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1.
Abstract. Protein and energy maintenance and optimum feed requirements are reported in the catfish, Clarias batrachus (L.), fed a purified diet (40% CP; 1487·1kJ/100g) at 0 to 8% (BW/day) ration levels. Linear (r = 0·985) increase was observed in daily average growth increment up to a ration level of 4% (BW/day), corresponding to 6·03g protein/(kg0·8BW/day) and 224·26 kJ energy/(kg0·8 BW/day). Maintenance requirements, obtained by regressing daily average growth increment to zero, were 0·942 g/(kg0·8 BW/day) for protein and 36·02 kJ/(kg0·8BW/day) for energy. Net gains in muscle protein and energy also depicted linear increase (r = 0·975) with feeding levels up to 6·03g protein/(kg0·8 BW/day) and 224·26kJ energy/(kg0·8 BW/day). On fitting the above data to regression equations, giving the amount of dietary protein and energy required to maintain a constant amount of body protein and energy, values of 1·005g/(kg0·8 BW/day) and 42·11 kJ/(kg0·8BW/day) were obtained for protein and energy respectively. The optimum feeding rate for this species, as evident from specific growth rate and conversion efficiencies, appears to be 3% (BW/day) at 30 ± 2°C. Moisture and lipid contents in muscle were found to be significantly ( P < 0·05) affected by the ration levels.  相似文献   

2.
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   

3.
Abstract. Clarias isheriensis Sydenham fingerlings (60·42 ± 1·13g) were fed for 180 days with pelleted diets in which maize was progressively replaced with graded levels (0, 15,30,45%) of cocoa-pod husk meal (CPHM). There was a decline in growth rate with increase in dietary CPHM level, though this was not significantly different (P < 0·05). Differences in feed conversion, nutrient digestibility and carcass characteristics among different dietary treatments were also not significant (P > 0·05). Fish mortality was low (< 2%) in all dietary treatments tested. Lack of significant difference in growth performance and nutrient utilization indicated that CPHM could be incorporated into low-cost diets for C. isheriensis up to the 30% level.
In a second experiment, three feeding regimes of 15% CPHM diet were tested with C. isheriensis fingerlings (60·81 ± 1·87g) over 180 days and results showed no significant (P > 0·05) differences among the feeding regimes tested, with regards to growth, feed conversion and fish yield. This suggests that the growth of C. isheriensis from fingerling to adult size (≥ 200g) can be satisfied in one single feeding equivalent to 3% body weight per day.  相似文献   

4.
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   

5.
由于水电梯级开发和过度捕捞等人类活动影响,长江上游珍稀特有鱼类圆口铜鱼（Coreius guichenoti）资源量显著下降。增殖放流是保护该物种的有效途径之一,而人工繁育过程中为圆口铜鱼提供营养全面的饲料对其性腺发育至关重要。通过分析比较不同年龄和性腺发育阶段的圆口铜鱼肌肉营养成分、肌肉和性腺氨基酸组成,可为其人工饲料的开发提供基础数据。结果显示：(1)随着年龄的增长,圆口铜鱼肌肉粗蛋白、粗脂肪和氨基酸含量均呈先降低、后增加的趋势;(2)性腺从II 期到IV 期的发育过程中,圆口铜鱼肌肉粗蛋白、粗脂肪和氨基酸含量均升高;(3)性腺中谷氨酸和亮氨酸在所有氨基酸中的占比较高,分别为9.82%和6.74%,其中10 种氨基酸的含量、必需氨基酸总量和氨基酸总量均显著低于肌肉组织中的含（P<0.05）,而每100 g 蛋白质中脯氨酸（3.19±0.22）g 和丝氨酸（3.56±0.27）g 含量显著高于肌肉组织中的含（P<0.05）。研究表明,圆口铜鱼肌肉营养成分、氨基酸组成与其年龄和发育期有着密切联系。随着性腺发育,其肌肉粗蛋白、粗脂肪和氨基酸含量呈增加趋势,谷氨酸、亮氨酸和脯氨酸在圆口铜鱼性腺发育过程中可能起关键作用。  相似文献   

6.
紫海胆黄基本营养成分的分析与评价   总被引：1，自引：0，他引：1  
为了测定紫海胆黄中的营养成分,并对其营养价值进行系统分析及合理评价,采用国家标准的生化测定方法以及美国化学分析方法(AOAC)检测海胆黄中的水分、粗灰分、粗蛋白质、粗脂肪、总糖、氨基酸、脂肪酸及矿物质。结果显示:海胆黄粉中水分含量(5.29±0.02)%,粗灰分(8.69±0.03)%,粗蛋白质(60.36±0.04)%,粗脂肪(25.32±0.09)%,总糖含量(0.044±0.002)mg/100 g;共检出18种氨基酸,总含量(46.50±0.89)%;谷氨酸含量最高,为(5.57±0.11)%;必须氨基酸占总氨基酸的(37.75±0.01)%;主要的限制氨基酸是色氨酸和亮氨酸;药效氨基酸占氨基酸总量的46.86%;蛋白质氨基酸评分(AAS)0.8,化学评分(CS)0.5;必需氨基酸指数(EAAI)为77.86;共检出30种脂肪酸,EPA(二十碳五烯酸)+DHA(二十二碳六烯酸)含量(2.43±005)%;海胆黄富含钾、磷、钠、镁、铁、锌等矿物质元素;常量元素中,磷元素含量最高,为(1 432.27±8.91)mg/100 g;微量元素中,锌元素含量最高,为(13.13±0.09)mg/100 g。研究表明,海胆黄中蛋白质含量丰富,氨基酸种类多、比例合理,脂质含量高且富含EPA、DHA等多不饱和脂肪酸,矿物质含量丰富。  相似文献   

7.
This study investigated the effects of serotonin (5-hydroxytryptamine or 5HT) on ovarian development in Macrobrachium rosenbergii de Man. Adult female prawns at the ovarian stage I (spent) were injected with 5HT at 1, 5, 10, 20 and 50 μg g− 1 body weight (BW) intramuscularly on days 0, 5 and 10, and sacrificed on day 15. The doses as related to the effect could be categorized into three levels: low (1 and 5 μg g− 1 BW of 5HT), medium (10 and 20 μg g− 1 BW of 5HT) and high (50 μg g− 1 BW of 5HT). The low-dose, especially at 1 μg g− 1 BW, caused prawns to exhibit a significant increase in ovarian index (ovarian weight/body weight × 100) (5.79 ± 0.09%) as compared to the control (1.49%). The ovaries of most of these prawns could develop to stage IV (mature) and contained synchronously mature oocytes while most of the control ovaries remained at stage I and II (proliferative), and contained only oogonia to previtellogenic (Oc1, Oc2) and early vitellogenic oocytes (Oc3). The medium- and high-dose treated prawns exhibited ovaries that could reach stages III and IV and contained various types of oocytes of different maturity. Pretreatment with 5HT receptor antagonist, cyproheptadine (CYP), at 10 μg g− 1 BW before 5HT injection significantly suppressed the effect of 5HT. Intramuscular injection of the 5HT-primed thoracic ganglion culture medium into CYP-pretreated prawns resulted in the increase of ovarian index about 5–6 times more than in the control, and in the groups injected with 5HT-primed media from muscle strip, eyestalk and brain. The ovaries of most prawn could develop up to stage IV and contained synchronously developed vitellogenic (Oc4) and mature oocytes (Oc5). These findings suggest that 5HT indirectly induces ovarian development and oocytes maturation in M. rosenbergii, probably via a putative ovarian stimulating factor released from the thoracic ganglia.  相似文献   

8.
Abstract. The effect of four environmental conditions was investigated upon sperm output in turbot, Scophthalmus maximus (L.), submitted to three different rhythms of stripping. Males kept under a natural light cycle and under a 6-month contracted light programme released a similar sperm output in terms of total volume of semen produced per fish during the experimental period (4·9 ± 0·9ml), mean sperm concentration (29·4 ± 2·8 × 109 spermatozoa/ml) and total sperm number (163·2 ± 40·5 × 109 spermatozoa). Attempts to stimulate spermiation for a second time just after the end of the natural reproduction period resulted in the release of low sperm output (total volume of semen: 1·6 ± 0·4 ml; mean sperm motility: 2 min 36s ± 0 min 47s; mean sperm concentration: 47·6 ± 10·2 × 109 spermatozoa/ml; total sperm number: 84·5 ± 25·3 × 109 spermatozoa). Stripping frequency had no effect on total volume of semen, mean sperm motility and total sperm number. Monthly collection did not modify sperm samples in relation to stripping rank. However, decreasing volume, motility and sperm concentration were observed when males were stripped fortnightly and weekly. During the natural spawning period, the presence of females in the tank enhanced mean sperm motility (from 3 min 27s + 0 min 52s to 6 min 38s ± 1 min 38s).  相似文献   

9.
卵形鲳鲹（Trachinotusovatus）幼鱼经短期饥饿处理后测定其鳃、肝脏和肌肉中的总抗氧化能力（T-AOC）、超氧化物歧化酶（SOD）活力、丙二醛（MDA）质量摩尔浓度、Na＋／K＋-ATP酶活力和全鱼生化组成。结果显示,饥饿7d后鳃丝和肌肉的T-AOC显著升高,肝脏的T-AOC显著下降（P〈0．01）;鳃丝和肌肉SOD活力均显著升高（P〈0．01）,肝脏的SOD活力变化不显著（P〉0．05）;鳃丝、肝脏和肌肉的b（MDA）在饥饿后上升,鳃丝b（MDA）与对照组差异极显著（P〈0．01）,肝脏b（MDA）与对照组相比差异显著（P〈0．05）,肌肉b（MDA）差异不显著（P〉0．05）。饥饿8d后鳃丝Na＋／K＋-ATP酶活力显著升高（P〈0．01）,肝脏Na＋／K＋-ATP酶活力显著下降（P〈0．01）,肌肉Na＋／K＋-ATP酶活力也有所升高（P〉0．05）;饥饿后鱼体水分质量分数上升,粗蛋白质量分数、粗脂肪质量分数和能值下降,而且相对损失率是粗脂肪〉粗蛋白,表明卵形鲳鲹幼鱼在饥饿早期主要消耗脂肪向机体提供能量,随着饥饿时间的延长,蛋白质将被消耗。  相似文献   

10.
Abstract. Fibreglass pools (3·5m diameter, 1·2m high) were evaluated as model ponds and used to compare the effects of fertilization strategies, designed to promote either phytoplankton blooms or benthic algal mats, on production of Penaeus monodon Fabricius and water quality over 8 weeks. As production results were similar to those reported from commercial ponds in Australia and Taiwan, the pools were considered appropriate experimental units for assessing pond management strategies. Large blooms of filamentous algae developed in four of the eight pools with benthic algae. In these, individual prawn growth (weight gain), biomass gain, food conversion efficiency and drain harvest efficiency were all lower ( P < 0·05) than in pools with phytoplankton. Abundance of filamentous algae was negatively correlated ( P < 0·05) with prawn weight gain (r =−0·80) and drain harvest efficiency (r =−0·76). Differences in water quality arising from alternative fertilization strategies occurred but did not explain differences in prawn production indices. The results indicate that ponds used for monoculture of P. monodon should be fertilized so as to stimulate and maintain phytoplankton blooms and to discourage blooms of filamentous algae.  相似文献   

11.
Abstract. A commercially prepared vaccine against Edwardsiella ictaluri was used to vaccinate 12-day-old channel catfish fry by immersion, or by immersion plus an oral booster 2 months later. One month after the fish were fed the booster vaccine, they were challenged by waterborne exposure to 2·1 × 106 cells ml−1 of E. ictaluri. Immersion only vaccinated fish suffered 6·7% mortality and immersion plus oral-boosted fish had a 3·3% mortality. Mortality among non-vaccinated controls was 96·7% and was significantly ( P < 0·01) above the vaccinated mortality. The relative per cent survival for the immersion-only fish was 93·1, while it was 96·6 for the immersion plus oral-boosted fish. Agglutinating antibody titres of the vaccinated fish were significantly ( P < 0·05) higher than the control fish. When the ponds were drained 6 months after stocking, 42·7% of non-vaccinated, 56·3% of immersion-only and 70·8% of immersion plus oral-boosted fish were harvested. Survival of immersion plus orally-boosted fish was significantly ( P < 0·05) higher than the controls of immersion-only fish. Duplicate populations of immersion plus oral-booster-vaccinated fish grew 34% and 56% faster, respectively, on an average daily gain than the control fish, while immersion-only fish in one pond grew 20% less per day and fish in the second pond grew 48% faster.  相似文献   

12.
Abstract. A feeding experiment was conducted in aquaria to evaluate growth, survival and food consumption by paddlefish, Polyodon spathula (Walbaum), fry fed live Daphnia pulex, brine shrimp nauplii, Artemia sp. (L.), from two different geographical sources, or one of three commercial dry diets. Fry were fed from first feeding (day 8 post-hatch) to day 17 post-hatch. All diets had similar percentages of crude protein and lipid. Fatty acid composition was similar in all diets except for Great Salt Lake brine shrimp nauplii which had a higher percentage of linolenic acid, 18:3 (n-3), and a lower percentage of eicosapentaenoic acid, 20:5 (n-3). Paddlefish fed live food organisms were significantly (P<0·05) larger than those fed non-living diets. Survival was significantly higher (P<0·05) for fish consuming live Daphnia (95·3%) than all other treatments. Percentage of fish with food in the digestive tract did not significantly differ (P>0·05) among treatments. Poorer growth and survival by fish fed prepared diets may have been due to limited digestibility of the dry diets by paddlefish.  相似文献   

13.
以不同比例大豆浓缩蛋白和花生麸为混合植物蛋白源替代不同水平鱼粉,并添加包膜赖氨酸和蛋氨酸,饲喂斑节对虾（Penaeus morlodoll）[（1．27±0．02）g]56d,研究不同鱼粉含量饲料对斑节对虾生长及非特异性免疫力的影响。结果表明：1）斑节对虾增重率（245．02％）、特定生长率（2．58％·d^-1）均在对照组获得最大值,显著高于除F1和F2组外的其他各组（P〈0．05）。当对虾摄食F1组饲料时饲料系数最小,显著小于F3～F5组（P〈0．05）。成活率在F4组最低,显著低于F0～F2组（P〈0．05）,但与其他各组无显著性差异（P〉0．05）;2）混合植物蛋白替代不同水平鱼粉的饲料对虾体成分无显著性影响（P〉0．05）;3）肝脏中超氧化物歧化酶（SOD）活性在F2组最高,显著高于对照组（P〈0．05）,与其他各组差异不显著（P〉0．05）。肌肉中S01）活性在F5组最高,显著高于其他各组（P〈0．05）,酸性磷酸酶（ACP）活性在F1组最高,显著高于F2～F4组（P〈0．05）,溶菌酶（LSZ）活性在F4和F5组最高,显著高于F1D～F3组（P〈0．05）。根据斑节对虾的增电率和特定生长率得出用混合植物蛋白并添加包膜氨基酸可替代饲料中20％的鱼粉,且随着饲料中植物蛋向含量的增加,对虾非特异性免疫力增强。  相似文献   

14.
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   

15.
ABSTRACT:   The effects of silvering state of wild female Japanese eels Anguilla japonica on the success of induced maturation and the following spawning were examined. Thirty-eight females, collected in Mikawa Bay, were divided into four stages based on their silvering state: yellow (Y1), late-yellow (Y2), silver (S1) and late silver eels (S2). Despite injections of salmon pituitary extract (SPE) through the standard technique, Y1 and Y2 eels did not respond to the treatment with undeveloped gonad (gonad-somatic index [GSI]: 0.3–0.9), and all these females died by 5 weeks, probably due to an abnormal physiological condition. Most S1 (81%) and S2 eels (100%) matured completely (GSI: 17.8–51.4), and finally spawned successfully (69% for S1, 89% for S2). S2 eels fully matured with oocytes of over 750 μm in diameter by significantly smaller number of injections of SPE (5–6 times) than the case of S1 eels (6–8 times). The amount of eggs released by S2 eels (0.65 ± 0.11 g/fish per body weight [BW]) was significantly larger than those by S1 eels (0.54 ± 0.09 g/fish per BW). There was no difference in fertilization and hatching rates between eggs released by S1 eels and those of S2 eels. These results indicate that the success of induced maturation and spawning in wild female Japanese eels depends on their silvering state, and matured eggs can be obtained efficiently through the use of S2 eels rather than other stages.  相似文献   

16.
在盐度为4、钠钾比为41.6的低盐井水环境下, 选取720 尾初始体质量为(0.32±0.006) g的凡纳滨对虾(Litopenaeus vannamei),  随机分成6 组, 基础饲料中分别添加0、0.3%、0.6%、0.9%、1.2%和1.5%钾离子(以KCl作为钾离子的添加形式, 分别记为D0、D1、D2、D3、D4 和D5), 探讨饲料中不同钾水平对凡纳滨对虾生长、氮代谢和渗透压调节的影响。结果表明, 随着饲料钾水平的增加, 凡纳滨对虾的增重率呈先升高后降低趋势, D2组最高(P<0.05), 但与对照组相比不显著, 蛋白质效率以D1组显著最高。体钾含量在各处理组之间呈现出显著差异, 以D1组最高, D5组最低(P<0.05)。同时凡纳滨对虾的耗氧率和排氨率随饲料中钾含量的增加均呈显著的先降低后上升趋势(P<0.05), 其中排氨率以D2组最低, 耗氧率以D3组最低, 且均显著低于对照组。血清精氨酸酶活性呈峰值变化趋势, 其中以D1组最低(P<0.05)。各实验组血清Na+和Cl-含量呈显著的先降低后升高的趋势(P<0.05), Na+含量以D1组最低, Cl-含量以D1和D2组最低。而鳃丝Na+-K+-ATPase活性呈显著先升高后降低的趋势(P<0.05), D3组最高, D2组与D3组无显著差异(P>0.05)。血清总蛋白含量呈显著升高趋势。D2组血蓝蛋白含量最高, 渗透压和血清K+含量在各组间无显著差异(P>0.05)。以生长、氮代谢、渗透调节相关指标为判据: 凡纳滨对虾饲料中添加0.3%~0.6%(含钾量: 0.96~1.26 g/100g饲料)的钾有利于低盐环境下对虾对饲料蛋白的利用及生理代谢平衡, 而过高的添加量(1.5%, 总含钾量: 2.17g/100g饲料)则会影响其生理代谢从而抑制生长。  相似文献   

17.
Abstract. In temperate regions of North America, the culture of rainbow trout, Oncorhynchus mykiss (Walbaum), in ponds is constrained to the period mid-November to early April by water temperature. Feeding practice may influence production time. The effects of three feeding practices on growth and body composition of rainbow trout raised in ponds during a 142-day winter growth period were investigated. Feeding practices were (1) hand-feeding to satiation, (2) feeding according to a fish size/water temperature chart, and (3) feeding by demand feeder.
Fish fed to satiation consumed 66% more diet than fish fed according to a feeding chart and 163% more than fish fed by demand feeders. Fish fed to satiation had significantly higher (P < 0·05) weight gain, harvest weight, specific growth rate, and protein gain with no significant increase (P > 0·05) in percentage body fat or feed conversion ratio (FCR) compared to the other two treatments. Survival percentage did not differ significantly (P > 0·05) between treatments. These data indicate that by using satiation feeding, marketable size rainbow trout can be produced in temperate region ponds without increases in percentage body fat or FCR.  相似文献   

18.
Abstract. An intensive growth trial conducted In pens in an earthen pond indicated that growth of Penaeus vannamei (Boone) increased with feeding frequency and suggested that day feedings produce greater growth than night feedings. The differences in growth due to feeding frequency were significant, instantaneous growth rates (IGR) increasing from 1·62% to 1·66% to 1·71%/day as the number of feedings increased from one to two to four per 24 h. Comparison of the IGR of shrimp fed at night (1·64%/day) to that of shrimp fed during the day (1·68%/day) suggested ( P = 0·0633) that growth was greater for shrimp given day feedings than for shrimp given night feedings. Survival of shrimp was not significantly different due to feeding frequency or due to time of feeding and averaged 74·7 ± 6·1%. Results indicate that P. vannamei cultured under conditions similar to those tested should be fed a minimum of four times daily and suggest that feeding during the day is at least as good as and may be preferable to feeding at night.  相似文献   

19.
Agave lechuguilla is a succulent plant species, mainly distributed in the northeast of Mexico and south of the United States of America. The main use for this plant is the fibre´s extraction (known as Tampico fibres), resulting in 15% of fibres and 85% of a by‐product waste named guishe. The lechuguilla collectors, normally incinerate the guishe, thus causing environmental contamination. Interestingly, recent studies showed that guishe contains molecules with nutritional properties, such as saponins, flavonoids and sugars. Therefore, in this work, we evaluated the effect of the crude extract of guishe as a feed additive in whiteleg shrimp diets. According to that, MS‐HPLC analysis of the extract showed the presence of saponins such as diosgenin, smilagenin, hecogenin, manogenin, tigogenin hexose, yucagenin, chlorogenin, diosgenin diglucoside and the flavonol, quercetin. After chemical analysis, the crude extract was included into an experimental diet in four levels; 0% (L0%), 0.1% (L0.1%), 0.3% (L0.3%) and 0.6% (L0.6%). Dietary incorporation of the extract was evaluated by zootechnical performance, haemolymph biochemistry, histomorphology and digestive enzyme activity of shrimps. After 5‐week feeding, the L0.3% diet showed significantly higher growth and better feed utilization among treatments. A significant increase in tubule epithelium height and tubule coverage area from hepatopancreas in shrimp under L0.3% diet compared with the control diet suggest an improvement of the health and nutritional status of the shrimp. Inclusion of L0.3% and L0.6% of the crude extract resulted in a reduction in amylase activity, without effect in glucose levels in the haemolymph. Thus, we suggest that lechuguilla guishe crude extract contains nutritional molecules that may be used as a feed additive to promote shrimp productivity.  相似文献   

20.
Abstract. The possibility of using eels from intensive rearing ponds to restock natural basins has been investigated by comparing growth, survival and rate of yellow-to-silver metamorphosis of 'wild type' eels and of eels from an intensive rearing pond. A total of 2243 marked eels were released into a closed natural environment of 22ha; 1254 were wild type (average length 45·6 ± 9·0cm), and 989 from an intensive rearing pond, split by a mechanical grader in two groups. The first group was made of 617 well-growing eels (44·9 ± 3·0cm), the second one of 372 smaller eels (36·9 ± 4·3cm) which had not adapted to the artificial conditions.
The starting size being equal the animals grew to the same extent; in some cases the animals previously adapted to the artificial pond grew better than the wild type. The rate of metamorphosis from yellow to silver eel was 28·4% for the wild type eels and 22% for the others, although the latter became mostly silver males. Survival of the wild type eels (starting with the 35-cm size class and covering the period from April to December) was calculated by mark-recapture at approximately 98·6%. For the eels previously well adapted to the intensive rearing pond it was only 85%, indicating some difficulty in competing in the natural environment. The good growth shown by the smaller eels, with a survival of about 90%, would seem to indicate that these animals might be effectively used for restocking purposes, thus favouring an integration between the intensive ponds and the extensive environments.  相似文献   

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