Davis Brittany E, Hammock Bruce G, Kwan Nicole, Pien Catarina, Bell Heather, Hartman Rosemary, Baerwald Melinda R, Schreier Brian, Gille Daphne, Acuña Shawn, Teh Swee, Hung Tien-Chieh, Ellison Luke, Cocherell Dennis E, Fangue Nann A
California Department of Water Resources, 3500 Industrial Blvd., West Sacramento, CA 95691, USA.
Department of Anatomy, Physiology, and Cell Biology, University of California Davis, 1 Shields Ave., Davis, CA 95616, USA.
Conserv Physiol. 2024 Dec 26;12(1):coae088. doi: 10.1093/conphys/coae088. eCollection 2024.
Freshwater fishes are increasingly facing extinction. Some species will require conservation intervention such as habitat restoration and/or population supplementation through mass-release of hatchery fish. In California, USA, a number of conservation strategies are underway to increase abundance of the endangered Delta Smelt (); however, it is unclear how different estuarine conditions influence hatchery fish. The goal of this study was to evaluate a year of Delta Smelt field deployments to inform species conservation strategies of suitable conditions for smelt physiology. Hatchery-reared Delta Smelt was deployed in experimental cages (seven deployments) throughout the Estuary in the winter, summer and fall of 2019. Effects of season and location of cage deployments on fish health (condition factor and histological condition of liver and gill), growth, thermal tolerance and survival were evaluated. The results indicate both seasonal and location differences, with high survival in the winter (100%) and fall (88-92%) compared to lower survival in summer (67%). In the summer, one of the study sites had no surviving fish following high temperature exposure, which peaked ~26°C. After 29 days in the cages, surviving Delta Smelt in summer and fall showed signs of nutritional stress that may be related to biofouling of the cages limiting passive food inputs, restriction of natural foraging behaviour by containment in the cages, and water temperatures that were too high given the chronically low pelagic productivity in the Estuary overall. Field measurements of upper thermal tolerance (CTmax) following caging exposures suggest that laboratory measures of CTmax may overestimate the realized tolerance in a more stochastic field environment. This study demonstrates the utility of using cages as an experimental tool to better understand aspects of Delta Smelt physiological responses to environmental changes across estuarine habitats in a more natural-field setting, while also highlighting potential limitations of using cages.
淡水鱼正日益面临灭绝的困境。一些物种需要进行保护干预，例如栖息地恢复和/或通过大规模放养鱼苗来补充种群数量。在美国加利福尼亚州，正在实施一系列保护策略以增加濒危的三角洲胡瓜鱼（Delta Smelt）的数量；然而，尚不清楚不同的河口条件如何影响鱼苗。本研究的目的是评估为期一年的三角洲胡瓜鱼野外投放情况，以为该物种在适合其生理条件下的保护策略提供参考。2019年冬、夏、秋三季，将人工养殖的三角洲胡瓜鱼放置在河口各处的实验网箱中（共七次投放）。评估了网箱投放的季节和位置对鱼的健康状况（肥满度以及肝脏和鳃的组织学状况）、生长、耐热性和存活率的影响。结果表明存在季节和位置差异，冬季（100%）和秋季（88%-92%）的存活率较高，而夏季（67%）的存活率较低。夏季，其中一个研究地点在高温暴露后无鱼存活，最高温度达到约26°C。在网箱中放置29天后，夏季和秋季存活的三角洲胡瓜鱼出现了营养应激迹象，这可能与网箱的生物污损限制了被动食物输入、网箱限制了自然觅食行为以及鉴于河口总体上长期的远洋生产力较低而水温过高有关。网箱暴露后对上热耐受极限（CTmax）的现场测量表明，在更具随机性的野外环境中，CTmax的实验室测量值可能高估了实际耐受能力。本研究证明了使用网箱作为实验工具的实用性，以便在更自然的野外环境中更好地了解三角洲胡瓜鱼对河口栖息地环境变化的生理反应，同时也突出了使用网箱的潜在局限性。
