Well known animals like the rougheye rockfish, which can be bought from the fish market, appear to be negligily senecent. Senecent cell buildup appears to play a key role in senecence, in mice at least (http://www.nature.com/nature/journal/v530/n7589/abs/nature16932.html). Is there no buildup of senecent cells in such negligible senescent animals over livetime?