[asdff]

They did mention they were looking at a couple of long lived examples like rockfish that live 200 years vs killifish that live for 1, so this seems to be variable among fish at least. As for mechanism, they were pretty hand wavey but cited reference 33 and mentioned that longer CpG tracts are thought to be protective against spontaneous methylation. Unmethylated CpG islands in promotors are associate with active transcription, especially found in housekeeping genes that are transcribed constantly by definition. Methylating these islands can silence the gene. Makes sense but needs an experiment to know for sure.