*Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA; Aquatic Systems Biology Unit, Department of Ecology and Ecosystem Management, Technische Universität München, Mühlenweg 22, D-85354 Freising, Germany; Department of Wildlife, Fish & Conservation Biology, University of California, Davis, CA 95616, USA.
Integr Comp Biol. 2013 Oct;53(4):620-34. doi: 10.1093/icb/ict082. Epub 2013 Aug 5.
Coastal estuaries are among the most heavily impacted ecosystems worldwide with many keystone fauna critically endangered. The delta smelt (Hypomesus transpacificus) is an endangered pelagic fish species endemic to the Sacramento-San Joaquin Estuary in northern California, and is considered as an indicator species for ecosystem health. This ecosystem is characterized by tidal and seasonal gradients in water parameters (e.g., salinity, temperature, and turbidity), but is also subject to altered water-flow regimes due to water extraction. In this study, we evaluated the effects of turbidity and salinity on feeding performance and the stress response of delta smelt because both of these parameters are influenced by water flows through the San Francisco Bay Delta (SFBD) and are known to be of critical importance to the completion of the delta smelt's life cycle. Juvenile delta smelt were exposed to a matrix of turbidities and salinities ranging from 5 to 250 nephelometric turbidity units (NTUs) and 0.2 to 15 parts per thousand (ppt), respectively, for 2 h. Best statistical models using Akaike's Information Criterion supported that increasing turbidities resulted in reduced feeding rates, especially at 250 NTU. In contrast, best explanatory models for gene transcription of sodium-potassium-ATPase (Na/K-ATPase)-an indicator of osmoregulatory stress, hypothalamic pro-opiomelanocortin-a precursor protein to adrenocorticotropic hormone (expressed in response to biological stress), and whole-body cortisol were affected by salinity alone. Only transcription of glutathione-S-transferase, a phase II detoxification enzyme that protects cells against reactive oxygen species, was affected by both salinity and turbidity. Taken together, these data suggest that turbidity is an important determinant of feeding, whereas salinity is an important abiotic factor influencing the cellular stress response in delta smelt. Our data support habitat association studies that have shown greater delta smelt abundances in the low-salinity zone (0.5-6.0 ppt) of San Francisco Bay, a zone that is also understood to have optimal turbidities. By determining the responses of juvenile delta smelt to key abiotic factors, we hope to aid resource managers in making informed decisions in support of delta smelt conservation.
沿海河口是全球受影响最严重的生态系统之一，许多关键动物物种处于极度濒危状态。斑尾鱵 Hypomesus transpacificus）是一种濒危的洄游鱼类，分布于加利福尼亚州北部的萨克拉门托-圣华金河口，被认为是生态系统健康的指示物种。这个生态系统的特点是水参数（如盐度、温度和浊度）存在潮汐和季节性梯度，但由于水资源提取，水流模式也发生了变化。在这项研究中，我们评估了浊度和盐度对斑尾鱵摄食性能和应激反应的影响，因为这两个参数都受到通过旧金山湾三角洲（SFBD）的水流的影响，并且已知对完成斑尾鱵的生命周期至关重要。幼年斑尾鱵暴露在浊度和盐度范围从 5 到 250 度尼尔森浊度单位（NTU）和 0.2 到 15 个千分比（ppt）的矩阵中，持续 2 小时。使用赤池信息量准则的最佳统计模型支持增加浊度会导致摄食率降低，尤其是在 250 NTU 时。相比之下，钠离子-钾离子-三磷酸腺苷酶（Na/K-ATPase）的基因转录的最佳解释模型-渗透调节应激的指标，下丘脑促黑皮质素原-a 促肾上腺皮质激素的前体蛋白（对生物应激做出反应），以及全身皮质醇仅受盐度单独影响。只有谷胱甘肽-S-转移酶的转录，一种保护细胞免受活性氧的二期解毒酶，同时受到盐度和浊度的影响。总的来说，这些数据表明浊度是摄食的重要决定因素，而盐度是影响斑尾鱵细胞应激反应的重要非生物因素。我们的数据支持栖息地关联研究，该研究表明在旧金山湾的低盐度区（0.5-6.0 ppt）有更多的斑尾鱵，该区域也被认为有最佳的浊度。通过确定幼年斑尾鱵对关键非生物因素的反应，我们希望帮助资源管理者做出明智的决策，以支持斑尾鱵的保护。
