"Long-Armed Prawn" @ Petco = Macrobrachium?

[YourPalChrisMal]

Hello everyone,

I was at Petco today and they had something called a "Long-Armed Prawn". By searching the internet, I gather that these are "Macrobrachium."

However, I also gather that there are many types of Macrobrachium.

1) Does anyone know what kind of Macrobrachium Petco is selling? The two girls working there were of no help.

2) How big do these things generally get? (I know that might be tough to answer without knowing the exact type.)

3) I read that they are omnivorous. I have a planted tank - do they do any damage to plants?

4) I read that they are "nippers" but fine with larger fish. I have a 46 gallon tank with a 3 Dwarf Gouramis, a pair of Angels and 6 Rummy Nose Tetras. I also have a Wood Shrimp in the tank, a few Corys and a Pleco. Would the Tetras, Wood Shrimp, Corys or Pleco be in any danger from the Prawn?

Thanks for your help and expertise!

[Mustafa]

Those are Macrobrachium rosenbergii. Those are largest shrimp around getting over a foot long in body size (without claws). They'll take out anything in your tank, including each other, except for cichlids that are about their size or larger in which case they become food. Either way, if you want to keep these guys you need a huge tank and you need to keep them pretty much alone.

[YourPalChrisMal]

Those are Macrobrachium rosenbergii. Those are largest shrimp around getting over a foot long in body size (without claws). They'll take out anything in your tank, including each other, except for cichlids that are about their size or larger in which case they become food. Either way, if you want to keep these guys you need a huge tank and you need to keep them pretty much alone.

Wow. That's pretty stupid of Petco. Why even sell those? How many people would be able to - or even want to - keep something that gets that big with nothing else? And they could at least tell you how big they get - the tag on the tank just had the price and nothing else.

[GunmetalBlue]

Hi Chris and welcome!

Chains such as Petco are in the business of making money and counting on you to make an impulse purchase. They actually lose money on some of the animals they sell but more than make up for it by selling supplies.

Chains are also notorious for having very little or even incorrect information. So the best way to deal with it is to do the research first so you know what you're getting into.

-GB

[Aphyosemion]

Don't forget that many pet stores and chains also sell pangasius catfish and certain types of knife fish that reach over 3 feet long. They also sell fish injected with dyes and treated with hormones. Why do they do that? Because there are enough stupid people out there to keep buying those fish.
As for a long arm prawn, I have always thought that they would make a fabulous shrimp for a single inhabitant of a tank. For those people that didn't buy them for that reason, I imagine they will turn out to be evil little monsters, though.
-Aphyosemion

[Jackie]

Wow. That's pretty stupid of Petco.

I don't see anything stupid.

Why even sell those?

Let me guess -because someone might buy them?

How many people would be able to - or even want to - keep something that gets that big with nothing else?

I would, for example. Don't think that everyone thinks as you do

And they could at least tell you how big they get - the tag on the tank just had the price and nothing else.

True.

[chlorophyll]

It seems likely that Petco doesn't know anything about those prawns, so that is a bit stupid. OTOH maybe they do know.
Personally I would never want to keep a common pleco, but almost every pet store sells them, and some people love those ugly overgrown poop machines.

M. rosenbergii don't really need too much space as individuals, but will eat other animals along with each other if the space is too small and lacking hiding places for the newly moulted. They're generally content to just sit around until feeding time where they become living trash disposals.

Recently had a pair mate, but a few days later the male couldn't resist trying to tear apart the mother of his unborn children (and damaging her quite badly). Luckily the beaten female and her eggs were saved, the thousand or so larvae (now about 3 days old) are being raised, and the female is being pampered.

[Jackie]

It seems likely that Petco doesn't know anything about those prawns, so that is a bit stupid. OTOH maybe they do know.

I don't know how it is in other countries, but in Poland it is very common that pet shops know very little or nothing about the animals they sell (this does NOT apply to my boyfriend's shop and a few others that belong to my friends - it mainly considers the "net" kind of stores, hope I translated it OK )
So to me this situation isn't very strange at all...

[GunmetalBlue]

> "I don't know how it is in other countries, but in Poland it is very common that pet shops know very little or nothing about the animals they sell

Same here . Chains (when you said "net," Jackie, perhaps it's what we refer to as "chains" here?) generally hires not on the merits of a person knowing about animals; rather, the trait they're looking for is someone who is willing to follow their policies and whatever rudimentary training they might receive. Chances are, if an animal lover works there, they will be appalled by the poor quality of care the animals receive and try to change it. They'll soon learn they can't.

> "It seems likely that Petco doesn't know anything about those prawns, so that is a bit stupid. OTOH maybe they do know."

To illustrate, a local Petco when it first opened had a grand opening special - something like the first 50 customers at that store would receive a free goldfish (since that's off topic, I'll say a free M. rosenbergii, though I think a couple of you would actually rush to the store if that were true .) So, these people receiving free goldfish, er, M. rosenbergii; why they were already conveniently at the petstore anyway, so need to buy a small container, gravel and food right? After they get home and do some research, they will realize this animal actually needs a larger home. So a few weeks down the road, back to the store they go to buy a larger aquarium and more supplies. So by Petco/chain store giving you something for free, they actually made money. So it's not about the prawns, it's about running a business I'm afraid.

Chlorophyll, whatever in the world are you going to do if those thousand or so larvae survive to adulthood?!! Lol, the petstore are licking their chops waiting for you to come in and buy up all their aquariums. Just kidding, glad the mom and larvae are doing well, congrats!

-GB

[chlorophyll]

Hi,
Thousand was just a rough estimate by eyeballing it (rarely accurate for me). Yesterday I mixed them around, swooped up three 20 ml samples, and came to a loose average of 12 larva per 20 ml (0.6/cc). They're in 4 liters, so the count is more like 2,400 larvae
That's quite a good amount from a beaten up mother prawn. What a nurturing soul. She will take awhile to moult because she has to regrow so much damage..

I don't know, this species of FW shrimp may be one of the easiest to breed and rear (of those that need to develop in seawater) but I don't expect to get 1000 to survive to PL, especially since they are in such high density in my setup. Should get quite a few though!

Maybe my prof will have something to do with them (give them to students for projects or something). Or maybe I'll give a bunch of them away ... only if you buy your 20-30 gall tanks from ME though!

[GunmetalBlue]

2,400 larvae!

> "Or maybe I'll give a bunch of them away ... only if you buy your 20-30 gall tanks from ME though!

Oh no, I'm not falling for THAT trick, did you think I was born yesterday? When I pick up my free shrimp from you, I'm going to say I accidently forgot my wallet, so let me go back home and get it (taking my freebie shrimp with me). But instead, I'll stop off at Petco and tah dah! buy my aquarium there... hey wait a minute, how come they always end up with all my money??? Ack, can't be helped, as I'm running low on goldfish food and need to pick some up.

-GB

[chlorophyll]

Hey hey, you can buy from me aquarium stands and other handy furniture too. And don't forget the heaters... yeah they do like their water pretty warm

2,400 seems like a lot (and it is more than I'm prepared to rear) though this was probably the female's first brood, which is normally their smallest. A medium size one like her (~4.5 inches) probably could have been expected to produce 10-15 thousand eggs. Larger more mature females might produce 50-100 thousand per brood. I believe most other types of FW shrimp which produce seawater larvae produce even much higher numbers, though that probably means higher attrition rates too.

In this case, there was surely a good deal of pre-hatch stripping/loss. Plus we weren't trying to condition her (nutritionally) to breed ... it just happened. As large as they are, they're very low maintenance in the fertility category. Frequent killers AND frequent lovers. Just call the prawn pond "Shrimp Sin City"

[chlorophyll]

Last count now down to about 1,500. But that's not alarming ... the brood appears healthy at about the halfway point.

I brought larvae pics -

Larval head
They're not exactly the cutest little babies, but pretty interesting looking at 10x magnification. Makings of a fierce rostrum already apparent in the young.

Same specimen, different area
This doesn't make me guilty of producing kiddie porn, does it? Nooo.... these are sprouting pleopod buds. The highly anticipated first sighting of pleopod development, which marks "Stage VI" of XII (which is PL) in M. rosenbergii.

Daddy doesn't like me alien-abducting his kids
This is big daddy. Proved to be an abusive husband. Yet, he did manage to spread his seed. Isn't that just all too typical in this world

errr, on that somewhat inappropriate note, happy Fathers Day weekend

[Jackie]

I brought larvae pics

They are absolutely fantastic!!!

[chlorophyll]

Thanks. I spotted stage VII today. With 5 more morphs I'm looking to see PL in 10 days. Although it probably will not work exactly that way. To reach PL in 24 days is better than I think I can do at a modest 28-29 degrees C.