Optimal stocking density of juvenile red king crabs Paralithodes camtschaticus under cannibalism consideration

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.     

Carbonic anhydrase and Na/K-ATPase activities during the molt cycle of low salinity-reared white shrimp <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis>

Changes in hemolymph osmolality, ion concentrations, and enzymatic activities of carbonic anhydrase (CA) in the gills and epidermal tissue, and Na/K-ATPase in the gills during the molt cycle were investigated in the white shrimp Litopenaeus vannamei. Hemolymph osmolality was high in the intermolt and early premolt stages, but started to decrease prior to ecdysis through to postmolt stages A and B. Changes in Na⁺ and Cl⁻ ion concentrations paralleled those in hemolymph osmolality. CA activity levels in the anterior and posterior gills were low at intermolt stage C₀ and premolt stage D₀, and maximum at premolt stage D₃. In the epidermal tissue, activity was relatively high at intermolt stage C₀ and premolt stage D₀, but fluctuated towards premolt stage D₃ and postmolt stage A. On the other hand, Na/K-ATPase activity in the gills decreased between intermolt stage C₀ and premolt stage D₂, but increased at premolt stage D₃ and postmolt stage A. The changes in patterns of CA activity during the molt cycle suggest that CA may be involved in supplying counter-ions for Na⁺ and Cl⁻ uptake during molting. Branchial Na/K-ATPase appears to be involved in producing local osmotic gradients in order to support water influx across the epithelium.     

Individual growth pattern of juvenile stages of the Chinese mitten crab (<Emphasis Type="Italic">Eriocheir sinensis</Emphasis>) reared under laboratory conditions

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?=?3.1059e^0.2149x 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.     

Limiting factors associated with nitrification in closed blue crab shedding systems

A study of factors limiting crab densities in closed blue crab Callinectes sapidus shedding systems was conducted using scaled down experimental units. Nitrification beds, activated carbon, dolomite and plants were used to maintain water quality. Nitrite (NO₂N) was found to be the most critical toxic element accumulating in the system as a result of the nitrification process. Concentrations of approximately 20 mg liter^?1 NO₂N and above caused increased mortality in intermolt crabs. Mortality in molting crabs was observed at concentrations as little as 2 mg liter^?1 NO₂N. Dissolved oxygen (DO) was identified as the factor limiting the efficiency of the nitrification beds. As DO concentrations decreased, the rate of nitrification slowed, apparently causing nitrification to be inhibited at the nitrite to nitrate conversion step. As nitrite concentrations increased, high mortalities resulted, further increasing the loading in the systems and depressing DO concentrations, due to the high BOD exerted by the dead crabs. Elevated crab populations were maintained in the systems when aeration and flow increases were supplied to the nitrification beds.     

Carbonic anhydrase and Na/K-ATPase activities at different molting stages of the giant freshwater prawn <Emphasis Type="Italic">Macrobrachium rosenbergii</Emphasis>

ABSTRACT:   In the present study, the role of carbonic anhydrase (CA) and Na/K-ATPase in the gill and epidermal tissues in the giant freshwater prawn Macrobrachium rosenbergii was examined as a function of molting stage. CA activity levels in the front and back gills were low at the intermolt stage C₀, but increased significantly at premolt stage D₃, and then decreased after molting. In the epidermal tissue, activity levels decreased gradually towards premolt to a minimum level at stage D₃, but became elevated at postmolt stages A and B. Na/K-ATPase levels in the front and back gills did not change significantly during the molt cycle. CA in the gill is possibly involved in supplying counter-ions for ion uptake, while CA in the epidermal tissue may play a role in mineralizing the exoskeleton after ecdysis. Na/K-ATPase in the gills may function in ion uptake from the ambient medium; however, since its activity was not influenced by the molt cycle, it probably does not have a major role in osmoregulation in the freshwater environment.     

Morphological and biochemical changes in the muscle of the marine shrimp Litopenaeus vannamei during the molt cycle

Morphological changes and biochemical composition of abdominal muscles over the molt cycle were investigated in juvenile Litopenaeus vannamei. Eight molt stages were characterized and clear uropod images are presented. Molt frequency was highly correlated with the age of the shrimp. Juvenile shrimps appeared to molt faster at one month of age (4.6 ± 0.5 days/cycle), slow to 11.8 ± 1.7 days/cycle at three months of age, and reach a long molt cycle at six months (17.2 ± 2.7 days/cycle). Myofiber cross-sectional images revealed specific morphological changes in abdominal muscle associated with each molt stage. Expanded fiber size was observed during intermolt stages. Water content and total soluble proteins were balanced throughout the molt cycle. Total DNA concentration increased in intermolt and premolt, while total RNA concentration remained stable except in late-premolt stages. SDS-PAGE analysis showed high levels of actin and myosin in postmolt, reaching a plateau in intermolt and declining in premolt. These results suggest the occurrence of muscle fiber rearrangement in both the premolt and postmolt stages. Abdominal muscle buildup occurs mostly during the intermolt stage.     

Effect of rearing density on the growth and welfare indices of juvenile spotted wolffish,Anarhichas minor (Olafsen)

The goal of this study was to determine the optimal stocking density for rearing juvenile spotted wolffish, Anarhichas minor (Olafsen), at two different sizes and assess the welfare status in relation to density. No major growth impairment was observed, although smaller fish (50–100 g) were significantly affected by density during the 120 days of the experiment, with final mean weights of 119.6 ± 11.6, 118.0 ± 5.8 and 88.7 ± 0.6 g for initial rearing densities of 10, 20 and 40 kg m^?2 respectively. No effect of rearing density was seen for larger fish (100–160 g) during the 90 days of the experiment, with final mean weights of 160.2 ± 5.9, 159.7 ± 3.7 and 163.7 ± 11.5 g at fixed rearing densities of 20, 30 and 40 kg m^?2 respectively. Our results suggest that the optimal rearing density of juvenile spotted wolffish is below 40 kg m^?2 for smaller size fish (～50–100 g) and probably ≥40 kg m^?2 for the larger fish (100–160 g). Furthermore, it appears that the range of rearing density used did not have a significant effect on a selection of stress indicators (Na⁺ and K⁺ concentration, haematocrit, hepatosomatic index, total amount of plasma proteins and liver and muscle water content) and immunity response (plasma lysozyme activity) of juvenile spotted wolffish, making it a very tolerant species to crowding.     

Dietary astaxanthin supplementation for hatchery‐cultured red king crab,Paralithodes camtschaticus,juveniles

We conducted large‐scale production trials in Seward, Alaska, USA to investigate effects of dietary astaxanthin supplementation on survival, growth and shell colouration of recently settled juvenile (C1–C4) red king crabs (Paralithodes camtschaticus). We supplemented a control diet of commercial crustacean feeds with astaxanthin, and fed these diets to juvenile king crabs at densities of 2000 and 4000 crabs m^?2 for 56 days. We assessed survival and growth by counting crabs and individually measuring carapace width and weighing crabs at the start and end of the experiment, and quantified crab colour (hue, saturation, brightness) in digital photographs. Diets containing astaxanthin had higher survival, suggesting that astaxanthin may provide nutritional or immune system benefits. Crabs had lower hue, higher saturation and lower brightness values when fed diets containing astaxanthin, suggesting that red king crab colouration is plastic and responds to diet. Astaxanthin is likely an important dietary component for hatchery or laboratory reared red king crab juveniles, and should be considered for aquaculture and other rearing of this and possibly other crustacean species.     

Effect of dietary <Emphasis Type="SmallCaps">l</Emphasis>-tryptophan on cannibalism,survival and growth in pikeperch <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.) post-larvae

The effect of supplemented commercial diets with crystalline l-tryptophan (TRP—5, 10 and 20 g TRP kg^?1) on cannibalism, survival and growth parameters of pikeperch post-larvae (Sander lucioperca) was evaluated. Fifteen-day-old pikeperch larvae (mean weight—6.8 mg) were reared during the next 28 days (20.5 °C, 16L:8D) in glass aquaria in a recirculating aquaculture system. The enzyme-linked immunosorbent assay showed that TRP-supplemented diets were effective in increasing the levels of serotonin (5-HT) in the body tissue of pikeperch. TRP supplementation resulted in a slight decrease in both types of cannibalism, although the reduction in cannibalism impact did not amount to more than a few percent. TRP treatment had no significant influence on the final survival of pikeperch post-larvae (ranged from 20.1 ± 12.4 to 29.0 ± 12.9 %). However, contrary to the earlier studies conducted on other fish species, no significant difference in the growth rates and feeding behavior of pikeperch between TRP-fed and control group were found. The final body weight and growth rate ranged from 0.211 ± 0.014 to 0.243 ± 0.016 and from 12.19 ± 0.38 to 12.76 ± 0.35 % day^?1, respectively. To our knowledge, this is the first study reporting the effects of TRP supplementation on the cannibalism–survival–growth relations in fish in the post-larval stage.     

不同规格中华绒螯蟹亲本子一代在扣蟹阶段养殖性能的比较研究

为探究中华绒螯蟹(Eriocheir sinensis)亲本规格对其子代在扣蟹阶段养殖性能的影响,本试验在相同的养殖环境下将4种规格河蟹亲本(规格I:雌90~110 g、雄140~160 g;规格Ⅱ:雌115~135 g、雄160~180 g;规格Ⅲ:雌140~160 g、雄220~240 g;规格Ⅳ:雌190~210 g、雄290~310 g)所产的大眼幼体养殖至扣蟹,并比较各组扣蟹的体质量、增重率、特定生长率、成活率及最终产量差异。试验结果显示:(1)不同规格的河蟹亲本,其子一代在大眼幼体至豆蟹阶段的平均体质量、成活率以及增重倍数均无明显差异(P>0.05);(2)在豆蟹至扣蟹养殖阶段,各组幼蟹的生长速度差异大体上与其亲本规格的差异相一致,其中Ⅰ组幼蟹在8—10月期间的平均体质量均显著低于Ⅳ组(P<0.05);(3)养殖效果方面,各组扣蟹平均规格和最终产量均随着亲本规格的提高而提高,其中Ⅳ组扣蟹的最终平均体质量显著高于Ⅰ组扣蟹(P<0.05);(4)就规格分布而言,Ⅳ组扣蟹2.00~3.99 g规格的比例显著低于另外3组,而≥6.00 g规格的比例显著高于另外3组(P<0.05)。结果表明,中华绒螯蟹亲本规格对其后代的养殖性能存在影响,大规格河蟹亲本子一代在扣蟹生产阶段生长速度快、养殖效果好,因此建议在生产上选择大规格亲本的后代用于扣蟹养殖。     

中华绒螯蟹Akt基因的cDNA克隆、序列分析及表达特征

为研究Akt基因在中华绒螯蟹蜕壳前后肌肉生长过程中的功能,应用RACE技术克隆得到编码中华绒螯蟹Akt(命名为Es Akt)的全长为2 200 bp的c DNA序列,包括159 bp的5′非翻译区(5′-UTR)、496 bp的3′非翻译区(3′-UTR)和长度为1545 bp编码514个氨基酸的编码序列。蛋白质结构域分析显示Es Akt含有丝氨酸/苏氨酸蛋白激酶家族的3个特征性保守结构域。多序列比对和系统发育分析显示,Es Akt与中国明对虾、凡纳滨对虾的Akt序列一致性都为0.889,在系统发育树中节肢动物Akt形成一个分支。应用荧光定量RTPCR技术分析Es Akt在性成熟中华绒螯蟹各组织及幼体不同蜕壳时期不同部位肌肉组织中转录水平上表达量的变化。结果显示,Es Akt在性成熟个体的肝胰腺、眼柄、表皮、卵巢、精巢、心脏、螯足、鳃、三角膜等组织中均有表达,其中卵巢、眼柄和精巢中表达量较高,肝胰腺中表达量最低。在幼体不同蜕壳时期不同部位的肌肉中,Es Akt表达量变化不同,步行足肌肉组织中Es Akt m RNA无显著的统计学差异。腹部肌肉组织中Es Akt m RNA水平在蜕壳前晚期D3~D4期表达量显著高于蜕壳后A~B期和蜕皮间期C期。螯足肌肉在蜕壳前晚期D3~D4期急剧下调,蜕壳后A~B期开始表达量显著升高,直至蜕皮间期C期。研究表明,Es Akt在中华绒螯蟹蜕壳过程中不同部位肌肉组织中的表达量变化与蜕壳周期密切相关,说明Es Akt参与中华绒螯蟹蜕壳诱导的肌肉萎缩、生长及重建过程。     

The effects of salinity on the survival, growth and haemolymph osmolality of early juvenile blue swimmer crabs, Portunus pelagicus

The blue swimmer crab, Portunus pelagicus, is an emerging aquaculture species in the Indo-Pacific. Two experiments were performed to determine the effects of salinity on survival, growth and haemolymph osmolality of early juvenile P. pelagicus crabs. The salinities tested for the first experiment were 10, 15, 25 and 40 ppt, and for the second experiment 5, 20, 30, 35 and 45 ppt. Each salinity experiment was triplicated, with each replicate consisting of 10 stage 4 juveniles. Each experiment lasted 45 days. Mortalities and incidence of “molt death syndrome” were recorded daily, while the intermolt period, carapace length, carapace width and wet weight were measured at each molt. At the end of the experiments the haemolymph osmolality and dry weights were measured.

Results demonstrate that salinity significantly affects both the survival and growth of early P. pelagicus juveniles. Mortality was significantly higher (p < 0.01) for juveniles cultured at salinities ≤ 15 ppt and at 45 ppt. At a salinity of 5 ppt a complete mortality occurred on day 20. In all salinity treatments, the majority of mortalities were due to “molt death syndrome”. In experiment 1, immediate effects of salinity on growth and development were seen at 10 ppt as the intermolt period was significantly longer (p < 0.01) and the mean carapace size increase was significantly less (p < 0.01) at the first molt compared to the other treatments. Meanwhile, the specific growth rates (carapace length, width and wet weight) were significantly lower (p < 0.05) at high salinities (≥ 40 ppt) due to longer intermolt periods and significantly lower (p < 0.05) carapace size or wet weight increases.

The haemolymph osmolality exhibited a positive linear relationship with the culture medium with an isosmotic point of 1106 mOsm/kg, equal to a salinity of approximately 38 ppt. Based on the osmolality graph, high metabolic cost for osmoregulation due to increased hyper- and hypo-osmotic stress appeared to cause lower survival and specific growth rates of the crabs. The results demonstrate that a salinity range of 20–35 ppt is suitable for the culture of early juvenile P. pelagicus.     

Effects of Limited Dissolved Oxygen Supply on the Growth and Energy Allocation of Juvenile Chinese Shrimp,Fenneropenaeus chinensis

Information about the effect of hypoxia exposure on energy allocation is helpful for better understanding how aquatic animals tolerate and adapt to a hypoxic environment. The growth, molting, and energy allocation were investigated in juvenile Fenneropenaeus chinensis exposed to five different dissolved oxygen (DO) seawaters (2.09 ± 0.15, 3.10 ± 0.29, 4.13 ± 0.25, 4.73 ± 0.12, and 5.48 ± 0.09 mg/L DO) for 30 d. When DO was below 4.13 mg/L, the growth of shrimp was depressed. Feed ingestion and feed conversion efficiency decreased with the decrease of DO. Less feed ingestion was caused by lower daily metabolic energy. Higher proportion of ingested energy lost in metabolism, exuviations, and nitrogen excretion caused lower feed conversion efficiency. More energy lost in exuviations, lower survival rate, soft carapaces of dead shrimp, and cannibalism were found in oxygen deficient groups and it implicated that hypoxia could delay the shrimp recovering from molting and cause cannibalism and higher mortality. The results indicated that hypoxia was an important factor affecting the amount and fitness of shrimp stock because it could cause a high rate of mortality and growth depression.     

中华绒螯蟹Smad3(EsSmad3)的cDNA克隆、序列分析及表达特征

为了研究Smad基因在中华绒螯蟹(Eriocheir sinensis)蜕壳前后肌肉生长过程中的功能,应用RACE技术克隆得到编码中华绒螯蟹Smad3(命名为Es Smad3)的cDNA全长序列2021 bp,包括36 bp的5′非翻译区(5′-UTR)、656 bp的3′非翻译区(3′-UTR)和编码442个氨基酸的开放阅读框。蛋白质结构域分析显示EsSmad3含有MH1和MH2两个特征性保守结构域。多序列比对显示,EsSmad3与人、斑马鱼、黑腹果蝇中的同源蛋白序列一致性分别为0.679、0.691、0.619。应用荧光定量RT-PCR技术分析EsSmad3在性成熟中华绒螯蟹各组织及幼体不同蜕壳时期不同部位肌肉组织中转录水平上表达量的变化。结果显示,Es Smad3在性成熟个体的肝胰腺、眼柄、表皮、卵巢、精巢、心脏、螯足、鳃、三角膜等组织中均有表达,其中眼柄和精巢中表达量较高,心脏和肝胰腺中表达量最低。在幼体不同蜕壳时期的不同部位的肌肉中,Es Smad3表达量变化不同:步行足肌肉组织中EsSmad3 mRNA表达在蜕壳间期高于蜕壳前D_(3–4)期和蜕壳后A~B期,但无显著的统计学差异(P0.05)。螯足肌肉在蜕壳前晚期D_(3–4)期急剧下调(P0.05),蜕壳后A~B期开始表达量显著升高(P0.05),直至蜕皮间期C期。腹部肌肉组织中EsSmad3m RNA水平在蜕皮间期C期显著高于蜕壳后A~B期,这种上调一直持续到蜕壳前晚前期D_(3–4)。上述结果表明,Es Smad3在中华绒螯蟹蜕壳过程中不同部位肌肉组织中的表达模式与蜕皮周期密切相关,推测Es Smad3参与了中华绒螯蟹蜕壳诱导的肌肉萎缩、生长及重建过程。     

日本沼虾蜕皮过程中头胸甲外骨骼超微结构的改变

采用HE染色及石蜡切片的扫描电镜观察方法,描述了日本沼虾(Macrobrachium nipponense)蜕皮间期(C期,intermolt stage)及新旧表皮更替变化剧烈的蜕皮前晚期(D4期,late premolt stage)和蜕皮后期(postmolt stage)A-B期头胸甲外骨骼的形态结构变化特点。结果显示,日本沼虾外骨骼分为上表皮、外表皮、内表皮三层,D4期出现新的上表皮和外表皮,B期出现新内表皮,外表皮强嗜碱性而内表皮弱嗜酸性。扫描电镜观察发现,C期头胸甲内、外表皮均为几丁质-蛋白质纤维构成的平行板层结构且板层内有发达的孔道系统(pore canals,pc),但内外表皮板层间排列紧密程度不同,外表皮板层切面边缘较整齐,结构致密,板层内pc大小均一、近似圆形,内表皮板层切面边缘粗糙,结构较疏松,板层内pc大小不等、多为梭形。在蜕皮前后,新外表皮结构变化显著,与C期相比,D4期新外表皮超微结构与旧内表皮结构相似,而在A期,外表皮超微结构由疏松变为致密,这可能与蜕皮后表皮的钙化相关。本研究旨为阐明沼虾的蜕皮机制提供基础资料。     

Effects of temperature, stocking density and diet on the growth and survival of juvenile Mithraculus forceps (A. Milne Edwards, 1875) (Decapoda: Brachyura: Majidae)

Mithraculus forceps (A. Milne Edwards) has demonstrated a great potential for ornamental aquaculture and the present study tests the effects of temperature, stocking density and diet on the survival and growth of M. forceps juveniles. For 28 days post metamorphosis (DPM), the newly metamorphosed juveniles were reared at two temperatures (25±0.5 or 28±0.5°C), stocked at five densities (1, 5, 15, 30 or 60 crabs ring⁻¹; approximately 226, 1132, 3395, 6791 or 13 581 crabs m² respectively) and fed with commercial pellets (CP), microalgae (Amphora spp.), live newly hatched Artemia nauplii (NHA), frozen Artemia nauplii (FNHA), or combinations of each of these diets with NHA. At the end of the temperature experiment, carapace width of the crabs cultured at 28°C was significantly larger than the crabs reared at 25°C and average intermolt period was significantly shorter. Increased stocking density had a negative effect on survivorship and growth. Survivorship at the end of the diet experiment was significantly different between the crabs not fed, fed with CP and Amphora and the crabs fed with the other diets. Between the diet treatments, the crabs fed with NHA+Amphora were significantly larger than the ones fed with NHA+FNHA, NHA, FNHA and NHA+CP, and these in turn larger than ones fed with Amphora.     

Optimum low salinity to reduce cannibalism and improve survival of the larvae of freshwater African catfish <Emphasis Type="Italic">Clarias gariepinus</Emphasis>

The freshwater African catfish Clarias gariepinus is carnivorous and cannibalistic even during the larval and juvenile stages and this behavior causes economic losses in aquaculture. This study examined for the first time the effect of salinity on cannibalism, survival, and growth of African catfish larvae in the hatchery. Larvae (4 days old, median 7.8 mm TL, 2.8 mg BW) of the African catfish were reared for 21 days at nominal salinity 0, 1, 2, 3, 4, 5, 6, and 7 ppt. After 21 days, they grew to 10–39 mm (median 22 mm) and 10–490 mg (median 90 mg), with no significant difference by salinity treatments. Survival ratios were similarly low (24–31%) at 0, 1, 3, and 7 ppt and significantly higher (49–55%) at 2, 4, 5, and 6 ppt. Cannibalism was significantly lower, 15–30% at 4–6 ppt, than the 40–50% at 0–3 and 7 ppt. Size variation was lower at 4–6 ppt and higher at 0–3 and 7 ppt. We recommend hatchery rearing of African catfish at the optimum low salinity of 4–6 ppt rather than in full fresh water at least up to 21 days. This rearing method fosters larval welfare and improves hatchery production.     

盐度突降对拟穴青蟹仔蟹生长发育和Na＋／K＋-ATP酶活性的影响

研究了盐度（6、13、20、27和33）对拟穴青蟹仔蟹（Scylla paramamosain）生长发育和Na＋/K＋-ATP酶活性的影响。结果表明,盐度对拟穴青蟹仔蟹特定生长率（甲宽和体重）、C3蜕壳间期、甲宽增量（C1至C2和C2至C3）及Na＋/K＋-ATP酶活性有显著影响（P〈0．05）,但对仔蟹存活率、C2蜕壳间期及C3至C4甲宽增量无显著影响（P〉0．05）.盐度13处理组特定生长率最高、蜕壳间期最短,盐度69．1：理组特定生长率最低,但与盐度20、27和33处理组无显著差异（P〉0．05）,而盐度33处理组蜕壳间期的延长降低了其生长速度;除C1蜕壳为C2的甲宽增量以盐度20处理组最大外,C2、C3蜕壳后的甲宽增量均为盐度13处理组最大;不同盐度条件下,仔蟹Na＋／K＋-ATP酶活性在实验开始后12h、48h、168h和264h时分别表现为盐度6〉13〉20〉27〉33、6〉13〉27〉20〉33、6〉13〉20〉27〉33和6〉13〉33〉20〉27的趋势,低盐环境下酶活性的升高可能有助于拟穴青蟹仔蟹对低渗环境的调节。试验结果表明,拟穴青蟹C1～C3的适宜盐度下限为13以上,C3后对低盐环境的适应能力明显增强,可在盐度6以上的低盐度环境中正常生长。     

The molt stages and the hepatopancreas contents of lipids,glycogen and selected inorganic elements during the molt cycle of the Chinese mitten crab <Emphasis Type="Italic">Eriocheir sinensis</Emphasis>

A rapid molt-staging technique was developed for the Chinese mitten crab Eriocheir sinensis, with the aim of investigating selected molt-linked biochemical and inorganic factors in these animals. The results allow the identification of four distinct molting periods (postmolt, intermolt, premolt and ecdysis) and the further classification of the premolt period into three substages (D₀, D₁ and D_3-4). These findings are consistent with the classical scheme elaborated by Drach and Tchernigovtzeff (Vie Milieu 18:595–610, 1967). The contents of lipids, glycogen and several inorganic elements (Ca, Mg, Cu and Zn) in the hepatopancreas fluctuated and agreed well with their functions and with the molting stages during the molt cycle.     

Egg cannibalism in Acartia tonsa: effects of stocking density,algal concentration,and egg availability

Cannibalism in copepod culture may limit its production yield and therefore affect the economic interests associated with the use of copepods as live feed in aquaculture. The effects of adult density, egg density, and algal availability were tested on the calanoid copepod Acartia tonsa to understand how these parameters affect cannibalism rates on eggs. The overall cannibalism within the range of adult densities tested (120–1,000 adult L^?1) was solely influenced by the egg and algal density, and not by the adult density. The increased densities of eggs lead to higher occurrences of cannibalism. Increasing the availability of alternative diets (e.g., algae) significantly diminished the adults’ cannibalistic behavior. The highest cannibalistic rates per adult were observed at low densities of adults and high densities of eggs (120 ind L^?1 and 20,000 eggs L^?1, respectively) and resulted in consumption rates >20 eggs ind^?1 h^?1. In this experiment, cannibalistic behavior reached 20 % of adult weight ind^?1 h^?1 under the aforementioned parameters. Additionally, the present study suggests that at high adult copepod density, the interactions between adults result in a decreased “time to feed.” Finally, it is argued that the separations of eggs from adult copepods, as well as the continuous access to an alternative food source, are necessary for decreasing the effects of cannibalism in copepod cultures.