My latest article Guppy Longevity (39 pages and 97 scientific references) discusses the genetics of longevity and answers the question of why fancy guppies don’t live that long. Article delves into the many factors (inbreeding, outcrossing, heterosis, purging, outbreeding depression, evolution, and disease) that are associated with longevity. It puts much of the blame for guppy fragility onto the all too common practice of using only young adults as breeders. I have tried to make the science understandable, educational, and interesting. Photo shows a 15 month old male and female. Still room for improvement, but this is progress. (Two years ago, my guppies were dying of old age or “what-not” at 5-8 months.)
I revised my 2018 article 
