The duration of the ammocoete life stage in Pacific lamprey (Entosphenus tridentatus) is not well understood, particularly in southern latitudes, hampering the development of conservation strategies. We studied the development of anadromous Pacific lamprey from hatchling to transformation into macrophthalmia near the southern extent of their range. Lampreys were absent from San Luis Obispo drainage in Southern California for over 6 years, but the drainage was naturally recolonized, with ammocoetes first detected again in 2017. This provided an opportunity to examine in-river growth and development using repeated sampling. We estimated ammocoetes transformed into macrophthalmia in as little as 2.6 years, one of the shortest larval durations documented for the species and at least half that assumed in studies of other wild populations. This is the first estimate of time-to-transformation for Pacific lamprey in its southern range and provides insights into adaptive strategies and refinement of recovery approaches for lamprey species worldwide.

太平洋七鳃鳗 ( Entosphenus tridentatus ) 弹药生命阶段的持续时间) 尚未得到很好的理解，特别是在南纬地区，这阻碍了保护战略的发展。我们研究了溯河性太平洋七鳃鳗从孵化到在其分布范围南部附近转变为大眼的发育过程。在南加州的圣路易斯奥比斯波排水系统中，七鳃鳗已经消失了 6 年多，但排水系统自然地重新定殖，2017 年再次发现了 ammocoetes。这为使用重复采样检查河流中的生长和发育提供了机会。我们估计 ammocoetes 在短短 2.6 年内转化为大眼科，这是该物种记录的最短的幼虫持续时间之一，并且至少是其他野生种群研究中假设的一半。