I'm new to this group, so bear with me if I goof .
I've read your articles and FAQ, but could not find the answer to this question. Are the dwarf shrimps born either male or female, or do they change as they become larger? Some marine shrimp are protoandrous hermaphrodites, i.e., they all start out as male, then change to female as they age.
With dwarf shrimp there are distinct male and female shrimp and they do not change sexes as they age. At what age the sex is determined I am not sure but it seems to be early in developement if not before hatching from the eggs.
This is an interesting experiment if someone is interested in recording age of sexual development and factors that effect sexual determination
It would be interesting to see what set of circumstances may determine gender in the shrimp. I wouldn't be surprised if pH or even hardness might have an affect, much as with some cichlids. It would take a few stable tanks and time.
Welcome to the forum and thanks for asking such an interesting question. It is entirely possible that external factors may affect gender development in freshwater shrimp, but I'll have to see if there are any scientific studies about this on caridean shrimp (which includes pretty much all saltwater shrimp kept in the hobby) in general and atyid or palaemonid shrimp in particular. So far I have not noticed any literature on this topic, but I wasn't specifically looking for it either. All I know is that it's impossible to visually tell gender in atyid shrimp for a while after birth as they all look the same. It would be interesting to examine hatchlings and see if any of them have a typically male endopod located on the first pleopod (swimming legs). This would, in my opinion, be the easiest external way of determining gender at birth. The other possibility would be genetic analysis of hatchlings.
As for hermaphridic freshwater shrimp...there is a species of Paratya in New Zealand that is confirmed to be a protandrous hermaphrodite. Xiphocaris elongata is suspected to be one also. I have not heard of any freshwater shrimp species that is a synchronous hermaphrodite (i.e. all individuals can fertilize each other and carry eggs), though, as is the case with the various ocean dwelling Lysmata sp. ("cleaner shrimp" species) and similar species.
If I find anything, I'll let you all know. Also, feel free to share if you happen to run into anything before I do.
I don't believe that I ever saw any scientific literature on the Lysmata sp., but I did see in some of my books, for example, "Armoured Knights of the Sea" by Helmut Debelius, pg. 106, where he writes, "Like other shrimps of this genus (Lysmata), the Monaco shrimp characeristically changes sex from male to female." There is no source cited, however. I will see if I can find a better source, because as I'm sure you know, sometimes wrong information can be perpetuated in popular books (and even scientific works).
OTOH, I've never seen a Lysmata sp. that didn't grow into a female at some point, and I've kept some dozens over the years. This is anecdotal, of course.
Yes, you are right. Wrong and/or outdated information does get perpetuated in books (very often) and even in scientific literature (less so).
I have kept Lysmata sp. species before and I can guarantee you that they are what's called "synchronous hermaphrodites." They are neither male, nor female; they are both...i.e. true hermaphrodites with fully functioning male and female reproductive organs. If you put any two Lysmata sp. (or reproductive age) in one tank and give them the right conditions, they will both carry fertile eggs. They fertilize each other's eggs.
You might want to also perform an internet search on this as there is lots of information out there on shrimp like Lysmata spp.. Of course you still have to sort out the good info from the bad, but that's an art in and of itself.
MikeR wrote:OTOH, I've never seen a Lysmata sp. that didn't grow into a female at some point, and I've kept some dozens over the years. This is anecdotal, of course.
Thanks for the information. I will have to search for the scientific literature (and get out the dictionary <G>).
If that is the case (and I don't doubt you), it explains why all large Lysmata sp. carry eggs. And if the Cherrys remain the gender they are born with, then it would behoove one to get a fairly large number if you want babies. Having never seen any outside sites like yours, I wouldn't know <G>.
The male to female ratio seems to be pretty close to 50/50 in all the ones I've seen. If you get 10 juvies you'll be just about 100% assured to get a mix of both sexes. What you do not want to do if buy imported cherries. These tend to be just about 100% female as they select for color, and the females have the best color.
If you buy adults you will also have high mortality in the 1st few weeks as adults don't handle stress nearly as well as juveniles.
Once you get a population going you can see if the normal things effect sex ratio like it does in many other species, like photo period, temperature and pH. I recently did this with Endlers live bearers and found sort of a hokey-stick response to temperature. Once water temps were below 68 degrees they shifted over to mostly males (which is what I wanted).
I had heard that about the wild shrimp, so had determined to find fish through a breeder. Haven't had any luck so far, though. I did find one place but they sold theirs for $6+. Since I want 100 or so, that seemed excessive .
I never recommend anyone to buy 100 shrimp. Just get 10 and if you are good at it, you'll have 100 in a month or so. If you are not good at it, it doesn't matter how many you want.
People have gotten so good at raising cherry shrimp that the going rate is now around $1-$2 each, so don't overpay.
Thanks for the recommendations. The reason I wanted to so many shrimp was that the tank is 150 gallons and in need of algae control (I also want some Amano shrimp), and I have a 3000 gallon pond that I grow guppies in. That, too, has lots of algae and I would like to use them along with Amanos in there as well. And with the cost of shipping, I thought I'd get a larger amount to save on some costs.
I believe that I can keep the shrimps properly, as I kept the Amano shrimp for a number of months back with my first planted tank. They did quite well w/o a loss. I even thought they had young until I read the articles by Mustafa here. When I tore the tank down, I found a number of 1/4-1/2" copies in the tank. Since I had never bought anything but adults (nothing else was available), I thought they were babies. They were not gammarus or other crustacean.
Although they are called algae eating shrimp, it would take thousands to do a respectable job. They eat algae, but like other things better, they are NOT algae cleaning shrimp. Besides, the guppies will have them for breakfast. Unles the fish is a confimed sucker mouth, your shrimp are on th menu.
If you want algae cleaning, get some bristle nosed plecos. I too started off with RCS as a clean up crew. It didn't work, but I got hooked on the little buggers.
As for your babies, it is likely you did not have amanos. There are lots of similar looking shrimp that get sold as amanos, but are not. So far 100% of the reports either can't be backed up, or proved to be a different species that does breed in fresh water. I know from personal experience that amano zoes die in less than a week in fresh water, and I've kept them alive for over a month in sea water.
The reason I wanted to so many shrimp was that the tank is 150 gallons and in need of algae control (I also want some Amano shrimp), and I have a 3000 gallon pond that I grow guppies in.
I would like to see pictures of these. What are the extreme temperatures your pond reaches?
The idea that the shrimp I had were not Amano shrimp crossed my mind when I read the articles here. After reading the books by Amano, I asked the LFS to get some. The shrimp he got were called that, and did look like that, but of course they probably weren't. Whatever the shrimp was, it did do a good job of keeping the algae down.
After reading the articles and posts here, I've decided I would like to get a variety of shrimps, though of different genera so they won't hybridize. I don't want something simply to eat the algae, but to keep the tank clean to improve conditions that prevent algae growth in the first place.
One of my favorite such creatures is the gammarus, but I can't seem to find those outside Aquabid, and I can't seem to access that. I'll keep looking at LFS tanks until I see some <G>.
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It is entirely possible that external factors may affect gender development in freshwater shrimp, but I'll have to see if there are any scientific studies about this on caridean shrimp (which includes pretty much all saltwater shrimp kept in the hobby) in general and atyid or palaemonid shrimp in particular. So far I have not noticed any literature on this topic, but I wasn't specifically looking for it either. All I know is that it's impossible to visually tell gender in atyid shrimp for a while after birth as they all look the same. It would be interesting to examine hatchlings and see if any of them have a typically male endopod located on the first pleopod (swimming legs). This would, in my opinion, be the easiest external way of determining gender at birth. The other possibility would be genetic analysis of hatchlings. 
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I would like to see pictures of these. What are the extreme temperatures your pond reaches?