A spikey new addition to the Perth Zoo family has been introduced — but four months after the puggle's entry into the world, it remains a mystery whether it is a male or a female.

The baby short-beaked echidna hatched in September and is the second offspring to parents Chindi and Nyingarn.

They became the first zoo-born echidnas to successfully breed when they had their first puggle Cojine at Perth Zoo in 2015, setting a new precedent for breeding programs across the world.

The puggle now weighs in at 1.6 kilograms and could eventually weigh 6kg, however it has not been named yet because its sex is still unknown.

The zoo will send the puggle's DNA for testing at a later date to determine whether it is a male or female.

The puggle's parents Chindi and Nyingarn were both bred at Perth Zoo. ( ABC News: Eliza Laschon )

Perth Zoo Keeper Katie Snushall said the short-beaked echidna was a fairly common species —but their closely related cousin, the long-beaked echidna found in Papua New Guinea, was endangered.

"The breeding program is still very significant to us especially here at Perth Zoo because we want to educate ourselves," Ms Snushall said.

"What we can learn [about] their very closely related cousins ... is going to be very important for the Long-Beaked Echidna."

The puggle will stay with its mother for six to seven months before it leaves the nursery.