Is there a way to keep my cherries red?
I currently have a planted aquarium, with Tropica substrate, mopani wood and Seiryu stone. Around five years ago I purchased 10 fire-red cherry shrimp, and since then the population has grown significantly, but the shrimp are gradually returning to their natural brown colour. Although interesting to watch, they lack the ‘wow’ factor of the red. How do breeders keep their shrimp red?
JONATHAN BROWN
NEALE SAYS: Cherry shrimp genetics is complicated, and I’m not sure how completely understood it is in terms of which genes and which alleles are responsible for all the different colours we see.
As you probably know, wild Neocaridina davidi are semitransparent and greenish-brown in colour, not dissimilar to the sorts of shrimps you’d see in rockpools and estuaries all around the UK.
Things like colour may be controlled by more than one set of genes. In humans, hair colour is regulated by something like over 20 different genes, and it’s the interaction between each of these genes that results in the wide range of hair colour we see. Unlike the simplistic versions we tend to learn at school, where a single gene controls something—such as the gene for tongue rolling, which you can either do or cannot do—most of the traits we see in living things are polygenic, resulting in a range of possible outcomes, rather than just two. There’s no reason to think colouration in shrimps is any different, and if your starter population of shrimps was genetically varied, over time, you’d see different combinations of all these genes crop up, and therefore different colours.
A couple of additional factors may be at play, too. One is what’s called ‘selection pressure,’ where certain genes are favoured over others. While I don’t know this for sure, it’s probable that the wild-type versions of the colour-regulating genes are, in some sense, ‘better’ than the mutant forms selected by shrimp breeders. That’s often the case with domesticated animals, where humans remove the selection pressures, like predation and sexual selection, that would work on those animals in the wild. Put another way, the wild-type shrimps might be able to grow faster, resist disease better, communicate with rivals more clearly, or attract mates more effectively, than the tank-bred forms of the same species. Over time, the red shrimps will lose out to the brown ones, and you’ll find more of the brown ones in each population.
Another possibility is that the shrimps sold aren’t purebreeding, and are carrying both red and non-red versions of the genes. Any offspring from these shrimps will be a mix of colours, and you’d have to remove or cull brown offspring if you wanted to keep just red shrimps in your tank.