Growth, osmoregulation, and Ionoregulation of Longfin Smelt (Spirinchus thaleichthys) yolk-sac larvae at different salinities

Longfin smelt (Spirinchus thaleichthys) is a threatened anadromous fish species that spawns in freshwater to moderately brackish (i.e. 5-10 ppt) reaches of the upper San Francisco Estuary and has declined to approximately 1% of its pre-1980s abundances. Despite 50+ years of population monitoring, the efficacy of 10+ years of conservation efforts for longfin smelt remain uncertain due to a limited understanding of how the species responds to environmental variation, such as salinity. For example, high mortality during larval stages has prevented culture efforts from closing the life cycle in captivity. Here, we investigated the effects of salinity on longfin smelt yolk-sac larvae. Newly hatched larvae from four single-pair crosses were acutely transferred to and reared at salinities of 0.4, 5, 10, 20, or 32 ppt. We compared whole-body water and sodium ion (Na+) content, notochord length, and yolk-sac volume at 12, 24, 48, 72, and 96 h post-transfer for each salinity treatment. We found t...

长鳍胡瓜鱼（Longfin smelt, *Spirinchus thaleichthys*）是一种受胁的溯河洄游鱼类，其产卵场分布于旧金山河口上游的淡水至中度咸水（盐度5~10 ppt）区段，种群丰度已降至1980年代前的约1%。尽管已开展了50余年的种群监测，但由于对该物种如何响应盐度等环境变量变化的认知仍较为有限，针对长鳍胡瓜鱼的十余年保护工作的实施成效仍不明确。例如，幼体阶段的高死亡率使得人工繁育工作无法在圈养环境下完成其完整生活史。本研究探讨了盐度对长鳍胡瓜鱼卵黄囊期仔鱼的影响。我们将来自4个单对杂交组合的初孵仔鱼，急性转移至盐度分别为0.4、5、10、20及32 ppt的水体中并进行饲养。我们比较了各盐度处理组仔鱼在转运后12、24、48、72及96小时时的全身体含水量、钠离子（Na+）含量、脊索长度以及卵黄囊体积。我们发现……