The only logical limit is conception. If you accept conception as a logical limit, then you'll have to explain the relevant moral distinction between a human e

The only logical limit is conception. If you accept conception as a logical limit, then you'll have to explain the relevant moral distinction between a human embryo and a fish embryo, besides that one can eventually become a person, given the right external conditions (an ovum can too). I propose sentience as a logical limit, acquired I suspect late in pregnancy.