冬季苦草分解速率及营养盐释放规律研究

采用分解网袋法研究了冬季苦草腐败分解速率及其氮、磷损失规律。结果表明：苦草腐败释放的磷大部分被底泥吸附,少量进入水体;释放到水体中的氨氮（NH4＋-N）、亚硝态氮（NO2--N）和硝态氮（NO3--N）数量也较少;底泥减缓了苦草干重损失速度,而加快了TN和TP损失速率;苦草分解过程中磷的释放速率比氮快;苦草腐败分解具有阶段性,前36d分解迅速,以后分解速率显著下降。     

养殖水体氨氮转化形式及调控(上)

正水体中的污染物主要来自有机物。水体中的有机物来源于两个方面:一是外界向水体中排放有机物;二是生长在水体中的生物群体产生的有机物以及水体底泥释放的有机物。在养殖水体中,有机污染物主要包括氮、碳、磷、硫4种,氮的分子氨态及亚硝酸氮态存在形式对水生动物产生很强的神经性毒害。高密度养殖模式加大了水体有机氮物质分解转化的负荷,微生物分解环节严重受阻,从而制约了水体系统循环     

生态基对大口黑鲈养殖池塘氮、磷累积的影响

为了研究生态基对大口黑鲈(Micropterus salmoides)养殖池塘氮,磷累积的影响,对大口黑鲈进行了6个月的室外池塘养殖试验。养殖期间不同时间段内分别对养殖水体亚硝态氮(NO_2-N)、硝态氮(NO_3-N)、铵态氮(NH~+_4-N)、磷酸盐(PO_4~(3-)-P)、总氮(TN)、总磷(TP)、总有机碳(TOC)含量以及养殖池塘底泥的TN、 TP、TOC含量进行了测定。结果显示:养殖水体氮相关指标中,生态基处理组TN、NO~-_3-N、NH~+_4-N含量极显著低于对照组,N累积显著低于对照组;生态基处理组TP含量极显著低于对照组,水体P累积显著低于对照组。池塘底泥中碳、氮、磷相关指标中,生态基处理组池塘底泥TOC、TN、TP含量与对照组无显著差异。实验结果表明,挂设生态基对降低大口黑鲈养殖池塘水体氮、磷含量有显著效果。     

养殖水体沉积物中氮的形态、分布及环境效应

养殖水体沉积物中的氮可分为有机态氮和无机态氮,以有机态氮为主(70％～90％)。无机态氮主要有NO3--N、NO2--N和NH4 -N,其中以NH4 -N为主。各形态的氮含量在水平方向上的分布随距污染源的远近而有小到大变化;垂直方向上的分布则是:NH4 -N随沉积深度的增加含量增大,NO3--N随沉积深度的增加含量减小,而NO2--N随沉积深度的变化不明显。     

基于15N稳定同位素技术的斜生栅藻对硝氮和氨氮吸收研究

硝氮(NO3--N)和氨氮(NH4+-N)是水体中无机氮的主要形态。利用15N稳定同位素技术研究了斜生栅藻(Scendesmus obliquus)对NO3--N和NH4+-N的吸收特征。结果显示,在相同浓度条件下,斜生栅藻对NH4+-N的吸收速率显著高于对NO3--N的吸收率,在180min的试验中,对15NH4+-N的吸收速率为0.62～1.15μmol/(g·min);对15NO3--N的吸收速率为0.08～0.15μmol/(g·min)。在NO3--N和NH4+-N2种形态氮源同时存在的混合组中,斜生栅藻对NO3--N的吸收速率[0.12～1.00μmol/(g·min)]显著低于NO3--N作为唯一氮源的单一组[0.78～1.23μmol/(g·min)],表明NH4+-N的存在对藻类吸收NO3--N有抑制作用。在14NO3--N和15NO3--N同时存在时,斜生栅藻优先吸收14NO3--N,产生同位素分馏效应,但不同形态氮对藻类氮吸收的影响远远大于同位素的影响。     

珠江三角洲基塘氮磷的含量分布及与水质关系初步探讨

采集珠江三角洲顺德基塘水和底泥样,测定NH4+-N、NO3-N、NO2——N以及水体中的TOC、DO、BOD,研究基塘水体中氮的形态分布及其水化学影响因素.测定结果表明,氮几种形态在水体中的垂直分布变化不明显,但在水体和底泥中的分布差别很大.水体中的硝酸盐氮含量比亚硝酸盐氮含量高,底泥中硝酸盐氮含量大幅度降低,亚硝酸盐氮和氨氮含量升高,表明底泥对硝酸盐氮释放通量较大.氮和水化学指标之间的关系:DO与硝酸盐氮呈负相关;TOC与总氮呈负相关,与亚硝酸盐氮呈正相关,总有机碳与氮相关性显著;回归方程显示水体环境中的氮主要和BOD关系密切.总氮与硝酸盐氮呈正相关,与亚硝酸盐氮呈负相关;基塘水体有效态无机氮的变化主要是由硝酸盐氮决定.磷和水化学因子之间的关系:DO与正磷酸盐呈正相关,BOD与正磷酸盐呈负相关;COD与总磷呈正相关.     

中华绒螯蟹有机和常规养殖池塘底泥氮磷溶出特性研究

采用室内模拟研究的方法,研究中华绒螯蟹(Eriocheir sinensis)有机和常规养殖底泥中氮、磷的溶出规律。结果显示:有机组氨态氮溶出总量明显高于常规组,覆水前期,底泥厚度是决定氨态氮溶出总量的主要因子,中后期底泥类型成为主要因素。相同厚度底泥中有机组硝态氮的污染负荷明显低于常规组。常规组较有机组更容易在短时间内溶出硝态氮和亚硝态氮。5 cm和10 cm底泥厚度下有机组溶出总磷量分别高于常规组60.5%和56.5%,但在前4 d有机组的溶出速率低于常规组,应提早换水以有效控制总磷浓度。     

基于^15N稳定同位素技术的斜生栅藻对硝氮和氨氮吸收研究

硝氮（NO3--N）和氨氮（NH4＋-N）是水体中无机氮的主要形态。利用15N稳定同位素技术研究了斜生栅藻（Scendesmus obliquus）对NO3--N和NH4＋-N的吸收特征。结果显示,在相同浓度条件下,斜生栅藻对NH4＋-N的吸收速率显著高于对NO3--N的吸收率,在180min的试验中,对15NH4＋-N的吸收速率为0.62～1.15μmol/（g·min）;对15NO3--N的吸收速率为0.08～0.15μmol/（g·min）。在NO3--N和NH4＋-N2种形态氮源同时存在的混合组中     

沉水植物苦草对沉积物各形态磷时空分布的影响

监测苦草生长过程中根系及沉积物中磷含量和形态的时空变化,探讨苦草根系在生长过程中对沉积物磷时空分布的影响。聚乙烯塑料桶中铺设沉积物为暴发水华水体的底泥,厚度10cm,干重4 821.00g,底泥铺设完毕后缓慢注入100L水(TP 0.02mg/L)。试验桶种植2g苦草休眠芽。沉积物样品磷形态分析采用国际通用的SMT法,在采集沉积物同时采集苦草样品,测定根系生长情况及根系在沉积物中的分布。结果表明:苦草在生长过程中能降低沉积物各层总磷(TP)、NaOH提取磷(NaOH-P)、HCl提取磷(HCl-P)、无机磷(IP)和有机磷(OP)的含量,沉积物各形态磷含量的下降速率为:NaOH-PHCl-PIP=OP;随着苦草根系的生长,在苦草根系分布区沉积物中各形态磷的含量明显低于非根系分布区。苦草根系通过对环境因子氧化还原电位和pH的改变从而影响根系周围沉积物磷的含量,沉积物中各形态磷含量随着苦草根系面积的增加而减小。     

海水养殖池塘底泥异养硝化作用的研究

以两种不同养殖对象池塘中的浅层底泥为样品,研究其在外加有机碳源(乙酸钠)的情况下硝化作用所受的影响,包括了NO2--N累积量的变化和培养液pH值的变化。结果表明,在外加有机碳源(乙酸钠)的情况下,供试底泥的硝化作用虽然受到了一定的影响,但仍然存在,且保持了较高的硝化能力。并进一步考察了上述两种底泥对水体中有机质、氨态氮和亚硝酸盐的去除能力,探寻了利用异养硝化作用改善水质环境的潜力。     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

Protein and amino acid composition from the mantle of juvenile O ctopus vulgaris exposed to prolonged starvation

Protein and amino acid composition of the mantle of juvenile O ctopus vulgaris (Cuvier, 1797) during fasting for 27 days were determined. Average protein content of octopus mantle was of 711.19 ± 46.80 g kg^?1 DW, and it decreased with increasing fasting days. The non‐essential amino acids content was higher (486.18 ± 11.08 g kg^?1 protein) than essential amino acids (425.82 ± 9.15 g kg^?1 protein) at the start of the experiment (unstarved animals). The results suggest that the amino acid profile of the mantle where the most abundant amino acids are Arg, His, Lys, Gly, Leu and Pro could indicate a prolonged fasting condition (>20 days) or poor nutrition of O . vulgaris. This study supports the idea of using mantle for metabolic needs of starved O . vulgaris suggesting that the degradation pathway of amino acids to pyruvate and tricarboxylic acid cycle intermediates was favoured contrary to the degradation pathway of ketogenic amino acids. Special considerations should be taken concerning Thr, Ile, Ser, Ala, Asx (Asp, Asn), Glx (Glu, Gln) (because of their fast intake) and Lys and His (due to their stable contents) during a prolonged period of fasting.     

Involvement of gonadal steroids in final oocyte maturation of white perch (Morone americana) and white bass (M. chrysops): in vivo and in vitro studies

Plasma estradiol-17 (E₂), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E₂ and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E₂ and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.     

Cardiac,ventilatory and metabolic responses of two ecologically dissimilar species of fish to waterborne cyanide

Changes in heart rate, ventilatory activity and oxygen consumption were determined in trout (Salmo gairdneri) and brown bullhead catfish (Ictalurus nebulosus) during exposure to a steadily increasing concentration of waterborne cyanide selected to produce death in 8–9 hours for each species. The lethal cyanide concentration for the bullheads was an order of magnitude higher than for trout. Trout developed an immediate and gradually increasing bradycardia throughout the exposure period. Cyanide produced tachycardia in the bullhead followed by a gradual onset of bradycardia as the concentration of cyanide was raised. Pericardial injection of atropine (a muscarinic cholinergic antagonist) indicated that bradycardia in the trout was due initially to increased vagal tone but later due to the direct effect of cyanide on the heart. Hyperventilation in the trout persisted throughout the exposure period, although the rate and amplitude fluctuated and was variable between individual fish. During the last hour of exposure (highest cyanide concentration), ventilation was characterized by rapid, shallow breaths followed by a sudden respiratory arrest. The bullheads exhibited hyperventilation during the first 3 hours of exposure followed by a gradual, linear drop in ventilation rate and amplitude until death occurred. Cardiac and ventilatory responses in both species were attributed to stimulation of central and peripheral chemoreceptors by cyanide. Evidence is presented which suggests the initial response in the bullheads was due, at least in part, to gustatory stimulation by the cyanide. Oxygen consumption of the trout remained above pre-exposure levels for the majority of the test period. Oxygen consumption in the bullhead paralleled the changes in heart and ventilatory rates. Whole-body lactate levels of fingerlings of both species during cyanide exposure were measured to estimate the extent of anaerobiosis. Whole-body lactate levels were much greater in the bullheads than the trout, indicating a higher capacity for anaerobiosis, possibly due to a greater fuel supply. Overall, the trout responded to cyanide in a manner similar to that produced by environmental hypoxia whereas the bullheads experienced a gustatory stimulus which masked the hypoxia-like response.     

An overview of stress physiology of fish transport: changes in water quality as a function of transport duration

This study brings an integrated analysis about the relationship between water deterioration and its physiological consequences in live fish transport. The analysis was focused on the transport water and its deterioration, and physiological challenges imposed on the fish. Usual commercial handling procedures employed to mitigate fish stress during transport were discussed. Future topics of research for the establishment of safer fish transport protocols were proposed. Transport was classified into short (≤8 h) or long transport (>8 h). The main issue in short transports should be the prevention of water pH reduction, while in long transports it is the increase in ammonia. Plasma cortisol is the most employed marker for stress and is acutely elevated upon short episodes of transport, but remains elevated even in long‐transport events. Plasma glucose is perhaps a better marker for handling stress. Plasma lactate, pH, osmolality CO₂ and ions should be more often evaluated. Plasma Na⁺ and Cl^‐ are very useful markers of acidosis, due to their respective exchange for H⁺ and , for acid–base regulation. The establishment of species‐specific transport protocols should be preceded by such combined analyses of water and physiological parameters.     

Are hatchery‐reared abalone naïve of predators? Comparing the behaviours of wild and hatchery‐reared northern abalone,Haliotis kamtschatkana (Jonas, 1845)

Abalone populations have declined worldwide, generating interest in enhancement using hatchery‐reared individuals. In many cases, such restoration efforts have met with limited success due to high predator‐induced mortality rates. Furthermore, the mortality rates of outplanted hatchery abalone are often considerably higher than for wild individuals. This study uses northern abalone (Haliotis kamtschatkana) as a case study to determine whether hatchery‐reared abalone behave differently than their wild counterparts. In the field, outplanted hatchery‐reared abalone were significantly less responsive than wild abalone, in terms of number of abalone responding and intensity of response, to nearby movement and to physical contact with an inert probe. Also, when encountering a cue to which all abalone responded (a seastar predator), hatchery‐reared individuals remained subdued. Anti‐predator behavioural deficits in hatchery‐reared abalone were more pronounced in 4‐year‐old individuals than in 1‐year‐old individuals, suggesting an influence of either age or amount of time spent in the hatchery environment. These behavioural differences are expected to increase the vulnerability of hatchery‐reared abalone to predators, and are likely a major cause of their elevated predator‐induced mortality when outplanted.     

Effects of cadmium on the kinetics of calcium uptake in developing tilapia larvae, Oreochromis mossambicus

The toxic effects of Cd²⁺ on Ca²⁺ influx kinetics in developing tilapia (Oreochromis mossambicus) larvae were evaluated. Addition of 20 µg l^-1 of Cd²⁺ to the environment of 0 and 3 day-old larvae competitively inhibited the Ca²⁺ uptake within 4h resulting in a great increase in K_m values for Ca²⁺ influx (19.3 and 17.4 fold, respectively) as compared with their respective controls. Consequently, the actual Ca²⁺ influx of larvae in solutions of 0.2 mM Ca²⁺ are suppressed by 32–45%. Also, 3 day-old larvae were more sensitive to internally accumulated Cd²⁺ than 0 day-old larvae. Although the Ca²⁺ influx in 0 and 3 day-old larvae may be restored to the levels of their respective controls with 24h of being transferred to a 20 µg l^-1 Cd²⁺ solution, total body Ca²⁺ content was significantly reduced in 3 day-old larvae. Increased Ca²⁺ uptake efficiency ensures sufficient Ca²⁺ for normal growth. However, rapid increase in Ca²⁺ influx after hatching also leads to higher Cd²⁺ uptake. Exposure to Cd²⁺ will lead to a drop in body Ca²⁺ content resulting in retardation of larval growth. Therefore, we conclude that if Ca²⁺ uptake is interfered with at this critical stage of development, larvae will not be able to maintain normal levels of body Ca²⁺ and will show signs of Cd²⁺ poisoning.     

Migratory dynamics of stream-spawning longnose gar (Lepisosteus osseus)

Abstract– Literature evidence suggests that lake-dwelling longnose gar (Lepisosteus osseus) enter tributary streams to spawn, Until the present study, the dynamics of this breeding migration had never been investigated quantitatively. During the summers of 1991 and 1992, longnose gar were captured as they entered Weaubleau Creek, Missouri, a tributary of Harry S. Truman Reservoir. The in-stream spawning migration began in early April and ended in late May, and was positively correlated with stream flow and water level, and negatively correlated with water temperature. In-stream residence times ranged from 15 to 94 days, with males exhibiting longer residence times than females. Once in-stream, longnose gar travelled as far as 10 km upstream and occupied certain pools at greater relative frequencies. Although the reason for this preferential utilization is not completely understood, it may relate to pool depth and riffle proximity. Longnose gar disperse from the spawning stream great distances, with gar captured in Weaubleau Creek being recaptured up to 48 km away. This information should provide fisheries biologists the means to consider the reproductive ecology of this species in their conservation and management decisions.