Dynamic Population Breeding: A Structured Colony Management Strategy to Improve Reproductive Performance and Early Survival in <i>Nothobranchius furzeri</i>.

The African turquoise killifish, <i>Nothobranchius furzeri</i>, has emerged as an important vertebrate model for aging research due to its naturally short lifespan and telomere(definition) attrition, cellular senescence(definition))." style="text-decoration:underline dotted; text-underline-offset:2px; cursor:help;">hallmarks of aging(definition). However, these characteristics create challenges for colony management, such as high breeder turnover, rapid generational change, and the risk of inbreeding or unintended selection in closed laboratory populations. Since new individuals cannot be introduced from the wild or purchased from commercial laboratory animal breeders, maintaining genetically stable laboratory stocks requires carefully controlled breeding strategies. Here, we describe an innovative colony management approach termed dynamic population breeding (DPB) and evaluated its performance in two commonly used laboratory lines with different lifespans, GRZ-D and MZCS-08/122. DPB integrates several key principles: the maintenance of overlapping breeding age cohorts, harem-based breeding groups, continuous monitoring of clutch quality and quantity, and the controlled use of embryonic diapause for flexible embryo storage and synchronized hatching. Embryos from multiple breeding groups were pooled, stored in diapause stage II, and hatched at defined time points to generate new cohorts while avoiding sibling-only populations. Using this approach, we systematically analyzed reproductive performance, embryo quality, hatching success, and survival in laboratory populations. Fertilization rates and clutch sizes remained within stable ranges across the reproductive period, although an age-dependent decline in fertilization efficiency was observed in both lines. Quality control at the clutch level allowed early identification and exclusion of low-performing breeding groups. Importantly, implementation of DPB reduced variability between cohorts and improved early-life survival of offspring, particularly during the first weeks after hatching. Overall, DPB provides a practical framework for maintaining stable and robust killifish colonies while minimizing unintended selection and inbreeding. By integrating diapause biology with structured breeding management, this strategy enhances reproducibility and sustainability of <i>N. furzeri</i> populations used in aging research.