The influence of fish size size on the avoidance of hypoxia and oxygen selection by largemouth bass

When an oxygen gradient ranging from c . 10 to 95% air saturation was formed in a 5 m chamber, largemouth bass Micropterus salmoides avoided water in which dissolved oxygen values were <27% air saturation. There was a significant ( P <0·05) correlation between fish mass and the level of dissolved aquatic oxygen that was selected. Small fish (23–500 g) utilized waters of lower oxygen levels than did the larger fish (1000–3000 g). The results of this study suggest that largemouth bass are able to sense and avoid hypoxic water, and select aquatic oxygen tensions that maintain their metabolic scope for growth and activity.     

Preliminary approach to find synthetic peptides from nodavirus capsid potentially protective against sea bass viral encephalopathy and retinopathy

Four synthetic peptides of 15 amino acids (aa), corresponding to sequences of the nodavirus DIEV RNA(2) protein, were chosen to test their potential immunogenicity in sea bass. Two of these included the N or C terminal regions (N-ter or C-ter) and the sequences of the others contained a potential external site (aa 127-140: Lp1 and as 266-279: Lp2). Two heat inactivated strains of nodavirus (HI Sb1 and HI Sb2), were used as positive controls and the carrier (KLH) as a negative control. ELISAs were performed to quantify serum antibodies specific to nodavirus, to peptides, and to the carrier in order to monitor their immunogenicity. All the fish reacted to the peptides C-Ter, Lp1 and Lp2 but only 55% of animals injected with N-ter produced specific antibodies. The proportion of fish that produced antibodies that cross reacted with nodavirus was very different with regard to the antigen injected: HI Sb1=88%; HI Sb2=85%; N-ter=38%; C-ter=27%. Protection against nodavirus was investigated by challenging the fish with a virulent viral suspension. The results showed that heat-inactivated Nodavirus protect fish and the N-ter peptide is a potential protective peptide. This initial approach showed that although vaccinating fish with peptides is possible, the tools and strategies of the research used in this field still need to be adapted to fish.     

Seasonal regulations of resting metabolic rate and thermogenesis in striped hamster (Cricetulus barabensis)

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Resting metabolic rate (RMR), nonshivering thermogenesis (NST) and mitochondria cytochrome c oxydase (COX) activity of brown adipose tissue (BAT), as well as weight of skin and fur were measured in striped hamsters (Cricetulus barabensis) that were live-trapped in the summer, autumn, winter and spring.     

A comparative study of blood oxygen transport in turbot and sea bass: effect of chronic hypoxia

A comparative study of blood oxygen binding and carrying capacities of turbot Scophthalmus maximus and sea bass Dicentrarchus labrax , two fish species differing in their demand for oxygen, was carried out under three levels of chronic hypoxia ( P o ₂ = 93, 65 and 40 mmHg) for 40 days. Blood O₂ affinity in normoxia was moderately high in both species ( P ₅₀ was c . 12–13 mmHg at pH 7·7). The Bohr factor was significantly lower in turbot (−0·52) than in sea bass (−0·85). In both species, blood O₂ affinity was not significantly affected by oxygen depletion whatever its level and duration. In turbot, however, P ₅₀ appeared to slightly decrease at the two more severe levels of hypoxia. In both species, blood O₂ carrying capacity was not affected by hypoxia and remained twice as high in sea bass than in turbot.     

黑线仓鼠肥满度的研究

1984—1989年,作者在呼和浩特地区野外捕获3008号黑线仓鼠标本进行了肥满度研究。结果表明,该鼠肥满度与栖息地和年龄无关,而有性别、季节和年度差异;肥满度年度变化与种群数量年度消长以及月均肥满度与月均捕获率的相关程度均未达到显著水平,说明该鼠的肥满度不能作为预测其种群数量的主要指标。     

Experimental assessment of predation risk for juvenile green sturgeon,Acipenser medirostris,by two predatory fishes

Predation is a common cause of early life stage mortality in fishes, with reduced risk as individuals grow and become too large to be consumed by gape-limited predatory fishes. Large-bodied species, such as sturgeon, may reach this size-refuge within the first year. However, there is limited understanding of what this size threshold is despite the value of this information for conservation management. We conducted laboratory-based predation experiments on juvenile green sturgeon, Acipenser medirostris, to estimate vulnerability to predation during outmigration from their natal reaches in California to the Pacific Ocean. Two highly abundant and non-native predatory fish species (largemouth bass, Micropterus salmoides, and striped bass, Morone saxatilis) were captured in the wild to be tested with developing juvenile green sturgeon from the UC Davis Green Sturgeon Broodstock Program. Experimental tanks, each containing five predators, received thirty prey for 24-hr exposures. Between sturgeon prey trials, predators were exposed to alternative prey species to confirm predators were exhibiting normal feeding behaviors. In addition to green sturgeon mortality data, trials were video recorded and predatory behaviors were quantified. Overall, these predator species displayed much lower rates of predation on juvenile green sturgeon than alternate prey. Predation decreased with green sturgeon size, and predation risk diminished to zero once sturgeon reached a length threshold of roughly 20–22 cm total length, or between 38% and 58% of predator total length. Behavioral analyses showed low motivation to feed on green sturgeon, with both predators attempting predation less frequently as sturgeon grew. Results of this study imply that optimizing growth rates for larval and juvenile sturgeon would shorten the time in which they are vulnerable to predation. Future experiments should assess predation risk of juvenile green sturgeon by additional predator species common to the Sacramento-San Joaquin watershed.     

温度对黑线仓鼠能量代谢及开场行为的影响

形态、生理及行为的季节性变化是动物生存和繁殖的适应性策略。温度可能是影响啮齿动物季节性繁殖和种群波动的重要气候因子。为了验证环境温度能诱导鼠类体重、能量代谢及行为产生适应性变化的假设,并探究其中的相互关系和意义,通过不同温度处理模拟四季温度,以野生雄性黑线仓鼠(Cricetulus barabensis)为研究对象,检测其体重、日食量、静止代谢率(RMR)及开场行为的变化。结果显示:随着处理温度的下降,黑线仓鼠的体重、日食量及静止代谢率均出现显著性或极显著性地增加趋势(P0.05或P0.01);以体重为协变量的协方差分析表明,日食量和静止代谢率的增加不完全是由体重增加而造成的;高温处理降低了黑线仓鼠的爬行格数(P0.01),低温处理降低了黑线仓鼠的爬行格数和后肢站立次数(P0.01或P0.05),并产生明显的颤抖现象。以上研究结果支持环境温度能诱导鼠类体重、能量代谢及行为产生适应性变化的假设。低温同时增加黑线仓鼠能量的摄入水平和维持基本生长的能量支出水平,同时降低动物在陌生环境中的自发活动与探索行为。高温则降低黑线仓鼠能量的摄入和支出水平,同时减少自发活动与探索行为。体重、能量代谢和行为学特征的变化有利于仓鼠度过寒冷的冬季和干热的夏季,同时也与仓鼠的季节性繁殖现象相一致,因此这些特征可能是黑线仓鼠对其寒冷的冬季及干热的夏季生存环境的适应。     

Regulation of progastricsin mRNA levels in sea bass (Dicentrarchus labrax) in response to fluctuations in food availability

In this study the sea bass (Dicentrarchus labrax) pepsinogen C gene was isolated. The nucleotide sequences of all exons are presented. The organization of the gene is compatible with that of other aspartic proteinases. The predicted 388-residue amino acid (aa) sequence of sea bass pepsinogen C consists of a signal sequence of 16 amino acid residues, an activation peptide of 43 residues, and the mature pepsin of 329 residues containing the two characteristic active-site aspartic acids. We also analyzed fasting-induced changes in the expression of progastricsin mRNA, using real-time RT-PCR absolute quantification. Progastricsin mRNA copy number was downregulated under conditions of negative energy balance, such as starvation, and upregulated during positive energy balance, such as refeeding. These findings offer new information about the sea bass progastricsin gene and support a role of this gastric digestive enzyme in the regulation of food intake in sea bass.     

Development and linkage relationships for new microsatellite markers of the sea bass (Dicentrarchus labrax L.)

Twenty-eight polymorphic microsatellites were isolated from the sea bass, Dicentrarchus labrax, using a microsatellite enrichment protocol and selective hybridization with oligonucleotide probes. Analysis for these markers and 11 recently described microsatellites of D. labrax found linkage between 26 loci and revealed eight linkage groups.     

Cellular activities during a mixed leucocyte reaction in the teleost sea bass Dicentrarchus labrax

In this investigation a number of "in vitro" activities of sea bass peripheral blood leucocytes (PBL) against allogeneic PBL inactivated by irradiation were studied. Stimulator PBL were cultured with inactivated allogeneic PBL, and direct counting of lymphocytes was done after 2 weeks by immunofluorescence and flow cytometry using mAbs DLT15 and DLIg3 specific for T-cells and B-cells, respectively. In a one-way mixed leucocyte reaction (MLR), results showed an increase of T lymphocytes, whereas B lymphocytes had values similar to those in control PBL. The increase of T-cells in MLR cultures was also confirmed using RT-PCR by analyzing the expression of the T-cell receptor (beta-subunit) mRNA. The addition of 5 microg/ml of cyclosporin A (CsA) to the MLR caused a significant decrease in T-cell proliferation. Leucocytes from MLR cultures displayed an enhanced cytotoxic activity against xenogeneic target cells with respect to control PBL, raising the possibility of the presence of cytotoxic-like T lymphocytes. Cellular activation of PBL was confirmed in 2 weeks MLR by measuring antibody-induced intracellular Ca(++) mobilization with Fura-2 AM. This work represents the first direct quantitative determination of an "in vitro" T-cell activity in a teleost species.