The Myth Of The "Reverting" Red Cherry Shrimp
For years various people have been reporting that their red cherry shrimp have suddenly "reverted" to their wild coloration. In other words, these people all of a sudden see clearish/brownish shrimp in their red cherry shrimp tank. Without putting much thought (or research) into it, these people promptly conclude that at some point red cherry shrimp will produce wild-colored shrimp, no matter what. Hence, they further conclude, these "wild-colored" shrimp have to be culled/separated periodically to ensure that ones population remains red. Often they imply that brownish/clearish shrimp all of a sudden appearing in a red cherry shrimp tank must be a natural and unavoidable occurrence. As we will see below, nothing could be further from the truth.
Let's think about this for a minute. The red cherry shrimp is a red color mutation of Neocaridina denticulata sinensis (which some people now call Neocaridina heteropoda). "Mutation" means that one or more genes had to spontaneously mutate (i.e. change) to produce red colored animals. Such mutations are quite rare. In very large populations, such a mutations can happen sporadically, but usually all kinds of odd-colored animals tend to stick out and get eaten by predators. Hence, such animals usually do not survive in nature. So, red-colored N. denticulata sinensis are the result of a rare mutation. Mutations seem to be pretty random, i.e. one cannot predict in which ways an animal will mutate. For a red cherry shrimp to "revert" to a brownish/clearish shrimp, not only would there have to be one of those very rare mutations happening, but it would have to be a mutation that produces a shrimp that is, once again, closer to its wild-type coloration, i.e. a "reverse" mutation (since the red cherry shrimp is already a mutation). The chances of that happening are extremely slim. This is similar to reporting that a pack of poodles suddenly produced an animal that looks like a wolf. So, the poodle must have "reverted" to its wild type. When was the last time anyone has seen a dog breed produce a wolf or anything similar to a wolf (without wolves having been crossed into the breed recently...which is exactly the point I am going to make about the "reverting" shrimp)?
So, how come there is a seemingly endless supply of reports of "reverting" red cherry shrimp? The solution to the mystery is an obvious one. These people do not have "pure" red cherry shrimp to begin with. It has been my experience, over the years, that "red cherry shrimp" that have been imported from farms in Asia tend to be all female. If that is because the females are much redder than the males or the farms don't want anyone to breed these shrimp is up in the air. I have yet to see a male red cherry shrimp pop up in any pet store that actually offered these shrimp for sale. What I do see, however, all the time are both males and females of undetermined species of wild Neocaridina mixed into these shipments. The males of various Neocaridina (including the males of red cherry shrimp) can look remarkably similar to identical to the untrained (and sometimes even to the trained) eye, so buyers usually don't notice that their "male red cherries" are not red cherries at all. In their desperate attempt to purchase "pale red cherries", which, people told them, are most likely males, they snap up all kinds of colorless shrimp in the red cherry shrimp tank at the pet store. Of course non-red shrimp pop up in the buyers' tanks and the buyers think that their red cherry shrimp have "reverted." Alternatively, when people buy ovigerous (=carrying eggs) females in the hopes that they can establish a colony with the offspring, they are not aware of the fact that many, if not most, of these females have mated with various species of wild Neocaridina males to produce those eggs. This mating may have occurred at the farm in Asia or in the tanks of your local pet store (or online source of shrimp/fish). As a result of this mixing, many, if not most populations of "red cherry shrimp" are actually either intraspecies hybrids (i.e. red cherrys shrimp mixing with wild-colored Neocaridina denticulata sinensis) or interspecies hybrids (red cherry shrimp mixing with various other Neocaridina species).
So, how about those people that insist that their red cherry shrimp population was red for several generations and then suddenly started producing non-red animals? There are two main reasons why these reports may be coming in. The first, and probably foremost reason, is that the reporting party is not aware that other Neocaridina species have been introduced into his/her tank. All kinds of Neocaridina sp. are sold under various generic names, including "blue shrimp", "mandarin shrimp", "algae shrimp" etc..etc.. Most people have no idea how to tell if a shrimp is a Neocaridina sp. or not. So off the new shrimp goes into the red cherry shrimp tank. And the reports of "reversion" start coming in....The second reason why such reports are coming in may be because such people have interspecies hybrids in their tanks to begin with. Such interspecies hybrids can be red, but can produce non-red offspring either in the next generation or in any of the generations further down the line. Once again, the owners of such hybrid colonies report that their red cherries have "reverted." Even if the red trait follows simple mendelian rules in "pure" Neocaridina denticulata sinensis (which is still to be determined), interspecies hybrids do not usually follow Mendel's rules when it comes to inheritence.
Fact is that my colony of red cherries (the oldest in existence in North America as far as I know) has *never* produced a single non-red shrimp "out of the blue." My colony has produced many thousands of offspring and must be in its double digits as far as which generation of shrimp are currently in my tanks. The only time I have ever seen non-red shrimp appear in one of my red cherry shrimp tanks was when a male wild Neocaridina denticulata sinensis managed to sneak into a tank full of red cherries. It took me a while do recognize the wild type male, but in the end I did and removed it. To be on the safe side I introduced some macros into that tank that gradually dined on the possibly hybrid population. This may sound harsh, but I did not want to risk contamination of my non-hybrid colonies. In the 4 years that this colony has been in existence I have never introduced any other red cherry shrimp out of fear that I might be introducing hybrids.
So, considering that most red cherry shrimp populations out there most likely consist of hybrids of one sort or another, it is not surprising that people think that their red cherry shrimp are "reverting" to their wild coloration. I acquired my shrimp back in 2003, when red cherry shrimp first entered the global market. It seems that at that point the red mutation was still kept relatively "pure" in the farm/farms in Asia due to its rarity. Even back then it was quite rare to receive males in shipments. This led to an unfortunate situation in the US, Germany and elsewhere, where, for the longest time, only females were available and people were desperate to get males. I didn't know back then how lucky I was to get both males and females in a shipment directly from Asia and start breeding them right away. Today, with red cherry shrimp easily the most commonly available shrimp in the hobby, the genetic "purity" of any given population cannot be taken for granted as the above examples show. But at least one thing we can be fairly certain about....red cherry shrimp don't suddenly "revert" to wild-coloration. That is and will remain a myth. I hope this article will make sure that our hobby has one less myth in the future.
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