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1.
Under aquaculture conditions, European eels (Anguilla anguilla) produce a high percentage of males (80–95%) that normally stop growing at 100–200 g. Females continue to grow to 500–750 g and obtain higher market value. Therefore, increasing the percentage of females in a population would be beneficial to the culture of eels. The present study was carried out in order to examine the effect of oestradiol and phytooestrogens on sex differentiation and growth rate of eels. Juvenile European eels with undifferentiated gonads were fed pellets containing oestradiol‐17β (E2) or phytooestrogens for 100–150 days. Feeding E2 resulted in 50–61% increase in body weight compared with the control. Oestradiol‐17β and phytooestrogens both elevated significantly the percentage of females in the population. Feeding E2 at 20 mg kg?1 feed resulted in 70% females, while lower concentration of E2 (2 mg kg?1) resulted in only 30% after 100 days (Experiment 1). The same dose given for 150 days (Experiment 2) resulted in 88% females, indicating that both, the concentration and duration of E2 treatments had a significant effect on sex differentiation. Fish fed genistein at 2 mg kg?1 for 100 days, resulted in 55% of females, but at a higher dose of 20 mg kg?1 there were only 15% females. These results demonstrate that phytooestrogens can be used as alternatives to gonadal steroids for sex manipulation in eels, but the optimal concentrations and duration are still to be determined.  相似文献   

2.
Female summer flounder grow considerably faster than males, and rearing temperature has been shown to influence sex differentiation in related species. The present studies were conducted to examine sex differentiation of post‐metamorphic juveniles reared at temperatures conducive for commercial production. In experiments 1 and 2, offspring produced from crosses with meiogynogenetic, sex‐reversed males and normal females were raised at 14, 16 or 18°C for ≥300 days or 12°C for 30, 60 or 120 days and then transferred to a male‐determining temperature (21°C). In all cases, the fish developed predominantly as phenotypic males (≥74%). In a third experiment, offspring produced from crosses with normal males and females were reared at 15, 17 and 19°C for 111, 227 and 278 days and then transferred to 21°C. Most fish (≥92.1%) developed as phenotypic males irrespective of rearing temperature or length of exposure. Several hypotheses are proposed for these findings and further research is necessary to understand the sex‐determining mechanisms in this species before the economic advantages associated with sexually dimorphic growth can be realized.  相似文献   

3.
Monosex male culture of C. quadricarinatus is proposed for increasing yields because males reach a larger size at harvest than females. An experiment was done to evaluate the effects of androgenic gland extract and temperature on sex reversal and somatic growth in early juvenile females. Females were exposed to the following experimental conditions: C: control food and temperature maintained at 26 ± 1°C; HT (high temperature): control food and temperature maintained at 28.5 ± 1°C; VHT (very high temperature): control food and temperature maintained at 31 ± 1°C; AG: food with enriched with androgenic gland (1/10 dose for each juvenile per day) and temperature maintained at (26 ± 1)°C. The juveniles were weighed, sexed, and growth increment (GI) and growth rate (GR) were calculated twice a month. The HT and AG groups differed from the C group in GI and GR indicating a greater somatic growth. At the end of the experiment, the HT and AG groups had similar weight but only the HT group had enhanced oocyte diameter, with some vitellogenic oocytes compared to the C group. In the HT group, there was significant sex reversal, as indicated by development of male and intersex male characteristics in different individuals. Both temperature and AG diet have a high potential for culture of this species because of their enhancement of somatic growth; higher temperature increases the proportion of males, a desirable characteristic of cultured populations.  相似文献   

4.
Catch statistics and biological data of the Japanese eel Anguilla japonica from 12 river systems in nine prefectures of Japan (36°N, 140°E–31°N, 130°E) during 1999–2004 were analyzed in order to evaluate the demography of A. japonica in Japan. Significant differences in biological characteristics of 6388 eels were found among the river systems. Fishery catches of eels in all locations have declined, but the magnitudes or patterns of decline seem to be different. Of sex-identified eels, mean total lengths ± SD (mm) of females (n = 3776) and males (n = 962) were 495.6 ± 104.3 and 412.9 ± 80.7, respectively, and overall sex ratio (% female) was 79.6 %. Mean age (years) and growth rate (mm year?1) were 5.0 ± 1.9 and 96.7 ± 38.6 for females (n = 3643) and 3.6 ± 1.7 and 120.5 ± 65.4 for males (n = 907), respectively. This study highlights the demographic heterogeneity of the A. japonica among the studied river systems, which suggests that it is important to conserve a variety of habitats in multiple river systems as an inclusive management target in addition to restoration of the diversity of habitats for eels in a single river system.  相似文献   

5.
Effects of temperature on vitellogenesis in Japanese eel Anguilla japonica   总被引：1，自引：0，他引：1  
ABSTRACT:   Cultured immature female Japanese eels acclimated to sea water at either 10 or 20°C were treated weekly with salmon gonadotropin fraction (sGTH) in order to investigate the effects of water temperature on artificial induction of ovarian maturation. In eels maintained at 20°C, ovulation was induced in 11 of 18 fish during the experimental period of 13 weeks, whereas at 10°C all fish showed a low gonadosomatic index (GSI) at the end of the experiment. Plasma vitellogenin levels were higher in eels kept at 20°C than in eels at 10°C throughout the experiment. However, no significant differences were observed in the plasma testosterone and estradiol-17β levels between groups. Eels pretreated with sGTHs at 10°C for 13 weeks were separated to two different temperature (10 and 20°C) groups, and received the same weekly sGTH injections. In eels transferred to 20°C, plasma vitellogenin levels, GSI and oocyte diameter were increased, but these values were maintained at low levels in eels that remained at 10°C. These results clearly indicate that water temperature is an important factor regulating vitellogenesis in the Japanese eel.  相似文献   

6.
Because environmental factors play an important role in the sexual proportions in fish and given that the studies that evaluate the interactions of such factors are scarce, the purpose of this work was to determine the combined effect of pH/temperature (23, 26 and 29 °C; pH 6, 7 and 8) on sex determination of Poecilia sphenops Valenciennes. The trial started with newborn organisms (n = 180) that were maintained in aquaria for 6 months until they could be separated by sex. Afterwards, nine groups of four females (0.81–1.48 g) and two males (0.36–0.63 g) were distributed in 20‐L aquaria until fertilization, gestation and offspring birth took part. The offspring were grown under the same conditions until they reached sexual maturity. The results indicated the strong interaction of the factors (P < 0.05) with a lower male/female ratio at pH 7 both at 23 °C (M/F = 0.12) as well as at 30 °C (M/F = 0.10) and higher ratios at pH 8 at similar temperatures (M/F = 0.7) to 23 °C and (M/F = 0.6) to 26 °C. The females dominated in all the combinations; the least favourable combinations were 23 and 26 °C at pH 8 with 0.7 and 0.6 M/F ratios respectively. The results obtained in the laboratory explain very closely the behaviour of the population of P. sphenops from Oaxaca in the natural environment that can be used in aquaculture for baitfish production and also for aquaculture purposes.  相似文献   

7.
Gametogenesis was monitored histologically in wild‐caught red snapper (Lutjanus campechanus, Poey) maintained in captivity under simulated natural photothermal conditions. Gonads were collected every 2–3 weeks (average n = 14) for histology during the pre‐spawning season (February to May, temperature increasing from 16°C to 24°C). Primary vitellogenic oocytes were first observed in one female when temperature reached 20°C. Subsequent samples revealed females in pre‐vitellogenesis or at early stages of vitellogenesis, although one female had tertiary vitellogenic (Vtg3) oocytes. The first histological signs of spermatogenesis were observed when temperature reached 17°C. Spermatozoa were observed in testicular lobules of all males sampled on 14 May (24°C) but little or no sperm was released during manual stripping. Ten males and 10 females were left in tanks and monitored for spawning. No egg release was observed during the monitoring period that encompassed the natural spawning season of wild red snapper. Ovarian biopsies taken during the late spawning season (16 July) revealed that four of eight sampled females had Vtg3 oocytes. Males were manually stripped but released no sperm. These results indicate that captive red snapper can complete gametogenesis in photothermal controlled systems. Additional research is needed to develop procedures that will achieve reliable maturation and spawning.  相似文献   

8.
Maturing male and female Atlantic salmon (Salmo salar L.) were held under three temperature regimes for 10 weeks between September and December: warm (constant 14–16 °C), ambient (decreasing from 11 to 5 °C), and cold (decreasing from 7 to 3 °C). Blood samples were analyzed for plasma steroid levels, and the fish were inspected for the presence of expressible milt (total volume and spermatocrit) and ovulation weekly. Samples of eggs were dry-fertilized with milt stripped from three males held at the same temperatures and incubated until the eyed stage. In females, levels of plasma testosterone (T) and 17β-oestradiol (E2) dropped as ovulation approached, concurrent with a rapid increase in levels of plasma 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P). In males, levels of T and 11-ketotestosterone (11-KT) peaked 2–3 weeks after the first appearance of expressible milt, while levels of 17,20β-P increased steadily and did not exhibit a definite peak. Exposure of females to cold water amplified and advanced the profiles of all three steroids compared with the ambient group, and increased the survival rates to the eyed egg stage. Cold water had no immediate effect on the male steroid profiles, but later, higher levels of 17,20β-P were evident compared with both the ambient controls and the warm water group, while the effects on 11-KT and T were more variable. Exposure to warm water completely inhibited both milt production and ovulation. Moreover, warm water modulated the steroid profiles of the males with lower 11-KT levels compared with ambient controls and lower 17,20β-P level compared with cold-water-treated males. In females, warm water resulted in total inhibition of the peri-ovulatory peak in 17,20β-P and prevented the normal decline of T and E2 levels associated with ovulation. The findings of the present study are highly relevant for broodstock management in aquaculture, as well in understanding the impact of climate change/temperature variability on wild salmon spawning.  相似文献   

9.
《水生生物资源》2003,16(2):90-94
In Eurasian perch (Perca fluviatilis), females grow significantly faster than males. Moreover, gonadal development has a significant negative impact on somatic growth and fillet yield. In order to induce sterility, triploidy induction was attempted by subjecting fertilised eggs to heat shocks. Different combinations of temperature (28, 30, 34, 35 and 36 °C), duration (2, 5, 10 and 25 min) and time of shock initiation (TI = 3, 5 and 7 min post-fertilisation) were tested. Flow cytometry analysis was used to assess ploidy level of control and heat-shocked larvae. Low intensity (28–30 °C) and long duration (10 and 25 min) shocks lead to significantly higher survival (44 ± 26%) and triploidisation (71 ± 26%) rates than high intensity (34–36 °C) and short duration (2 and 5 min) shocks (17 ± 19% and 21 ± 26%, respectively). The most effective conditions for efficient triploidy induction were low intensity shock of 30 °C, applied 5 min post-fertilisation for 25 min. This treatment led to the production of all-triploid populations (100%) with up to 43% survival rate.  相似文献   

10.
《水生生物资源》1998,11(5):341-345
Two experiments were developed in France to assess whether growth and processing traits differ for males and females in the European catfish, Silurus glanis. In the first experiment, fish were raised from 5 to 200 g in a pond for 7 months. A significant sex effect is demonstrated in males for live weight at the end of the experiment (males 147.5±5.4 g vs females 132.9±4.9 g) and head index (males 20.6±0.1 % vs females 21.2±0.1 %, P < 0.05). In the second experiment, fish were raised from 885±196 g to 2 266±418 g in a recirculated system at 20.7±1.4 °C for 120 days. A differential growth between the sexes is also registered. Males are heavier and longer (+ 357 g or + 17.0 % and + 6.2 % in length at day 120) and present a higher gutted weight and yield (+ 367 g or + 18.7 %; 95.0±0.9 % vs 93.8±1.8 %) and fillet weight (+ 233 g or + 20.9 %) than females after slaughter.  相似文献   

11.
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12.
The ideal water conditions for maximizing the performance of the nursery culture of glass eels harvested from the wild for aquaculture need to be determined for the New Zealand shortfin (Anguilla australis) and longfin (Anguilla dieffenbachii) eels. This study determined the survival and growth of glass eels reared under different temperature and salinity conditions in the laboratory. The growth and survival of shortfin and longfin glass eels reared in salt water (35‰) maintained at 25 °C was examined over 84 days from capture. The mean specific growth rate (SGR) was higher in shortfin [2.30±0.29% body weight (b.w.) day?1] than longfin glass eels (1.52±0.06% b.w. day?1), and survival was also higher in shortfin (76.0±4.16%) than for longfin glass eels (28.7±6.36%). A second experiment identified the effect of salinity (0, 17.5‰ and 35‰) and temperature (17.5 and 26.5 °C) on the acclimation, growth performance and survival of shortfin and longfin glass eels over a period of 84 days from capture. There was no incidence of mortality for either shortfin or longfin glass eels reared across all salinity treatments (0‰, 17.5‰ and 35‰) at 26.5 °C, while survival of shortfin and longfin glass eels reared at 17.5 °C was the highest in 17.5‰, followed by 35‰ and 0‰ treatments. Both temperature and salinity affected the SGR of shortfin glass eels, with the highest SGR observed for shortfin glass eels reared in 0‰ water maintained at 26.5 °C. In longfin glass eels, salinity alone had an effect on the SGR, with the highest SGR observed in glass eels reared in 0‰ water regardless of the water temperature (17.5 and 26.5 °C). In addition, the adaptability of glass eels to salinity was evaluated from the development and the physiological responses of gill chloride cell (CC) morphology. The number and size of CCs increased significantly with increasing salinity in both shortfin and longfin eels.  相似文献   

13.
Two adult male freshwater eels, Anguilla japonica, were captured in June 2008 in the West Mariana Ridge (13°N, 142°E) in the North Pacific, but collections of females have yet to be reported. In September 2008, we successfully caught two adult female A. japonica, 55.5 and 66.2 cm in total length, in the adjacent but northern area (14°N, 143°E). Six newly hatched eel larvae (pre-leptocephali) were also collected by subsequent plankton sampling conducted near the female catch area. Female adults appeared to be in the post-spawning state, probably a considerable time after spawning, since a small number of remarkably regressed oocytes (50–250 μm in diameter) were observed in the ovaries. Capture of post-spawning female eels and newly hatched larvae near the Suruga Seamount (14°N) together with the previous collection of mature males in the southern area (13°N) corroborates that the area along the West Mariana Ridge is the spawning area of this species, but suggests that the eel spawning may occur over a wider area than previously expected.  相似文献   

14.
ABSTRACT: Functional sex reversal of all-female nigorobuna Carassius carassius grandoculis to phenotypic males was examined by immersion exposure of fry to 17-methyltestosterone (17-MT) and controlled water temperature during early development. Fry were reared in water containing different concentrations of 17-MT at 24 and 30°C for 80 days starting 20 days after hatching. Although the fish exposed to 0.1 and 1.0 μg/L 17-MT at 24°C were all male, treatment with 10.0 μg/L 17-MT resulted in 43% females. Twenty-two percent males appeared in the control treatment at 30°C but the control at 24°C was entirely female. The proportion of males in treatments exposed to 0.01– 1.0 μg/L 17-MT at 30°C was slightly lower than in the respective treatments at 24°C. These results indicate that the phenotypic expression of sex in nigorobuna is thermolabile and that sex determination is under the control of genetic factors and temperature. Also, control of temperature during early development has been shown to be important for the production of all-female offspring for use as breeding stock for pond culture of fish suitable for preparation as 'funazushi'.  相似文献   

15.
Tilapia aurea were fed a single level of androgen-treated feed (ethynyltestosterone at 60 mg/kg of feed — ET-60) under a variety of conditions to determine the effect on sex reversal. Sex ratios were significantly altered in favor of males in 16- and 19-day treatments at 21 and 30° C; all-male populations were produced in 21- and 28-days at 21° C, but a few females persisted in the groups at 30° C. Feeding regimes of 12% body weight/day and satiation had variable impacts on growth but did not adversely affect success of sex reversal, except at higher temperatures. Because of higher metabolic rate at 30° C and the concomitant increase in appetite, a fixed level of feeding at 12% of body weight was considered to be limiting and was later increased to 15%. High stocking density (2600 fry/m2 of surface) reduced growth rate but did not affect sex reversal. A 21-day treatment with ET-60 fed at 15% body weight/day at water temperatures between 21 and 30° C should consistently produce all-male populations of T. aurea at stocking densities up to 2600 fry/m2.  相似文献   

16.
ABSTRACT

An experiment was conducted to evaluate the spawning performance and egg quality of Clarias batrachus at variable latency periods (11, 14, 17, 20, and 23 h) and doses of carp pituitary extract (10, 20, 30, 40, and 50 mg/kg). The fish could not be stripped at 11 h latency with 10 or 20 mg carp pituitary extract (CPE). The highest quantity of eggs was obtained at 14 to 23 h latency with 30–40 mg CPE or 50 mg CPE with 14 to 17 h latency, which did not vary significantly (P < 0.05) at a water temperature of 27°C–28.5°C. The eggs did not fertilize and hatch when stripped at 11-h latency period. Over 80% of total eggs stripped from females injected with 30 and 40–50 mg CPE per kg body weight, and stripped at 14 to 23 h and 14- to 17-h latency, respectively, were fertilized. However, the highest (P < 0.05) number of larvae was obtained from females injected with 40 mg CPE and stripped at 14 or 17 h latency periods. Therefore, this CPE dose and 17 h latency period combination was regarded as the best for obtaining the highest number of larvae during induced spawning of C. batrachus.  相似文献   

17.
The rice field eel, Monopterus albus (Zuiew), is an important aquaculture fish in many Asian countries. Productivity, however, is limited by low fecundity as a result of sex reversal of female juveniles of this fish. This study was conducted to investigate the effects of estradiol valerate on the sex reversal process of this fish by determining sex changes of initial 2‐yr‐old female eels (26.5 ± 2.6 cm, 21.9 ± 2.1 g) treated with three concentrations of estradiol valerate: 0 mg/kg (Control, Group A), 10 mg/kg (Group B), and 50 mg/kg (Group C). In Group A, sex reversal took place with significantly higher percentage of sex change: about 45% of female eels to intersexes and males. Only about 22% of female eels changed to intersexes and males in Group B, but no sex reversal occurred in Group C during the experimental period. The result also indicated that the gonadal development and the concentrations of serum estradiol (E2) and testosterone (T) varied significantly with different concentrations of dietary estradiol valerate. Serum T significantly reduced but serum E2 significantly increased in Group C compared to the control Group A. The results demonstrated that estradiol valerate affected the secretion of sex steroid hormones in rice field eels and thus inhibited the sex reversal process at a low concentration (10 mg/kg) or stopped the sex reversal process at a high concentration (50 mg/kg) of estradiol valerate. These results suggest that a higher yield of mature female eels could be achieved by treatments with estradiol valerate, thus enhancing the fecundity of this rice field eel.  相似文献   

18.
The preferred temperature (PT) of Poecilia sphenops (Pisces, Poeciliidae) (n = 240; 1.13 ± 0.06 g wet weight; 3.26 ± 0.88 cm standard length) from Presa Piedra Azul, Oaxaca, Mexico, was measured at acclimation temperature of 20 °C, 23 °C, 26 °C, 29 °C, 32 °C and 35 °C. The thermal preference of males was 25.5 °C in summer and 29.6 °C in winter; whereas females preferred 29 °C in both seasons. Fish held at 20 °C and 23 °C preferred temperatures 36% higher than their acclimation temperature (AT), and those held at 35 °C and 32 °C preferred 30% and 20% lower temperatures than their AT. In intermediate temperatures, no significant differences between PT and AT were found. The interval of thermal selection based on the higher (HAT) and lower (LAT) avoidance temperatures was of 10–14 °C and not different between sexes in both seasons. Knowledge of the thermal biology of P. sphenops based on the preferred and avoidance temperatures was very important in order to understand the capacity of the species to adapt to the thermal changes occurring in its habitat. Based on the results, we can recommend the use of P. sphenops in aquaculture owing to its thermal plasticity.  相似文献   

19.
《水生生物资源》1999,12(2):151-154
Observations were made in Senegal between 1997–1998 on the length of embryonic development in Octopus vulgaris. The data were from eggs which had been laid by two females in the open sea and fourteen females in concrete tanks. The observations in natural surroundings are the first concerning this species. Hatching occurred after 15–42 d at 27 °C, 29–49 d at 22–23 °C, 57–65 d at 21 °C and 80–87 d at 17 °C. These values are higher than the few data previously recorded in European aquariums, particularly for temperatures under 20 °C.  相似文献   

20.
To determine the optimum temperature for growth of the endangered intertidal purple snail Plicopurpura pansa (Gould 1853) (Prosobranchia, Muricidae), 731 adult specimens were reared in the laboratory on squid for 86 days at temperatures ranging from 20 to 32°C. The snails showed extremely slow growth, if at all. Males and females raised at 26°C grew the fastest, an average of 0.85 and 0.43 mm respectively. No statistically significant differences were observed at other temperatures or between males and females. The best temperature for growth for the intertidal purple snail appears to be in the range between 26 and 30°C.  相似文献   

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