栉孔扇贝外套膜和鳃粘液细胞的类型与分布

采用AB PAS染色法显微观察和分析人工养殖 3龄栉孔扇贝 (Chlamysfarreri,壳长 4 0～ 5 0mm)外套膜和鳃粘液细胞类型与分布规律。结果表明 ,粘液细胞分为 4种类型 ,Ⅰ型呈红色 ,Ⅱ型呈蓝色 ,Ⅲ型呈紫红色 ,Ⅳ型呈蓝紫色。不同部位 ,粘液细胞类型、密度及形态不同 ,这与其功能密切相关。外套膜边缘膜及生壳突起内、外表皮粘液细胞均以Ⅱ型为主 ,密度较小 ,形态主要为梨形、杯形、圆形 ,并多为大型细胞 ;中央膜内表皮以Ⅰ型和Ⅲ型较多 ,形态多为圆形或不规则形 ,外表皮只有Ⅱ型细胞分布 ;鳃轴表皮粘液细胞以Ⅰ型和Ⅲ型为多 ,形态为圆形、杯形或不规则形 ;鳃丝表皮粘液细胞多为Ⅱ型和Ⅳ型 ,形态多为圆形 ,少量为杯形 ;外套膜感觉突起和缘膜突起的表皮中无明显着色的粘液细胞 ,而是被大量棕色颗粒充满     

Zn~(2+)对青蛤的胁迫效应

在盐度25和水温26~28℃下,将壳长为(35.32±0.89)mm的青蛤暴露于Zn~(2+)质量浓度10.00、19.95、39.81、79.43、158.49、316.23mg/L试验组及空白对照组,得出Zn~(2+)的半致死质量浓度和安全质量浓度;之后又研究了Zn~(2+)在青蛤鳃和内脏团中的蓄积和血淋巴液中超氧化物歧化酶、过氧化氢酶、酸性磷酸酶的活性。试验结果表明,Zn~(2+)的96h半致死质量浓度为191.56mg/L,安全质量浓度为1.92mg/L;96h半致死质量浓度下,Zn~(2+)在青蛤鳃中蓄积速度快于内脏团,血淋巴液中超氧化物歧化酶、过氧化氢酶和酸性磷酸酶活性呈先诱导再抑制的趋势,安全质量浓度下无明显变化,但均高于对照组;两种组织中的Zn~(2+)质量浓度与处理时间呈正相关。本研究结果为青蛤健康养殖和毒理学研究提供了参考。     

铜、锌对褐牙鲆鳃丝Na↑（+）-K↑（+）-ATPase活力的影响

以幼体褐牙鲆(Paralichthys olivaceus)为研究对象.Cu2+浓度梯度设置为0.10 mg/L、0.20 mg/L、0.50 mg/L和1.00 mg/L;Zn2+浓度梯度为1.00 mg/L、2.00 mg/L、5.00 mg/L和10.00 mg/L.实验周期为20 d.结果表明,在6 d内Cu2+(除1 mg/L处理组外)、Zn2+各处理组褐牙鲆鳃丝Na+-K+-ATPase活力随取样时间变化显著(P<0.05),且呈峰值变化,在24 h时达到最大值,然后缓慢下降;6～15 d,各处理组酶活力趋于稳定;而1 mg/L Cu2+处理组在12 h时酶活力达到最大值,3～15 d酶活力趋于稳定.2种重金属离子各处理组对鳃丝Na+-K+-ATPase活力的影响在同一取样时间差异显著(P<0.05),其影响程度与重金属离子浓度呈负相关,且1 mg/L Cu2+和10 mg/L Zn2+处理组在6～15 d酶活力与对照组差异不显著(P＞0.05).同时2种重金属离子在1～15 d内对褐牙鲆鳃丝Na+-K+-ATPase活力的诱导率表现为Zn2+(1 mg/L)＞Cu2+(1 mg/L).     

pHi regulation and ultrastructural analysis in cultured gill cells from freshwater or seawater-adapted trout

Primary cultures of gill cells from freshwater and seawater-adapted trout were compared. These cultures, developed from an explant technique, exhibited a similar growth. Ultrastructural comparison between cultured and in situ cells showed that most of the cells in primary culture resembled the so called 'pavement' cells, whereas chloride cells were not observed in the cultured epithelium. Several other cells types, representing a minority of cells in primary culture, were observed (mucous cells, vesicolar cells, cells with large dense granules and cells containing lysosomes). Morphological observations of cultured pavement cells from freshwater and seawater trout gills were similar, although the density of cellular organelles in cells was less under freshwater conditions. In addition to the morphological comparison, the regulation of intracellular pH in cultured cells from freshwater and seawater gills was examined. Resting pHi was not different for freshwater or seawater gill cells. A sodium-dependent and amiloride-sensitive mechanism was found in cultured cells. Under the experimental conditions used here, this mechanism was most likely a Na⁺/H⁺ antiporter in pavement cells from freshwater and seawater-adapted trout. The comparison of pHi recovery after acidification of cells from freshwater and seawater gills showed that the activity or the number of antiporters was higher for cells from seawater trout gill.     

Effect of cadmium on the cytoskeleton and morphology of gill chloride cells in parr and smolt Atlantic salmon (Salmo salar)

This study documented the effect of cadmium on salmon parr and smolt gill morphology. Cadmium-induced changes in chloride cell (CC) cytoskeletal elements were investigated, as well as the modifications of CC surface area and density. In cadmium-treated parr (10 µg Cd l^-1 for 2 days), immunofluorescent light microscopy revealed the appearance of an intense actin staining located in the CC apical part. Transmission electron microscopic observations revealed a change in the organization of the microfilaments at the CC apex, with the appearance of numerous aggregates of filamentous actin. Higher cadmium concentrations (30 and 50 µg l^-1) and prolonged treatment times (7 to 14 days) did not modify such reorganisation. Microtubules were not significantly affected by similar treatments. Further, scanning electron microscopic analysis revealed that cadmium induces a significant increase of parr CC surface area as early as the second day of exposure. After 2 days, mature CC density had also increased. In smolt, a rise in CC surface area was observed, although CC density did not significantly increase.     

Effects of environmental Ca2+ levels on branchial chloride cell morphology in freshwater-adapted killifish Fundulus heteroclitus

ABSTRACT: To examine the involvement of chloride cells in the uptake of Ca²⁺ in freshwater (FW) killifish, chloride cell morphology was compared in fish acclimated to different defined FW environments with Ca²⁺ concentrations of either 0.1 mM, 0.5 mM, or 2.5 mM. Numerous chloride cells were detected in whole-mount preparations of the gill filaments, which were stained with an antiserum specific for Na⁺, K⁺-ATPase. Chloride cells, located mostly on the afferent–vascular edge of the filaments, were larger at lower Ca²⁺ concentrations. Electron microscopic observations showed that in the 0.1 mM and 0.5 mM Ca²⁺ experimental groups, the apical membrane of chloride cells were flat or slightly projecting and equipped with numerous microvilli. In the 2.5 mM Ca²⁺ group, some chloride cells formed an apical pit, whereas other cells were similar to those observed in the 0.1 mM and 0.5 mM Ca²⁺ groups. Plasma osmolality decreased with decreasing ambient Ca²⁺ concentration, suggesting that environmental Ca²⁺ affects the permeability of the body surfaces. Gill Na⁺, K⁺-ATPase activity in the 0.1 mM and 0.5 mM Ca²⁺ groups were significantly higher than that in the 2.5 mM Ca²⁺ group, implying the involvement of the Na⁺–Ca²⁺ exchanger in Ca²⁺ uptake in the gills. These findings suggest that chloride cells function as the site for Ca²⁺ uptake in killifish acclimated to low Ca²⁺ environments.     

The wheat germ agglutinin binding sites and development of the mitochondria-rich cells in gills of tilapia (Oreochromis mossambicus)

By labelling with gold-colloid-conjugated wheat germ agglutinin (WGA), the WGA-binding sites were identified in the apical region of certain mitochondria-rich (MR) cells in gills of freshwater-adapted tilapia (Oreochromis mossambicus). Bromo-deoxyuridine (BrdU) injection was used to discern the differentiation of the WGA binding sites during development of MR cells. Double labeling of gill sections of fish 2, 4, 6, and 8 days after a single BrdU injection showed that the BrdU labeled MR cells 2 and 4 days after injection were mostly WGA negative, whereas 6 and 8 days after injection, WGA and BrdU-labeled MR cell increased gradually in number. Furthermore, the ratio of the WGA-positive to total MR-cells was higher in gills of tilapia adapted to low calcium ([Ca] = 0.015 mm) freshwater than in hard freshwater ([Ca] = 1.898 mm). The results indicate that WGA binding site may be a marker expressed late during differentiation of MR cells, and physiologically functional in assisting uptake of calcium when environmental calcium is low. According to their WGA binding and also characteristics their likely function in calcium absorption, the WGA positive MR cells shown in this study are considered to be similar to the cells described by Pisam et al. (1995).     

Pb2+对泥蚶鳃、肝脏等组织结构的影响

为了进一步了解重金属Pb对贝类的毒性毒理影响,研究了4个暴毒浓度(5、15、45和90μg/L)Pb2+对泥蚶鳃和肝脏组织显微结构的影响,及其中2个高浓度组Pb2+暴毒对泥蚶鳃和肝脏组织超微结构的影响,处理时间为96 h。结果显示,低浓度组Pb2+造成泥蚶鳃丝脱离其相连的软骨组织;高浓度组Pb2+使其鳃丝呼吸上皮细胞出现脱落,鳃腔肿胀、内有血细胞堆积,鳃丝断裂;超微结构分析发现,随着浓度的升高,鳃上皮细胞中次级溶酶体和线粒体数量均增加。Pb对泥蚶肝脏组织的显微结构影响仅见高浓度组肝小管附近有黄色物质沉积,消化管界限缺失,超微结构表明随着浓度的升高,肝细胞内沉积大量的黑色嗜锇性物质,次级溶酶体亦大量增加,细胞胞质及细胞核出现空泡,最后将导致细胞坏死,造成肝细胞永久性损伤。结合其他重金属毒性研究可发现,重金属引起的病理学变化并不具有金属特异性,主要还是氧化胁迫造成的氧化损伤。研究推测,生物体的抗氧化体系在重金属解毒中发挥了重要作用。     

Interrelationships between gill chloride cell morphology and calcium uptake in freshwater teleosts

The involvement of the freshwater fish gill chloride cells (CCs) in trans-branchial calcium uptake (JinCa²⁺) was investigated. This was accomplished by assessing the interspecific relationships between the apical surface area of CCs exposed to the external environment and JinCa²⁺. Three species of freshwater teleosts, the rainbow trout (Oncorhynchus mykiss), the American eel (Anguilla rostrata) and the brown bullhead catfish (Ictalurus nebulosus), were used. Chronic (ten-day) treatment with cortisol in each species was used as a tool to evoke variations in both JinCa²⁺ and gill CC morphology in order to assess intraspecific relationships between CC surface area and JinCa²⁺. The results of quantitative morphometry, based on analysis of scanning electron micrographs, demonstrated that catfish possessed the lowest fractional area of exposed CC (CCFA) on the gill filament epithelium (12,744 ± 2248 m²/mm²) and was followed, in increasing order, by American eel (21,355 ± 981 m²/mm²) and rainbow trout (149,928 ± 26,545 m²/mm²). With the exception of catfish, chronic treatment with cortisol caused significant increases in CCFA owing to proliferation of CCs and/or enlargement of individual CCs (eel only). The rates of JinCa²⁺ closely reflected the CC fractional area in each species. The results of correlation analysis revealed significant correlations between CC fractional area and JinCa²⁺ in trout and eel. Owing to the absence of an effect of cortisol treatment, there was no significant correlation in catfish because of insufficient variation in CC fractional area in this species. CC fractional area was significantly correlated with JinCa²⁺ among the three species examined. These results suggest that CC is involved in calcium uptake in freshwater teleosts and that both intra- and interspecific differences in the rates of calcium uptake can be accounted for by variability in the surface area of exposed CCs on the gill epithelia.     

尼罗罗非鱼表皮和鳃黏膜共生菌结构特征及其与鱼体健康状况相关关系

黏膜及其表面的共生菌群是鱼类抵御外界不利环境的第一道屏障。为探索养殖罗非鱼表皮和鳃黏膜共生菌菌群的结构特征是否与其健康状况间存在相关关系,本研究运用高通量测序技术,以无乳链球菌腹腔注射攻毒48 h后存活和濒死尼罗罗非鱼为检测对象,检测攻毒前后罗非鱼表皮和鳃黏膜共生菌群落结构差异。结果显示,健康尼罗罗非鱼表皮和鳃黏膜共生菌均存在优势菌群,主要为特吕珀菌属、硫杆菌属、弓形杆菌属、海单胞菌属和弧菌属。人工感染无乳链球菌后存活尼罗罗非鱼表皮和鳃黏膜共生菌菌群与感染前无显著差异;与存活组相比,濒死尼罗罗非鱼的表皮和鳃黏膜共生菌菌群多样性下降,其中弓形杆菌属、假交替单胞菌属、海单胞菌属、假单胞菌属和弧菌属等含量显著下降,链球菌属含量占总菌群的55.30%±1.24%,表明养殖尼罗罗非鱼表皮和鳃黏膜共生菌群落结构可能与其健康状况相关。     

Functional partition of cells in the gill epithelium of the Japanese eel, Anguilla japonica, and the role of hormones

Viable chloride and pavement cells were isolated from the gill epithelium of Japanese eel, Anguilla japonica, by a 3-step percoll gradient centrifugation at low speed. Viability of the isolated cells were tested by the trypan blue exclusion test, rhodamine-123, or pre-labelling the cells with fluo-3 Ca²⁺ dye and examined by laser confocal microscopy. Isolated chloride cells responded to ionomycin with a rapid increase in Ca²⁺ fluorescence, which was abolished by chelating external Ca²⁺ with EGTA. Peptide hormones, including arginine vasotocin, isotocin, insulin-like growth factor I and II, and urotensin I increased Ca²⁺ entry, urotensin II had no effect, and eel corpuscles of Stannius extract reduced residual Ca²⁺ fluorescence. Isolated chloride cells and pavement cells from eels were analyzed for their enzymatic activities involved in intermediary and nitrogen metabolism. Chloride cells had high levels of glutaminase I, glutamate dehydrogenase, glutamate oxalacetate transaminase, HCO₃-ATPase and carbamoyl phosphate synthetase II. Pavement cells had highly active glucose-6-phosphate dehydrogenase and AMP deaminase. Both had high levels of lactate dehydrogenase compared with other tissues.     

草鱼鳃组织蛋白双向电泳技术的建立及优化

为建立并优化草鱼鳃蛋白质组双向电泳的技术体系,实验将草鱼鳃经裂解处理后,通过固相p H梯度胶条进行一向等电聚焦和SDS聚丙烯酰胺凝胶垂直电泳进行蛋白分离,对不同的裂解液配方、蛋白纯化方法、IPG胶条的分离范围、上样量和染色方法等进行了探索和优化,并应用lmage Master 2D Platinum 7.0软件对电泳图谱进行了分析。结果表明:采用裂解液中添加DTT来取代Tris和TBP、选择分离范围为pH4-7的IPG胶条和150μg的主动水化上样,电泳结束后对凝胶进行硝酸银染色,获得了覆盖范围广、低背景、高分辨率、适合差异蛋白分析的双向电泳参考图谱。     

怒江裂腹鱼鳃的显微和超微结构

通过光镜、扫描电镜及透射电镜技术,研究了怒江裂腹鱼(Schizothorax nukiangensis)鳃的组织结构和超微结构。结果表明,怒江裂腹鱼鳃基本结构与其他硬骨鱼相似,均由鳃耙、鳃弓、鳃丝以及鳃小片构成,且各部分具有不同的组织结构和细胞类型。扁平上皮细胞覆盖于整个鳃表面,其表面的纹路主要有3种类型,在鳃上不同的部位具有不同的结构和功能。线粒体密集细胞主要分布于鳃小片基部,仅有一种细胞类型,顶端膜内凹呈浅滩型,细胞内具有大量圆形的线粒体。怒江裂腹鱼鳃内扁平上皮细胞和线粒体密集细胞的形态结构与其在急流中游泳和摄食活动等生活习性相适应。本研究结果丰富了怒江裂腹鱼的基础生物学资料,并为阐明鱼类鳃的结构特征与其生活习性之间的关系提供参考。     

NaCl盐度和NaHCO3碱度对大鳞鲃幼鱼生长及鳃组织特征的影响

在水温22~25℃的条件下,研究不同盐度、碱度水体对大鳞(Barbus capito)幼鱼生长、摄食和鳃组织的影鲃响,探索了幼鱼生长的最适条件.单因素盐度梯度值设置为0(对照组)、2.0、4.0、6.1、7.8、10.0和11.9,实验结果表明,当盐度高于6.1时,大鳞幼鱼的体长和体质量受到显著影响(P<0.05);盐度2.0时幼鱼的终末体质量值最鲃大;盐度4.0时体质量特定增长率和饵料转化效率最高,盐度11.9时均降至最低;盐度到达7.8时对幼鱼生长有抑制作用,依据理论公式推算,幼鱼的最适生长盐度应为1.88.单因素碱度梯度值为10.00、15.83、25.10、39.80和63.12 mmol/L,碱度高于25.10 mmol/L时对幼鱼的体质量、饵料转化效率及总摄食量均有显著影响(P<0.05);碱度15.83 mmol/L时幼鱼的终末体质量、体质量生长率和饵料转化效率值最高,碱度63.12 mmol/L时最低.碱度到达39.80 mmol/L时对幼鱼生长有抑制作用,依据理论公式推算,幼鱼的最适生长碱度为20.57 mmol/L.从鳃组织的显微结构观察结果来看,随着盐度和碱度的升高,鳃小片上皮细胞出现肿胀、脱落和坏死的现象,泌氯细胞的体积膨胀,从而影响了幼鱼的生长.综上所述,大鳞幼鱼期,养殖盐度不宜超过6.1,碱度不超过25.10 mmol/L.鲃     

Arachidonic acid metabolism in gill homogenate and isolated gill cells from rainbow trout,Oncorhynchus mykiss: the effect of osmolality,electrolytes and prolactin

An assay method based on thin layer chromatography to study the arachidonic acid (AA) metabolism in gill tissues was optimized and the effect of osmotically different incubation mediums on AA metabolism was evaluated. Rainbow trout gill tissues metabolize AA into PGE₂ in highest concentration followed by PGD₂, PGF₂ and 6-keto-PGF₁ (the stable metabolite of PGI₂) among the prostanoids tested. Approximately 40% of PGE₂ is synthesized within the first minute of incubation and is directly dependent on the substrate concentration (AA). As in mammalian tissues, PGE₂ synthesis in fish gills is inhibited by the cyclooxygenase inhibitor indomethacin. PGE₂ synthesis in gill homogenate and isolated gill cells incubated in trout Ringer was 0.45 and 1.9 ng/mg protein, respectively, and increased to 8.9 and 4.3 ng/mg protein, respectively, when incubated in KPO₄ buffer, due to a ten-fold increase in the free AA. The hydroxy acid synthesis of the gill homogenate was higher (13%), and that of the isolated gill cells incubated in KPO₄ buffer was lower (44%) compared to gill homogenate and cells incubated in trout Ringer. Gill homogenate incubated in 50 mM phosphate buffer with increasing sodium or potassium concentrations (up to 250 mM) exhibited a concentration-dependent increase in PGE₂ synthesis (220% and 72%, respectively). Prolactin stimulated the PGE₂ synthesis up to 30% while PGD₂, PGF₂ and 6-keto-PGF₁ synthesis was not affected. This effect of prolactin was maximal when PGE₂ synthesis was estimated 30 minutes after prolactin addition and diminished after two hours. These results suggest that rainbow trout gills possess the ability to metabolize AA through the cyclooxygenase and lipoxygenase pathways. PGE₂ synthesis may be under the influence of ion balance and prolactin availability, indicating the probable involvement of AA metabolites in the regulation of ion balances across the gill membrane.     

重金属离子Cd2+对泥蚶鳃及肝脏细胞显微和超微结构的影响

研究了镉(Cd)的各个不同暴毒浓度(5,15,45,90μg/L)对泥蚶鳃和肝脏组织显微结构的影响,及高浓度暴毒情况下对泥蚶鳃和肝脏组织超微结构的影响。实验处理时间为96 h。结果发现,随着暴毒浓度的升高,鳃丝内腔隙肿胀,内有血细胞堆积,最后鳃丝出现断裂融合,其上的呼吸上皮细胞脱落,超微结构发现鳃上皮细胞中出现黑色嗜锇性物质,且次级溶酶体和线粒体数量都增加,最后细胞内出现空泡现象;Cd对肝脏显微结构的影响不大,仅出现了黄色沉积物,超微结构表明,肝细胞内亦出现了嗜锇性物质,次级溶酶体亦大量增加,这些现象与鳃丝内出现的情况一致,且肝细胞核还出现变形皱缩,甚至产生空泡,细胞出现了不可逆的损伤。最为敏感的线粒体和内质网没有出现损伤现象,研究推测可能是由于机体内Cd诱导产生的抗氧化活性酶作用的结果。     

温度、盐度、pH对卵形鲳鲹幼鱼离体鳃组织耗氧量的影响

运用SKW-3微量呼吸仪对卵形鲳鲹（Trachinotus ovatus）幼鱼离体鳃组织的耗氧量进行了测定,研究了温度、盐度、pH对卯形鲳鲹幼鱼离体鳃组织耗氧量和单位呼吸面积耗氧量的影响。结果显示,卵形鲳鲹幼鱼离体鳃组织的耗氧量和单位呼吸面积的耗氧量均随着温度、盐度、pH的上升而逐渐增高,在水温27℃、盐度28和pH8．5时,离体鳃组织的耗氧量达到最大值;在水温27℃、盐度23和pH8．5时单位呼吸面积的耗氧量达最大值;随后耗氧量均逐渐减小。经方差分析,温度、盐度、pH对离体鳃组织耗氧量的影响均显著（P〈0．05）;温度和盐度对离体鳃组织单位呼吸面积的耗氧量影响极显著（P〈0．01）;pH对离体鳃组织单位呼吸面积的耗氧量影响也达显著水平（P〈0．05）;其中盐度为18和33这2组的离体鳃组织耗氧量差异不显著（P〉0．05）。     

Effects of ambient ion concentrations on gill ATPases in fresh water eel,Anguilla anguilla

Branchial activities of Na⁺,K⁺-ATPase (ouabain sensitive), Mg²⁺ ATPase (ouabain insensitive) and kinetic analysis of high and low affinity Ca²⁺ ATPase were measured inAnguilla anguilla that had been acclimated to demineralized water (DW, Ca < 10 M), freshwater (FW, Ca = 2 mM), and Low calcium freshwater (L-Ca, Ca = 0.9 mM). Na⁺,K⁺-ATPase activity decreased while ouabain insensitive activity increased when ambient Ca²⁺ decreased. Two kinetic forms of Ca²⁺ ATPase could be resolved in each environmental condition. The stimulation coefficients of both sites or enzymes were not affected by ambient Ca²⁺ concentrations. The maximal velocity of both the high and the low affinity Ca²⁺ ATPase was increased when external Ca²⁺ was decreased during acclimation. The low affinity Ca²⁺ ATPase and the Mg²⁺ stimulated enzyme could be a non specific enzyme accepting either Ca²⁺ or Mg²⁺. Results are compared with previous results in the literature and in relation to the branchial morphology and ionic exchanges in fish.     

氨氮胁迫对青鱼幼鱼鳃丝Na+/K+-ATP酶、组织结构及血清部分生理生化指标的影响

氨氮是诱发鱼病的主要环境因子,以初始体质量(7.00 0.14)g的青鱼幼鱼为研究对象,研究氨氮胁迫对其鳃丝Na+/K+-ATP酶、组织结构及血清部分生理生化指标的影响。实验设置低(对照组0 mg/L)、中(10 mg/L)和高(20 mg/L)3个氨氮浓度处理组,将暂养在自然淡水(对照)中的青鱼幼鱼分别放入各实验梯度中,进行0、6、12、24、48和96 h氨氮胁迫。结果表明:与对照组相比,中、高氨氮组鳃丝Na+/K+-ATP酶活性分别在12 h和6 h降至最低,然后升高,48 h达最大值,96 h后与对照组水平相当。鳃组织光镜观察表明,中氨氮组鳃小片基部泌氯细胞数量12 h有所增加,24 h呼吸上皮细胞出现部分脱落,96 h泌氯细胞出现空泡化,部分鳃小片充血;而高氨氮组鳃小片基部泌氯细胞数量6 h呈增加趋势,12 h呼吸上皮细胞部分脱落,24 h大面积脱落,96 h鳃小片基部严重充血。血清皮质醇和血糖含量在胁迫12 h均升高至最大,含量与氨氮浓度呈正相关,48 h恢复至对照组水平。氨氮胁迫下,血清总超氧化物歧化酶(SOD)活力呈先升高后降低的趋势,6 h时显著高于对照组(P<0.05),中氨氮组12 h后与对照组差异不显著,而高氨氮组96 h时显著低于对照组(P<0.05)。过氧化氢酶(CAT)活力12 h内均呈先降低后升高趋势,48 h均恢复至对照组水平。氨氮胁迫前期,血清总抗氧化力和谷胱甘肽均呈下降趋势,丙二醛和谷丙转氨酶活力呈升高趋势。谷胱甘肽和谷丙转氨酶活力在96 h恢复至对照组水平,而丙二醛96 h仍显著高于对照组,高氨氮组总抗氧化力显著低于对照组(P<0.05)。由此可见,氨氮胁迫初期,鱼体抗氧化系统受到严重干扰。随着胁迫时间延长,鱼体进行适应性生理调节,但机体抗氧化能力下降,鳃组织已受到损伤。     

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.