0, 60, and 120 mg/kg for 30 d. Histological examination of gonads revealed that all E2‐supplemented diets resulted in significantly higher (P &lt; 0.05) feminization rates (97.22–100%) than did the control (39.69%) but with no difference between the two E2 diets (P &gt; 0.05). Female and male gonads were observed in fish fed the 60 mg E2/kg diet. No significant differences were observed in the survival rate, weight gain, gonad weight and length, specific growth rate (SGR), or gonadosomatic indexes, except for gonad length and SGR at the end of the experiment. Although the ovary length of fish fed the 60 mg E2/kg diet was significantly shorter than that of the control groups, no abnormalities were detected. In contrast, fish fed 120 mg E2/kg grew faster than the other fish and showed sexual dimorphism. Our results suggest that supplementation of E2 at 60–120 mg/kg diet could be applied to establish all‐female populations of silver perch.

On the Fecundity and Sex-ratio of Labeo bata (Hamilton) (Cypriniformes: Cyprinidae)

The fecundity and sex- ratio of 2200 Labeo bata (Hamilton) specimens were studied. The fecundity of 234 gravid females varied from 51,354( for a fish with total length of 127.3 mm and total body weight of 20.0 g) to 91,568( for a fish with total length of 256.6 mm and total body weight of 156.70g).The mean fecundity was recorded as 67,617.50±13,510.15 for the average length and weight of 192.98±41.06 mm and 87.79±49.07 g, respectively .The mean total length and weight of gonad was 67.62± 24.01 mm and 20.35±13.50 g, respectively .The relationship between fecundity ( F.) and other parameters such as total length ( TL ), Standard length ( SL), total weight( TW), gonadal length (GL), gonadal weight (GW) and gonadal depth (GD) were studied. DOI: http://dx.doi.org/10.3329/jsf.v11i2.21595 Journal of Science Foundation, 2013;11(2):43-48

Ultrasonography as a non-invasive tool for sex determination and maturation monitoring in silver eels

In the context of the severe decrease in temperate eel abundance, understanding and control of eel maturation has strong interest for scientific and commercial purposes. Possible use of ultrasonography for improvement of sex determination and maturation monitoring in silver eel was investigated. Gonads of 96 Anguilla anguilla silver eels were observed using portable equipment associated to a 6–15MHz probe, and sex determination was tried before artificial induction of maturation. To estimate gonad mass and monitor individual gonadosomatic index (GSI) in females, cross-sectional images were captured at different times of maturation and gonad length was measured at scanning. Two methods were tried for ovary mass estimation using ultrasonography: one based on a linear model and another on calculating ovary volume from a representation of gonad shape. Ultrasonography resulted in 100% success in sex determination. Ovary mass estimated by ultrasonography was strongly correlated to true ovary mass (R2=0.97). The use of a linear model for gonad mass and then GSI estimation seemed more appropriate than the use of a representation of gonad shape. Evolution of GSI estimates during maturation supports possible detection of early inter-individual differences in maturation using ultrasonography in female silver eels. This non-invasive tool can then obviously be exploited to improve sex determination in silver eels caught in the wild and to monitor maturation at the individual level. Ultrasonography thus has great potential for use in eel both for conservation and aquaculture. To our knowledge, this is the first report on the use of ultrasonography on eels or any anguillid species.

Ovarian Development and Reproductive Cycle of Two Freshwater Barbs, Puntius sophore and Puntius ticto

Puntius sophore and Puntius ticto are two important small indigenous fish species of Bangladesh. The present study is aimed to resolve the ovarian development and reproductive cycle of these two species. The ovary of these species passes four major maturation stages viz. Immature (mean ova diameter 0.133±0.05mm for P. sophore and 0.125±0.04mm for P. ticto), Maturing (mean ova diameter 1.096±0.06mm for P. sophore and 0.908±0.06mm for P. ticto), Mature (mean ova diameter 1.512±0.04mm for P. sophore and 1.332±0.07mm for P. ticto) and Ripe (mean ova diameter 1.879±0.05mm for P. sophore and 1.697±0.05mm for P. ticto). Reproductive cycle was determined on the basis of four methods viz. percentage occurrence of gravid females, gonadal length index (GLI), gonado somatic index (GSI) and variation in ova diameter. All four methods focused that the spawning period of these two species extends from May to August. The results of the study will play a vital role for the proper management and conservation of the species.

Some aspects of the reproductive biology and sex-ratio of &lt;i&gt;Cirrhina reba&lt;/i&gt; (Hamilton) (Cyprinidae : Cypriniformes)

Some aspects of the reproductive biology viz. sex-ratio gonadal length index (G.L.I.), gonado somatic index (G.S.I.) and sex-ratio of Cirrhina reba were studied during September 2004 to July 2005. In present study the highest values of GLI (33.76) and GSI (0.63) were in the month of July. Total length (TL) and gonadal length (GL), total weight (TW) and gonadal weight ( GW ), standard length (SL) and gonadal length ( GL ) and gonadal weight relationships were found to be positive; and the relationships were: GL = -3.873 + 0.219 TL (r = 0.992), GW = 0.01511+0.000815 TL (r = 0.979), GL = -2.6030+0.253 SL (r = 0.990), GL = 0.01997+0.000938 SL (r= 0.976), GW = 13.2952+0.6064 TW (r = 0.958), GW = 0.0772+0.00233 TW (r = 0.979). The sex- ratio of C. reba were 1:1.62 for male and female respectively. The Chi-square test showed significant differences of sex-ratio among months and totals.DOI: http://dx.doi.org/10.3329/ujzru.v30i0.10739Univ. j. zool. Rajshahi Univ. Vol. 30, 2011 pp. 21-24

Use of Veterinary Ultrasound to Identify Sex and Assess Female Maturity of Pacific Halibut in Nonspawning Condition

AbstractUltrasound was used for sex identification and female maturity assessment of Pacific halibut Hippoglossus stenolepis ranging from 64‐ to 144‐cm fork length collected during their nonspawning period (boreal summer) in the central and eastern Gulf of Alaska. Ultrasonic sex identification employed inspection of gross morphology and gonadal morphometrics, the latter involving determination of gonad length (maximum posterior gonad extent [MPGE]) and testing for difference between sexes. Morphometric analysis was refined further for females by removing ovaries, macroscopically determining maturity status, and comparing MPGE and proportional ovarian length (POL) among maturity stages. Ultrasonically determined gross morphology was sufficient to achieve accurate sex identification in even the smallest individuals examined. Ovaries were rounded anteriorly with no apparent internal structure, whereas testes were sickle‐shaped with characteristic internal structure formed by the junctures between testicular lobes. Maximum posterior gonad extent was significantly greater for females but did not provide accurate sex determination because values overlapped considerably between sexes; 80% of all fish (n = 147) exhibited MPGE within the range of overlap. Values of both MPGE and POL overlapped considerably between mature and immature females, but threshold values were identified for both metrics above which all individuals were mature. Only for POL was a lower threshold apparent, below which all individuals were immature. Considering MPGE and POL simultaneously suggested a possible means for identifying first‐time spawners and may warrant additional investigation.Received January 13, 2011; accepted June 2, 2011

Minor Abnormalities of Testis Development in Mice Lacking the Gene Encoding the MAPK Signalling Component, MAP3K1

In mammals, the Y chromosome is a dominant male determinant, causing the bipotential gonad to develop as a testis. Recently, cases of familial and spontaneous 46,XY disorders of sex development (DSD) have been attributed to mutations in the human gene encoding mitogen-activated protein kinase kinase kinase 1, MAP3K1, a component of the mitogen-activated protein kinase (MAPK) signal transduction pathway. In individuals harbouring heterozygous mutations in MAP3K1, dysregulation of MAPK signalling was observed in lymphoblastoid cell lines, suggesting a causal role for these mutations in disrupting XY sexual development. Mice lacking the cognate gene, Map3k1, are viable and exhibit the eyes open at birth (EOB) phenotype on a mixed genetic background, but on the C57BL/6J genetic background most mice die at around 14.5 dpc due to a failure of erythropoiesis in the fetal liver. However, no systematic examination of sexual development in Map3k1-deficient mice has been described, an omission that is especially relevant in the case of C57BL/6J, a genetic background that is sensitized to disruptions to testis determination. Here, we report that on a mixed genetic background mice lacking Map3k1 are fertile and exhibit no overt abnormalities of testis development. On C57BL/6J, significant non-viability is observed with very few animals surviving to adulthood. However, an examination of development in Map3k1-deficient XY embryos on this genetic background revealed no significant defects in testis determination, although minor abnormalities were observed, including an increase in gonadal length. Based on these observations, we conclude that MAP3K1 is not required for mouse testis determination. We discuss the significance of these data for the functional interpretation of sex-reversing MAP3K1 mutations in humans.

Reproductive biology of the lessepsian Reticulated leatherjacket Stephanolepis diaspros (Fraser - Brünner, 1940) in the Gulf of Gabes (Eastern Mediterranean Sea)

Fundamental information on the reproductive biology of the lessepsian fish Reticulated leatherjacket Stephanolepis diaspros from the Gulf of Gabes (Eastern Mediterranean Sea) was considered in this study. The study was carried out on a sample of 1,053 specimens of the Reticulated leatherjacket caught by trawlers and were monthly collected from May 2003 to December 2005. The length frequency distribution indicated that males are taller than females. The sex-ratio was 0.87:1 which significantly deviated from the hypothetical distribution of 1:1. The size and the season have an effect on this sex-ratio. Gonadosomatic Index (GSI%) values were highest in July for both sexes and this species accumulates energy reserves in the liver to be spent during the maturity of gonads and the spawning. First maturation occurred at 7.96 cm for females and 10.58 cm (L50) for males. The fecundity of S. diaspros ranged from 28,250 to 218,000 with a mean of 100,778.76 ± 17,702.1. The relationships between absolute fecundity and total length, eviscerated weight and weight of gonads were will described and the correlation coefficients calculated between fecundity and each of these independent variables, are judged to be either significant (R2 > 0.8) indication of a very good model for the fecundity study.

Morphometric analysis of testis cord formation in Sox9-EGFP mice.

Sox9-EGFP knockin mice were generated to label Sertoli cells and visualize testis cord formation during development. Confocal microscopy and morphometric analysis of developing cords were performed. Serial histological sections were used for three-dimensional cord reconstruction. Initially, gonad length decreased from embryonic day (E) 11.5 to E13.5, but increased thereafter, while gonad width doubled every 12 hours from E11.5 through E14.5. At E12.5, the average number of cords was 12.5, whereas this decreased to 10.4 at E13.5 and E14.5. Cord number at a given time point varied between gonads and influenced dimensions. The initial cords that formed were complex and branches were common. Time-lapse imaging revealed an intricate behavior of the Sertoli-germ cell mass and cellular exchange between connected neighboring cords. These results suggest that cord formation is a highly dynamic process that subsequently becomes refined to establish the final number of seminiferous tubule precursors.

Growth, secondary production and gonad development of two co-existing amphioxus species ( Branchiostoma belcheri and B. malayanum) in subtropical Hong Kong

The present study investigated the growth, secondary production and gonad development of two co-existing amphioxus species Branchiostoma belcheri and B. malayanum in subtropical Hong Kong from June 2005 to June 2006. Based on the modal progression analysis, amphioxus populations were decomposed into separate cohorts. The von Bertalanffy growth models were also estimated according to the size incremental data. From the growth models, the size ranges of one, two and three-year-old B. belcheri were estimated to be 5–28 mm, 28–38 mm and 38–45 mm BL, respectively; while the one and two-year-old B. malayanum were estimated to be 7–30 mm and 30–35 mm BL, respectively. The secondary production was calculated at 1.15 g m − 2 yr − 1 DW or 0.63 g m − 2 yr − 1 AFDW for B. belcheri with density 424 ind m − 2 , and 0.51 g m − 2 yr − 1 DW or 0.40 g m − 2 yr − 1 AFDW for B. malayanum with density 121 ind m − 2 . The production to biomass ratio ( P/ B) was 1.13 for B. belcheri and 0.98 for B. malayanum. Changes in the gonad length index indicated that B. belcheri spawned mainly in June and July, while B. malayanum mainly in April and August. As compared with B. belcheri, B. malayanum was characterized by rapid growth, shorter life span, early maturity and lower population density. Such differences in population dynamics may allow both species to share a similar habitat and co-exist in subtropical waters of Hong Kong.

Spatial distribution, size structure, and prey of Craspedacusta sowerbyi Lankester in a shallow New Zealand lake

The spatial distribution and size structure of the invasive freshwater jellyfish, Craspedacusta sowerbyi Lankester was measured in Lake Kainui, a shallow lake in the Waikato region of New Zealand. Population size structure conformed to a normal distribution with bell diameters ranging from 2–18 mm. Tentacle numbers were significantly correlated with medusa diameter and circumference. Similarly gonad length and volume increased with diameter, but the greatest contribution to reproductive effort was estimated to be in the 11–15 mm size range. Craspedacusta sowerbyi was present with a mean density of 12.7 per 100 l in the surface waters with highest densities at the lake surface. The distribution of C. sowerbyi along two transects showed an irregular contagious distribution with patches of C. sowerbyi recorded in open water away from the immediate littoral zones. The stomach contents of C. sowerbyi medusae included most of the taxa abundant in the zooplankton, with the exception of nauplii and small rotifers. There appeared to be a positive selectivity for the active copepod Ceriodaphnia with an estimated daily mortality rates of 3.41% of prey population compared to less than 0.5% per day for most zooplankton taxa. It seems unlikely that C. sowerbyi predation was a very significant component of zooplankton mortality in Lake Kainui but may shape the zooplankton community and availability of zooplankton prey for other predators such as fish.