A Macro Diver in Australia Documents Gobbleguts Mouthbrooding - Observation of the Week, 3/9/21

Our Observation of the Week is this mouth-brooding male Eastern Gobbleguts (Vincentia novaehollandiae) fish, seen in Australia by @emikok!

“I’m just a scuba diver,” Emiko Kawamoto tells me, “I learned how to dive in Japan back in 1994. I moved to Sydney in 2003 but I only started to dive here 2-3 years ago so I am not an experienced Sydney diver yet.” She’s been posting her her photos to iNat for ID help.

Rather than cover a lot of ground when she dives, Emiko likes to “macro dive,” staying in one place and observing the life in front of her. “I stay in a small area and watch the same critters, so my diving style can look very boring but it allows me to observe their particular behavioral patterns,” she explains. 

This technique allowed her to get some great photos of eastern gobbleguts brooding behavior over the past few years. Like some other fish, this Australian endemic engages in paternal mouthbrooding. After the eggs are fertilized, the male holds them in his mouth, protecting them until they’ve hatched (or even longer). Last March, Emiko followed a gravid female:

As I watched, she met a male and they started to dance. It looked like kissing, hugging, and holding. Then the female released two coloured egg masses (orange and white), and fertilization occurred during the ‘‘holding’’ behavior and took about 1- 2 minutes to be completed. I felt quite long, though. During this period the female held the male with her pectoral fin - the “holding” position - while the male kept his genital papilla over the egg clutch as it was being released. I was so excited when the eggs were transferred to male’s mouth. He looked very tired and could not swim with such a heavy mouth. The female disappeared as soon as the eggs were transferred.

She saw the same behavior again this year and posted her shots to iNat, curious as to why the egg mass consisted of two colors. iNat user @markmcg, with the help of a colleague, found a paper describing a similar species. It said the egg mass contained two types of eggs, “a smaller part composed of a compact white mass of small non-functional oocytes and a larger part composed of the bright orange mature ova.” (Vagelli, 2019)

Learning that the eggs are kept in the male’s mouth for days (and sometimes much longer), Emiko (above, with a sea dragon) continued to dive in the same area until she found a male with maturing eggs in his mouth - perhaps even the same one she saw earlier.

Orange eggs had become silver and I could see the developing fish's eyes. The male often kept his mouth closed, but he opened it for regular churning of the eggs so I stayed quiet, sneaking up on him, and waited until he opened his mouth so I could take photos.

After I got home, I saw in my photos that one of the eggs hatched in this mouth. I believe that they stay in dad's mouth for another 4-8 days. I hope to watch them moving and playing in their dad's mouth next time!

(Some quotes have been lightly edited for clarity.)

- Emiko’s photo of a gorgeous sea spider (and its eggs) was iNat’s Observation of the Day last June!

- Check out the Australasian Fishes project, created by @marckmcg and curated by many others, they’ve done amazing outreach work with underwater photographers.

- Here’s some footage of a Banggai cardinalfish (Pterapogon kauderni) - same family as gobbleguts - engaging in paternal mouthbrooding.

Posted by tiwane tiwane, March 10, 2021 05:46


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