How long do Riffle Shrimp take to grow?

[Baccus]

Does anyone know how quickly or slowly Riffle shrimp actually grow? I think it was around 2 years ago (maybe 3) that I went to Cairns and got to collect some riffle shrimp. Since then I have purchased riffle shrimp and all have been large full grown females. But my dilmeia is I still am finding small riffles in the tank. Surely they cant still be the original small riffles wild caught in Cairns, that for some reason just arent growing.

The only other option I can come up with is that by some miracle the riffles are breeding in the tank. Highly unlikely I know but stranger things have happened in peoples tanks.

The tank is a 4ft around 200L with lots of structure and plants, filtered by a 800L/hr HOB. I rarely actually do any plant maintence on the tank and everything is pretty much let go, hence the constant suprise of new baby corys emerging. It was only because I removed the current falling apart java fern tree and remade it with new timber that I rediscovered that I still have plenty of small approx 1-2cm riffle shrimp hiding out in the tank. Other tank inhabitants include Threadfin rainbows, Pygmy rainbows, otocinclus, Borneo Suckers and chameleon shrimp. I was also pleasantly suprised by how many chameleons where in the tank and showing lots of various patterns and colours.

So do I have particularly slow growing riffle shrimp? Are they gradually breeding? Or is there some other alternative I cant think of happening.

[Callan]

Hello Bacchus,

The male of the species is and stays a lot smaller. The females grow to  approximately 6cm and the male to approximately 3cm. Suspected to be "sequentially hermaphroditic" or " dichogamous" in that they all start off as males and eventually turn into females when larger (similar to Riffle Shrimp). This may be true unless sexual dimorphism limits males' growth to around 3cm giving them the appearance of being younger. They are slow growing and I think from memory 3 years seems to come to mind but perhaps someone with more knowledge about natives can confirm or give a more accurate answer.

 

 

[northboy]

Howdy

 

I must have missed this one, where you originals came from they are a small one, maxing at around 3cm and not sure when the sex change happens, how ever they grow reasonably well at 2 years they are 3cm, can not shed any more light on them.

 

There is a population on the Atherton Tablelands that are 5 to 6cm in size and never a male to be seen and the females have eggs most months of the year??, it is high on a creek and it has been sampled many many times, go figure

 

There is a population near Cooktown that the shrimp Scientist wants samples from, I think because he has seen material from there before and suspects they MAY be different, That is a field trip report to come.

 

Back to yours!! you got them when they were migrating up stream and on that creek they go 2+km further up, that is of no help BUT. May be more meaty type stuff in there diet, they will eat small shrimp when they catch them, that was a recent observation and where they live there is a lot of insect lava??

 

Bob

[Baccus]

Sorry I missed your reply.

I really don't know what is going on with the little riffles.

They get a varied diet of tropical fish flakes, micro pellets, first fry powder, catfish wafers, sinking catfish pellets, shrimp pellets and basically bits of whatever other food I am feeding the fish, they also get IAL and mulberry leaves. The tank is also open topped and would get mozzies laying eggs in the tank all the time, the odd beetle and moth also often bumbles into the tank and their doom.

Most of the riffles tend to spend all day hidden in the recesses of a large overgrown jarva fern tree that gives them height near the filter return. If I really want to upset the riffles all I have to do is pick up the tree and gently swirl it in the water and riffle shrimp will come zooming out all over the place. Even with that if I put the jarva fern tree in a bucket of water while I do tank maintenance I can be certain when I go to put the tree back in the tank there will be riffle shrimp in the tub of water.

I suspect that I must have some mini riffles, that is the only logical explaination I can think of besides them actually breeding in the tank. The breeding I don't think is happening, even though the tank is fairly over grown and jungle like, but the co-habitants in the tank I think would like eating riffle shrimplets a lot. Maybe not so much the corydoras but the dwarf rainbows and threadfins, possibly even the Borneo Suckers I think would see small shrimp as food.