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1.
Abstract— The broad-finned galaxias, Galaxias brevipinnis , spawned during high flows in mid autumn. Spawning took place over inundated riparian areas where eggs were laid amongst substrate, mainly in the interstices of cobbles and pebbles. Between subsequent high flows, eggs were out of water for days or weeks, lying up to 7 m from the water's edge. When exposed, eggs and streamside substrate remained damp, shaded by surrounding forest. Hatching would only occur when eggs were inundated by a subsequent flood. In the field, most eggs had hatched within 30 days of the spawning period, but some remained unhatched for up to 60 days. In the laboratory, eggs remained unhatched for up to 57 days under moist conditions but out of water, and up to 120 days when kept in water. However those kept under drier conditions died. It would appear that riparian cover may be important in providing shaded and moist conditions for the survival of eggs in the wild. Evidence of some adult mortality following spawning was noted. Newly hatched larvae were carried to sea during high flows. Predation on eggs by both adult G. brevipinnis and introduced brown trout Salmo trutta Linnaeus was found to occur.  相似文献   

2.
This paper describes the relationship between the egg vitamin concentrations and the egg quality in the Japanese eel Anguilla japonica . No notable relation was found between any vitamin and the fertilization rate. Hatching and survival rates of larvae, however, significantly increased with an elevated level of egg vitamin C (VC). In contrast to VC, the relation between vitamins E (VE) and A (VA) concentrations and survival rate showed a clear peak, with a reduced survival rate at both higher and lower vitamin concentrations. The ratio of VE to lipid or highly unsaturated fatty acid (HUFA) in eggs positively correlated with hatching and survival rates of larvae. High-quality (HQ) eggs were determined as eggs that produced larvae having a survival rate higher than 80% at 8 days post hatch, and low-quality (LQ) eggs were determined as eggs that did not hatch. The level of VC of HQ was significantly higher than LQ. The results of this study suggest that HQ eggs, which produce larvae having a high survival rate, must have high levels of VC and VE/HUFA ratio and contain optimum levels of VA and VE in Japanese eel.  相似文献   

3.
Abstract – There is a strong, positive correlation between egg size and the discharge variable mean annual runoff among populations of Cyprinella venusta Girard from streams in different drainages ranging across the Gulf Coastal Plain of the southern United States. This variation may have resulted from selection for larger egg size, hence larger offspring size, because of greater environmental fluctuation or a greater number of floods in streams with higher runoff. In the present study, we examined C. venusta from populations inhabiting streams varying in mean annual runoff within a single drainage and found a similar correlation between ovum size and runoff. Therefore, the egg size–runoff relationship exists at a much smaller (i.e., intra-drainage) spatial scale than previous research (based on widespread inter-drainage variation) has shown. We also attempted to establish a link between mean annual runoff and streamflow-mediated disturbance as indicated by predictability of streamflow, monthly coefficients of variation in discharge and number of days with extreme low and high flows. Although the overall predictability of discharge did not differ among streams, the streams with high mean annual runoff were characterized by smaller coefficients of variation in winter, fewer days of extremely low flows and a trend toward higher flows in late summer and early fall. At the intra-drainage scale, higher coefficients of variation did not accurately reflect the numbers of extreme flows. These results call into question the use of coefficients of variation in discharge as indicators of disturbance. Given that eggs, larvae and small juveniles of C. venusta are present in late summer and early fall, when flows in high runoff streams tend to be high relative to low runoff streams, we conclude that these high flows may act as a selective force causing the evolution of larger egg size.  相似文献   

4.
The collection of fertilized eggs for mass culture of Pacific bluefin tuna (PBT) relies on the spontaneous spawning of broodstock in captivity, and the spawning season of the broodstock is generally from mid‐May to September. The diameter of fertilized eggs from the broodstock decreases during the spawning season. To investigate the influence of three potential factors, the egg diameter (larger or smaller), the rearing water temperature (25 or 28 C), and the aeration rate during the night (strong or weak), on early survival and on growth of PBT larvae, replicate trials were conducted to assess these three factors until 7 d after hatching (d.a.h.). At 7 d.a.h., survival rates of larvae reared with strong nighttime aeration were found by a three‐way ANOVA to be significantly higher than for larvae reared with weak aeration. Furthermore, growth rates of PBT larvae hatched from larger eggs were significantly faster than those from smaller eggs. However, a significant difference in the survival rate was not detected for the factors, egg diameter and rearing water temperature. The results indicate that rearing with strong nighttime aeration significantly improved the early survival of PBT larvae and the egg diameter (a proxy for egg quality) and influenced growth.  相似文献   

5.
Low survival of vendace (Coregonus albula) eggs incubating on natural spawning grounds (due to silting, oxygen deficits and action of predators) is discussed as one of the reasons for the great fluctuation in numbers of commercial fish. Incubation of eggs in hatcheries where the survival rate averages 60% could compensate for the great numerical disparity between the eggs spawned naturally and those taken for hatcheries. In the absence of the effects of mass stocking of lakes with vendace larvae, one can conclude that apparent mortality during the larval stage also determines the strength of the successive year-class.Vendace larvae are usually stocked immediately after the ice cover recedes from lakes. At this time they often face a period of cold weather when water temperature is low and food organisms are scarce. Poor environmental conditions cause slow growth of larvae. This increases the period of highest vulnerability of the larvae to predation.It is possible to accelerate the growth of larvae by synchronizing the time of stocking with the development of favourable thermal conditions and food availability in lakes. In Polish climatic conditions the first 10 days of May seem to be a suitable time for stocking lakes.A technique for delaying vendace egg hatching by cooling the hatchery water has been developed. It enables hatching of vendace to be delayed from the beginning of April until the beginning of May, thereby inducing mass hatching of larvae when lake conditions are optimal for stocking.  相似文献   

6.
Fish differentially provision resources to eggs and larvae to optimise survival during the critical early life‐history period. Resource allocation is limited by a trade‐off between egg size and fecundity, and the optimal strategy varies with habitat type. This study examines the consequences of egg size differences for the early life‐histories of four closely related galaxiid species which occur in contrasting habitat types on the South Island, New Zealand. Headwater species had substantially larger water‐hardened eggs, longer incubation times, and newly hatched larvae were on average up to 41% longer than lower catchment species. Significant interspecific differences in gape diameter, eye diameter and myomere depth were also observed. Swimming ability was positively associated with larval length at hatch. Interspecific differences in length and swimming ability were generally maintained throughout the larval period, despite larvae being reared under relatively benign conditions where many other studies suggest initial differences should disappear. These results demonstrate the consequences of differential maternal provisioning to the egg for larval traits. The larger larvae of headwater species are likely to be more resistant to starvation and have improved foraging ability compared to lower catchment species; traits which are likely to confer them survival advantages in the low productivity, food‐scarce environments they occupy. The smaller larvae of lower catchment species are likely to be a consequence of females investing in fecundity in these relatively resource‐rich streams.  相似文献   

7.
Samples of halibut eggs in nature have led to theories that development occurs near the sea bed and, alternatively, well up in the water column. Resolution of the conflicting theories and information which should assist culturists in providing the proper environmental conditions for egg development and hatching were the subjects of this study. The neutral buoyancy salinity (NBS) of Pacific halibut eggs and larvae ranged between 29.8–34%. Eggs and larvae with higher NBS (> 35%) were usually abnormal or stressed. Thus, eggs found near the seabed may be nonviable.  相似文献   

8.
The effects of four light intensities on growth and survival of first‐feeding stage black sea bass larvae Centropristis striata were investigated in a controlled‐environment laboratory. Fertilized eggs, obtained from LHRHa‐induced spawning of captive broodstock, were stocked (72 eggs L?1) into twenty 15 L black tanks under light intensities of 100, 500, 1000 and 1500 lx, with five replicate tanks per treatment. The photoperiod was 12L:12D, the temperature was 20°C and the salinity was 35 g L?1. Larvae were fed rotifers Brachionus rotundiformis from day 2 post‐hatching (d 2ph) at 5–10 rotifers mL?1. Microalgae Nannochloropis oculata and Isochrysis sp. were added (1:1) daily to maintain a density of 300 000 cells mL?1. Hatching success and larval growth and survival from d 2ph through d 15ph were monitored. Hatching success was 28–38% under all light intensities, and notochord length at hatching ranged from 2.8 to 3.0 mm, with no significant differences among treatments. By d 15ph, growth (mg wet weight) was significantly higher in the 1000 lx (0.914) and 1500 lx treatments (0.892) than in 100 lx (0.483), and a highly significant trend (P<0.01) towards increased survival with increasing light intensities was observed, from 1.3% at 100 lx to 13.9% at 1500 lx. Higher light intensities within the range of 100–1500 lx improved growth and survival of early larval black sea bass, suggesting that even higher light intensities may improve culture performance. This is consistent with conditions in shallow, near‐shore locations where eggs and larvae are distributed in nature.  相似文献   

9.
The efficacy of iodine and glutaraldehyde as fish egg surface disinfectants were assessed in red porgy (Pagrus pagrus) and white sea bream (Diplodus sargus sargus) eggs, two species of interest for Mediterranean aquaculture. Iodine was effective in reducing the bacterial load of the 1-day-old eggs when applied at 50 mg L−1 for 5 min. The same concentration did not cause any significant change in hatching success or survival of the larvae for the first 5 days. Glutaraldehyde failed to reduce the bacterial load of the fish eggs at concentrations that were safe for the eggs (100 mg L−1 for 5 min), as it had a significant effect in preventing hatching of the developed embryo. Disinfecting 0-day-old eggs with iodine resulted in a significant reduction of hatching percentage, while larval survival thereafter was unaffected. The results of the present study suggest that iodine may be an appropriate egg disinfectant for both red porgy and white sea bream.  相似文献   

10.
Fish eggs and larvae are often subject to very high mortality, and variation in early life survival can be important for population dynamics. Although longnose suckers (Catostomus catostomus) are widespread in northern North America, little is known about their early life history. We examined fecundity and early larval survivorship during sucker spawning events in three small Lake Michigan tributaries. Although egg deposition varied 25% among spawning events, estimated larval export to the lake varied over 25,000‐fold from around 1000 to 26 million. Based on variation in environmental conditions across years, it appears that spring flow and temperature may be important determinants of egg survival to larval outmigration. Larval age data suggest that most individuals that survived to outmigration hatched during a 2‐day period despite adult spawning across at least 10 days. Most larvae spent <2 weeks in the stream and emigrated around the time of transition from endogenous to exogenous feeding before substantial growth occurred. In two of three cases, larvae drifted exclusively at night; however, high drift rates occurred during both day and night in the case where larvae were very abundant, suggesting density‐dependent drift behaviour. Our results indicate that survival in tributary streams from egg deposition to larval export is highly variable in longnose suckers. These large differences in early life survival may translate into variability in recruitment, thereby influencing population structure and dynamics.  相似文献   

11.
Along the Atlantic coast black sea bass occur from the Gulf of Maine to Florida and support important commercial and recreational fisheries. Interest in commercial production of black sea bass has increased in recent years due to high demand and limited seasonable availability. Efforts towards large-scale production have been hampered by a high incidence of early larval mortality. Two of the most important environmental variables affecting hatchery production of marine finfish larvae are temperature and salinity. In the wild, larval black sea bass are found in waters with temperatures of 12–24 C and salinity levels of 30–35 ppt. Studies were conducted to define the temperature and salinity ranges that support growth and development of black sea bass during early life stages. Three developmental phases were investigated: 1) fertilization to hatch: 2) hatch through yolk sac absorption: and 3) during the initial exogenous feeding stage (5–14 days post hatch: DPH). Fertilized eggs were obtained by manual spawning of fish following administration of LHRHa. Fertilized eggs were transferred to 300-mL glass Petri dishes or 500-mL beakers to assess the effects of salinity and temperature through hatch and yolk sac absorption, respectively. To determine environmental effects on growth and survival during initial exogenous feeding 400 actively feeding larvae were cultured in green water and fed enriched rotifers for a 9-d period. For investigation of the effect of salinity, sea water (35 ppt) was diluted gradually to 15, 20, 25, and 30 ppt and maintained at 21 C. For examination of the effect of temperature, seawater was adjusted from 21 C to 12, 15, 21, 27, or 30 C at a rate of 3 C/h. No eggs hatched at 12 C or when salinity was maintained at 0 or 5 ppt. Hatching was uniformly high (≥ 85%) at temperatures between 15 and 27 C and at salinities ≥ 15 ppt. Survival through yolk sac absorption was greatest at temperatures between 18 and 27 C and at salinities ≥ 20 ppt. Survival through first feeding stage was highest at temperatures ≥ 18 C and 30 ppt salinity. Larval growth through first feeding was not significantly affected by salinity level but did increase with rearing temperature. The results indicate that survival and development of black sea bass during early life stages are most favorable at temperatures >18 C with salinity levels approaching full strength seawater.  相似文献   

12.
The effects of temperature and salinity on the embryonation period and hatching success of eggs of Benedenia seriolae were investigated. Temperature strongly influenced embryonation period; eggs first hatched 5 days after laying at 28 degrees C and 16 days after laying at 14 degrees C. The relationship between temperature and embryonation period is described by quadratic regression equations for time to first and last hatching. Hatching success was >70% for B. seriolae eggs incubated at temperatures from 14 to 28 degrees C. However, no B. seriolae eggs embryonated and hatched at 30 degrees C and <2% of eggs hatched when incubated at 24 degrees C after transfer to 30 degrees C for 48 h. Embryonation period was similar for eggs incubated in sea water at 25, 30 and 35 per thousand salinity, but increased for eggs incubated at higher or lower salinities. When incubated at salinities ranging from 25 to 45 per thousand, more than 70% of B. seriolae eggs embryonated and hatched. Hatching success was lower at 20 and 50 per thousand salinity and few or no eggs hatched at 10 and 15 per thousand. Hatching of B. seriolae eggs can be prevented by desiccation for 3 min, by immersion in water at 50 degrees C for 30 s or by treatment with 25% ethanol for 3 min.  相似文献   

13.
Variable quality and yield (percentage development from eggs) D-veligers of the scallop, Pecten fumatus Reeve, prompted assessment of fertilization and incubation protocols. Various sperm to egg ratios were tested on eggs suspended in sea water at different densities. Ratios of 1000:1 led to the highest D-veliger yield when eggs were incubated in suspension at one per millilitre. With increasing egg densities, the addition of 1000 sperm per egg led to increasing average numbers of sperm visible at the periphery of each egg, indicating that fewer sperm were necessary for fertilization at higher egg densities. The time period and temperature over which released gametes were stored before fertilization were also found to significantly affect D-veliger yield. Decreasing gamete storage temperature from 26 to 14oC increased D-veliger yield, as did a reduction in the gamete storage period from 6 to 1 h. The incubation of embryos at densities in the 5-50 ml-1 range did not affect D-veliger yield. A significant increase in total bacterial counts in the culture water occurred with increasing embryo stocking densities. However, presumptive Vibrionaceae counts did not increase significantly with increasing embryo stocking densities. In a comparison of the viability of self- and cross-fertilized embryos and larvae, fewer self-fertilized embryos developed to D-veliger stage; however, percentage survival, although highly variable, did not differ significantly in subsequent larval rearing. Cross-fertilized larvae had attained a significantly larger size by day 7.  相似文献   

14.
This study assessed the effect of immersing striped trumpeter eggs in 0 (control), 200, 400, 800, 1600 or 3200 ppm glutaraldehyde for 10 minutes, two days before hatching. High concentrations of glutaraldehyde (1600 and 3200 ppm) resulted in no eggs hatching and only 1% of eggs hatched after treatment with 800 ppm glutaraldehyde. Hatching success of eggs treated with 0, 200 or 400 ppm glutaraldehyde did not differ (77 ± 6%, n = 3). However, only 2% of larvae from the control treatment survived to day 5 post-hatching, compared to 45 and 69%, respectively of the larvae from the 200 and 400 ppm glutaraldehyde treatment. By day 9 post-hatching, larvae from the 400 ppm glutaraldehyde treatment had significantly higher survival (59%) than larvae from the 200 ppm glutaraldehyde treatment (28%). Thiosulphate citrate bile salt sucrose agar (TCBS) medium confirmed the presence of bacteria within the seawater medium, on all control eggs and on 83% of eggs disinfected with 200 ppm glutaraldehyde, but no bacterial colonies formed on eggs treated with 400, 800, 1600 or 3200 ppm glutaraldehyde. This study found highest survival of striped trumpeter larvae from eggs disinfected with 400 ppm glutaraldehyde and suggests that increased survival was a result of reduced bacterial loading.  相似文献   

15.
Immunological detection of yolk protein was used to assess predation by pelagic amphipods (gammarid and hyperiid), mysids, and euphausiids on eggs and yolk-sac larvae of walleye pollock Theragra chalcogramma during 1988 and 1989. Consumption estimates were made on the basis of frequency of positive immunoassays, assay detection times (gut clearance time), predator abundance, and spatial overlap of predators and prey. From our results gammarid amphipods and euphausiids were important predators on eggs and yolk-sac larvae, respectively. Gammarid amphipods alone consumed about 14% of the standing stock of pollock eggs in 1989. These results were compared with those from clearance rate experiments of predators feeding on pollock eggs in 300-1 bags. In general, clearance rate estimates of egg consumption were lower than those determined from gut contents.  相似文献   

16.
ABSTRACT:   To determine an optimal temperature range for efficient production of healthy eel larvae Anguilla japonica , the effect of water temperature on hatching, survival, and deformity rates was examined. The early ontogeny of morphological features in this species by incubating eggs at five different temperatures (19, 22, 25, 28 and 31°C) was examined. Hatching occurred at 24, 28, 46 and 58 h after fertilization when incubated at 28, 25, 22 and 19°C, respectively; no eggs hatched at 31°C. The growth rate of prefeeding larvae increased as water temperature was elevated and acquisition of feeding ability was also accelerated at higher temperature. Significantly high hatching rates (76–86%, P  < 0.05) and survival rates (61–86%, P  < 0.05) were observed at relatively high temperatures (22–28°C). The deformities were 'open lower jaw', 'pericardial edema', and 'notochordal bending', in which the mouth was deformed with a downward projecting lower jaw, the pericardial cavity was swollen, and the notochord was bent or twisted to various degrees, respectively. Open lower jaw and pericardial edema were especially predominant at 19°C, with rates of 68 and 92%, respectively, compared with 31 and 10% at 25 and 28°C, respectively. The occurrence of notochordal bending was not affected by temperature. The optimal temperature for incubation and rearing A. japonica eggs and prefeeding larvae is approximately 25–28°C.  相似文献   

17.
Hatching rates and hatching times (50% hatch) of red sea bream, Pagrus major (Temminck & Schlegel), eggs in culture media that were prepared to dilute rotifer Brachionus plicatilis Muller extract at 4000-, 6000-. 8000- and 10 000-fold with artificial sea water (σ15, = 24.0) were investigated. Although differences in hatching rate between the culture media and control artificial sea water were negligible, hatching time was significantly shorter in media at 4000- and 6000-fold dilutions than in media at 8000- and 10 000-fold dilutions and in the control artificial sea water, when the eggs immediately post spawning were incubated. The hatching rates of eggs at three developmental stages, immediately post-spawning, gastrula stage and heart-beat initiation stage, incubated respectively in the medium at 6000-fold dilution and the control, did not differ either, yet the hatching times at each egg stage in the medium were significantly shorter than that in the control. These results suggest that hatching enzyme secretion from the hatching glands is promoted to perceive chemical stimuli in the water-soluble fraction of rotifer extract via the embryo's chemoreceptors, from the heart-beat initiation stage to immediately before hatching, thus shortening the hatching time.  相似文献   

18.
Abstract The production of viable larvae is critical to any aquaculture venture. Since lipids are important components of fish eggs, the amount and nature of the lipid may be crucial to the survival of the larvae. In this study the lipid content of unfertilized eggs from first-time and repeat spawning Atlantic halibut females was compared. The egg lipid content for the first-time spawner ranged from 0·18 to 0·41mg/egg; the range for the repeat spawner was 0·27 to 0·38mg/egg. However, the mean total lipid per egg values were similar for both fish at ca. 0·31mg/egg. The repeat spawner prodticed more eggs than the first-time spawner, thus allocating more lipid to egg production. In the eggs from the two fish 62–84% of the lipids was phospholipid.  相似文献   

19.
Wolffish, Anarhichas lupus L. has internal fertilization. The eggs are released into water before the beginning of cleavage and stick together in clutches. To develop methods for separating eggs for subsequent incubation, changes during egg swelling and egg shell hardening were observed. Uninseminated eggs did not swell in ovarian fluid, but a perivitelline space formed in sea water because of a partial cortical reaction. In inseminated eggs kept in ovarian fluid, a cortical reaction took place and swelling was caused by elevation of the yolk membrane. Shrinkage of the yolk and absorption of water were observed after inseminated eggs were placed in sea water. Eggs swelled in ovarian fluid diluted by less than 30% sea water showed abnormal cleavage during subsequent development. An effective method for preventing egg stickiness after fertilization was to distribute them in trays with stagnant sea water for at least 5-6 h. Milk was effective for loss of egg adhesiveness at 50% concentration, but some eggs cleaved abnormally and subsequent mortality was high. The influences of ovarian fluid and milk on initial egg development with respect to peculiarities of egg swelling are discussed.  相似文献   

20.
Eggs of spotted wolffish (Anarhichas minor Olafsen)were incubated at constant 4, 6 and 8 °C, and disinfected withglutaric dialdehyde (150 p.p.m. for 5 min) once ortwice a month during two thirds of the incubation period, to prevent growth ofmicroorganisms. Hatching of apparently normal larvae started earlier when eggswere disinfected twice a month compared to once a month at all incubationtemperature regimes. The time to 50% hatch was 900 and 920 day-degrees (16 and16,5 weeks) at 8 °C, 835 and 880 day-degrees (20 and 21 weeks)at 6 °C and 725 and 800 day-degrees (26 and 28,5 weeks) at 4°C, in the egg groups disinfected twice or once a month,respectively. The best survival until hatching was noted when eggs weredisinfected twice a month and incubated at 6 and 8 °C.Survivalwas very low at 4 °C. Prematurely hatched larvae wereregistered in all egg groups disinfected twice a month and the highestfrequencywas noted in the 8 °C groups. The larval weight at normalhatching in the 6 and 8 °C groups was negatively correlatedwith incubation temperature and intervals of disinfection during the incubationperiod, but after 42 days feeding with live feed (unenrichedArtemia) the weights of the larvae were not significantlydifferent. The specific growth rates of the larvae from the eggs incubated at 6°C and 8 °C were 3.0% and 3.2%, respectively.The mean survival of larvae was between 88% and 96% at 42 days post-hatching.Young wolffish originating from the 6 °C incubation groupsshowed lowest mortality.  相似文献   

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