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Opae Ula Crazed.
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Discussion Starter · #1 ·
As some of you already know, I have a tankful of Opae Ula, or Hawaiian Red Shrimp.

I've noticed some minor differences in the shrimp and wonder if what I see is sexual dimorphism. I've googled "sexual dimorphism in Halocaridina rubra" and got nothing. It's obvious to me that they can't be "sexed" the way we do with Crystals and Cherries.

Notice in the two photos the shape of the "claws"...

I assume in the first photo the subject is male, the second a female.

Any ideas?
 

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I don't really know much about the species themselves... but shrimp are generally the same.

Personally I can't tell the difference between the two. Gonna list a couple of things you can use as I have no other way of helping.

The curve of the body
The appearance of the ovaries (when backlit)
The shape of the claws (males have more fan-like claws for gripping females)
Females tend to have larger swimmers (the little fans that are under the last half of their bodies)
Males have pointy tails while females have broader tails.
In most shrimp the males are usually clear/spotted while the females are more vibrantly colored
 

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Opae Ula Crazed.
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Discussion Starter · #3 ·
I know it's difficult to see in the photo, but in #1 the shrimp has claws very similar to a lobster, only very tiny, while in #2 the claws aren't obvious.

Body shape, though, seems to make me think that it's a FEmale in photo #1, a Male in photo #2.

If that is so, would we assume that it's the FEmale Opae Ula that has the dominant role (due to claw size) in their little shrimpy societies?
 

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Opae Ula Crazed.
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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.
 

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Opae Ula Crazed.
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Opae Ula Crazed.
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1,408 Posts

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Opae Ula Crazed.
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Discussion Starter · #9 ·
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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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.

UHHH YEAH! THE POWER OF GOOGLE-FU!
 

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Opae Ula Crazed.
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Discussion Starter · #11 ·
Dadgum, you're too good!

Thanks!

Sent from my Samsung Galaxy S III using Tapatalk 2
 

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OH YEAAAAH, THAT'S WHAT I WANT TO HEAR!

Anyways glad I could help. You did guess right the first time though, you must have some sort of shrimp sex sense!
 

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Opae Ula Crazed.
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Discussion Starter · #13 ·
Lol!

I got something, that's for sure!

Sent from my Samsung Galaxy S III using Tapatalk 2
 

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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,

Scott

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.

Cheers,

Scott
 

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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.
 

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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.
 

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Opae Ula Crazed.
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Discussion Starter · #18 ·
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
 

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Opae Ula Crazed.
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Discussion Starter · #19 ·
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!
 
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