Beside this, how did otohime give birth to shirahoshi?
Fishmen and Fishwomen are mammals. If Shirahoshi was not born from egg the most logical explanation behind her birth is that she was probably born small and had a massive growth spurt. Growing to a massive growth is not impossible because she has royal blood and her father Neptune is of a giant size merman after all.
Also, is Fishman Island in the New World? Fish-Man Island is the home of the fish-men and merfolk. It serves as an underwater gateway to the New World for those who do not wish (or are not legally permitted) to cross over the Red Line above.
Considering this, what did humans do to Hody Jones?
He recalls what he asked what Humans did to Hody and Hody answers "nothing" and that they've been chosen by the heavens to punish humans and granted power.
How old is shirahoshi?
Shirahoshi at age 6.