Big guys better at gas exchange, possibly explaining their appeal to females!
https://leapflash.blogspot.com/2015/06/big-guys-better-at-gas-exchange.html
BREATHLESS Among the broad-nosed Pipefish (shown), males carry fertilized eggs to term inside a long, narrow brood pouch with mediocre oxygenation or worse.
When a pipefish dad gets pregnant, his brood pouch delivers a surprisingly meager amount of oxygen to the embryos developing inside.
Broad-nosed pipefish (Syngnathus typhle) swimming in 100 percent oxygenated water in lab tanks delivered on average only about 50 percent of the oxygen to embryos in their brood pouches, says Inês Braga Gonçalves of the University of Zurich. Males stuck with worse water that was only 40 percent oxygenated kept the fluid in their brood pouches at only about 35 percent oxygenation.
Yet oxygen matters for embryo growth. After two weeks, the youngsters in the lowest-oxygen environment were shorter and weighed less than the ones in airier pouches, Braga Gonçalves and her colleagues report June 3 in the Journal of Experimental Biology.
