Differential expression of branchial Na+/K(+)-ATPase of two medaka species, Oryzias latipes and Oryzias dancena, with different salinity tolerances acclimated to fresh water, brackish water and seawater

Previous studies on non-diadromous euryhaline teleosts introduced a hypothesis that the lowest level of gill Na⁺/K⁺-ATPase (NKA) activity occurs in the environments with salinity close to the primary natural habitats of the studied species. To provide more evidence of the hypothesis, two medaka species, Oryzias latipes and O. dancena, whose primary natural habitats are fresh water (FW) and brackish water (BW) environments, respectively, were compared from levels of mRNA to cells in this study. The plasma osmolalities of O. latipes and O. dancena were lowest in the FW individuals. The muscle water contents of O. latipes decreased with elevated external salinities, but were constant among FW-, BW-, and seawater (SW)-acclimated O. dancena. Expression of NKA, the primary driving force of ion transporters in gill ionocytes, revealed different patterns in the two Oryzias species. The highest NKA α-subunit mRNA abundances were found in the gills of the SW O. latipes and the FW O. dancena, respectively. The pattern of NKA activity and α-subunit protein abundance in the gills of O. latipes revealed that the FW group was the lowest, while the pattern in O. dancena revealed that the BW group was the lowest. Immunohistochemical staining showed similar profiles of NKA immunoreactive (NKIR) cell activities (NKIR cell number × cell size) in the gills of these two species among FW, BW, and SW groups. Taken together, O. latipes exhibited better hyposmoregulatory ability, while O. dancena exhibited better hyperosmoregulatory ability. Our results corresponding to the hypothesis indicated that the lowest branchial NKA activities of these two medaka species were found in the environments with salinities similar to their natural habitats.     

Brood protection at a cost: mouth brooding under hypoxia in an African cichlid

This study quantifies the behavioral response of the widespread mouth brooding African cichlid Pseudocrenilabrus multicolor victoriae to progressive hypoxia. We exposed four gender/stage classes of P. multicolor (males, brooding females, females that had just released young, and non-brooding females) to progressive hypoxia and recorded the percent time spent using aquatic surface respiration (surface skimming, ASR) and gill ventilation rates. This was done for fish collected from three sites in Uganda (lake, swamp, and river) after long-term acclimation to normoxia. There was no effect of site of origin on response to hypoxia, but ASR thresholds did differ between gender/stage classes. The oxygen level (threshold) at which spent 10, 50, and 90% of their time at the surface using ASR was much higher for brooding females than for males, whereas ASR thresholds did not differ between non-brooding females and males. Similarly, the level at which ASR was initiated was much higher in brooding females than males, but did not differ between males and non-brooders, or between males and females than had just released young. The rate of gill ventilation dropped significantly in males and all stages of females after initiation of ASR, suggesting that surface skimming increases efficiency of oxygen acquisition. These results suggest that mouth brooding in female P. multicolor ASR improves oxygen uptake but imposes a cost in terms of time spent at the water surface, and this may affect maternal predation risk in low-oxygen habitats.     

Physiological response in the European flounder (Platichthys flesus) to variable salinity and oxygen conditions

Physiological mechanisms involved in acclimation to variable salinity and oxygen levels and their interaction were studied in European flounder. The fish were acclimated for 2 weeks to freshwater (1 per thousand salinity), brackish water (11 per thousand) or full strength seawater (35 per thousand) under normoxic conditions (water Po(2) = 158 mmHg) and then subjected to 48 h of continued normoxia or hypoxia at a level (Po(2) = 54 mmHg) close to but above the critical Po(2). Plasma osmolality, [Na(+)] and [Cl(-)] increased with increasing salinity, but the rises were limited, reflecting an effective extracellular osmoregulation. Muscle water content was the same at all three salinities, indicating complete cell volume regulation. Gill Na(+)/K(+)-ATPase activity did not change with salinity, but hypoxia caused a 25% decrease in branchial Na(+)/K(+)-ATPase activity at all three salinities. Furthermore, hypoxia induced a significant decrease in mRNA levels of the Na(+)/K(+)-ATPase alpha1-subunit, signifying a reduced expression of the transporter gene. The reduced ATPase activity did not influence extracellular ionic concentrations. Blood [Hb] was stable with salinity, and it was not increased by hypoxia. Instead, hypoxia decreased the erythrocytic nucleoside triphosphate content, a common mechanism for increasing blood O(2) affinity. It is concluded that moderate hypoxia induced an energy saving decrease in branchial Na(+)/K(+)-ATPase activity, which did not compromise extracellular osmoregulation.     

Hg2+在中华绒螯蟹幼蟹鳃内的积累及其对组织结构的影响

采用生态学单因子梯度实验,研究不同浓度汞(Hg2 )的水环境中中华绒螯蟹(Eriocheir sinensis)幼蟹鳃内汞积累情况及对鳃组织结构的影响。结果表明,中华绒螯蟹幼蟹的鳃能够从水环境中迅速积累汞,Hg2 浓度为10、50、100μg/L组的水环境中幼蟹鳃内汞含量分别为4.56、25.53、46.51μg/g干重,均显著高于对照组幼蟹鳃内汞含量1.68μg/g干重(P<0.05);水环境Hg2 浓度为200、300μg/L组的幼蟹鳃内汞含量达到了183.75和283.36μg/g干重,对水体Hg2 蓄积倍数达到了910.35和939.60。光镜观察低浓度组汞能够诱导鳃组织结构发生变化,如上皮细胞肿胀、鳃叶厚度增加、端部膨胀等;高浓度组则会导致鳃叶上皮细胞崩解,鳃组织结构完全破坏。以统计学方法分析了鳃内汞含量同水体汞浓度的相关性,结果表明,两者之间存在明显的相关性,并能够在组织形态上有所体现。鳃是中华绒螯蟹最容易接触水体Hg2 的器官,同时也是蓄积汞的主要器官之一,水体高浓度的Hg2 能够对鳃的组织结构造成明显的破坏,严重影响幼蟹存活率。     

Variation of specific proteins, mitochondria and fatty acid composition in gill of Scylla serrata (Crustacea, Decapoda) under low temperature adaptation

The mud crab Scylla serrata is an important commercial crustacean inhabiting estuarine water along the coast of southeast China. Metabolism in the gill is affected continuously by fluctuating water temperature and, therefore, the ability to cope with temperature change is essential to maintain physiological function. This experiment was conducted to help understand the mechanism of low temperature adaptation in S. serrata gill. In this study, 40 healthy juvenile male S. serrata from the same broodstock were grouped randomly into four groups, which were kept at 5 °C, 10 °C, 15 °C and 27 °C, with the same feeding regime during a 3-week adaptation period. Two-dimensional electrophoresis of the proteome was conducted to separate the specific proteins responsible for low temperature adaptation. Variations in the mitochondria were observed using transmission electron microscopy, and fatty acid composition was determined using gas chromatography. The results showed that different numbers of specific proteins were expressed under different low temperature adaptation, with more expressed at 5 °C and 10 °C than at 15 °C. Mitochondrial morphology also varied under different low temperature adaptation, but there was no linear relationship between microbial density and adaptation temperature. The composition of different fatty acids in the gill varied considerably with adaptation temperature, but elongation of the carbon chain and transition from fatty acids occurred at lower temperatures. Thus, changes in the specific proteins, mitochondria and fatty acid composition of the gill were the positive effects of low temperature on metabolism, leading to improved adaptation ability in S. serrata.     

黄斑篮子鱼和金钱鱼鳃的扫描电镜观察

对两种鲈形目鱼类黄斑篮子鱼(Siganus oramin)和金钱鱼(Scatophagus argus)的鳃结构进行扫描电镜观察。结果表明,黄斑篮子鱼和金钱鱼鳃的表面结构及微细结构与其他硬骨鱼类基本相似,鳃丝表面都具有规则或不规则分布的环形微嵴、沟、坑、孔等结构。黄斑篮子鱼的鳃片中部鳃丝表皮有大量凸起,而端部鳃丝表皮的凹凸程度明显较低,黄斑篮子鱼的鳃小片高度较金钱鱼鳃小片高。黄斑篮子鱼和金钱鱼鳃上皮的扁平上皮细胞、氯细胞和黏液细胞的形态结构及数量分布存在细微的差异。黄斑篮子鱼鳃片鳃丝的端部和中部表面有黏液细胞,金钱鱼鳃丝表面的黏液细胞很难观察到,与大多数淡水鱼类相似。黄斑篮子鱼鳃丝表面分布的氯细胞数量多于金钱鱼,这可能与两种鱼生活环境、生活习性的长期演变相关。     

早寒武世原始脊椎动物云南虫鳃丝的发现

云南虫类(yunnanozoans)是早寒武世澄江动物群中重要的原始脊椎动物,包括云南虫(Yunnanozoon)和海口虫(Haikouella)。由于保存原因,对云南虫的形态学了解十分有限。海口虫鳃弓保存了明显的鳃丝构造,而这个特征在云南虫中却没有报道。通过最近观察研究云南澄江小滥田5.3亿年前下寒武统帽天山页岩中采集的云南虫化石标本后,发现了类似海口虫的鳃丝构造,为该类动物的相互联系及脊椎动物起源和早期演化提供了新的化石根据。     

Suitability of a cytotoxicity assay for detection of potentially harmful compounds produced by freshwater bloom-forming algae

Detecting harmful bioactive compounds produced by bloom-forming pelagic algae is important to assess potential risks to public health. We investigated the application of a cell-based bioassay: the rainbow trout gill-w1 cytotoxicity assay (RCA) that detects changes in cell metabolism. The RCA was used to evaluate the cytotoxic effects of (1) six natural freshwater lake samples from cyanobacteria-rich lakes in central Ontario, Canada; (2) analytical standards of toxins and noxious compounds likely to be produced by the algal communities in these lakes; and (3) complex mixtures of compounds produced by cyanobacterial and chrysophyte cultures. RCA provided a measure of lake water toxicity that could not be reproduced using toxin or noxious compound standards. RCA was not sensitive to toxins and only sensitive to noxious compounds at concentrations higher than reported environmental averages (EC₅₀ ≥ 10³ nM). Cultured algae produced bioactive compounds that had recognizable dose dependent and toxic effects as indicated by RCA. Toxicity of these bioactive compounds depended on taxa (cyanobacteria, not chrysophytes), growth stage (stationary phase more toxic than exponential phase), location (intracellular more toxic than extracellular) and iron status (cells in high-iron treatment more toxic than cells in low-iron treatment). The RCA provides a new avenue of exploration and potential for the detection of natural lake algal toxic and noxious compounds.     

Phosphofructokinase from the posterior gills of the euryhaline crab,Eriocheir sinensis: evidence for its regulation by phosphorylation

Phosphofructokinase from the posterior gills of the euryhaline crab Eriocheir sinensis acclimated to freshwater is likely regulated in part via phosphorylation induced by endogenous cyclic nucleotide-dependent protein kinases. Phosphofructokinase from gill extracts devoid of low molecular weight compounds by chromatography through a PD10 Sephadex column, incubated in the presence of cAMP or cGMP protein kinases activators (cAMP or cGMP, Mg-ATP and Mg²⁺), shows an increased catalytic activity. This treatment is accompanied by ³²P incorporation into the proteins immunoprecipitated with anti-mammalian phosphofructokinase polyclonal antibodies cross-reacting with the analog crustacean enzyme. Our results indicate that the covalent modification induced by these nucleotide-dependent protein kinases activates the glycolytic enzyme by increasing its affinity for its substrate and, when the activation is specifically due to cAMP-dependent protein kinases, by also reducing the homotropic cooperativity between its multiple substrate binding sites.