Urchin spawn?

[dizzy]

I was looking at my orange eye urchin (diadema setosum) when it started to excrete a white cloud from the five outer white dots that are arranged around the anus (orange eye) I guess it was spawning. My blue hippo tang was very interested in getting in as close as possible to try and eat what I assume to be the eggs. I grabbed my camera and snapped a few shots. Sorry about the flash line in the picture with the hippo, but my compact flash card got full. I should add that the anus was completely pulled in and not visible while the spawning was occuring.
Mitch

 

[sorenb]

Nice pics!

My tuxedo urchin did the same thing a short while ago. I assumed it was sperm, since I gather eggs would be larger??

The fish was also interested, but didn't seem to be able to feed on it as such.

sorenb

 

[John_Brandt]

Mitch, it's a boy!

 

[dizzy]

John,
Thanks. I tried to look it up in "The Modern Coral Reef Aquarium Vol IV. by Nilsen & Fossa by it didn't have much information on reproduction. Apparently they have large mass spawnings in nature that has been demonstrated to be tied to the lunar phases according to Nilsen/Fossa.

 

[John_Brandt]

Mitch, I don't think the spawning cues are entirely based on the lunar cycle. I have consistently observed urchins spontaneously spawn with a large water change, especially with an exchange of cooler water. I think they may also be cued by environmental changes that might coincide with tides. Of course tides are ultimately caused by the moon, but it seems that rapid temperature and/or salinity changes set them off.

This could be caused by natural selection whereby mass spawnings at a changing tide or current bring about greater reproductive success.

 

[Anonymous]

FWIW, urchins can be caused to instantly spawn by injecting them with KCl. We do this to make urchin larvae for bio labs. The cool thing is that after you inject them, it only takes about 2-3 seconds to start spawning. When you place a spawning one back in the tank, all the others will immediately begin spawning as well. I'm sure galleon could enlighten us on the biology of it all a bit more than I can. I'm just curious how someone decided to jab an urchin with a salt to see what would happen!

 

[shr00m]

i sleeps with my urchin under my pillow

 

[fishfanatic2]

I have also had the experience that Matt describes. Typically, urchins will spawn when they are in favorable conditions. Possibly the reason that urchins in the same tank spawn when one starts is to make sure that the eggs get fertilized, and that you don't have a whole bunch of infertilities if they all spawn at different times.

 

[sorenb]

i sleeps with my urchin under my pillow

LOL, do you inject it with KCl first??? Otherwise it may not work methinks.

sorenb

 

[Anonymous]

Well, I didn't mean to imply that they do it *only* in favorable conditions. Actually, they do it after we remove them from the water, handle them a lot, and jab a fat needle in them. It's sort of an involuntary response.

I have no idea what cues they use in nature, but light, temp, water level, etc. could all play a role.