首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 23 毫秒
1.
Abstract.— A 12-wk experiment was conducted to test the effects of 50, 100, 200, and 300% stocking densities (ventral fish area to bottom tank area ratio) on growth, survival, and aggressive behavior in 2-moold juvenile winter flounder Pseudopleuronectes americanus . Over the course of the experiment, there were no differences ( P > 0.05) in growth between treatments at any given week. Survival decreased in all treatments over time, however, proportionately more fish died in the high (200 and 300%) density treatments. At the end of 12 wk, the 300% treatment had significantly lower survival ( P < 0.05). There were no differences in the degree of caudal fin damage between any of the treatments ( P > 0.05) suggesting that aggressive behavior. such as fin nipping, was not affected by stocking density. However, fish size was inversely related to caudal fin damage. When fish were sorted by length, the two smallest size categories (<2 cm and 2-3 cm) suffered the greatest fin nipping compared to each other ( P < 0.001) and all larger size categories ( P < 0.001). These results indicate that 50 to 300% stocking densities do not affect growth or aggressive behavior in juvenile winter flounder. Although survival was affected by density, the final yield (weight per treatment) at higher densities was still greater than at lower densities. Our hatchery recommendations are to stock at ≥200% but to monitor fish health carefully. Size grading should be employed to minimize aggression between fish size classes.  相似文献   

2.
Recent advances on feeding in intensive rearing of juvenile astacids enable research of other factors influencing growth and survival without the confounding effect of inadequate feeding. Two experiments were conducted to evaluate the effects of the number of shelters per crayfish and to test different lighting conditions. Stage 2 juvenile Pacifastacus leniusculus were stocked in fibreglass tanks and fed a dry diet for salmonids combined with restricted amounts of decapsulated Artemia cysts. In experiment 1, four, two or one shelters per crayfish were tested for 80 days. No significant differences were found among groups either in survival (final mean: 86.67%) or in growth [final mean: 11.41 mm mean carapace length (CL), 355.45 mg mean weight]. In experiment 2, three lighting conditions were tested for 120 days: continuous lighting of 925 lx, continuous darkness and natural photoperiod. Survival rates ranged from 76.7% to 88.3%, with no significant differences among groups. The crayfish kept under continuous darkness grew faster (final mean: 12.70 mm CL, 543.08 mg weight) than those reared under the other two light conditions. This study shows that, under improved feeding conditions, a minimum number of shelters can be provided, and faster growth can be obtained in continuous darkness.  相似文献   

3.
Recent advances in intensive rearing of astacid juvenile crayfish have greatly improved the results. This challenges the current application possibilities of the studies performed previously, and new research on density is required. A 100-day experiment was carried out under controlled conditions to evaluate density effects on survival and growth rates of juvenile crayfish in optimal conditions of feeding. Juvenile stage 2 Pacifastacus leniusculus were stocked in fibreglass tanks (1 m2, 200 l water) at 20 ± 1°C and fed a dry diet for salmonids supplemented with restricted amounts of Artemia nauplii. Stocking densities were 100, 300, 600 and 1,000 crayfish m−2. Mean survival rate was reduced significantly with increased stocking density, ranging from 86.33% (100 m−2) to 39.13% (1,000 m−2). All checks showed that at the lowest initial density (100 m−2) animals grew significantly faster those at higher densities, recording a final carapace length of 15.28 mm and weight of 1.08 g. Among the treatments of 300, 600 and 1,000 m−2 no differences were found either in carapace length or in weight throughout the experimental period, with a final mean growth of 14 mm carapace length and 0.72 g weight. The final proportion of animals with chelae autotomy rose significantly with increasing stocking density, ranging from 14.44% (100 m−2) to 41.45% (1,000 m−2). This study shows that diet is a decisive factor for stocking successfully high densities under controlled conditions and provides useful information to set adequate densities in accordance with the production objectives.  相似文献   

4.
将体质量0.527 g(幼虾)和6.100 g(亚成体虾)的克氏原螯虾饲养在底面积为113 cm^2 、高为12 cm的圆形塑料盒中,一组放入内径为1.9 cm的PVC管作为隐蔽所为隐蔽组,以不放PVC管为对照组,其他条件同隐蔽组,定期测量各组克氏原螯虾的体长、体质量增长量、存活率和蜕壳率等指标,研究隐蔽所对不同规格克氏原螯虾生长的影响。2个月的饲养结果显示,试验第1个月隐蔽组幼虾组体长增长、体长相对增长率、体质量增长及蜕壳量均显著大于对照组( P <0.05),第2个月两组各数据无显著差异( P >0.05);隐蔽组亚成体螯虾摄食量、体质量及蜕壳量均小于对照组。研究结果表明,隐蔽所在螯虾的早期生长阶段对其生长有促进作用,但随着螯虾体格的增大,隐蔽所的促进作用随之减弱,甚至最终抑制螯虾的生长。本研究围绕克氏原螯虾穴居的习性以及趋触性等行为的特点,为生产提供了合理建议。  相似文献   

5.
Development of artificial crayfish egg incubation is a milestone in intensive culture of crayfish as commercially important freshwater animals. This study evaluated experimental treatments combining continuous UV lighting, a non‐chemical antifungal treatment, with an initial formaldehyde bath for noble crayfish (Astacus astacus) eggs incubated in semi‐recirculating systems, which requires less than 1 per cent the amount of water necessary for conventional flow‐through systems. The one‐time administration of a pre‐incubation bath to reduce formaldehyde exposure was ineffective. Ultraviolet irradiation of recirculating water provided poor results (13.5% and 35.2% final survival rates to stage 2 juveniles) and led to deteriorating water quality. An inability of hatchlings to successfully moult and the occurrence of limb deformities was observed in UV‐treated groups, and juvenile mortality was found across all experimental treatments.  相似文献   

6.
The effects of tank bottom substrates and presence of shelter on growth, survival and condition of cheliped in the juvenile (stage 2) signal crayfish, Pacifastacus leniusculus (Dana), with an initial stocking density of 200 individuals m?2 were investigated. In the first trial, three different tank bottom substrates with or without shelter were used. The three bottom types were loose gravel, glued gravel and bare bottom. The fastest growth both in terms of wet weight and carapace length was observed on loose gravel bottom. Also survival (range 30.1% to 49.8%) was affected by bottom type being higher on gravel bottoms than on bare bottom. Shelter improved survival only on loose gravel bottom. Bottom type influenced also the number of animals with cheliped injuries. The highest proportion of animals with no injuries (59.5%) was found on bare bottom and the proportion was about 12% and 13% units less on loose gravel and on glued gravel bottom. The presence of shelter had a marginal probability in increasing the number of animals without injuries. In the second trial, the substitution of ordinary gravel as tank bottom substrate with crushed limestone was studied. The mean final wet weights were 0.517 g on ordinary gravel bottom and 0.481 g on limestone bottom. The survivals were about 74% and 80% respectively. Limestone bottom decreased marginally final wet weight, and increased survival but did not affect the final carapace length that had a mean value of 13.6 mm. We conclude from the present experiments that the type of tanks and the rearing system used supported good growth of juvenile signal crayfish. The best growth results could be obtained by using loose gravel (or loose limestone) on the bottom of the tanks with a sufficient quantity of hiding places. However, there appears to be an increased risk for cheliped injuries on bottoms with loose materials.  相似文献   

7.
水温(25±1) ℃时,将体质量(3.11±0.10) g的克氏原螯虾幼虾饲养在120 cm×60 cm×20 cm的水族箱中,密度分别为14尾/m^( 2) (低密度组)、28尾/m^( 2) (中密度组)和42尾/m^( 2) (高密度组),研究室内养殖不同密度对生长、摄食、消化酶活性及非特异性免疫的影响。8周的养殖结果显示,克氏原螯虾的存活率随养殖密度的增大而降低。在28尾/m^( 2) 组中,其特定生长率[(1.82±0.12)%/d]和质量增加率[(196.73±0.76)%]显著高于其他两组( P< 0.05)。摄食率与养殖密度成正相关,即42尾/m^( 2) 组的摄食率高于14尾/m^( 2) 组和28尾/m^( 2) 组。28尾/m^( 2) 组消化酶活性显著高于14尾/m^( 2) 组的消化酶活性( P< 0.05),但与42尾/m^( 2) 组差异不显著( P >0.05)。不同养殖密度对非特异性免疫有显著影响,28尾/m^( 2) 组显著优于其他两组( P< 0.05)。综合所有指标,在本试验条件下,28尾/m^( 2) 的养殖密度最适合克氏原螯虾幼虾的养殖。  相似文献   

8.
Redclaw crayfish, Cherax quadricarinatus, early juveniles were reared at different stocking densities in a closed recirculation system using 12-L plastic containers as rearing tanks. Initial stocking densities were 1.0, 1.5, 2.0, 2.5, and 3.0 per liter (66, 89, 111, 133, and 156 crayfish/m2, respectively). Rearing period was 42 days. Each density was tested with five replicates. Shelter (0.112 m2) was added to double the surface area of rearing tanks. Animals were fed ad libitum twice a day with a commercial diet containing 35% crude protein. There were no significant differences (P < 0.05) in length and specific growth rate (SGR) among stocking densities. Final weight and daily weight gain, however, were significantly higher at the density of 66 per m2 (1.0 per liter). Total biomass at harvest increased with density. Survival was affected by stocking density from day 28 onward, decreasing with density from 62.7 ± 7.6% obtained at 66 crayfish/m2 to 44.85 ± 8.18% at 156 crayfish/m2.  相似文献   

9.
Juvenile red king crabs (RKCs) Paralithodes camtschaticus have a strong tendency for cannibalism, which is an obstacle for seedling production. We investigated the effects of density-dependent cannibalism on the survival rate and on growth, and estimated the optimal stocking density. Four different stocking densities of juvenile first instar crabs were maintained in tanks (50, 100, 200 and 400 individuals per 100-l tank: bottom area was 0.25 m2) during the 209 or 216 days of rearing. The survival rate was affected by stocking density, elapsed days, and the interaction between these variables. Although carapace length, an index of body size, was also affected by density, elapsed days, and the interaction between these variables, the effect associated with density was quite small, suggesting that cannibalism did not intensely affect growth of juvenile crabs. We then estimated the initial stocking density that maximizes the number of survivors using parameters of analyses. Optimal initial stocking density was predicted as 416, 197 and 149 individuals per tank when the target size was assumed as 5.0, 10.0 and 15.0 mm, respectively. This estimation provides a baseline for seedling production in RKCs and could be further improved by considering other factors that affect survival and growth of RKCs.  相似文献   

10.
The specific growth pattern of Chinese mitten crab, Eriocheir sinensis, during the juvenile stages was investigated under an individual rearing system for 160 days, including parent crab selection, hatchery management, larval stages, and juvenile cultivation. There were 36 males and 40 females developed from megalopa to the juvenile crab stage 10 (M–C10), with a total survival of 38%. The survival rate in early stages (M–C3) remained less than 80%, which was lower than that in latter stages (>?90%). The intermoult duration sharply increased in an exponential manner (y?=?3.1059e0.2149x R2?=?0.9383) from 4?±?0.54 days to 38?±?6.26 days. The increments in wet weight, carapace width, and carapace length per moult were recorded throughout the experiment, which followed certain patterns with progressing moulting time. In addition, moulting increment in wet weight varied greatly from C1 to C6, with a minimum increment of 108.09%. Meanwhile, the specific growth rate markedly increased in the early stages and subsequently decreased, mainly because of significant increases in the intermoult duration starting from C6 stage. Males and females could be differentiated at C4 based on sexual dimorphism in the abdomen, and the most distinct changes in female and male juvenile crabs occurred in the shape of the abdomen and amount of cheliped fluff, respectively.  相似文献   

11.
Limb‐loss in crustaceans can reduce moult increment and delay or advance the timing of moulting, both aspects that are likely to impact upon soft‐shell crab production. Pond‐reared blue swimmer crabs Portunus pelagicus were harvested and maintained in a crab shedding system. The wet weight, carapace width (CW) and the occurrence of limb‐loss were assessed before stocking in the shedding system and after each of the next three moults. Many of the crabs were initially missing one or two limbs and these did not grow as much as the crabs that were intact at the start of the trial. Despite its strong correlation with wet weight, CW changes proved to be misleading. Limb‐loss reduced the %CW increment but not the per cent weight increment (where the later is calculated from the actual pre‐moult weight). Pre‐moult weight explained much of the variation in post‐moult weight, with crabs moulting to approximately double their weight. Limb‐loss reduced ‘growth’ and production from the pond because it reduced pre‐moult weight but limb‐loss did not alter the weight change on shedding a given weight of crabs, although some of that change now included regeneration of limbs. One can hypothesize that much of the size variation seen in pond‐reared crabs may be due to accumulated effects of repeated limb‐loss, rather than genetic variation.  相似文献   

12.
Effects of size grading and stocking density on growth and survival of 3.5‐month‐old signal crayfish (Pacifastacus leniusculus Dana) juveniles were investigated in a 3 × 2 factorial design with size group (small, large and mixed) and stocking density (25 and 200 individuals m?2) as factors for 90 days. Carapace length and wet weight growth of the juveniles were affected by the presence or absence of other size groups, stocking density and animal size. All factors had statistically significant interactions, which make the interpretation of the results more complicated. The smaller crayfish grew faster in the absence of large animals and larger animals benefited from the presence of smaller cospecies. Increasing density decreased the growth in length and weight. Survival (82–100%) was good in all groups. Subsequently, the within population dynamics was studied by selectively removing the largest individuals (selectively removing (SR) group). Effects on growth and survival of the remaining juveniles were evaluated on 6‐month‐old P. leniusculus juveniles reared in plastic tanks (100 juveniles m?2) for 122 days. Size distribution manipulation was performed at days 34 and 70. Juveniles in SR group grew significantly faster in comparison with a control group (RR), from which juveniles were removed randomly. Also, the survival rate was significantly higher in the SR group than in the RR group. In conclusion, size grading of juvenile P. leniusculus either at the start of the experiment or repeatedly during the experiment increased growth performance of smaller animals in length and weight.  相似文献   

13.
The red swamp crayfish, Procambarus clarkii (Girard), is one of the most commonly farmed freshwater species in inland China due to its high market value and consumer demand. The aim of this study was to determine the optimum combinations of photoperiod, water calcium concentration and pH for juvenile survival, growth and moulting. In our orthogonal experiment, the three environmental factors were varied at three levels (photoperiod: 16L:8D, 12L:12D and 8L:16D; calcium concentration: 45.5, 65.5 and 85.5 mg L−1; and pH: 6.8, 7.8 and 8.8). Range analysis showed that the maximum survival of juvenile crayfish occurred at photoperiods of 16L:8D or 8L:16D, water calcium concentration of 45.5 mg L−1 and pH of 7.8; maximum weight gain at photoperiod 16L:8D, water calcium concentration 65.5 mg L−1 and pH 7.8; maximum length increase at photoperiod 16L:8D, water calcium concentration 65.5 mg L−1 and pH 7.8; and the highest moult frequency at photoperiod 12L:12D, water calcium concentration 65.5 mg L−1 and pH 7.8. Analysis of variance indicated that photoperiod, water calcium concentration and pH significantly influenced only the weight gain of juvenile crayfish ( P <0.05). Taking growth into consideration, we suggest that a photoperiod of 16L:8D, calcium concentration of 65.5 mg L−1 and pH 7.8 might be optimal conditions for rearing juvenile P. clarkii .  相似文献   

14.
With recent advances in aquaculture techniques, captive‐breeding of the endangered white‐clawed crayfish Austropotamobius pallipes for restocking is becoming a widespread conservation method. Establishing optimal stocking densities for aquaculture is essential in maximizing productivity, and increases the likelihood of crayfish survival when released. A 240‐day experiment took place using 2‐month‐old juvenile, captive‐born, A. pallipes, within a small‐scale, closed‐circuit hatchery to investigate survival, growth and aggression at three treatment densities, low (100/m2), medium (200/m2) and high (300/m2). Crayfish were counted and measured every 60 days between August 2015 and April 2016. Mean survival rates were high across all three densities (87.7% ± 2.8%). Carapace length was significantly longer at low density than at medium and high densities. While growth rate was not significantly different between treatments, it was significantly higher in the first 2 months, across all three treatments (47.1% ± 6.6%) than in subsequent periods (14.1% ± 5.8%). Size variation within groups increased with density, suggesting that social dominance hierarchies are established with increasing stocking density: dominant individuals are larger and competitively exclude smaller individuals from food resources. Males were significantly larger than females from 6 months of age, (when they could be reliably sexed), in all three treatments. The larger male size suggests that sexual dimorphism begins prior to sexual maturity, with males growing faster and being more dominant and aggressive than females. In conclusion, young‐of‐the‐year A. pallipes can be reared at high densities without compromising survival; however, the optimal stocking density that maximizes growth and health is 100/m2.  相似文献   

15.
Understanding ecological effects of altered stream flows is an essential objective. In a comparative field study of juvenile steelhead trout (Oncorhynchus mykiss) that compared natural‐ and reduced‐flow sites, we used mark–recapture modelling and information theory to quantify spatially and temporally explicit patterns of density, specific growth rate, survival and outmigration; and test predictions for biotic and abiotic drivers. Densities were lower in water withdrawal treatments, resulting in lower intraspecific competition and, higher specific growth rate and survival. We observed yearly differences in density and intraspecific competition, with a negative relationship between density and specific growth rate over a wide range of densities, but reductions in survival only at the highest densities. Moreover, individual variability within sites was important. At high density (sites and years), survival related negatively to body size. In contrast, when overall density was lower, specific growth rate was negatively related to body size. Lastly, individuals were more likely to outmigrate when they had larger body size, lower survival or reared in habitats with reduced flows, and these patterns appeared mediated by the intensity of intraspecific competition. Our results underscore the harsh bioenergetic conditions induced by higher temperatures and densities during summer baseflow (relative to other seasons), particularly for larger fish demanding more resources, and suggest a density‐dependent mechanism for why this period is important for regulating salmonid populations. We found that a complex combination of natural (e.g., density) and anthropogenic (e.g., withdrawal) factors affected juvenile salmon populations and life history expression in the face of altered flows.  相似文献   

16.
研究了放养密度和饵料种类对幼中国大鲵（Andrias davidianus）生长发育的影响,跟踪分析了自胚胎孵化至一龄幼鲵的存活与生长发育状况。结果表明,自胚胎孵化至一龄幼鲵的养殖密度为每0.1m210～20尾时,其成活率可达到100%,投放密度每0.1m2自20尾增加到60尾,平均存活率、年体长增加和年体重增加均显著降低。投喂摇蚊幼虫、猪肉、牛肉、羊肉和小鱼虾,幼苗的存活率分别为100%、90%、95%、85%和95%,体长增加分别为8.09cm、5.45cm、5.28cm、4.57cm、6.82cm,体重增加分别为25.97g、12.68g、11.82g、10.86g和20.67g。可见,摇蚊幼虫和小鱼虾是一龄幼大鲵的适宜饵料。  相似文献   

17.
Three independent studies were conducted in which supplemental food was provided to juvenile Orconectes virilis reared at varying densities. One study was conducted in fiberglass tanks (densities of either 13, 27 or 54 individuals/m2) and two were conducted in outdoor pools (densities of either 2.5, 5, 10, 20 or 30 individuals/m2). Crayfish were offered a variety of foods ranging from a formulated diet to agricultural forages. Weight gain of crayfish fed a formulated diet and reared at varying densities was similar in the study conducted in tanks, but survival was significantly lower at the two highest densities (27 and 54/m2). Weight gain, survival and yield decreased as density increased in the studies conducted in outdoor pools. The highest weight gain and survival were at a density of 2.5/m2. Wheat straw was used as the source of nutrients. Use of formulated diets did not result in rapid weight gain when crayfish were reared at higher densities.  相似文献   

18.
Pond growout of Cherax tenuimanus to two years of age provided data for mean crayfish weight, surviving density and distribution of individual sizes at intervals and final harvest for 12 single year-class cohorts. Final mean size (47–156 g) was most significantly related to surviving density (4.5–0.7/m2). A hyperbolic model with a harvest date variable accounted for 89% of the variation in mean weight. The biological basis of this model is that the reciprocal of density, i.e., pond area per crayfish, represents food supply for a bottom-dwelling crayfish. By incorporating the Richards growth function, the hyperbolic model can be more realistically fitted to include the limit to potential size at very low densities. The growth-density relationship developed after an initial period of 300 days of low growth (to ∼ 10% of final size) and high mortality. Then, mean weight increased rapidly and density stabilized. Final cumulative production (1.401–3,922 kg/ha) and harvest biomass (1,110–2,991 kg/ha) both increased linearly with density. Survival of the total amount of crayfish produced was about 75% at harvest. Although cohort size distributions were positively skewed, the arithmetic mean size employed in the model was very closely and linearly related to the geometric mean of the lognormal distribution, The causal basis and assumptions of the growthdensity model are discussed in relation to resource sharing by individuals and the disproportionate influence of size-related dominance behaviour.  相似文献   

19.
亲缘关系对克氏原螯虾仔虾种内斗争的影响   总被引：2，自引：0，他引：2  
将源于1、2、3、4尾雌虾的克氏原螯虾仔虾以4种方式混养,每个混养群体共有仔虾24尾,设3个重复。结果表明:亲缘关系对幼年螯虾种内斗争影响显著。随着仔虾来源的增多即亲缘关系复杂性的提高,螯虾的存活率总体呈下降趋势,而残虾率、体长变异系数、体长增长率总体上显著上升。  相似文献   

20.
饵料和养殖密度对中国对虾幼虾生长及存活率的影响   总被引：6，自引：0，他引：6  
在实验用虾遗传背景一致的情况下,分析了3种饵料(配合饲料、冰冻鲜鱼肉和活卤虫)和4个不同的养殖密度对小水体中国对虾幼虾生长和存活率的影响。结果表明,饵料和饲养密度对中国对虾幼虾生长及存活率有显著影响。在饵料、养殖密度单因子实验及饵料和养殖密度相结合的双因子实验中,幼虾的生长均表现出极其显著的差异(P<0.01),活卤虫对幼虾生长的效应尤为突出。而养殖密度对中国对虾的行为生物学、个体间体重增量均有影响。随着养殖密度的提高,中国对虾增重变慢;同时,个体间体重增量差异变大。随着养殖密度的增加,中国对虾幼虾的存活率呈下降趋势,但不同饵料对存活率影响变化幅度较大,波动在58.1%～85.2%之间,其中投喂活卤虫养殖密度为50尾/桶的存活率最高(85.2%);投喂配合饵料4个养殖密度梯度的存活率变化不明显;而投喂冰冻鱼肉4个养殖密度梯度的存活率变化较大。因此,采用合适的饵料和养殖密度,能够提高中国对虾的生长速度,提高对虾养成存活率,改善生长过程中对虾群体体长、体重的整齐度。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号