Fasting increases investment in soma upon refeeding at the cost of gamete quality in zebrafish

Fasting increases lifespan in invertebrates, improves biomarkers of health in vertebrates, and is increasingly proposed as a promising route to improve human health. Nevertheless, little is known about how fasted animals use resources upon refeeding, and how such decisions affect putative trade-offs between somatic growth and repair, reproduction, and gamete quality. Such fasting-induced trade-offs are based on strong theoretical foundations and have been recently discovered in invertebrates, but the data on vertebrates is lacking. Here we report that fasted female zebrafish, Danio rerio , increase investment in soma upon refeeding but it comes at a cost of egg quality. Specifically, an increase in fin re-growth was accompanied by a reduction in 24-hours post-fertilization offspring survival. Refed males showed a reduction in sperm velocity and impaired 24-hour post-fertilisation offspring survival. These findings underscore the necessity of considering the impact on eggs and sperm when assessing evolutionary and biomedical implications of lifespan-extending treatments in females and males and call for careful evaluation of the effects of fasting (both during and post) on fertilisation. ### Competing Interest Statement The authors have declared no competing interest.