Comparative Gametogenesis of Spisula solidissima solidissima and Spisula solidissima similis Cultured in Coastal Georgia

Abstract— The reproductive cycle of two subspecies of surfclams, Spisula solidissimu solidissima and Spisulu solidissimu similis , cultured under similar nursery and field conditions were examined. Monthly gonadal examination showed that S. s. similis initiated gametogenesis, achieved mature status, and spawned earlier than S. s. solidissimu. S. s. similis spawned from January to June, while S. s. solidissimu spawned in May. S. s. similis exhibited an equal sex ratio; whereas, S. s. solidissima had significantly more males than females (1.00 M: 0.32 F). Implications for aquaculture development of surfclams are discussed.     

Effects of Temperature and Salinity upon Larval Growth, Survival and Development in Hatchery Reared Southern Atlantic Surfclams Spisula solidissima similis

Abstract.– Parameters associated with optimum larval-rearing conditions are important in developing the culturing protocol of potential aquacultural species, and have yet to be addressed in terms of water temperature and salinity for Spisula solidissima similis , the southern Atlantic surfclam. Hatchery spawned S. s. similis larvae were reared to late pediveliger stage in five simultaneously conducted water temperature and salinity treatments. This larval growth and survival experimentation consisted of three salinity treatments (15, 25 and 30 ppt) in conjunction with a water temperature of 20 C, and two water temperature treatments (15 and 25 C) in conjunction with a salinity of 25 ppt. In the 20 C temperature treatment, significantly higher larval survival and greater growth occurred (both, P < 0.0001) as compared to the 15 C and 25 C treatments by day 22. Complete larval mortality occurred in the 20 C, 15 ppt salinity treatment by day 4. No significant differences in larval survival occurred between the 25 ppt, 20 C and 30 ppt, 20 C treatments by day 22 (P = 0.714). However, significantly greater larval growth occurred in the 25 ppt, 20 C compared to the 30 ppt, 20 C treatment (P = 0.009). The optimum rearing temperature and salinity for hatchery spawned S s. similis larvae to late pediveliger stage are 20 C and 25 ppt, respectively, within the temperatures and salinities tested.     

Intertidal Growth and Survival of Northern Quahogs Mercenaria mercenaria (Linnaeus 1758) and Atlantic Surf Clams Spisula solidissima (Dillwyn 1817) in Georgia

This work reports on the effects of intertidal planting heights upon the growth and survival of the northern quahog, Mereenaria mercenaria (L.) and the Atlantic sod clam, Spisula solidissima (Dillwyn), in the castal waters of Georgia. Quahogs (N = 100 per cage) at 19.5 mm in shell length were planted in replicate cages (N = 3) placed at the spring (SLW), mean (MLW), one (+1), two (+2), and three (+3) hours above mean low water mark. Surf clams (N = 200 per cage) at 41.5 mm in shell length were placed in replicate cages (N = 3) deployed, as above, in all sites except +3. Quahogs grown at the SLW mark after 15 months were significantly larger than clams planted at other tidal heights. Quahogs planted at the MLW mark were significantly greater in shell length than those planted at the +3, +2, and +1 marks. Clams at the upper three sites were not significantly different in size. An inverse relationship between clam growth and intertidal planting height was evident among surf clams. Surf clams grown at the SLW mark for six months were signplificmtly larger than those at the MLW mark which were larger than those grown at the +1 above MLW mark. No significant differences in quahog survival were detected between intertidal planting sites. There was no significant difference in surf clam survival between SLW (77.5%) and MLW (61%) marks, but there was significantly lower survival at the +1 mark (15%) and no survival at the +2 mark.     

Some effects of gas-supersaturated seawater on Spisula solidissima and Argopecten irradians

Two size classes of the surf clam, Spisula solidissima, and the bay scallop, Argopecten irradians, were exposed to different concentrations of gas-supersaturated seawater in a flowing seawater system. Both species tested experienced no mortality when held in the control treatment maintained at 96% oxygen and 109% nitrogen. Mortality, gill tissue damage, gas emboli, membranous tissue blisters, and abnormal secretion of shell material were induced experimentally at elevated levels of gas supersaturation. Results indicate significant mortalities of surf clams and scallops held at 114% O₂ and 195% N₂, and at higher levels of gas concentration. These values suggest a point of reference for the bivalve culturist in identifying potential problems which can be caused by gas-supersaturated seawater.     

珠母贝人工苗中间培育的研究

2004年6-9月,分别采用不同养殖方法、光照度和水层对珠母贝人工苗进行中间培育。试验结果表明:不同养殖方法的成活率和壳高存在显著的差异(P<0.05),拱形笼吊养法、柱形笼吊养法、网箱法、开放式吊养法成活率分别为9.4%、27.3%、24.5%、0,壳高分别为26.5、31.4、29.8 mm、-,拄形笼吊养法和网箱法生长快且成活率较高;不同光照度对稚贝的壳高和成活率的影响显著(P<0.05),自然光组、800~1000 lx、300~500 lx成活率分别为24.7%、29.6%、36.5%,壳高分别为29.8、28.3、33.6 mm;2~3 m、4~5 m、6~7 m、8~9 m水层成活率分别为27.3%、29.1%、33.6%、38.9%,随着水层的加深而提高(P<0.05),壳高分别为31.4、30.6、29.5、30.2 mm,差异不显著。     

海水贝类养殖中污损生物的防除研究进展

据2002年统计,我国贝类养殖产量占海水养殖总量的79．4％,贝类养殖面积占海水养殖面积的66．9％,贝类养殖种类已发展到了30余种,其中主要为贻贝、扇贝、蛤、蚶、牡蛎等。贝类养殖已成为我国海水养殖业的重要组成部分。目前广泛采用的贝类养殖方式是网笼养殖,但是贝类在笼内放养一定时间后,一些海生动物、植物和微生物会在贝壳表面和养殖网笼的表面附着从而影响养殖贝类的正常生长。污损生物的大量出现严重影响了贝类养殖业的生产效率。如何有效地防止和减少污损生物对养殖贝类和养殖器具的危害,已成为水产养殖业的重要研究课题之一。     

两种方法培育的仿刺参幼参(Apostichopus japonicus)越冬期的成活率与生长

2005年11月至2006年4月，将室外土池培育（简称土池苗）和室内工厂化培育的仿刺参（Apostichopus japonicus）幼参（简称工厂苗）放养在室外池塘和蓄水池的网箱中，比较了越冬成活率和生长速度，测定了水质变化。经113d的越冬后，土池苗和工厂苗体重分别增加了79．2％和93．0％；土池苗（92．09％）的成活率比工厂苗（82．18％）高12．3％。蓄水池中的幼参体重增加了110．0％，成活率为10．2％。实验期间，蓄水池和土池中水温分别变化在．2．0℃～10．2℃和1．70℃～6．81℃；溶解氧量变化在2．51mg／L-7．21mg／L和6．75mg／L-15．19mg／L；土池水中溶解氧和氨态氮的含量随水温的“高-低-高”而呈“低-高-低”和“高-低-高”的变化；底栖硅藻的生物量变化在1．20mgim2～1553．56mg／m2之间，优势种为舟形藻（Navfcula sp）和新月拟罄形藻（Nitzschiella closterium）．文中还讨论了海参室外土池或网箱越冬的可行性。     

Ichthyophthiriasis of Atlantic salmon, Salmo salar L., at the Montta Hatchery in northern Finland in 1978–1979

Abstract. The occurrence of the ciliated protozoan Ichthyophthirius multifiliis on Atlantic salmon yearlings at a hatchery in northern Finland is described. During August 1978 a severe epizootic occurred in two earth ponds resulting in mortality of over 50%. Water temperature at this time was about 15°C. Fish were treated with a 1:4000 formalin bath administered every 3 days. Parasites disappeared from the fish by October after which they were refractory to further infection. The parasite occurred in other stocks in 1979 but was successfully controlled with formalin. Some aspects of the ecology of I, multifiliis are discussed.     

对虾育苗中常用海洋微藻抑菌作用的研究

研究了等鞭金藻、三角褐指藻、扁藻对对虾育苗中致病菌鳗弧菌、假单胞菌的抑菌效果。结果表明,等鞭金藻、三角褐指藻、扁藻的水溶性物质及脂溶性物质对鳗弧菌有抑制作用;等鞭金藻、三角褐指藻的水溶性物质及等鞭金藻、三角褐指藻、扁藻的脂溶性物质对假单胞菌有抑制作用。在抑菌试验中,等鞭金藻、三角褐指藻、扁藻密度达10×104/ml时,对对虾育苗池水的抑菌作用较好,特别是对弧菌的抑制效果明显。     

Pond Culture of Larval and Juvenile Cobia,Rachycentron canadum,in the Southeastern United States

Abstract

The potential of growing larval and juvenile cobia, Rach-ycentron canadum, in ponds was investigated. Larval cobia, obtained from tank spawning of wild-caught adults, were stocked 48-72-h post-hatch at a rate of 700,000/ha into three fertilized 0.25-ha ponds. At one week post-stocking (WPS), fish were observed consuming formulated feed. Growth was rapid, with specific growth rates (SGR) ranging from 12.5-19.2% body weight/day. At harvest (5 WPS) fish reared in two ponds weighed 7.9 and 9.3 g and total length (TL) was 118.9 and 129.3 mm, respectively (all fish reared in remaining pond died the night prior to harvest due to aerator failure). Feed conversion ratio (FCR) was 3.8 for both ponds and survival was 5.3 and 8.5%. Low survival rates were thought to be due primarily to cannibalism. Immediately after harvest, fish were restocked into two 0.25-ha ponds at a stocking rate of 14,400/ ha. Fish were fed formulated, pelleted feeds. Growth was rapid up to ～9 WPS, after which pond water temperatures declined. Ponds were harvested at 13 and 15 WPS, respectively. Final weight of fish was 309.9 and 362.5 g. Final TL was 343.1 and 355.7 mm. FCR was 3.8 and 4.5 and survival was 27.5 and 30.5%. Major losses of fish were associated with avian predators and possibly a toxic algal bloom. Results of trials indicate that cobia larvae and juveniles can be reared in pond-based culture systems, however additional research is needed to refine this approach.     

河蟹仔蟹管道式饲养初步研究

采用封闭式的蜂窝状塑料管道作为蟹穴,对河蟹仔蟹进行两个月的饲养观察试验,每隔１５ｄ测定一次壳长、壳宽和体重,用数理统计方法分析了河蟹的个体生长特点,比较了蟹穴饲养和非蟹穴饲养以及不同形式的蟹穴饲养效果。结果表明,仔蟹的个体生长为跳跃式的非连续增长。蟹穴饲养对河蟹的壳长、壳宽和体重的生长无不利影响,而增重率明显优于散养,且Ｌ型蟹穴的生长效果比Ｉ型蟹穴要好     

Effect of Salinity on Growth and Survival in Juvenile Opossum Pipefish,Microphis brachyurus,in Culture Conditions

Natural populations of the opossum pipefish, Microphis brachyurus, are affected in Mexico by anthropogenic alteration of their habitat and unregulated fishing as this species is traded as an aquarium fish without formal records as occurs with other syngnathids around the world. M. brachyurus is an estuarine fish adapted to salinity fluctuations. The aim of this study was to examine the effect on growth, condition, and survival of juvenile pipefish cultured for 4 wk at salinities of 0, 8, and 16 g/L. Pipefish were fed enriched Artemia nauplii maintaining a ration rate of 14% body weight per day (dry weight Artemia: wet weight fish). Pipefish cultured at 16 g/L showed lower survival (40%) than those at 0 and 8 g/L (100 and 96%, respectively), while juveniles cultured in 8 and 16 g/L were heavier (0.393 and 0.388 g, respectively), longer (9.9 cm), and grew faster (1.4) than those in 0 g/L (0.294 g, 9.1 cm, and 0.44, respectively). This study is the first to report that a salinity of 16 g/L compromises M. brachyurus culture potential and a salinity of 0 g/L caused poor growth while the optimal salinity for the species appears to be around 8 g/L.     

Intraspecific Differences in Physiological Efficiency of Juvenile Atlantic Halibut Hippoglossus hippoglossus L.

We compared growth efficiency, feeding consumption, metabolism, excretion, and energy allocation in populations of juvenile Atlantic halibut from Norway, Iceland, and Canada reared at low (8 C), medium (12 C, 15 C) and high (18 C) experimental temperatures. Our findings show that protein utilization and energy allocation in juvenile Atlantic halibut varies among different populations, as the Norwegian population displayed the highest protein efficiency ratio, protein production value, and energy conversion efficiency compared to the Canadian population, while the Icelandic population showed overall intermediate growth performance. The results do not conform to a simple thermal adaptation model but might represent an example of: 1) local adaptation of fish populations; or 2) countergradient variation where shorter growing season at higher latitudes is compensated with higher physiological efficiency. These findings have implications for halibut culture, particularly in selection work focusing on growth performance.     

Size Economies of a Pacific Threadfin Polydactylus sexfilis Hatchery in Hawaii

A spreadsheet model has been developed to determine the viable scale for a commercial Pacific threadfin Polydactylus sexfilis hatchery in Hawaii. The production scheme is modeled after current practices performed at the Oceanic Institute in Waimanalo, Hawaii. For a hatchery enterprise producing 1.2 million fry per year, the cost associated with raising one 40‐d‐old 1.00‐g fry is estimated at 22.01ø. The largest variable costs are in labor and supplies, which comprise 49% and 9% of the total production cost. The combined annualized fixed cost for development and equipment is approximately 12% of total production cost. At a sale price of 25ø per fry, the 20‐yr internal rate of return (IRR) is 30.63%. In comparison to the 22.01ø unit cost for 1.2 million fry production, analyses of smaller enterprises producing 900,000 and 600,000 fry per year reflected significant size diseconomies with unit costs of 27.41ø and 38.82ø, respectively. Demand to support a large scale Pacific threadfin commercial hatchery is uncertain. Since smaller scale commercial hatcheries may not be economically feasible, facilities may seek to outsource live feed production modules or pursue multiproduct and multiphase approaches to production. An analysis of the production period length, for example, indicates that the cost for producing a day‐25 0.05‐g fry is 17.25ø before tax and suggests the financial implications of transferring the responsibility of the nursery stage to grow‐out farmers. Evaluation of the benefits gained from changes in nursery length, however, must also consider changes in facility requirements, mortality, and shipping costs associated with transit, and the growout performance of and market demand for different size fry. Sensitivity analyses also indicate the potential cost savings associated with the elimination of rotifer, microalgae, and enriched artemia production. Managerial decisions, however, must also consider the quality and associated production efficiencies of substitutes.     

Portals of Entry for Gram-Negative Bacteria in a Freshwater Prawn Hatchery

We sought the source of gram-negative bacteria associated with giant freshwater prawns in a hatchery that was previously observed with severe mortality of prawn larvae during the sixth to seventh zoea stages. After thorough disinfection, the gram-negative bacterial microflora of broodstock, larvae, larval rearing tank (LRT) water, and other intake systems were examined for bacteria. Enterobacteriaceae and Vibrio were the major bacteria isolated from the larvae. The present study suggests that Enterobacteriaceae may be introduced via the broodstock and Vibrio via the LRT water.     

Dietary Trace Metal Supplements Promote Blood Vessel Melanosis in Fillets of Juvenile Farmed Atlantic Cod,Gadus morhua L.

Chronic over‐exposure to diet‐borne copper has been implicated in the development of black stripes caused by melanin deposits (melanosis) around the blood vessels in fillets of farmed Atlantic cod, Gadus morhua L. To test this hypothesis a 6‐mo pilot study using feeds containing controlled amounts of copper has been performed. Cumulative data from each feed group showed that 56% of cod fed a diet containing 10 mg/kg of added copper had black stripe while 58% of cod on a diet containing 5 mg/kg of added copper were affected. Cod on a diet with no added copper had 33% of individuals positive for black stripe, and in a final group on a diet containing no supplementary trace metals and minerals 16% of individuals were affected. Weight gain, increase in length, hepatosomatic index, and condition factor were unaffected by the changes made to mineral supplements. Melanosis has been observed in 24% wild cod of market size (n = 30) whilst 85% of market‐sized farmed cod examined have had black stripe (n = 403).     

Effect of Shelter, Broodstock Number, and Sex-Ratio on Juvenile Production in the Swordtail Xiphophorus helleri under Intensive Culture Conditions

Abstract.— Filial cannibalism has been identified as a constraint to the intensive production of swordtails Xiphophorus helleri . The objective of this study was to quantify the effect of refuge availability and quantity, broodstock population density, and adult sex-ratio on the rate of cannibalism under culture conditions. The availability of shelter had a significant effect on the number of harvestable juveniles, while the quantity of shelter did not affect harvest size. At a constant sex-ratio of 1:1 and broodstock population densities of four, ten, and 16 fish per 300-L tank the amount of juveniles harvested was lowest at the stocking density of four fish per tank, but did not increase significantly when stocking density was raised from ten to 16 fish per tank. Rate of cannibalism was lowest at the lowest population density. At a constant stocking density of ten fish per tank and sex-ratios of 1:1, 1:4, and 4:1 (male: female), the highest number of juveniles was obtained at a social structure of two males and eight females. Rate of cannibalism was independent of sex-ratio, indicating that males and females are equally cannibalistic. These results suggest that the 300-L broodstock tanks should be stocked with a maximum of two males and between five and eight females to obtain the greatest number of harvestable juveniles per tank.     

刺参苗种池塘小网箱培育试验

近年来,随着刺参（Apostichopus japonicus）虾池养殖和浅海围堰养殖规模的不断扩大,其人工育苗技术也得到迅速发展,刺参苗种的培育就显得尤为重要。室内培育幼参费用既高,又易出现病害,直接投放小个体成活率极低。采用池塘小网箱培育幼参费用既低,效益又高,是一种值得推广的好方法。