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Thread: Opae Ula sexual dimorphism? Reply to Thread
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  Topic Review (Newest First)
11-20-2012 02:14 AM
Rob in Puyallup The only photo that I found at PetShrimp didn't show the "claws" very well, certainly not as well as my lame pics earlier in this thread.

In the larger of the two versions of these shrimp in my tank the "claws" resemble more those of a scorpion, vs what you'd see on our typical freshwater shrimp, which the other type pic shows. Their are lots of both versions of claw type in my tank, all from the same source.
11-20-2012 02:03 AM
KenP I do not believe H.palahemo is a legitimate species name. I think it is synonymous with rubra. You should check out the species page. It has a female with eggs and large 'claws'. I think the difference in the claw size may be due to damaged and replaced claws.
11-20-2012 12:18 AM
Rob in Puyallup Thanks Ken.
11-19-2012 11:57 PM
KenP Rob I will ask.
11-18-2012 07:34 PM
Rob in Puyallup I have noticed, BTW, that the shrimp with the larger claws (pinchers?) also have larger carapaces. (head end).

I've been googling again and found a related species, also native to Hawaii. It's name is Halocaridina palahemo. No mention of larger claws in either sex.

All a bit puzzling to me!
11-18-2012 05:43 PM
Rob in Puyallup Thanks for that, Ken! Hi again AVN!

I've noticed that all of my Opae Ula have the dark area behind their heads. It's color a bit variable depending on what they've been eating, just like what I see in my ghost shrimp, (only its even more obvious in them). I did assume that it had nothing to do with gender/developing eggs like what I see in my Cherries.

It does seem to me that the best way to sex the shrimp in question is by claw type, and think it strange that it wasn't mentioned in your emails, Ken. Perhaps you can email them back and directly ask about the claws?

I'm guessing you've noticed the different claw types...

Thanks again guys!

Sent from my Samsung Galaxy S III using Tapatalk 2
11-18-2012 05:29 PM
KenP Did not ask. I was not going to put the shrimp under a microscope. Second problem is like Rob I have too many shrimp to distinguish one from another. Maybe with only 10 shrimp in a small tank you could. You could separate the females with eggs and observe them over time. But I read somewhere that they may only breed once or a couple times a year. I do not have this type of commitment.
11-18-2012 05:12 PM
AVN Okay, so micro-lobsters have their reproductive organs behind their eyes, not where shrimp have them, what we thought were ovaries is a poop chute, that's good to hear.

At least now you know that the reproductive organs are behind their eyes, a good place to try to check with a flashlight and magnifying glass.

Eggs would be a tell-tale sign.

Did you ask them what differences they did notice between males and females? It only says that they had trouble distinguishing between them, and doesn't go on to reveal the differences they did notice.

The claws on the males and females are VERY distinguishable, they're not the same in both sexes. Check out a group picture of Opae Ula and you'll see different claws, and stated before the tip and underside of the tail is different also.

We can't check the swimmerets without harming the shrimp, so that method rules out.
11-18-2012 04:48 PM
Male vs. female

I e-mailed a similar question to Pros. Scott Santos of
Auburn University. He and his people have researched this species quite extensively. Here is our e-mail chat:

> Hello Scott Santos,
> While I was researching halocaridina rubra on the internet I came across pictures that you took in Hawaii. Very nice. I have one question at this time. Are there noticable differences between males and females? ie. color, size Does the female have a noticable saddle when she is producing eggs?
> Thank you in advance,
> Ken P
Hi Ken,

Nice to meet you and thanks for the email.

In my experience, there is no easy way to visually identify males vs females based on gross overall appearance like size and/or color. We have had some luck sexing individuals via microscopy, but it is labor intensive and not always easy.

Hope this helps,


Here is a thread from David Weese a doctorate student under Pros Santos.

As far as sexing the shrimp, I haven't had any luck. When the females go reproductive its easy when they are carrying 12-24 eggs, but other then that I don't know. A couple of people have told me that when they go into reproductive mode you should be able to see the developing ovaries forming right behind the eyes in females or developing testes in males. However I have not been able to reliably sex them with any confidence yet.

Yet another question and answer:
Another question. Do you think this is a female?
> I suspect that the dark area on the shrimp's back are developing eggs.
> Ken P

Hi Ken,

I'm sorry to say, but I don't think you have a female there. What you are seeing is the hepatopancreas, which is part of the digestive system of arthropods like crustaceans and insects. Most people know it as the green spongy material that is encountered when they get up into the head area of their lobster dinner. I see it among individuals animals in my tanks at various intensities, some being more apparent (like your example) than others.


11-18-2012 01:42 AM
Originally Posted by Rob in Puyallup View Post

I got something, that's for sure!

Sent from my Samsung Galaxy S III using Tapatalk 2
im acutally going to order a little handbook about them and hopefully it should be able to tell the sex and reprduction of them..
11-18-2012 01:34 AM
Rob in Puyallup Lol!

I got something, that's for sure!

Sent from my Samsung Galaxy S III using Tapatalk 2
11-18-2012 01:33 AM

Anyways glad I could help. You did guess right the first time though, you must have some sort of shrimp sex sense!
11-18-2012 01:31 AM
Rob in Puyallup Dadgum, you're too good!


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11-18-2012 01:28 AM
AVN I looked through every distributor's journals, even forums that have bred them before, none tell you anything about sexing them, only raising their larvae and the peculiar way they do it.

But then I found bits across several scientific research journals detailing the environments they live in because they're endangered!

Researchers report:
The first pair of swimmerets on the underside (from the top down) on the males are hard, females are soft. You can't really figure this out unless you crush your shrimp, LOL.

Males have larger "crusher" claws which they use to rip out algae, females have the same claws but smaller and pointier, used for digging in sand to find bacteria.

Coloration in females tends to be more solid, whereas males are usually spotted or translucent.

Females have broader tails, males have pointy tails.

And as with all other shrimp/lobsters/crayfish, the appearance of a saddle (ovaries) which extends from the base of their body to the end of their tail is very telling.

11-18-2012 01:09 AM
Rob in Puyallup
Originally Posted by AVN View Post
I found numerous articles on how to raise the larvae, but none of those detail how to sex an adult shrimp. My Google-fu is not strong enough!

I did however find an interesting tidbit of information, their breeding habits are similar to those of crayfish, delving further in a Taxonomy book I've found that they're closely related to lobsters, digging even deeper online I found they are classified under micro-lobsters, but called shrimp for convenience purposes.

Might help you in sexing them a bit.
Okay... I'll take a look. Thanks!
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