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1.
在盐度２４－２７‰的海水中，用大小不同的网箱对不同规格欧洲鳗进行了不同的养殖密度的生长比较。结果表明，欧洲鳗在海区网养养殖条件下可以正常摄食生长，６０天饲养期最高产量达６１．８ｋｇ／ｍ＾２，增重量达３４．５ｋｇ／ｍ＾２，增重率为１２６．６％，在一定范围内密度、网箱大小对其生长速度无明显影响，大体上体小的鳗种，生长速度快，但２５ｇ／尾以上鳗鱼，增重率上的差异并不明显。  相似文献   

2.
Various body dimensions were measured in relation to weight in warm-water cultured European eels (0·2–120 g) at 16 and 25°C in seawater and at 25°C in freshwater to provide reference standards for use in aquacultural engineering management and research. The different conditions had no significant effects on relationships between weight and body, head or tail length, or trunk, head or pectoral dimensions. There were also no significant differences between small and large eels and no obvious variations were found that could be used to distinguish the sexes. However, the eyes tend to enlarge and the mouth decrease in size relative to weight in larger eels. Possible relationships between morphology and feeding are discussed.

The combined data yielded the relationship, log L(cm) = 1·0306 + 0·27 log W(g) for eels from elver stage up to about 120 g. A condition factor, CF = L/10 W0·2711, is derived and its usefulness in aquaculture and research discussed. Morphometric and growth differences between cultured and wild eels are discussed.

Body girth dimensions are considered and recommendations made for mesh apertures and bar spacings for basket and grid size-graders.  相似文献   


3.
Abstract. Ammonia excretion rate of the marine bivalve Tapes decussatus (L.) varied with body weight, temperature and starvation. There was a steady state in the excretion rates, in which these rates neither increased nor decreased during the first 6 days of starvation. The highest rates of ammonia excreted during the steady state (before decline to lower level) depended on the temperature (715 ± 86 and 395 ± 55 μg NH4.N/clam/h × 10−2) at 28°C and 20°C, respectively. At 16°C, the steady state extended from 6h to 18d starvation. Ammonia excretion rates were higher for starved clams than for fed clams at all sizes, e.g. clams of 0·07 g dry flesh weight (28 ± 9 and 13 ± 5 μg NH4.N/clam/h × 10−2 respectively) at 16°C but not at 20°C and 28°C. At each temperature, weight-specific ammonia excretion rates were related to dry flesh weight of starved clams but were not related to fed ones.  相似文献   

4.
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   

5.
Abstract. Field-caught fry of the common wolfish, Anarhichas lupus L., and the spotted wolffish, A. minor Olafsen, were reared on a commercial dry pellet. Both species experienced the same environmental conditions, including an annual fluctuation in temperature from 5·8 to 13·7°C. The spotted wolffish reached 1·58 kg in 2 years from hatching, more than four times the weight of common wolffish (0·37kg). Analysis showed that for both species the specific growth rate decreased with increasing fish size and increasing temperature. Estimates, based upon optimum conditions, indicate that the spotted wolffish would reach a total wet weight of 5 kg (<7°C) in 2 years from hatching, and the common wolffish (7–9°C) a total wet weight of 2·5kg within that same period. Female common wolffish matured at a weight above 0·5kg, whereas those of the spotted wolffish matured at a weight above 2·5kg. The spotted wolffish had a significantly higher fillet proportion (∼50%) than the common wolffish (∼45%) and a significantly lower hepato-somatic index (3·7% and 5% respectively).  相似文献   

6.
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   

7.
Abstract. Four feeding trials with Israeli carp, Cyprinus carpio L., were performed in cages or in ponds in order to investigate responses to lysine supplementation of low protein carp feeds under different practical conditions. In each of the trials one of the basic conditions was different: fish size—small (80–125g) or large (560g); temperature—22°C or 26°C; density—cages or ponds. In each trial 2–3 ration sizes × 2–3 lysine levels were tested. A basal diet of 25% protein and 1·35% lysine served for all the trials.
At low feeding levels, no responses to lysine supplements were found either at 22 ± 2°C or at 26 ± 2°C (0600 h) for all fish sizes. At higher feeding levels, at both temperatures, 0·5% lysine-HCl supplements to 1·7% total lysine yielded significant growth increases. Further supplements to 2·1% lysine (=8·4% of the protein) brought an additional response only from small fish of 90g in cages at the highest ration and temperature. In ponds at 26°C, the effects on small fish of 80g were smaller, probably due to available natural food. The reduction in lysine retention suggested that 1·7% lysine might have been adequate even at optimal conditions in ponds.  相似文献   

8.
Abstract. The eggs and yolk sac fry of the mouth brooding tilapia. Oreochromis mossambicus (Peters), were artificially reared in an experimental hatchery system at different temperatures. The hatchability, embryonic development of eggs and growth of yolk sac fry were studied under controlled conditions. It was shown that the upper lethal temperature for O. mossambicus eggs was above 40°C and the lower lethal temperature between 11°C and 17°C. For yolk sac fry these values lay between 34 and 40°C and 17 and 20°C respectively. Fry survival between 24·3 and 34·0°C was near to 100% while al 20°C it was less than 60%. The somatic growth rates of fry at temperature between 20 and 34·5°C up to 10 days post hatch are presented and were found to differ significantly. At 34·6°C a negative SGR was recorded during the period 6–9 days post hatching, but, during the first 6 days, the SGR at this temperature was more than four times higher than at 20°C. At the elevated temperatures, the utilization of yolk is faster and the loss of weight observed was due to starvation. This should be taken into account when incubating under artificial rearing condition so that initiation of exogenous feeding is timed most appropriately.  相似文献   

9.
Abstract. Chinese catfish, Clarias fuscus (Lacepède), within three size ranges were evaluated for growth, survival and feed conversion ratios (FCR). A 4 × 3 factorial design was used during year-long trials which included four temperatures (20,25,30 and 35 °C) and three feeding rates with commercially formulated salmon/trout feed. Specific growth rates of juvenile fish (1–60g) were highest, ranging from 1–64% body weight/day at 20°C (2%/day feed rate), to 4–94%/day at 25°C (6%/day feed rate). Specific growth rates of sub-adult fish (60–150g) averaged 0–65%/day, with no significant difference between temperature-feed rate treatments. Specific growth rates of adult fish (>150g) were lowest, averaging 0–30%/day for grouped feed rate treatments at 25°C, and 0–16%/day at 30°C. Most mortalities occurred during the juvenile stage, with survival ranging from 0% at 35°C(2% feed rate) to 96% at 30°C(6% feed rate). Survival was 95–100% with sub-adults and adults. FCR were 1 to 4 with juveniles, 2 to 12 with sub-adults, and 3 to 22 with adults. These trials suggest that optimal growth and FCRs were obtained at 25°C; with feed rates of 6%/day with juveniles, 2%/day with sub-adults, and 1%/day with adult fish. Final yields at 25 and 30°C indicate that even though growth and FCR are optimal at 25°C, survival was greater at 30°C, which compensated for reduced growth performance at this temperature. Yields at 25 and 30°C were almost double those at 20°C.  相似文献   

10.
Four experimental growth studies for juvenile Atlantic surfclams, Spisula solidissima solidissima and Spisula solidissima similis , under hatchery conditions were conducted in 10-cm diameter forced-flow upweller units. Experiments were designed to determine optimum food ration (2%, 5%, and 8% g dry weight of algae/g wet weight of clam), water culture temperature (20, 25, and 30°C), flow rate (2, 4, and 6 Lpm), and stocking density (7, 14, and 21 g wet weight of clams) for rearing juvenile clams in upweller units. Each experimental trial was performed for a 14-d period. Nested Analysis of Variance showed that juvenile surfclams Spisula solidissima similis grew significantly faster at a temperature of 20°C and food rations of 5 % and 8%. In all four experiments, clam mortalities were not observed except in the temperature experiment, where total mortality occurred for clams cultured at 30°C. Clam growth in biomass and size decreased significantly with increases in culture temperature. For Spisula solidissima solidissima , clam growth was significantly reduced in terms of size and biomass at a flow rate of 6 Lpm. No difference in size or biomass was determined between clams grown at a flow rate of 2 or 4 Lpm. Surfclams at the lowest stocking density of 7 g wet weight significantly increased more in net biomass compared to those at higher stocking densities. Clams were significantly larger in shell length when grown at the two lower stocking densities compared to those at the highest stocking density. Hatchery-rearing protocol for juvenile surfclams is discussed.  相似文献   

11.
The growth and mortality of Neptunea arthritica juveniles hatched from different egg masses (controlled conditions and field) reared at 10 and 15 °C, and provided with sardine (D1) and polychaete (D2) as foods were evaluated. Results showed that diet type and water temperature significantly affect the growth and mortality. Interaction between these factors reflected robust relationship among them, but restricted exclusively to growth. Through the study period, juveniles treated at 10 °C showed maximum increments of 2.5 mm (shell length), 2.3 mm (shell width) and 0.25 g (body weight) from their initial size. While maximum values of those treated at 15 °C for the above-mentioned parameters were 7.6 mm, 5.5 mm and 1 g respectively. In both cases, these increments were recorded for individuals fed with sardine. Mortality was significantly affected by diets and water temperature, which significantly increased under D2 [10 °C (20–67%), 15 °C (70–87%)] or 15 °C [D1 (30–83%), D2 (70–87%)]. According to the results, juveniles of N. arthritica could be maintained under controlled conditions, which allows growth improvement. Mortality appears to be the limiting factor, but this could be improved by the implementation of efficient culture method, basically oriented to increase the water quality.  相似文献   

12.
Abstract. Oocyte maturation, ovulation and spawning were successfully achieved in the African catfish, Heterobranchus longifilis Valenciennes, using frog pituitary extract. During artificial spawning, oocyte maturation and ovulation were induced at a dosage of 7mg per kg of individual fish weight. Latency period varied from 7 h at 29°C to 11 h at 25°C. Dead eggs became opaque between 8 and 10h after fertilization while embryogenesis was found to be temperature dependent. Mean hatching and larval deformity rates were 63·08%± 7·56 and 8·08%± 1·93 respectively. During induced natural spawning, the extract was applied at a dosage of 35 mg per kg of female fish weight. Spawning occurred between 10 and 11 h after hypophysation. Mean hatching and larval deformity rates were 41·38%± 8·48 and 10·00%± 2·00 respectively.  相似文献   

13.
This study aimed to determine the effect of feeding rates and water temperatures on the growth, feed utilization and size heterogeneity changes in subadult pikeperch. Fish with an average weight of 84±19 g were fed with a commercial trout diet for 18 weeks at a water temperature of 20 °C and 25 °C. Four feeding rates (PSFR) were predicted at both temperatures, which corresponded to 1.0%, 1.25%, 1.50% and 2.0% of body weight per day (bw day−1) for the first, and to 0.8%, 1.0%, 1.2% and 1.4% of bw day−1 for the second 9 weeks respectively. At the end of the experiment, the individual weight averaged 273±82 g. Pikeperch showed a better growth rate [specific growth rate (SGR)] and apparent feed conversion rates (AFCR) at the higher temperature. Thermal-unit growth coefficient (TGC) was better at the lower temperature. The values of SGR, TGC and AFCR significantly increased with increasing PSFR at both temperatures. The values of TGC plotted against the computed feeding rates allowed estimation of the maximum feeding rates (1.25% and 1.15% of bw day−1 for pikeperch of 150–180 g at 25 and 20 °C respectively). Size heterogeneity changes were affected neither by the feeding rate nor by temperature.  相似文献   

14.
Abstract. Artificially reproduced pacu, Colossoma mitrei Berg, fingerlings (initial weight 41 g) were stocked (100/m3) in plastic cages (1·0m3) within a freshwater reservoir. Three diets containing 30, 35 and 40% protein were tested in quadruplicate over a 76-day experimental feeding period. Fish were fed 7 days a week, twice daily at a feeding regime of 4% body weight/day from stock to 100g and thereafter at 3% until harvest. Mean water temperature over the trial was 26·7°C. Significant differences were observed in total and daily gain and in protein efficiency ratio, while no differences were obtained in the feed conversion ratio between treatments. Based on this study a 35% protein ration is recommended for pacu within floating cages.  相似文献   

15.
The overall objective of the study was to evaluate a slaughter method of eels, which consisted of chilling until their body temperature was <5 °C for stunning, and subsequently placing them in cold brine at −18 °C for 15 min for killing. Three distinct experiments and a control were performed.

Firstly, 19 eels with an average live weight of 758±44 g were restrained and equipped with EEG, ECG electrodes and a temperature sensor inside the body. Then, they were placed in the ice water. Indices for the induction of unconsciousness and insensibility were the appearance of theta and delta waves and no response on pain stimuli, which disappeared at a body temperature of 8.0±2.1 °C after 12±5 min in 15 eels. The responses to pain stimuli did not disappear in three eels. Within a confidence level of 95%, the percentage of eels that is not effectively stunned during the procedure in ice water of <5 °C was at least 5%. The heart rate decreased from 24±10 beats/min (n=14) to 7±4 (n=11) and became irregular during cooling down. When placed in the brine water of −18 °C, the EEG showed rapid and extreme depolarisation of the membranes, which started after 27±17 s (n=18). The ECG showed fluttering of the heart in all eels. None of the eels recovered after this procedure.

For 10 eels with an average live weight of 128±27 g, it was observed that the body temperature decreased from 17.1±0.6 to 4.0±0.5 °C in the ice water. After 15 min in the brine water of −16.1±2.2 °C, the body temperature decreased to −3.1±2.3 °C.

Finally, three groups of seven eels and eight single eels were placed in ice water of −0.0±0.1 °C. The observation of unrestrained eels revealed four phases. Animals were (1) swimming around in the water, (2) attempting to escape from the ice water, (3) pressing their nose to the wall or corner while showing clonic muscle cramps, and finally (4) breathing only, while all other muscle activity was totally suppressed. Afterwards, they were transferred to cold brine at −18 °C, and none of the eels recovered.

The eight control eels, which were transferred to water at 18 °C, swam around, except for one that was lying in an S-shape position at the bottom. After 570 and 605 s, two eels tried to escape from the box.

The obtained results show that the eels, which were transferred from water at 18 °C to ice water, might be stressed, a specific behaviour and an irregular heart rate were observed. From an animal welfare point of view, it is therefore not recommended to stun eels by live chilling. Moreover, at least 5% of the eels will not be stunned at a body temperature of <5 °C. Placing eels in brine water of −18 °C is an effective method to kill the eels before slaughter. However, it cannot be recommended to place conscious eels in cold brine water, because it takes more than 27 s before unconsciousness may be induced.  相似文献   


16.
Abstract. The effects of varying temperature, salinity and pH on the activation and subsequent motility of sperm of the yellowfin bream, Acanthopagrus australis (Günther), were assessed using a linear scale based on the overall activity of the sperm over time. Motility half-life was calculated using log transformation.
Conditions reflecting the natural habitat of the fish, oceanic salinity (1200 mOsM) and slight alkalinity (pH 8-8-5), were shown to produce both maximum activation and subsequent motility duration. The half-life of activated sperm was shown to be greater at 4°C than at 20-23°C (5·13 min:22·8 min). Storage of freshly stripped semen was shown to be most successful at 4°C with a half-life of 98·9 min.
The cryopreservation of semen was tested using the cryoprotectants glycerol and dimethyl sulphoxide at concentrations ranging from 0·5M to 2·0M, and pre-freezing equilibration times of 5 and 15 min. Glycerol at 20 M was shown to give significantly superior results. There was no significant difference between sperm activation or sperm half-life for fresh-stripped semen and frozen semen, using glycerol at 2·0M as the cryoprotectant.  相似文献   

17.
The effects of varying water depths and temperature on the growth, feed utilization, mortality rates and body composition of Nile tilapia, Oreochromis niloticus (L.), were evaluated. Triplicate groups of 20 fish (mixed-sex) m-3 were stocked into 200-m2 freshwater earthen ponds maintaining four water depths: 50, 100, 200 and 300 cm. The fish were fed on commercial fish pellets (23% protein), twice a day for 10 months (May 1991-February 1992). Water temperatures ranged from 5 oC to 33 oC. Growth performance and survival were significantly affected by pond depth and water temperature. Fish weight gain was lowest (250 g per fish), feed conversion poorest (3.15), and mortality highest (41.5%) at 50 cm depth, whereas 100-200 cm depth produced the best growth rates at warm water temperatures (> 21 oC). At 100-200 cm depth, weight gain was significantly (P<0.001) increased to 348-362 g per fish, feed conversion improved to 2.53-2.59 (P<0.01) and mortality reduced to 21-27% (P<0.001). Fish growth was significantly reduced (P<0.001) below 21 oC. Below 10 oC, fish stopped feeding and developed severe stress, fungal infection and high mortality. However, mortality rate was significantly reduced at 300 cm depth. Body lipid and protein were sharply decreased (P<0.001) with decreasing water temperature and pond depth, whereas body ash showed irregular patterns.  相似文献   

18.
Abstract. In southern Africa rainbow trout, Oncorhynchus my kiss (Walbaum), are generally cultured at temperatures between 18 and 22°C, which is higher than the optimal thermal range for maximum growth in this species. Experiments were undertaken on two size classes of fish (<4·5g and >25g) to determine the gross changes in protein and lipid requirements at these temperatures. The optimal protein and lipid requirements of the smaller fish were found to be 40% and 20–30% of the diet respectively. These levels are significantly different to those under optimal thermal conditions. The protein requirements of the larger fish remained at the 'threshold level' of 35% of the diet, although lipid requirements rose lo between 20 and 23% of the diet. The results are discussed in terms of the animal's scope for growth.  相似文献   

19.
Abstract. The effect of stocking density on growth and survival of Oreochromis niloticus (L.) fry was evaluated. O. niloticus fry (average weight, 10·56 ± 0·28mg and average length. 9·09 ± 0·05nim) were stocked in 2–1 tanks at 2, 5, 10, 15 and 20 fry/1 and reared for 33 days post fertilization, at 30°C (±1°C). Mean lengths, mean weights, and specific growth rates were found to be significantly lower ( P < 0·05) at the higher stocking densities. The coefficient of variation for the five stocking densities was significantly ( P < 0·05) different. Condition factors, however, were not significantly ( P < 0·05) different and survival was high at all density treatments. These data suggest that the culture of O. niloticus is feasible at the density groups tested but 5–10fry/I is recommended for fry culture in the hatchery, if a more uniform size is desired.  相似文献   

20.
Abstract. Tiger shrimp, Penaeus monodon Fabricius, post-larvae (32·0±3mg, 1·43±0·03 cm) were exposed to control, 0·12, 0·60, 1·20 and 2·40mg/l ammonia-N (un-ionized plus ionized ammonia as nitrogen) which is equivalent to control, 6,32,63 and 126μg/1 NH3-N (un-ionized ammonia as nitrogen) for 8 weeks in 25 ppt, as pH of 7·85–8·18 and 26–28°C by static renewal method. Growth in weight and length of the shrimps exposed to 1·20 and 2·40 mg/l ammonia-N were significantly lower (P < 0·05) than those exposed to control. The EC50 (concentration that reduced growth by 50% of that of the controls) was 1·33 mg/l ammonia-N, 70 μg/l NH3-N for weight gain, and 2·35 mg/1 ammonia-N, 123μg/l NH3-N for length gain of P. monodon post-larvae. The'maximum acceptable toxicant concentration'(MATC) of ammonia-N and NH3-N for P. monodon post-larvae was 0·60mg/l and 32μg/l, respectively after 6 weeks of exposure.  相似文献   

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