Along with that, the more expensive method that scales a bit easier is DNA methylation: most vertebrates, including fish, have a strong correlation between the

Along with that, the more expensive method that scales a bit easier is DNA methylation: most vertebrates, including fish, have a strong correlation between the percentage of their genomes that has been methylated and the age. It's like r=0.99, the older, the more methylated. (however, artificially de-methylating doesn't make you younger) So you can sequence these genomes and count. Definitely more expensive than digging out a tiny bone, but you can sequence a few hundred or thousand genomes at once. Random example paper: https://www.nature.com/articles/s41598-023-36773-2 https://www.nature.com/articles/s41598-023-36773-2