Management of paddlefish fry and juveniles in Bulgarian conditions

When paddlefish larvae were reared in tanks and fed on zooplankton, a length of 12–15 cm and a weight of 9.2 g had been obtained by the second month after hatching. After a further 2-months of pond rearing, the survival rate was 48%, and the juveniles had reached an average weight of 27.74 g and length of 22.5 cm. Much better growth rate was achieved when both paddlefish fry and juveniles were reared only on artificial food in tanks. At the end of the first month, a weight of 11.6 g had been reached; at the second month the paddlefish weight was 33.29 g, at the third month it was 60.2 g, and at the fourth month it was 127.7 g. There were two cases in which, respectively, 1,000 and 1,500 paddlefish with an average body weight of 33–60 g were stocked in a reservoir. At the age 5 months the fish had reached, or exceeded, an average weight of 500 g, and, after 1 year, it was over 700 g, which is an indicator of the good rearing opportunities this reservoir offered.     

饲料蛋白质水平对匙吻鲟生长、体组成及健康状况的影响

为探讨饲料蛋白质水平对匙吻鲟生长、体组成、消化酶活性、血清生化指标、抗氧化性能的影响。配制了5个不同蛋白质水平(35.44%、37.20%、39.19%、42.05%和45.30%)的等脂饲料,将初始体质量为(158.00±0.29) g的匙吻鲟在室外养殖系统中进行56d的饲养。结果显示:①随着饲料蛋白质水平的提高,实验鱼的增重率(WGR)和特定生长率(SGR)呈先上升后下降的趋势,其中39.19%、42.05%组的WGR和SGR显著高于35.44%、45.30%组;45.30%饲料组的蛋白质效率(PER)显著低于其他各组。以WGR和SGR为参考指标,回归分析结果表明,匙吻鲟获得最佳生长时对饲料中蛋白质水平的要求分别为40.67%和40.84%。②随饲料蛋白质水平的提高,实验鱼体成分没有显著性变化。③39.19%组蛋白质表观消化率显著高于其他组,45.30%组脂肪表观消化率和干物质表观消化率显著高于39.19%组和42.05%组;42.05%组肠蛋白酶活性和肝脏脂肪酶活性显著高于其他组;42.05%组肝脏淀粉酶活性略高于其他组;肝脏蛋白酶活性没有明显变化趋势。④饲料蛋白质水平对匙吻鲟血清生化指标有显著影响。39.19%、42.05%组实验鱼的谷丙转氨酶(ALT)显著低于其余各组;37.20%、39.19%组的球蛋白(GLOB)含量显著高于其他组,35.44%组白蛋白(ALB)含量显著低于其他组;总蛋白(TP)含量39.19%、42.05%和45.30%组之间无显著性差异。⑤饲料蛋白质水平为39.19%以上时,血清过氧化氢酶(CAT)活性显著高于低蛋白质水平组;除37.20%组,其余各组间超氧化物歧化酶(SOD)活性差异不显著;丙二醛(MDA)含量各组之间没有显著性差异。研究表明,在本实验条件下,匙吻鲟适宜饲料蛋白质水平为40%～41%。     

匙吻鲟亲鱼培育及规模化人工繁殖技术

采用分阶段培育方式培育匙吻鲟亲鱼,后备亲鱼（5～6龄）在水库及坝下池塘培育,催产用亲鱼在流水池中强化培育,各阶段通过控制水流速度、水温、水质和饵料条件,满足其性腺发育需求。2008年至2010年共培育后备亲鱼1017尾,性腺发育成熟亲鱼110组,并逐尾包埋电子标签,建立不同年龄段亲鱼种源库。采用B超结合体形观察判断早期性别,结合挖卵检查准确判断亲鱼的成熟度,依据成熟度确定催产剂量,并通过控制水温、水流速度、挤卵排精时间等催产和孵化条件,人工繁殖的催产率、受精率和孵化率显著提高,年均分别达到95%、95%、78.3%,三年共孵化匙吻鲟鱼苗1246.6万尾。实现了匙吻鲟规模化人工繁殖的目标。     

Spermiation of paddlefish (Polyodon spathula,Acipenseriformes) stimulated with injection of LHRH analogue and carp pituitary powder

The potential of carp pituitary powder (CPP) at one dose, or the luteinizing hormone-releasing hormone (LH-RH) analogue, des–Gly¹⁰,(d–Ala⁶)–LH-RH–ethylamide, at three different doses to stimulate spermiation in paddlefish (Polyodon spathula) was tested. Single injections of the LH-RH analogue at 0.2, 0.1, or 0.05 mg·kg^–1 increased the number of spermatozoa per kilogram of body weight (kg^–1 b.w.) by 4.7, 3.4, and 3.4 times respectively compared to control, but the number of spermatozoa per kilogram of body weight decreased with CPP (4 mg·kg^–1) by 1.7 times compared to the control. The LH-RH analogue prolonged active spermiation, with numbers of spermatozoa ranging from 7.69 to 1.19 × 10⁹ kg^–1 b.w. up to 96 h after treatment. Analysis of variance showed significant influence of experimental groups on volume of sperm per male and per kilogram of body weight, and the total number of spermatozoa per kilogram of body weight, but insignificant influence on the total number of spermatozoa per male. The percentage of motile spermatozoa was not different between experimental groups for sperm collection at different times after injection. A very high positive correlation (r = 0.93) was obtained between sperm concentration and sperm transmittance measured with a spectrophotometer. This relationship was described with the following linear regression: sperm concentration (× 10⁹ mL^–1) = 1.3244 X^–0.9969, where X is the percentage of sperm transmittance.     

Growth, survival and fillet composition of paddlefish, Polyodon spathula (Walbaum) fed commercial trout or catfish feeds

Paddlefish are gaining increasing acceptance as an aquaculture species worldwide. Commercial trout feeds, containing high protein and lipid levels, are currently used in intensive culture; however, nutritional requirements of paddlefish are not currently known. A study was conducted examining the effects on growth, survival and fillet composition of juvenile paddlefish when fed commercial feeds differing in protein and lipid levels. Paddlefish larvae were first stocked in 14.0 m³ round tanks and fed trout starter feeds for 43 days until trained to accept a 1.6 mm pellet. Paddlefish juveniles of mean weight (±SE) 20±0.27 g were randomly stocked into six0.02 ha ponds at 12 500 ha^?1 and fed floating commercial trout or catfish (lower protein and lipid) feeds, twice daily (08:00 and 15:30 hours) for 92–97 days. At harvest, there were no significant differences in final weight, percent survival, specific growth rate , relative growth and feed conversion ratio between treatments, which averaged 223.6 g, 96.2%, 2.5% day^?1, 10.2 and 1.98 respectively. Surface feeding activity index was significantly higher in ponds supplied with catfish feed than in ponds supplied with trout feeds. Relative pellet buoyancy was not a factor in feeding activity. Fulton's condition factor averaged0.238, was not significantly different, and was similar to a reported value for extensively cultured paddlefish (zooplanktivore). There was no significant difference in liver somatic index between treatments, which averaged 1.91%. Percent protein and moisture of fillets averaged 14.9% and 80.9%, respectively, and were not significantly different between treatments. However, lipid content of fillets was significantly higher in paddlefish fed the trout feed (4.45%), compared with paddlefish fed the catfish feed (2.42%). Fillet lipid content for both treatments was higher than reported values for extensively cultured paddlefish. Percent abdominal fat was significantly higher (0.82%) in paddlefish fed the trout feed compared with paddlefish fed the catfish feed (0.52%). Results from this study indicate that paddlefish can be fed a commercial catfish feed labeled to contain 32% protein and 4.5% lipid without adverse effects on growth, survival and fillet composition, lowering production costs.     

Quantity, motility and fertility of tench Tinca tinca (L.) sperm in relation to LHRH analogue and carp pituitary treatments

The spermiation of tench males was stimulated with Supergestran containing mammalian LHRHa lecireline at the following doses: 5, 10, 20 and 40 g kg⁻¹ b.w.; then with carp pituitary suspension (CPS) at a dose of 2 mg kg⁻¹ b.w. and with a control of saline physiological solution. The following days, meaning 24, 48 and 72 h after injection, sperm was collected to evaluate volume and the number of sperm per male per kg body weight (B.W.) The percentage of motile sperm and velocity of spermatozoa were measured 48 h after hormonal injection, and 72 h after hormonal injection the sperm was evaluated for fertilization and hatching ability. All 42 males in experimental groups were diploid. Live weight did not differ significantly among experimental groups. The strongest stimulation of spermiation was achieved with LHRHa in dosage of 20 and 40 g kg⁻¹ b.w. and CPS compared to males of the control group and lower dosage of LHRHa. Analysis of variance showed no significant influence of the treatment on the velocity and percentage of motile spermatozoa. The effect of different treatment on the fertilization capacity (the number of spermatozoa per egg was equilibrated) was significant. Significantly the highest quality of sperm collected 72 h after injection expressed by percentage of fertilization and hatching (62–65% fertilization and 61–64% hatching rates, respectively) was found for LHRHa in dosage of 20 and 40 g kg⁻¹ b.w. Significantly the lowest parameters of fertilization and hatching were found for the control group, on the 12% level.     

饲料脂肪水平对匙吻鲟生长、体组成、消化酶活性、血清生化及抗氧化性能的影响

为探讨饲料脂肪水平对匙吻鲟生长、体组成、消化酶活性、血清生化指标、抗氧化性能的影响,将鱼油与豆油等比例混合作为脂肪源,配制成脂肪水平分别为3.01%、5.12%、7.14%、9.35%和11.64%的5种等氮膨化实验饲料,将270尾匙吻鲟[初始体质量（81.38±0.14）g]分为5组,每组3个重复,每个重复18尾鱼,在室外养殖系统微流水养殖56 d。结果显示：①随着饲料脂肪水平的升高,实验鱼增重率（WGR）、特定生长率（SGR）、饲料转化率、蛋白质效率（PER）、肝体比（HSI）及肥满度（CF）均呈现先升高后下降的趋势,回归分析确定,当SGR达到最大值时,饲料脂肪水平为7.88%;当PER达到最大值时,饲料脂肪水平为9.47%;②实验鱼肌肉、肝脏粗脂肪含量随饲料脂肪水平上升而上升,11.64%组显著高于3.01%、5.12%和7.14%组,全鱼及肌肉粗蛋白含量随饲料脂肪水平增加呈上升趋势,3.01%组显著低于其他组,7.14%、9.35%组之间没有显著性差异;③实验鱼肌肉和肝脏主要脂肪酸组成与饲料脂肪酸组成相关,随着饲料脂肪水平的升高,肌肉和肝脏中n-6多不饱和脂肪酸（n-6 PUFA）比例升高,n-3/n-6降低,肝脏中饱和脂肪酸（SFA,C16：0、C18：0）随着饲料脂肪水平上升而下降;单不饱和脂肪酸C18：1n-9呈先上升后下降趋势;肌肉和肝脏脂肪酸组成中,组间n-3高不饱和脂肪酸（n-3 HUFA）、n-3 PUFA比例没有显著性差异;④7.14%组肠蛋白酶活性显著高于9.35%组,肝脏淀粉酶活性在脂肪水平7.14%以上组趋于稳定,肝脏蛋白酶和脂肪酶活性在组间没有显著性差异;⑤血清总蛋白（TP）、白蛋白（ALB）及球蛋白（GLOB）浓度随饲料脂肪水平升高呈上升趋势,血清总胆固醇（TC）、高密度脂蛋白胆固醇（HDL-C）浓度11.64%组显著高于3.01%组,谷丙转氨酶（ALT）和谷草转氨酶（AST）活性未受到饲料脂肪水平的影响;⑥饲料脂肪水平的上升可以显著提高血清超氧化物歧化酶（SOD）活性,回归分析得出当SOD活性达到最大值时,饲料脂肪水平为9.69%;但对谷胱甘肽过氧化物酶（GSH-Px）活性、丙二醛（MDA）含量没有显著影响;肝脏SOD活性11.64%组显著低于其他各组,GSH-Px活性9.35%组显著高于3.01%、5.12%、7.14%组,与11.64%组没有显著性差异,GSH、MDA含量在组间没有显著性差异。通过对饲喂不同脂肪水平饲料实验鱼生长、饲料利用率、鱼体组成、消化酶活性及鱼体健康等方面指标综合分析,认为本实验条件下,匙吻鲟适宜脂肪水平为7.88%~9.69%。     

Motility of spermatozoa ofAlburnus alburnus (Cyprinidae) and its relationship to seminal plasma composition and sperm metabolism

The composition of seminal plasma and metabolism of sperm of the cyprinid fishAlburnus alburnus were investigated. Statistically significant correlations were found between motility parameters and seminal fluid osmolality, pH, Na⁺, K⁺ and protein levels (negative correlations: % immotile spermatozoa-Na⁺, K⁺; positive correlations: % motile spermatozoa-osmolality, pH, Na⁺, K⁺, protein; % linear motile spermatozoa-pH protein; swimming velocity of spermatozoa-pH, Na⁺, protein). Spermatozoan motility and ATP metabolism and glycolysis were correlated as indicated by measurement of ATPase, pyruvate kinase, adenylate kinase and lactate dehydrogenase activity. The physiological meanings of these correlations and their possible significance for quality control of semen are discussed.Abbreviations used ACP acid phosphatase - ADP adenosine diphosphate - AK adenylate kinase - ALP alkaline phosphatase - ASPAT aspartate aminotransferase - ATP adenosine triphosphate - ATPase magnesium dependent adenosine triphosphatase - CRPO creatine phosphate - -GLU \-D-glucuronidase - ICDH isocitrate dehydrogenase - LDH lactate dehydrogenase - PK pyruvate kinase     

Chemical composition and osmolality of seminal fluid of Acipenser persicus; their physiological relationship with sperm motility

Determination of semen quality is necessary to understand the basic biochemical processes occurring during motility of sperm and during fertilization to evaluate the reproductive ability of different fish species and to create an optimal environment for storage of spermatozoa; in this regard less information is available for Acipenseridae compared with Cyprinidae and Salmonidae. The aim of the present study is to determine chemical composition and osmolality of seminal fluid and their relationship with sperm motility in Acipenser persicus. The results obtained show that sodium (Na⁺), chloride (Cl^?) and potassium (K⁺) were predominant ions in the seminal plasma and the average of osmolality of seminal plasma was 82.56 mOsm kg^?1. The higher chemical contents and osmolality compared with other sturgeon species reveal species‐specific characteristics and high secretory activity of spermatic duct in A. persicus. Significant positive correlations were observed between osmolality‐Cl^?, Na⁺‐osmolality and Na⁺–Cl^? (P<0.05, P<0.001 and P<0.05 respectively). But statistically significant correlation was not observed between seminal plasma parameters and sperm motility. Probably, the Na⁺ and Cl^? are the main electrolytes playing a major role in maintaining the osmolality of the seminal plasma and the viability of the spermatozoa in vivo.     

Insemination, fertilization and gamete management in tench, Tinca tinca (L.)

Various procedures for artificial insemination in tench, Tinca tinca (L.) were re-examined with evaluation of fecundity of males and females among different tench strains. The objectives of this study were to enhance fertilization and hatching rates through optimization of the activation solution, the insemination process, the activation of gametes, and the elimination of eggs stickiness. Sperm for all experiments was collected directly into immobilization solution of modified Kurokura solution containing 180 mM of NaCl and stored at 2 °C for 2.5–5 h prior to the experiment. When dechlorinated tap water was used for activation a gamete ratio of 1150 spermatozoa per egg showed the best significant fertilisation and hatching rates. Optimal ratio between eggs (weight in g) and activation solution (in cm³) was 1:1. Different concentrations of activation solutions such as NaCl from 0 to 68 mM (0–136 mOsmol kg⁻¹) without buffer statistically decreased fertilization and hatching rates. The activation solution containing 17 mM of NaCl, 10 mM Tris–HCl, pH 8 and 9 significantly increased fertilization and hatching rates compared to dechlorinated tap water of pH 7 or activation solution containing 17 mM of NaCl, 10 mM Tris–HCl, pH 6 and 7. Adhesiveness of the eggs was successfully removed by incubation in Alcalase and activity: 3.16 Anson units per cm³.     

金乌贼纳精囊组织结构及其精子的储存和利用

为揭示金乌贼精子进入纳精囊及产卵过程中的精子利用方式,丰富金乌贼繁殖生物学研究内容,本研究利用实验生态学和组织切片技术,检测了交配后不同时间段雌性口膜表面精子囊和纳精囊中精子数量的变化,观察分析了雌性金乌贼纳精囊的组织结构。结果显示,金乌贼纳精囊位于繁殖期雌性个体口膜腹面的突起处,共1对。纳精囊开口于口膜内表面,通过一根中央管连通整个纳精囊。中央管内壁含有大量褶皱和纤毛。在中央管两端,有12~20个储精小囊与之相连。储精小囊四周具有发达的环肌,其中储存有大量精子,并且大部分精子头部均朝向腔室内壁。完成一次交配后,雌性金乌贼对精子囊和纳精囊中精子的利用可以分为三个阶段,主要利用精子囊中的精子(交配后1~2 d);由利用精子囊中的精子向纳精囊中的精子过渡(交配后2~3 d);主要利用纳精囊中的精子(交配后3 d以上)。研究表明,从精子囊释放出的精子进入雌性口膜表面的褶皱中,通过自身运动到达纳精囊。进入纳精囊的精子通过自身运动及中央管内壁纤毛的摆动进入储精小囊,其中大部分精子头部朝向储精小囊内壁有规律地分布。在产卵过程中,雌性优先利用精子囊中的精子,而在精子囊中精子不足时,纳精囊通过肌肉收缩以及纤毛摆动将其中的精子逐渐释放出来,卵子在雌性口膜附近完成体外受精。     

Variation in prey selection and foraging success associated with early‐life ontogeny and habitat use of American paddlefish (Polyodon spathula)

Many fishes are planktivorous during early life and switch to piscivory or consume larger food items as ontogeny progresses. In contrast, paddlefish start as particulate feeders and later become filter feeders. Few studies have identified food items essential for paddlefish growth, survival and recruitment surrounding this ontogenetic diet shift. The objectives of this study were to investigate (i) prey types consumed by paddlefish, (ii) variability in prey selection surrounding an ontogenetic diet shift and (iii) whether habitat affected paddlefish prey selection or foraging success. We analysed gut contents of 189 wild age‐0 paddlefish from the middle Mississippi River (MMR) and also conducted a laboratory experiment to address these objectives. We found that paddlefish primarily foraged on benthic macroinvertebrates in the MMR, which differed from previous studies in lentic systems, suggesting young paddlefish prey selection may be labile depending on habitat (i.e., lotic versus lentic). Dominant prey of wild‐caught and experimental age‐0 paddlefish were caddisfly larvae (Trichoptera), followed by hemipterans and amphipods. We found little evidence that habitat attributes affected foraging success, but the most common prey items consumed were associated with wing dike habitat and the upstream and downstream tips of alluvial islands. Our experimental study revealed that if provided a mixture of organisms, age‐0 paddlefish will primarily consume macroinvertebrates while age‐1 paddlefish will mainly filter zooplankton. Overall results suggest young paddlefish prey selection can be highly variable, but also heavily reliant on a narrow group of prey resources.     

Reproduction of hatchery-reared and transplanted wild bay scallops, Argopecten irradians irradians, relative to natural populations

Efforts to restore bay scallop populations in the United States throughtransplantation of wild stock and reseeding of hatchery-reared individuals haveincreased due to declines in natural populations, yet little is known of thecomparative spawning patterns and relative reproductive investment of thesedifferent groups. In this study, spawning patterns of wild scallops from asource population in Northwest Harbor, New York and of scallops transplanted toa distant site in the same embayment (Flanders Bay) were similar.Hatchery-reared scallops held in pearl nets in Hallock Bay, New York showed thesame temporal spawning pattern and level of reproductive investment as scallopsfrom adjacent wild populations and wild scallops held in pearl nets. We suggestthat hatchery-reared scallops may be equally valuable as potential broodstockfor reseeding operations as wild scallops of the same size, provided thatappropriate conditioning and rearing practices are maintained. Both wild andhatchery-reared scallops may be transplanted a short period (i.e. 2–4weeks) prior to expected spawning to provide a source of potential broodstockinareas where natural population densities are low.     

匙吻鲟含肉率及肌肉营养成分分析

测定了10尾匙吻鲟(Polyodon spathula)含肉率、肌肉营养成分及其氨基酸含量,并对其营养价值进行了评价。结果显示:匙吻鲟含肉率达62.72%;鱼鲜肉中蛋白质含量为15.55%,脂肪为11.06%,灰分为1.28%,水分为72.08%,无氮浸出物为0.43%;17种氨基酸总含量为15.04%(鲜样),8种人体必需氨基酸总含量为5.37%。     

First multi-generation culture of the tropical cuttlefish Sepia pharaonis Ehrenberg, 1831

Sepiapharaonis, the pharaoh cuttlefish was cultured through multiplegenerations in the laboratory (5 consecutive generations) using closed,recirculating water filtration systems. The eggs of the original parentalgeneration (G_P) were spawned by a wild caught Gulf of Thailandfemale in alocal fisheries laboratory, then packed and shipped air cargo to Texas wherehatching occurred. The culture temperature ranged 25°–28°C, except for one generation that was chilled intentionallyto21 °C and then warmed to 25 °C after 9.6months. Spawning occurred as early as day 161. Spawning output was high in allgenerations except the group that was cultured at 21 °C. Eggfertility was low in captivity (< 20%), but hatchling survival was high(>70%). The average egg incubation time was 13.6 d at 25–28°C. The largest spawn resulted in 600 viable hatchlings andthesmallest resulted in 11 hatchlings. The cuttlefish ate a wide variety ofestuarine crustaceans and fishes as well as frozen shrimp. There were noapparent disease problems since survival from hatching to maturity was over70%.The average life span for cuttlefish cultured at 25–28°Cwas 8.9 months and 12.3 months at 21 °C. Size at hatching wasmeasured for fourth generation (G₄) hatchlings; the mean weight athatching was 0.103 g and the mean mantle length was 6.4mm. The largest cuttlefish cultured was a male 300 mmML and 3,045 g; the oldest cuttlefish lived 340 d.This cuttlefish species presents an excellent choice for commercial mariculturebecause of its rapid growth, short life span, tolerance to crowding andhandling, resistance to disease and feeding habits.     

长江鲟类资源现状及保护

归纳了白鲟、长江鲟、中华鲟近40年自然资源量变化情况,统计了长江鲟和中华鲟人工增殖放流数据,评估了增殖放流成效。因物种特性和分布的差异,放流无效的原因迥异。过度捕捞使人工放流长江鲟在放流后6个月之内难逃被“误捕”,而中华鲟放流数量不足及长江和近海过度捕捞导致中华鲟人工增殖放流的贡献甚微,其结果是长江鲟和中华鲟增殖放流均无法达到自然繁殖群体的补充水平。本文探究了近40年来白鲟、中华鲟和长江鲟在保护、管理和决策上存在的误区和不足,提出在生态大保护的背景下,(1)应编制和实施《长江鲟拯救行动计划》优先项目;(2)应以《中华鲟拯救行动计划》为指引,在就地保护、迁地保护和遗传多样性保护方面提出更具有可操作性的优先计划;(3)应设立中华鲟和长江鲟物种拯救行动计划专项,对现有涉栖息地或保护区生态补偿项目进行优化整合。唯有以恢复长江鲟和中华鲟自然繁殖为核心,才有望延续和恢复其自然种群,实现人与自然的和谐共处,推动长江流域社会经济绿色可持续发展。     

Kurokura Solution as Immobilizing Medium for Spermatozoa of Tench (Tinca tinca L.)

This study tested KUROKURA solution (Kurokura et al., 1984, Aquaculture 37, 267–274) and its modifications (by increasing NaCl content to 160, 180 and 200 mM) on immobilizing properties for sampling and short-term preservation of potential motility of tench spermatozoa. The immobilizing solution is used because, when collected, the sperm of most samples is contaminated by urine, causing spermatozoa to be of poor quality, with low motilities and velocities (almost 0), thus resulting in a worsened fertilization and hatching rate. Sperm was sampled with a syringe containing an immobilizing solution (IS), allowing an IS:sperm ratio of 2:1, under aerobic conditions at 0–4°C. This sperm solution was stored for 10 h and untreated sperm was collected prior to fertilization as a control. Spermatozoa quality was evaluated for the cell motility and velocity parameters and also for fertilization ability and hatching rate. Results obtained for tench sperm motility, velocity, fertilization and hatching rate showed that only sperm collected in the various immobilizing solutions can be successfully used for artificial insemination and preservation after 10 h at 0–4°C. The best immobilizing solution was found to be KUROKURA 180 (180 mM NaCl, 2.68 mM KCl, 1.36 mM CaCl₂· 2H₂O and 2.38 mM NaHCO₃), giving a fertility and hatching rate of 41%, with no change in rates after 10 h storage of sperm. Control sperm without immobilizing solution showed a fertilization and hatching rate of only 6–7%.     

Individual growth variation and its relationship with survival in juvenile Pacific oysters, Crassostrea gigas (Thunberg)

In order to study individual growth variability and its relationship with survival in juvenile Crassostrea gigas, parental oysters were sampled at four sites located along the French Atlantic coast and bred under controlled hatchery conditions. Four groups of larvae were obtained by crossing five males and five females from each of the four sites, and a fifth group by crossing these 20 males and 20 females together in a pool. Larvae were reared under conditions allowing the maintenance of a maximum variability of size and gave five experimental groups. Oysters were individually monitored for growth and survival from 3 to 10 months after fertilization. The individual growth performances were relatively stable over time and no noticeable compensation for growth occurred. Early growth rate was a very good predictor of size later in life: 66% of variation in the live weight at 10 months could be explained by variation in the initial growth rate calculated between 3 and 4 months. A significant group effect was observed on survival and on growth rate. Mortality mostly occurred between 3 and 5 months and appeared to affect the slow-growing animals more. However, two groups can be distinguished among those which died during the experimental period, one which showed a decrease in weight and the other whose growth was similar to surviving oysters. These results are discussed in the light of usual oyster farming practices and selective breeding. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of dietary coconut oil on reproductive traits and egg fatty acid composition in rainbow trout (Oncorhynchus mykiss)

Two hundred and twenty rainbow trouts (IBW: 700 g) were randomly allotted to four tanks, with a male/female ratio of 0.56. Fish were fed for 168 d with four experimental diets containing herring oil, cod liver oil and coconut oil with the following inclusion rates: diet A: 12-1-0% respectively; diet B: 6-1-6%; diet C: 0-1-12%; diet D: 0-0-13%. Irrespective of the dietary treatment, weight gains of broodstocks were high (> 3 g/d) and FCR below 2. No significant difference was observed concerning the total amount of eggs spawn, egg average weight (82.5 mg/egg) and lipid content (5.4 mg/egg). However, the fatty acid profile of eggs was significantly affected by the dietary treatments. The content of unsaturated fatty acids, particularly the n-3 fatty acid series (EPA and DHA) significantly decreased with increasing levels of coconut oil in the diet.