Dr Whittington said the moment of intimacy was one of the most amazing things she has witnessed.

The male and female do a dance (humans sometimes do that as well) on the ocean, or in this case the aquarium, floor. Once they decide to mate, the female aligns herself with the male and deposits her eggs in the male brood pouch.

"The female then swims off and has nothing more to do with things," she said. "The male adds his sperm and looks after things from then on."

Male seahorses can have more than a thousand embryos in the pouch at once but, until now, researchers had limited understanding of how the babies are fed.

"This work adds to the growing evidence that male pregnancy in seahorses could be as complex as female pregnancy in other animals, including ourselves," said Dr Whittington, from the School of Life and Environmental Sciences.

"We now know that seahorse dads can transport nutrients to the babies during pregnancy, and we think they do this via a placenta. It's not exactly like a human placenta though – they don't have an umbilical cord, for example. We need to do further histological work to confirm this."

The research published in the Journal of Comparative Physiology B was led by University of Sydney honours student Zoe Skalkos in collaboration with Dr James Van Dyke at La Trobe University.

"It's really exciting because it's a big step in understanding the relationship between Dad and baby in male pregnancy," Ms Skalkos said.