Hoffman Nick F, Medeiros Lea R, Graham Neil D, Nuetzel Hayley M, Pierce Andrew L, Nagler James J
Department of Biological Sciences, University of Idaho, 875 Perimeter Dr., Moscow, ID 83844, USA.
Columbia River Inter-Tribal Fish Commission, Fishery Science Department, 700 NE Multnomah St., Suite 1200, Portland, OR 97232, USA.
Conserv Physiol. 2023 Jan 20;11(1):coac085. doi: 10.1093/conphys/coac085. eCollection 2023.
Hatchery programs designed to conserve and increase the abundance of natural populations of spring Chinook Salmon O have reported high proportions of males precociously maturing at age 2, called minijacks. High proportions of minijacks detract from hatchery supplementation, conservation and production goals. This study tested the effects of rearing juvenile Chinook Salmon under continuous light (LL) on minijack maturation in two trials. The controls were maintained on a simulated natural photoperiod for both trials. For trial 1, LL treatment began on the summer solstice 2019 or the autumn equinox 2019 and ended in late March 2020 (LL-Jun-Apr and LL-Sep-Apr, respectively). A significant reduction in the mean percent of minijacks (%MJ) was observed versus control (28.8%MJ) in both LL-Jun-Apr (5.4%MJ) and LL-Sep-Apr (9.3%MJ). Trial 2 was designed to evaluate whether stopping LL treatment sooner was still effective at reducing maturation proportions relative to controls. LL treatments began on the summer solstice 2020 and continued until the winter solstice (LL-Jun-Dec) or the final sampling in April 2021 (LL-June-Apr). LL-Jun-Dec tanks were returned to a simulated natural photoperiod after the winter solstice. Both photoperiod treatments showed a significant reduction in mean %MJ from the control (66%MJ): LL-Jun-Dec (11.6%MJ), LL-Jun-Apr (10.3%MJ). In both trials, minijacks had higher body weights, were longer and had increased condition factor when compared to females and immature males in all treatment groups at the final sampling. In both trials, there was little or no effect of LL treatment on fork length or body weight in immature males and females versus controls, but an increase in condition factor versus controls was observed. This study shows that continuous light treatment reduces minijack maturation in juvenile male spring Chinook Salmon and could provide an effective method for Spring Chinook Salmon hatcheries interested in reducing minijack production.
旨在保护和增加春季奇努克鲑鱼自然种群数量的孵化场计划报告称，有很高比例的雄性在2岁时就早熟，即所谓的小雄鱼。高比例的小雄鱼不利于孵化场的补充、保护和生产目标。本研究在两项试验中测试了在持续光照（LL）条件下饲养幼年奇努克鲑鱼对小雄鱼成熟的影响。两项试验的对照组均维持在模拟自然光照周期下。对于试验1，LL处理分别于2019年夏至或2019年秋分开始，并于2020年3月下旬结束（分别为LL-Jun-Apr和LL-Sep-Apr）。与对照组（28.8%小雄鱼）相比，LL-Jun-Apr组（5.4%小雄鱼）和LL-Sep-Apr组（9.3%小雄鱼）的小雄鱼平均百分比均显著降低。试验2旨在评估相对于对照组，更早停止LL处理是否仍能有效降低成熟比例。LL处理于2020年夏至开始，持续到冬至（LL-Jun-Dec）或2021年4月的最终采样（LL-June-Apr）。LL-Jun-Dec组的水箱在冬至后恢复到模拟自然光照周期。两种光照周期处理的小雄鱼平均百分比均比对照组（66%小雄鱼）显著降低：LL-Jun-Dec组（11.6%小雄鱼），LL-Jun-Apr组（10.3%小雄鱼）。在两项试验的最终采样中，与所有处理组中的雌性和未成熟雄性相比，小雄鱼的体重更高、体长更长且肥满度增加。在两项试验中，与对照组相比，LL处理对未成熟雄性和雌性的叉长或体重几乎没有影响，但观察到肥满度相对于对照组有所增加。本研究表明，持续光照处理可降低幼年雄性春季奇努克鲑鱼的小雄鱼成熟率，并可为有兴趣减少小雄鱼产量的春季奇努克鲑鱼孵化场提供一种有效方法。
