In our newsletter No. 11 we ran the following contest:
“This month we are running another photo contest. I’m changing the contest from fish identification to something a bit more interesting (read, “more difficult”). The blurry photo below shows a mixed pair of Archocentrus nigrofasciatus, the convict cichlid. The striped fish in the background is the male. The pink fish in front of him is the female. The fry scattered around them consist of both normal striped fish and pink fish in roughly a 50:50 ratio. The winner will be the person who provides the best explanation for the roughly equal numbers of normal and pink fry in the brood. Email your answer to email@example.com. Please put “contest photo” in the tag line to make it easier for me to separate contest emails from others. The person providing the best answer will receive a free (including shipping) two pound bag of Simple Pet Products (www.simplepetproducts.com) #100 Grind fish food, which is perfect for most fish including all livebearers and small (1-2”) cichlids. I’ll be the sole judge of which answer is the best.”
The first correct answer came from Ron Bows. It’s a bit terse, but correct:
“The male is Heterozygous for the gene that produces a pink convict coloration. Because the male carries half the Pink genes a 50/50 ratio is born.”
Several others got the correct answer, but Ron beat them to the punch.
In convict cichlids pink is a semi-albino characteristic. Semi-albino because the fish produces no black coloration except in the eyes. It’s a recessive characteristic, meaning a fish must inherit the pink allele (an allele is a version of a gene) from both parents. The female in this case is pink because she has two pink alleles. This is termed homozygous, meaning the two alleles are the same. The male is heterozygous, meaning the two alleles differ and he has one for normal coloration and one for pink. He’s not pink because the allele for normal is dominant.
If the male had been homozygous for normal, then all of his offspring in this mating would have been normal colored because he could have only passed on normal alleles. But, since roughly half the offspring were pink and half normal, he must have had both alleles to pass on.
By the way, the pair successfully raised the spawn and many of their offspring of both colors are now independent from their parents and are large enough to not be eaten by their tank mates, which include about 80 large cichlids, mostly from Lake Malawi.