Biochemical indices (RNA/DNA ratio and protein content) in studying the nutritional status of Ruditapes decussatus (Linnaeus 1758) juveniles

In this work, we investigated the nutritional status of Ruditapes decussatus juveniles under different rearing conditions, using biochemical indices (RNA/DNA ratio and protein content) and the linear instantaneous growth rate (IGR). Two experiments were conducted to study the effect of starvation, addition of substrate (sand) as rearing support and diet composition on somatic growth and biochemical indices. Results show that biochemical indices of fed juveniles were significantly (P<0.05) higher. Highest RNA/DNA values and protein content were recorded in fed juveniles reared with substrate (P<0.05); conversely, lowest values were recorded in starved ones reared without substrate. In the second experiment, the highest RNA/DNA ratio was recorded in juveniles fed with control algal mixture composed of species commonly used in bivalve nurseries [Isochrysis galbana (clone T-Iso), Chaetoceros calcitrans and Tetraselmis suecica] and lowest in those fed with algal species isolated from Tunisian coasts. This confirms the usefulness of the RNA/DNA ratio and protein content in the clam's nutritional status evaluation. This assay is useful to provide information about the nutritional status and health of the clam in field conditions.     

稀有白甲鱼含肉率及肌肉营养成分分析

试验结果表明,稀有白甲鱼含肉率为69．92％;肌肉中蛋白质、脂肪和灰分含量分别为16．58％、2．05％、0．99％;肌肉中17种常见氨基酸（除色氨酸）总含量（占肌肉干重）为77．89％。其中必需氨基酸含量为36．27％,占氨基酸总含量的46．56％。必需氨基酸与非必需氨基酸含量的比值为0．87。鲜味氨基酸含量为26．26％,占氨基酸总含量的33．70％。必需氨基酸指数为70．44。缬氨酸和异亮氨酸分别为第一、二限制性氨基酸。     

低盐胁迫对细角螺幼螺呼吸排泄的影响

为了评估细角螺苗种对低盐胁迫的耐受能力,将细角螺(Hemifusus ternatanus)幼螺养殖盐度自27逐渐降低至22、18和14,测定处理后不同时间细角螺幼螺的耗氧率和排氨率。结果显示,盐度27降至22后幼螺耗氧率先显著降低,在第二天升至对照组水平,此后略有波动但均与盐度27无显著差异;盐度降至18与对照组无显著性差异;盐度降至14,细角螺的耗氧率先有显著升高,后与对照组相比无显著差异。盐度从27降至22后,幼螺的排氨率在第一、第二天显著升高,其后逐渐降低,盐度自22降至18和14,排氨率呈先降低后升高的趋势。盐度22处理后幼螺的氧氮比先降低后升高,盐度18和14处理组先升高后逐渐降低,说明低盐胁迫影响细角螺幼螺能量物质分解代谢的比率,胁迫条件下幼螺以脂肪和碳水化合物为主要供能物质。实验结果表明,第一次低盐处理对幼螺呼吸排泄的影响较大,此后再逐渐降低盐度,幼螺具有一定的适应能力。本实验结果可为细角螺养殖和放流前盐度驯化提供参考。     

Effects of C/N ratio and periphyton substrates on pond ecology and production performance in giant freshwater prawn Macrobrachium rosenbergii (De Man, 1879) and tilapia Oreochromis niloticus (Linnaeus, 1758) polyculture system

The production performances of giant freshwater prawn Macrobrachium rosenbergii and Nile tilapia Oreochromis niloticus in C/N‐controlled periphyton‐based polyculture systems were evaluated in triplicate. Three different management practices were compared: the traditional practice without addition of periphyton substrates and carbohydrate (Control), addition of maize flour to maintain a carbon: nitrogen rate of 20:1 (treatment CN) and addition of both maize flour and periphyton substrates (treatment CN+P). This experiment used a pre‐optimized stocking density of tilapia and freshwater prawn by Asaduzzaman et al. Aquaculture [286 (2009) 72]. All ponds were stocked with prawn (3 m²) and monosex Nile tilapia (1 m^?2). Bamboo side shoots were posted vertically into the pond bottoms as periphyton substrate covering an additional area of 171 m² for periphyton development. A locally formulated and prepared feed containing 17% crude protein with C/N ratio close to 15:1 was applied twice daily in all ponds considering the body weight of freshwater prawn only. Water quality parameters, except total alkalinity did not vary significantly (P > 0.05) among treatments. Both, organic matter and total heterotrophic bacterial loads (THB) in the sediment were significantly (P < 0.05) higher in treatment CN+P followed by treatment CN and control. Periphyton biomass in terms of dry matter and chlorophyll a values constantly decreased during the culture period. Substrates contributed 66% and 102% higher net yield of freshwater prawn than CN and control treatment respectively.     

Soybean molasses as an organic carbon source in the farming of Litopenaeus vannamei (Boone, 1931) in a biofloc system

Soybean molasses was evaluated as a partial replacement for sugarcane molasses as a carbon source for biofloc development in the superintensive culture of Pacific white shrimp (Litopenaeus vannamei). A 50‐day study was conducted with juvenile (3.2 g) shrimp stocked in 16 800 L tanks at a stocking density of 250 shrimp m^?3. Control of total ammonia concentration was performed by the addition of combined mixtures of soybean and sugarcane molasses to the culture water. Three different molasses treatments were evaluated using different soybean‐to‐sugarcane molasses ratios: 15–85%, 38–62% and 60–40% respectively. The control group was treated only with sugarcane molasses. Water quality, chlorophyll a concentration, heterotrophic bacterial load, Vibrio spp. concentration and zootechnical indexes were all evaluated. Total ammonia concentration was controlled by heterotrophic and chemotrophic pathways. Biofloc formation, as quantified by measuring the total suspended solids, was not altered. The Vibrio spp. concentration showed a significant reduction in treatments with soybean‐to‐sugarcane molasses ratios of 38–62% and 60–40%. All combined mixtures of soybean and sugarcane molasses could maintain water quality and productivity in the superintensive culture of L. vannamei using the biofloc system. Thus, the potential use of a residue from agroindustry as a carbon source in a biofloc culture is demonstrated.     

应用氮稳定同位素技术研究辽东湾海域主要渔业生物的营养级

应用氮稳定同位素技术分析了2010年6月和8月辽东湾海域主要渔业生物的氮稳定同位素比值,研究了28种鱼类和26种无脊椎动物的营养位置。结果表明,辽东湾海域主要渔业生物的营养级处于2.98～4.84,集中在3.70～4.56;相比6月δ15N值的分析结果,8月有50%的鱼类δ15N值增加,孔鳐(Raja porosa)增幅最大,增加了1.06‰;9种鱼类δ15N值减少,鯒(Platycephalus indicus)减幅最大,减少了1.84‰,可见鱼类样品的δ15N值随季节的变化因种类而各异;8月有87.5%的无脊椎动物δ15N值减少,其中,减少幅度大于1‰的有6种,占37.5%,可见无脊椎动物的δ15N值随季节的变化较明显。通过对不同采样点同种生物δ15N值的比较发现,辽东湾近岸海域的10种无脊椎动物的δ15N值均高于远岸海域,差值范围为0.05‰～1.49‰,差异极显著(P<0.01),说明人类活动引起的陆源污水排放使近岸海洋生物的δ15N值升高。     

Structural and Rheological Characteristics of Alginate from Sargassum cristaefolium Extracted by Twin Screw Extruder

This study aimed to investigate the effects of process extrusion on the characteristics of Sargassum cristaefolium sodium alginate (SCSA) extracted using twin-screw extruder. Box-Behnken Design (BBD) from response surface methodology (RSM) was established to understand the effects of temperature, screw speed, and pH on the multiple-responses of alginate characteristics including intrinsic viscosity, yield, and molecular weight. The results revealed that temperature, screw speed, and pH significantly affected (P < .05) all responses. The optimum extraction condition was found at temperature of 58.18°C, screw speed of 77.99 rpm, and pH 10.11. At this condition, the response of residence time distribution was 7.07 ± 0.029 min, yield of 34.01 ± 0.12%, intrinsic viscosity of 460.13 ± 14.75 mL/g, and molecular weight of 217.94 ± 7.14 × 10³ g/mol. This alginate had mannuronic acid to guluronic acid (M/G) ratio of 0.28, and the L-guluronic acid block was 0.78, which was higher than the D-mannuronic acid block. Rheological characterization of SCSA in aqueous solution was shear-thinning pseudoplastic, and alginate gel in 1 M CaCl₂ was more elastic than liquid.     

大鲵幼体蛋白质的需求量

为评定大鲵幼体对饲料蛋白质的需求量,以鱼粉为主要蛋白源配制6种蛋白质水平(干样基础)的实验饲料:D1(43.7%)、D2(47.1%)、D3(51.3%)、D4(55.7%)、D5(59.9%)和D6(64.4%),饲喂初始体质量为(20.99±0.15) g的大鲵幼体92 d。结果显示,①饲料蛋白质水平对大鲵增重率有显著影响,在D4组达到最大值,较D1组增加了276.4%,且全鲵蛋白质沉积率和肌肉RNA、RNA/DNA值、胃蛋白酶、H⁺-K⁺-ATPase、胰蛋白酶、脂肪酶和Na⁺-K⁺-ATPase、肝脏超氧化物歧化酶(SOD)均在D4组达到最佳,而肝脏和肠道丙二醛(MDA)在该组均达到最低;②随饲料蛋白质水平增加,肌肉粗蛋白线性增加,全鲵脂肪线性下降,全鲵水分和粗灰分在各组间差异不显著,全鲵粗蛋白先增加后趋于稳定,在D4组达到最大;③大鲵皮肤胶原蛋白含量在D4组达到最高,较D1组增加了27.83%。研究表明,以增重率、肌肉RNA/DNA值、蛋白质沉积率和皮肤胶原蛋白含量为评价指标,通过二次回归...     

Bioindicator role of aquatic Ranunculus in Mediterranean freshwater habitats

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Temperature‐dependent feed requirements in farmed blue mussels (Mytilus edulis L.) estimated from soft tissue growth and oxygen consumption and ammonia‐N excretion

Feed requirements were estimated from specific growth rates in standardized soft tissue dry weight (SGR_DW’) and atomic O:N ratios for mussels fed seven rations of microalgae (5–735 μg C h^?1 ind^?1) at 7 and 14°C respectively. The mean oxygen consumption and ammonia‐N excretion rates were significantly higher at 14°C (0.29 μg O² and 27.3 μg N ind^?1 h¹) compared with those at 7°C (0.16 μg O² and 11.4 μg N ind^?1 h^?1) (P < 0.05), resulting in O:N ratios between 3 and 45 at 7°C and 7 and 28 at 14°C. Low O:N ratios indicate protein catabolism and an unfavourable condition, whereas high ratios indicate that carbohydrate is the primary energy source. The measured SGR_DW’ suggests minimum feed requirements of ~240 and ~570 μg C ind^?1 h^?1 for weight maintenance at 7 and 14°C, with corresponding O:N ratios of 24 and 16, respectively, indicating a more stressed condition at 14°C. A 0.5% SGR_DW’ day^?1 was obtained by ~565 (O:N = 29) and ~680 (O:N = 23) μg C ind^?1 h^?1 at 7 and 14°C respectively. A positive and significantly higher SGR_DW’, with the lowest feed ration at 7°C compared with a negative SGR_DW’ at 14°C (P < 0.05), indicated that storage time can also possibly be prolonged at low temperatures if the mussels are not fed.