Predation by Dragonfly Naiads Anax junius on Young Crawfish Procambarus clarkii

Anax junius (Odonata: Aeschnidae) predation on young crawfish, Procambarus clarkii , was measured in the laboratory. Predation rates (0.066–1.16 crawfish/day) were estimated at 25, 15, and 5 C and for two sizes of crawfish (11–20 and 21–30 mm total length). Naiad predation increased with increasing temperature and decreasing crawfish size. At 5 C, naiads had no significant effect on survival of large crawfish but did significantly reduce survival of small crawfish. At 15 and 25 C, predation rates were significantly affected by temperature and prey size. Relative naiad abundance in a 0.8 ha crawfish pond was estimated from September through May. Larger naiads (head width, >6.5 mm; total length, >30 mm) capable of preying on young crawfish were not present until after most crawfish had reached invulnerable sizes. Large naiads, as a result, may not affect crawfish production under normal management conditions.     

克氏原螯虾的生态养殖⑤ 上海海洋大学克氏原螯虾生态养殖课题组协办 克氏原螯虾高效生态养殖模式

近年来,克氏原螯虾的养殖发展迅猛,已在全国各地形成各具特色的高效生态养殖模式,前面介绍的池塘生态养殖和稻田生态养殖只是众多模式中的一部分,下面介绍其它几种养殖模式,供广大养殖户借鉴.     

克氏原螯虾的池塘生态养殖(三）克氏原螯虾的池塘生态养殖

池塘饲养克氏原螯虾,对水体水质和池塘条件没有特别的要求,只要水质无工业污染,水中有机质丰富,即可进行粗放饲养.但如果要充分利用水体,提高单位水体的产量,则要对池塘进行一些必要的改造,辅以投喂饲料和日常管理,进行池塘精养.     

Growth of Crawfish Procambarus clarkii as a Function of Density and Food Resources

This study utilized enclosures (cylindrical, 5-mm wire mesh, O.5 m² bottom surface area) placed over rice-forage substrates in experimental crawfish ponds to contain crawfish under typical pond culture conditions. Juvenile Procambarus clarkii were stocked at six densities (2, 4, 6, 10, 14, and 18 crawfish/m²) for 12-wk growth trials in October and again in February. Crawfish relied solely on the detrital food system for their nutritional needs. Supplemental feed was supplied to crawfish in additional enclosures at two of the test densities (2 and 10 crawfish/m²). The commercially formulated feed (25% crude protein) was fed (2.02 g dry feed/m²) 3 d/wk (Monday, Wednesday, Friday). All treatments were replicated with six enclosures. Crawfish growth was inversely correlated to culture density. Mean final weights for crawfish feeding from the detrital-system only were 15.3, 13.8, 11.2, 7.9, 7.2, and 5.8 g for crawfish densities of 2, 4, 6, 8, 10, 14, and 18/m², respectively. Mean final weights for crawfish receiving supplemental feed were 20.7 and 12.4 g for densities of 2 and 10 crawfish/m². When compared with density as a factor influencing growth, feed influenced growth less than density abatement. Supplemental feeding improved crawfish growth in detrital systems an average of 46%, while decreasing initial density improved growth an average of 80.5%.     

Double-Cropping Malaysian Prawns,Macrobrachium rosenbergii,and Red Swamp Crawfish,Procambarus clarkii

Prawns, "Macrobrachium rosenbergii," and crawfish, "Procambarus clarkii," were alternatively grown in ponds to determine if they were compatible and if total production could be increased. Brood crawfish were stocked into replicated ponds at rates of 0,60, 120 or 180 kg/ha on 18 April. Water was removed to encourage burrowing. Following this, rice was planted as forage. Post-larval prawns (0.02 g) were stocked 3 July in all ponds at 17,500/ha. Prawns in half the ponds were fed and those in the other ponds were not. Ponds were drained from 7 to 11 October. Prawn production ranged from 157 to 248 kg/ha; survival ranged from 69% to 88%, and average size ranged from 11 to 7 g. There was no significant difference (P > 0.05) between fed and non-fed treatments. The ponds were reflooded and crawfish were harvested by trapping from 15 January to 15 May. The average yield of crawfish ranged from 746 to 1,266 kg/ha. Stocking rate had no effect of crawfish yields (P > 0.25). Total yield, with prawns and crawfish combined, ranged from 1,037 to 1,237 kg/ha. Overall, prawns and crawfish were compatible in rotation. Prawns were a good size for soft shell production during months when crawfish are not available for soft shell production.     

Evaluation of Trap Density and Type for Harvesting Crawfish Procambarus spp. from Small Ponds

Harvested crawfish were stocked into 0.15-ha earthen ponds in March and May at rates of 114, 227, and 455 kg/ha to evaluate the effects of trap density, 27 and 54 traps/ha, on their recapture over 14 d following 3 d of acclimation. Two-funnel, stand-up pillow traps and three-funnel pyramid traps were compared. About 39% and 55% of stocked crawfish were recovered in March and May, respectively. There was considerable growth of those crawfish. Overall catch with both trap densities was equivalent in March but the higher trap density caught 1.3 times more crawfish in May. Pyramid traps caught 1.5–1.9 times more crawfish than pillow traps.     

饥饿对克氏原螯虾仔虾消化酶和生化成分的影响

对照组连续饱食投喂6 d,处理组分别饥饿1、2、3、4、5、6 d,每组3个重复,研究了短期饥饿对克氏原螯虾仔虾消化酶活力和主要生化成分的影响.试验结果表明,在饥饿过程中,处理组胃蛋白酶、类胰蛋白酶、淀粉酶及纤维素酶变化趋势相同,先减小后增大,饥饿2 d后,4种消化酶均最小;淀粉酶与类胰蛋白酶活力比值(A/T值)不断增大.随着饥饿时间的延长,克氏原螯虾仔虾体内水分含量逐渐增多,总蛋白含量和碳水化合物含量不断减少,总脂含量变化不显著(P>0.05).     

角落空间与克氏原螯虾生活状况的关系

通过试验法研究了不同角落数与克氏原螯虾个体数比例的空间资源环境,对存活率、蜕壳率和SOD值的影响.试验结果表明,角落空间对克氏原螯虾的生存有影响,克氏原螯虾在角落资源合适时(角落数∶虾数=1～1.2∶1)生存较好,角落资源过多或过少对克氏原螯虾的生存都有负面影响.本试验结果利用了克氏原螯虾是一种具有优势等级序列的社会性动物的基本规律,表明空间资源过剩有可能升高其建立和维持其等级低位的能量代价.     

The Effect of Five Stocking Densities on Growth and Yield of Red Swamp Crawfish Procambarus clarkii

A 34-day study was conducted to estimate the effect of stocking density on growth, biomass, and yield of harvestable animals in red swamp crawfish, Procambarus clarkii (Girard). Juvenile crawfish were stocked at l, 2, 4, 8, and 16 crawfish per m² into plastic-lined metal pools planted with rice ( Oryza sativa ) with three replicate pools at each density. Crawfish averaged 35 ± 1.5 mm (SE) total length at the time of stocking.
Growth in total length and weight was significantly affected by density ( P < 0.01), ranging from 91.5 mm and 20.7 g for crawfish stocked at 1 per m² to 62.5 mm and 6.3 g for crawfish stocked at 16 per m². The total crawfish biomass ranged from 20.7 g per m² for crawfish stocked at 1 per m² to 88.7 g per m² at 16 per m². The portion of that biomass made up of harvestable sized animals (>75 mm total length) ranged from 100% at 1 per m² to 0.7% at 16 per m². Gross revenues per ha were projected for crawfish yields at each stocking density with and without a graded product.     

克氏原螯虾的营养保健功能及相关食品的研究与开发

综述了克氏原螯虾(俗称小龙虾)的营养保健功能以及小龙虾虾尾罐头、冻煮小龙虾仁、整肢冻煮熟小龙虾、小龙虾酱油等食品的加工技术,以期引起食品科技工作者对开发小龙虾食品的重视,供小龙虾养殖、加工企业同仁们参考,促进小龙虾产业链的形成.     

Substitution of Soybean Protein for Fish Protein in Formulated Diets for Red Swamp Crawfish Procambarus clarkii1

A 10 week laboratory growth trial was conducted with red swamp crawfish Procambarus clarkii to determine the amount of soybean protein that could be substituted for fish protein in formulated crawfish diets without reducing growth. Crawfish received 32% crude protein, isocaloric diets in which protein was supplied by soybean (soy) meal, menhaden fish meal or an isonitrogenous mixture of soybean and fish meal calculated to provide graded levels of each protein source. Dietary protein was provided as: 1) 100% soy protein; 2) 75% soy protein: 25% fish protein; 3) 50% soy protein: 50% fish protein; 4) 25% soy protein: 75% fish protein; and 5) 100% fish protein. Crawfish fed soy protein: fish protein (SP:FP) mixtures or fish protein alone exhibited better (P < 0.05) weight gain than crawfish fed a diet containing soy protein as the only protein source. Diets containing 25% soy protein: 75% fish protein (1:3 ratio) and 50% soy protein: 50% fish protein (1:1 ratio) produced greater (P < 0.05) weight gains than a diet in which fish protein was the sole protein source. Survival, feed efficiency ratio, maturation rate, net protein and energy retention, and body composition of crawfish did not differ (P > 0.05) among diets with SP:FP ratios of 1:3, 1:1 and 3:1. However, maximum (P < 0.05) weight gain occurred in crawfish fed the 1:3 SP:FP ratio. Although crawfish fed SP:FP ratios of 1:1 and 3:1 had lower weight gains in the laboratory than crawfish fed a 1:3 SP:FP ratio, SP:FP ratios of 1:1 and 3:1 might be adequate for supplemental diets fed to pond-reared crawfish that have access to natural sources of food.     

克氏原螯虾(Procambarus clarkii)与河蟹生态高效养殖技术

克氏原螯虾,俗称小龙虾,营养丰富,深受市场消费者青睐.作者简要概述克氏原螯虾(Procambarus clarkiai)与河蟹生态高效养殖技术与方法.     

Effects of Supplemental Feeding on Harvest of Red Swamp Crawfish,Procambarus clarkii,in Forage‐based Ponds

Procambarid crawfish aquaculture in the USA relies on an established forage‐based system for providing sustenance for growing crawfish. These systems may become inadequate at times for providing sufficient nourishment to support maximum growth of the population. Supplemental feeding is not routinely used because management recommendations for the cost‐effective use of supplemental feeds in ponds are not available. Because crawfish under confinement readily consume and grow well when fed single feedstuffs, such as rough rice seed and whole, raw soybeans, this study was initiated to investigate the use of these readily available low‐cost feedstuffs as supplemental feeds in aquaculture ponds. Earthen ponds (0.2 ha), constructed and managed to simulate commercial crawfish ponds, were used over three consecutive production seasons to evaluate the effects of supplemental feeding on yields and size of crawfish. Treatments for Seasons 1 and 2 consisted of (a) hull‐on rough rice seed, (b) whole raw soybean, (c) formulated 25% crude protein pellet, and (d) no supplementation and were replicated in four and three ponds for Seasons 1 and 2, respectively. Treatments for Season 3 consisted of (a) whole raw soybean and (b) no feed, with 10 replicated ponds each. Feeding frequency was established each year, and feeding rates were adjusted according to predetermined guidelines and monitoring of feeding trays. Crawfish harvesting was conducted by baited wire‐mesh traps and all harvested crawfish were subjected to a mechanical grader and sorted into three size classes. Results show that supplemental feeding, while trap‐harvesting operations are underway, can reduce yields and generate a negative economic benefit, perhaps as a result of residual feed within the pond rendering the baited trap less effective.     

Retention of Intermolt Crawfish in a Hydraulic Soft-Shell Crawfish Separation Unit

Physcial configuration and operational parameters of a prototype hydraulic soft-shell crawfish separator tray are described. The tray takes adavantage of the inability of soft-shell crawfish to resist a continuous water velocity to effectuate their rapid separation from a mixed population of pre-molts and intermolts. Removal of molted crawfish is rapid, and research therefore has focused on retaining intermolts in the separation tray. Given a well desigend separation tray, intermolt loss rates were found to be prinipally controlled by flow rate and intermolt retention time. Electrical inhibition gates powered by twelve-volt alternating current were used to discourage downstream migration of intermolts through administration of a mild shock upon contact. Crawfish became condioned to avoid the tray exit to the extent that they would not voluntarily approach the inhibition gate.     

Effects of Added Substrate on Production of Red Swamp Crawfish, Procambarus clarkii, in Earthen Ponds without Planted Forage

The effects of addition of substrate consisting of plastic mesh fencing to experimental earthen ponds were evaluated for the culture of the red swamp crawfish, Procambarus clarkii, without planted forage. Mean daily yield (kg/ha/d), number of crawfish harvested (number/ha/d), and mean individual harvest weight were compared for ponds with and without substrate during a 2‐yr period. The surface area of added substrate was equivalent to 50% of the bottom surface area of the pond. Mean daily yield in the ponds containing substrate, based on a comparison with that of the previous year, increased by 80.2% and was principally attributed to a 66.7% increase in the number of crawfish harvested. Comparative values for the ponds without substrate were ?13.1 and ?11.7%. For the second year, the treatment‐dependent response was consistent. Mean daily yield for the substrate ponds increased by 48.8% compared to 15.0% for the ponds lacking substrate. The primary benefit of the substrate appears to be provision of refuge and three‐dimensional distribution of crawfish in the pond, thereby reducing the incidence of cannibalism and increasing the total number of crawfish harvested per hectare per day. The benefit of the substrate in a commercial production setting must be weighed against its cost and longevity as well as the conditions of the particular management scenario into which it may be incorporated.     

Diversification of Crawfish Management Schedule1

Six 0.02 ha ponds were used to evaluate crawfish production and standing crop biomass of rice forage in ponds managed on a standard (control) and delayed (experimental) schedule over a two year production cycle. Delayed schedule followed the same sequence of events except the management activities were delayed approximately one month. Control and experimental ponds had statistically similar amounts of forage. No statistical difference was detected in crawfish production between the management schedules or between production years; however, analysis revealed a significant treatment × year interaction. Overall average crawfish production was 986 kg/ha. Variation in crawfish production is explained within the context of annual temperature variations and differences in population density.     

Predicting Crawfish Molting with Machine Vision

The objective of this project was to develop a vision system that could predict when crawfish will molt. Different sections of the crawfish shell were examined to determine how the color changed as the time of molting approached. A strip on the tail section of the crawfish showed the greatest, most consistent color change. The average red/green × red/blue ratio decreased for every crawfish as the molting time approached. Using this ratio as a predictor, it was possible to predict the molting of a crawfish within 3 d with an accuracy greater than 80%. The limitation on accuracy was primarily the result of the large variations in natural shell color among the crawfish.     

出口淡水小龙虾产品加工工艺及质量控制

综述了出口淡水小龙虾的加工工艺、操作要点及质量指标,对微生物和药物残留危害进行了分析,提出通过有效蒸煮及加强员工和环境卫生管理控制微生物污染,通过实施原料基地备案、源头管理和良好的员工操作行为等有效预防药物残留,在质量安全控制方面为加工企业提供参考依据.