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Baby Sword Tail

Badmans Tropical Fish Message Center: General message area: Baby Sword Tail


Thursday, January 17, 2002 - 06:38 pm
I just have a simple question (I hope)
My Female Sword tail just gave birth and all the fry are the same color. They are sort of greyish. Does that mean they are all female or do they change colors when they get older. My male adult sword is red.
Any information would be helpful



Thursday, January 17, 2002 - 08:24 pm
Hey David,

You may have wanted a simple answer, but I'm afraid that genetics is not always so =) First off, the fry will sometimes change color hue a little, but usually the base color of the fry will give you some idea of whether or not they will be reddish or greyish, for example.

As for the genetics part, you have to know some things about the pedigree of the parents to know for sure (in other words, what color their grandparents were). But you can usually assume that the ones sold by a dealer are pure color strains (unless the strains are themselves hybrid, but I won't get into that here). In most cases with fish, the melanism gene is dominant over other colors. So, calling the gene for dark (D) and the gene for red (r), and assuming both parents are homozygotes (DD X rr cross):


You'll get 100% heterozygous "Dr" young. Because D is dominant to r, this allele will mask the other, and you *see* dark young if there is complete dominance (you can't see their genes, after all). If you were to breed these to each other (not that I'm supporting inbreeding, but hypothetically), in the next generation you should get 75% dark young (1/3 of those homozygous dark, 2/3 heterozygous) and 25% red (all homozygous).

Sorry if any of this is confusing, but actually I've simplified quite a bit. You may want to look up actual genotypes for swordtails, sometimes incomplete dominance, codominance, multi-locus alleles, etc. can add even more complexity, since there aren't just 2 alleles for color.



Thursday, January 17, 2002 - 08:33 pm
Oh, and one more thing... you asked if the fry were all female BECAUSE they were all greyish like the mom. Color is not a sex-linked trait, and the color of the young will have nothing to do with their gender, the alleles assort independently.



Thursday, January 17, 2002 - 11:09 pm
Well alrighty then. So I guess I will tell the male by the sword on the tail right?



Sunday, January 20, 2002 - 11:22 am
David, you won't see a sword in fry. This trait doesn't develop in growing fish until well after primary sexual maturation, which is often several several months... varying time period. It's more reliable to look for the male modified anal fin, the gonopodium, in livebearer fish... this develops sooner, but even then not for more than 2 months, in most cases (until then, all your young will look female).



Sunday, January 20, 2002 - 11:27 pm
Wow, somebody knows their biology. Mendel and his pea plants would be proud



Monday, January 21, 2002 - 11:24 am
LOL, William. Years of genetics & ecology, and here I am back to (punnett) square one....


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