Dissolved oxygen controls summer habitat of Clear Lake Hitch (Lavinia exilicauda chi), an imperilled potamodromous cyprinid

Clear Lake Hitch is an imperilled minnow endemic to Clear Lake, Lake County, California, United States listed as threatened under the California Endangered Species Act (ESA) and a candidate for listing under the United States ESA. It exhibits a potamodromous life cycle whereby adults, which reach up to 6 + years in age and over 350 mm in length, migrate into Clear Lake's ephemeral tributaries briefly during spring to spawn. Conservation and management of Clear Lake Hitch is inhibited, in part, by a lack of information on the lacustrine habitat of nonbreeding individuals within Clear Lake. To address this problem, we sampled Clear Lake Hitch with gill nets in a stratified random sampling design to determine the distribution and habitat associations in early summer 2017 and 2018. We identified abundance-habitat relationships for juveniles and adults using Bayesian zero-inflated negative binomial generalised linear mixed modelling. Results indicated that dissolved oxygen concentration was the most important habitat feature measured; juveniles and adults were substantially more abundant in normoxic (≥2 mg/l) than in hypoxic (<2 mg/l) habitat. Both also exhibited weak positive relationships with chlorophyll fluorescence, suggesting relatively productive habitats may support higher numbers of Clear Lake Hitch. Spatially, juveniles were most abundant in nearshore habitats while adults were ubiquitous, indicating an ontogenetic habitat expansion that may be associated with a resource availability-predation risk trade-off. Management actions undertaken to improve hypoxia problems in Clear Lake would also improve Clear Lake Hitch habitat.     

高温和低氧胁迫对两种规格刺参半致死时间及生理机能的影响

通过实验生态学方法,针对2种规格的刺参(Apostichopus japonicus)(大:28.00~36.00 g;小:9.00~13.00 g),测定温度为(25.0±0.5)℃溶解氧(DO)水平为(1.0±0.1)mg/L条件下刺参的半致死时间(LT_(50));比较分析了DO水平分别为(1.0±0.1)mg/L、(3.0±0.1)mg/L及6.5 mg/L(正常DO含量)条件下2种规格刺参的昼夜代谢水平;监测了DO水平分别为(1.0±0.1)mg/L和(3.0±0.1)mg/L时低氧胁迫24 h及复氧72 h期间,2种规格刺参体腔液和呼吸树中的谷胱甘肽(GSH)含量、总抗氧化能力(T-AOC)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性及体腔液中皮质醇水平的变化,以探究夏季高温期(25.0±0.5)℃低氧胁迫对不同规格刺参半致死时间及生理机能的影响。结果显示:当DO浓度为1 mg/L时,大规格刺参半致死时间(LT_(50))为33.37 h,小规格刺参为28.84 h,2种规格刺参的代谢水平显著低于常氧对照组,夜间代谢强度高于白天,且小规格刺参的代谢强度高于大规格刺参。1 mg/L低氧胁迫期间,大规格刺参体腔液及2种规格刺参呼吸树中上述4种抗氧化指标的变化趋势大致相同,与对照组相比,随着低氧暴露时间的延长,GSH含量下降,SOD和T-AOC活力降低,CAT活力升高;然而胁迫结束时其GSH含量、CAT、SOD和T-AOC活力均与对照组无显著差异(P0.05)。解除胁迫复氧72 h后,2种规格刺参体腔液的4种抗氧化指标均恢复到对照组水平;而呼吸树的这4种指标则未完全恢复。3 mg/L低氧胁迫期间,2种规格刺参体腔液和呼吸树的GSH含量、CAT、SOD和T-AOC活力的变化趋势与1 mg/L组大体一致,复氧72 h后体腔液的各项指标恢复到对照组水平;除T-AOC,呼吸树的其余3种指标亦完全恢复。低氧胁迫后小规格刺参的恢复能力高于大规格刺参。在DO为1 mg/L和3 mg/L条件下,胁迫结束时2种规格刺参体腔液中的皮质醇含量显著高于对照组(P0.05),且大规格刺参皮质醇含量高于小规格,复氧后二者均恢复到对照水平。结果表明,低氧胁迫持续时间不超过其半致死时间(本研究以24h为例),刺参可通过自身调节减轻机体的氧化损伤;一旦超出半致死时间,将产生不可逆损伤,最终导致死亡。     

Appetite,metabolism and growth regulation in Atlantic salmon (Salmo salar L.) exposed to hypoxia at elevated seawater temperature

High temperature combined with low dissolved oxygen (DO) is one of the most challenging environmental conditions farmed fish experience; thus, understanding their impact on growth regulation is of relevance to cultured and wild populations. This study examines appetite‐ and growth‐regulating mechanisms in Atlantic salmon postsmolt exposed to either high (HO) or low oxygen (LO) at a suboptimally high temperature (17°C). Additionally, the effects of high (HE) and low (LE) dietary energy (DE) were examined. After a month of treatment, analyses of hormones, regulating appetite (ghrelin) and growth (growth hormone receptor ghr1 and insulin‐like growth factor IGF‐1), and free amino acids (FAA) were measured pre‐ and postprandially at ?4, ?2, 0, 2, 4 and 6 h. No preprandial ghrelin peaks were detected despite a significant reduction in feed intake and growth under hypoxia compared to normoxia. LO treatment also had an overall negative effect on survival compared to HO, while nutrient retention efficiency, FCR and plasma FAA concentrations were unaffected (P > 0.05). Feeding HE diet resulted in increased growth (+17%) and improved FCR (?14%) and energy retention efficiency (+26%) independent of DO. Plasma FAA concentrations were unaffected by LO treatment and DE (P > 0.05). Growth regulatory gene expressions possibly reflect an overall lower growth at a high temperature overriding the impacts of DO and DE. This study also indicates that optimal adaptation time to environmental conditions and feeding regime is crucial for establishing a regular hormonal appetite signalling that reflects real feeding anticipation in salmon.     

Survival and respiration of marbled rabbitfish (Siganus rivulatus) fingerlings at various oxygen tensions

Marbled rabbitfish, Siganus rivulatus, is an economically valuable herbivorous fish and a potential candidate for warmwater aquaculture. This study was carried out to: (1) assess the effect of various oxygen concentrations on survival and behaviour of S. rivulatus fingerlings and (2) investigate the response of S. rivulatus to hypoxia and determine its critical oxygen tension (P_crit). In the first experiment, groups of rabbitfish (15 fish per group) were maintained for 1 h in waters of various oxygen concentrations. They were then transferred to well‐aerated tanks and observed for 72 h. Survival was recorded, fish behaviour at low oxygen concentrations observed, and LC₅₀ after 1‐h hypoxia and 72‐h recovery evaluated. In the second experiment, a series of stop‐flow respirometry experiments were performed during which dissolved oxygen was allowed to drop to 0.5 mg L^?1 and respiration rate recorded at various oxygen concentrations. In the first experiment, all fish survived for 1 h at oxygen concentration of 1.44 mg L^?1 and greater, but started dying at oxygen concentrations below 0.65 mg L^?1 (16% survival). The LC₅₀ of S. rivulatus fingerlings was 0.6 mg L^?1. Results of the second experiment showed that S. rivulatus is an oxyregulator until P_crit (1.7 mg L^?1 O₂) is reached, becoming an oxyconformer below this concentration. Findings allow for a better understanding of environmental oxygen tolerances and minimum acceptable oxygen concentration in rabbitfish aquaculture.     

Hypoxia inducible factor 1α expression and effects of its inhibitors in canine lymphoma

Hypoxic conditions in various cancers are believed to relate with their malignancy, and hypoxia inducible factor-1α (HIF-1α) has been shown to be a major regulator of the response to low oxygen. In this study, we examined HIF-1α expression in canine lymphoma using cell lines and clinical samples and found that these cells expressed HIF-1α. Moreover, the HIF-1α inhibitors, echinomycin, YC-1 and 2-methoxyestradiol, suppressed the proliferation of canine lymphoma cell lines. In a xenograft model using NOD/scid mice, echinomycin treatment resulted in a dose-dependent regression of the tumor. Our results suggest that HIF-1α contributes to the proliferation and/or survival of canine lymphoma cells. Therefore, HIF-1α inhibitors may be potential agents to treat canine lymphoma.     

Effects of maternal limb ischemic preconditioning on structural and functional changes of mitochondria in fetal hippocampal neurons induced by intrauterine distress-reoxygenation in rats

AIM: To investigate the effects of maternal limb ischemic preconditioning (LIP) on the mitochondrial structures and functions of the hippocampal neurons induced by reoxygenation in the intrauterine distress fetal rats. METHODS: Pregnant rats (n=40) were randomly divided into 4 groups: sham (S) group, LIP group, fetal distress (FD) group and LIP+FD group. Intrauterine ischemia model was established through the experimental design. The ultrastructure of the mitochondria in CA1 area of the hippocampus was observed. The mitochondrial membrane potential and reactive oxygen species (ROS) were measured. The content of ATP and MDA in the hippocampus tissue was detected. The activity of Mn-SOD was observed. RESULTS: Compared with sham group, the ultrastructure of mitochondria in CA1 area of the hippocampus was damaged in FD group and LIP+FD group. The mitochondrial membrane potential, the content of ATP and the activity of Mn-SOD were decreased. However, the content of ROS and MDA was increased. Compared with FD group, the ultrastructure of mitochondria in CA1 area of the hippocampus was intact in LIP+FD group. Furthermore, the reduced mitochondrial membrane potential and ATP content were inhibited. The activity of Mn-SOD was increased, but the content of ROS and MDA was decreased in LIP+FD group. CONCLUSION: Limb ischemia preconditioning inhibits the damage the mitochondria of fetal hippocampal neurons induced by reoxygenation in the intrauterine distress fetal rats.     

低氧胁迫对河川沙塘鳢抗氧化酶及ATP酶活性的影响

研究了在急性低氧1.5 h、5 h和慢性低氧3 d下,河川沙塘鳢(Odontobutis potamophila)5种组织(心、脑、肝、鳃和肾)的超氧化物歧化酶(SOD)、过氧化氢酶(CAT)及谷胱甘肽过氧化物酶(GPX)3种抗氧化酶和ATP酶活性的变化规律。结果显示:在急性低氧暴露1.5 h时,河川沙塘鳢SOD和GPX的活力在各组织中与对照组相比均无显著差异,CAT活力在心、鳃和肝3种组织呈现显著升高(P0.05),ATP酶活力在心和肝组织极显著升高(P0.01);在急性低氧暴露5 h时,除肝组织SOD酶活性显著降低外(P0.05),其它4种组织的CAT、GPX和ATP酶均不同程度显著升高(P0.05);在慢性低氧处理3 d时,心、脑组织的抗氧化酶已基本恢复至与对照组无显著差异的水平,但鳃、肝和肾中酶活力仍较高(P0.05)。研究表明,河川沙塘鳢能通过自身调节抗氧化酶及ATP酶活性,改变代谢底物,提高机体适应低氧环境的能力。     

低氧热泵干燥技术的国内外研究概况

低氧热泵干燥技术是采用其他气体，如二氧化碳和氮气等代替常规空气作干燥介质，密闭循环系统进行低氧环境的气调干燥加工。该技术提升干燥品质，节约能耗，提高干燥效率，有效解决氧敏性、热敏性物质的干制问题，有广阔的应用前景。本文介绍低氧热泵干燥技术中不同气体作干燥介质的物性研究、对干燥品质特性的影响、相关装置的研制等方面的国内外研究概况。