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Uploaded:2020-06-20
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Happy Father's day! Today we're talking about the fintastic Nurseryfish, which is one of the best dads you can fish for.

Hosted by: Hank Green

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Sources:

https://doi.org/10.1023/A:1020523905635
https://mansfield.osu.edu/assets/mansfield/tberra/pdf/observationegg.pdf

https://doi.org/10.1643/CI-15-365
https://doi.org/10.1093/icb/25.3.807
https://doi.org/10.1111/evo.13846
https://doi.org/10.1071/ZO16041
https://pfeil-verlag.de/wp-content/uploads/2015/05/ief14_4_02.pdf
https://doi.org/10.1111/j.0022-1112.2004.00454.x
https://doi.org/10.1071/ZO07033
https://doi.org/10.1643/0045-8511(2003)003[0384:ELHOTN]2.0.CO;2
[SciShow intro]

FAST FACT
Fish eggs are really important; without them, we wouldn't have fish anymore.

They're also somewhat fragile: they need to bathe in waters that are just right to develop properly. So fish have all sorts of weird strategies to ensure that their eggs are safe and kept in the right conditions for growth.

But special props have to go to the nurseryfish, the males of which hang bunches of eggs from hooks on their heads. Here's the situation: fish don't always live in waters that are great for their eggs' development. So if you're an egg-laying fish, it may be prudent to care for them somehow.

And more often than not in fish, if parenting occurs, that duty is performed by the male parent. We're not entirely sure why this is, but it may be because their eggs are usually fertilized externally, which means a male can be more confident that he's the father. And therefore, it's more guaranteed to be worth his while to invest in parental care in an evolutionary sense, because remember, these are fish.

They aren't making parenting decisions on the fly. Now there are lots of ways to care for eggs, but if you could ask a male nurseryfish, he would tell you that the best way is to carry them around using a hook on your forehead. Just out in the open, like you're dangling a bunch of teeny-tiny grapes between your eyes.

If grapes came in bunches of like, a thousand or more. Nurseryfish are hatchet shaped 10-30 centimeter long fish native to the fresh and brackish waters of Northern Australia and Southern New Guinea. And they got their name because each male has a hook for carrying eggs which stems from the supraoccipital bone at the top of what we would call his forehead.

The skin around this bony hook is fleshy and full of blood vessels. And it has a cavity that scientists think helps hold the eggs in place. In fact, this tissue may feed the eggs and help them breathe, too.

No one has ever seen how a male gets eggs onto his hook, but they're most likely transferred before they're fertilized. He may even, like, pull them straight out of the female, just like yoink!  But however he acquires the eggs, ichthyologists think that after they're attached, the male nurseryfish releases a cloud of sperm and swims through it to fertilize them, which of course, ensures they are his own brood. They're not certain of all this though, because the species doesn't do well in captivity and they're tough to observe in the murky waters where they live, especially with all the saltwater crocs that live in the area.

Basically scientists have had to deduce what they can from fish that turn up in nets. But they're eager to learn more about this unique species and not just to satisfy their curiousity about sperm clouds and such. When it comes to reproduction, forehead brooding falls somewhere in the middle between egg-laying and internal gestation, so these fish could help us understand how and why that transition occurs.

Plus, knowing the particulars about how animals protect their developing young can provide insights into parenting in all sorts of species, from fish to mammals like us.

Thanks for watching this episode of Scishow. If you want to learn more about parenting in the animal kingdom, you might like our episode on awesome animal dads and if you simply love learning about the wonderful universe we live in, you can click the subscribe button to subscribe, and if you want to get notified when we post a new video, that's what the little bell is for.

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