Manuscript total length = 4461 words 14 15What is already known: Telomeres shorten with age in most endotherm species, but the 16 picture in other vertebrate species and especially in fish remains less clear. In endotherms, 17 telomeres shorten more rapidly when facing stressful environmental conditions, but this has 18 never been tested in fish species. 19What this study adds: We first review the results of the 14 studies investigating age-related 20 changes in telomere length in fish species (Table 1) and then provide new data showing 21 telomere shortening with age in a very long-lived fish, both at the intra-and at the inter-22 individual levels. In addition, we showed that a chronic sublethal heat stress could accelerate 23 telomere erosion, suggesting that stressful environmental conditions could also accelerate 24 telomere shortening in fish species. 25
Abstract 26Telomeres shorten at each cell division due to the "end-replication problem", but also in 27 response to oxidative stress. Consequently telomeres shorten with age in many endotherms, 28 and this shortening is accelerated under stressful environmental conditions. Data in 29 ectotherm vertebrates remain scarce so far, so our goal was to review existing data for fish, 30and to test the influence of age and stress on telomere length in a very long-lived fish, the 31
Siberian sturgeon (Acipenser baerii). 32Our review of the literature revealed age-related telomere shortening in approximately half 33 of the published studies. In the Siberian sturgeon, we found a significant telomere 34 shortening with age, both at the intra-individual level using red blood cells (-12.5% in 16 35 months) and at the inter-individual level using cross-sectional samples of fin over an age-36 range of 8 years. We also found that heat stress (30°C) significantly reduced telomere length 37 by 15.0% after only 1 month of exposure. Our results highlight that both age and stressful 38 environmental conditions might be important determinants of telomere length in fish. 39 40