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Fly on the Wall 

May 13, 2010

Venomous Fish Reproduce (and Rewrite Song Lyrics)

Aquarium biologists have succeeded in spawning the lacy scorpionfish, Rhinopias. This is the first documented case of captive reproduction in this genus, which was extensively studied by a former Academy scientist, Bill Eschmeyer. Here is a picture of the proud Rhinopias parents.

These venomous fish are not overly abundant in the wild or common in the aquarium industry. They don’t have the best track record in captivity, often living for less than two years. Academy biologists thought very hard before deciding to put them on display, but were confident they could provide them with high-quality animal care.

Things seem to be working out, fish style. Since going on display last November, the two individuals have been eating well, regularly shedding their skin (a normal behavior for Rhinopias), and challenging guests to spot them among the corals.

I will admit that the ever-active whimsical lobe of my brain has sprung into action to imagine how Tin Pan Alley would have been different if people, too, signaled contentment with their lives by regularly shedding their skin. Song lyrics would be very different. “I’ve Got You Under My Skin” would need a new second verse. There surely would be a new take on that great song sung by Frank Sinatra and Ella Fitzgerald: “There I go again. About to shed my skin again. All aglow again. Takin’ a chance on love!” And so forth.

But I digress. Back to the fish.

In early March, Academy biologists found an egg raft in the Rhinopias tank. Eggs signal mucho happiness in the piscine set, even more than skin shedding. The eggs were hard to spot because they are almost completely clear. It’s possible that they mimic a comb jelly to discourage predation. Should you wonder, a “comb jelly” is an animal that looks like a jellyfish and behaves like a jellyfish, but is a different animal altogether. Since it’s transparent and about the same shape as the egg raft, it would be easy to mistake one for the other.

Our biologists have asked around among those who would know, and it appears that these are the first Rhinopias eggs that have been laid in captivity, or at least the first that have been observed and reported. The biologists assumed the eggs were infertile, and then were surprised to see them develop, and even more surprised when they hatched. Two batches of eggs have now been laid, and it has been amazing to watch the larvae develop: growing fins, a mouth, and a gut where none existed before.

Feeding really tiny larval fish of this sort is a major challenge, so every day that they survive is another triumph. Pictures of the larvae at day 2, 3, and 8 are shown below.

The scorpionfish parents live in the Water Planet exhibit (Lower Level), next to the Burmese vine snakes. Come and visit!

Filed under: Aquarium,Sustainability — Greg Farrington @ 10:17 am


  1. Congratulations! A job well done. Are the fry big enough to eat baby brine shrimp? What about baby brine shrimp and spirulina ground into a paste in a fed blender 3x a day (with excess siphoned off)? Good luck raising the fry!

    Comment by Cary — May 14, 2010 @ 6:44 am

  2. I love this story – it should be February and Valentine’s Day. I’m going to look for those lacy scorpionfish soon. These spotlights are such a great idea! A little bit of interesting science that highlights a species in the Academy – a point of reference for the next visit and adds to our science understanding. The pieces are well written and with humor. Please keep doing this!

    Comment by Marita Beckum — May 14, 2010 @ 6:51 am

  3. Wow! That’s the stuff that makes my son Ethan (5 years old), want to be a scientist at the Academy of Science! In his words “I want to work with animals! It’s cool and congratulations!”

    Comment by Ethan Myers — May 14, 2010 @ 7:20 am

  4. How wonderful, congratulations!!! Obviously something is very good with the environment to produce such a rare occurrence. Hope to see the little ones soon.

    Comment by May — May 14, 2010 @ 7:35 am

  5. Wow ! It is a marvel of civilization that little things can be appreciated.

    Comment by Bill Weber — May 14, 2010 @ 7:37 am

  6. Thanks so much for sharing this! Congratulations! And I have a question. Do the babies need to be separated from the parents? ie. As a child I had a fresh water aquarium and many live bearers would eat their babies. Is that a concern with these fish?

    thanks…… Bhavani

    Comment by Bhavani Kludt — May 14, 2010 @ 8:06 am

  7. Good job! Congratulations!

    Comment by Paul Spiegel — May 14, 2010 @ 8:42 am

  8. Sounds like a fish story to me. No really, congratulations on providing what must be a very natural habitat.

    Your story left me hanging. What do the larva eat, and how is it being provided? Are the larva still in the tank, or were they removed to develop in a lab somewhere?

    Comment by David Madfes — May 14, 2010 @ 9:10 am

  9. Awesome!!! Your fish team are justifiably proud. As an avid snorkler, I love the Academy’s aquarium, as the next best thing to being on the reef. But of course I would have missed the larvae out in the wild.
    Again, great job keeping the Mr and Missus so happy.

    Comment by Evelyn Wilson — May 14, 2010 @ 9:12 am

  10. Great job! I was wondering, since they are rare, are there any plans to release them into the ocean wherever their natural habitat is located?

    Comment by fifi — May 14, 2010 @ 9:26 am

  11. Well, human beings do shed their skin, right? But it only gets truly spectacular after a bad sunburn. Can fish get sunburns? Thank you, Chief Penguin, for shedding light on the world of song-inspiring fish.

    Comment by S. R. Gilbert — May 14, 2010 @ 9:26 am

  12. Wow !! How exciting… but I also have a question. Do the eggs, and now larvae, have to be removed from the tank that the parent’s live??? Looking forward to an answer…Keep us updated on their progress…. I’m looking forward to visiting the Academy in July, and hope will see some “teenage” scorpionfish..Thanks for your fabulous work!!!

    Comment by jackie — May 14, 2010 @ 10:09 am

  13. Congrats! Love hearing about success, keep on telling us about new discoveries.

    Comment by joelene maher — May 14, 2010 @ 10:37 am

  14. Congratulations! What a marvelous achievement! I am also interested to know whether they’ll need to go in a separate tank.

    Comment by RKB — May 14, 2010 @ 11:48 am

  15. What a wonderful story! Congratulations. Please keep us updated on how they are doing.

    Comment by Nan Wieser — May 14, 2010 @ 2:32 pm

  16. Wish I were Ethan’s age (see above!) I’m 71 and I’d like to be a marine biologist (too) after reading this most fascinating report. Thanks so much for posting this report. Great success to you.

    Comment by Eleanor Jantzen — May 14, 2010 @ 4:10 pm

  17. Fantastic! Where are the babies now? Do you seperate them? What will you do with them? Hope to see them on our next visit!

    Comment by Kendra — May 15, 2010 @ 12:34 am

  18. Well done! We’ll be coming to visit soon.

    Comment by Pat — May 15, 2010 @ 7:46 am

  19. ICTHYOLOGY ROCKS! Congradulations on this milestone of achiements.

    Comment by T Yim — May 15, 2010 @ 8:39 am

  20. Great story! What is the length of time for the scorpion fish to reach adulthood? What is their life expectancy?

    Comment by Flo Huang — May 15, 2010 @ 9:35 am

  21. Dear Academy members: Thanks for all your great comments! Here are the answers to some of your questions…

    1.) Do the babies need to be separated from the parents?

    The egg mass was removed from the display immediately, mostly to try to raise the larvae (babies) in controlled conditions. If left in the display tank, all the different filters would harm the larvae. Marine fish start as larvae that float in the soup of the ocean, and take time to develop eyes, fins, guts, and a variety of other body parts. They go through significant changes before “settling out” as juvenile fish. The larvae are very fragile so too much light, too much flow, slightly degrading water quality, and a host of other issues can cause them to quickly leave the land of the living. The eggs were put into a special low-flow tank behind the scenes with no corners (larvae don’t do well with corners) that is kind of like tanks we often keep jellies in. The larvae started out at about 1 mm long, so the parents eating them was really not an issue.

    2.) What do the larvae eat, and how is it being provided?

    This is one of the stumbling blocks to raising marine larvae – what do they eat? The Rhinopias larvae are especially small, so feeding them is a real challenge, and of course, they need live food. We tried rotifers, a common first food for captive raised larvae, but none of the larvae seemed to have eaten them. While we saw gut action in the larvae around day 6, we were never able to see anything actually in the gut. For the next batch of larvae (we hope!) we will be trying an even smaller food, just hatched copepods (Tisbe spp.) along with anything else we think they might eat.

    3.) Since they are rare, are there any plans to release them into the ocean wherever their natural habitat is located?

    We were able to keep the first batch of larvae alive for 10 days, which is actually a very good showing for such small animals that no one has ever raised before (and we are prepped and ready to try again!). When we are able to raise them, there are currently no plans to introduce them into the wild due to several issues. It is unclear where these particular animals were collected (they range from the South Pacific to West Africa), so it would be difficult to decide where to actually release them. More importantly, since these fish are kept in water with animals from all over the world, there are issues with released fish carrying diseases that are not native to a particular location, and we would be very much saddened to introduce a non-local pathogen that could potentially decimate local animals. On the plus side, when we are able to raise these fish, we will be able to supply them to other public aquariums, lessening the collection pressure on wild populations.

    4.) Can fish get sunburns?

    It appears that they might be able to get sunburns. Most fish are able to swim down to areas where getting sunburned is not an issue. Some fish that live near the surface of the water may be prone to sunburn, especially when high amounts of UV are present from ozone depletion or other factors. There are also reports of pond fish chronically resting their heads above water and getting what looks like sunburn.

    Comment by California Academy of Sciences — May 18, 2010 @ 10:55 am

  22. Is the skin shedding rubbing off mucus, or does the skin peel off like a snake? Are the fish particularly vulnerable then?

    Comment by Grace — June 17, 2010 @ 11:39 pm

  23. Grace, thanks for the great question. According to our aquarium biologists…

    It’s mucus, and is a way for them to shed external parasites, fouling growth etc. It comes off in thin sheets that look like cellophane. Most scorpionfish do this, and they are not particularly vulnerable during shedding. They’re usually bright and shiny afterward!

    Comment by California Academy of Sciences — June 18, 2010 @ 11:53 am

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