Outcrossing Guppies with Endlers

In November 2025, I gave a talk to the Bucks Co. Aquarium Society in Pennsylvania. Great club! During their auction, a bag of pretty Endlers caught my eye. I purchased them and am now crossing them with my Rainbow guppies. Goal is to increase the fitness of my guppies. [Forthcoming article in ALA newsletter (American Livebearers Association) explains why.]

All the females I used for the outcrosses were non-virgins with stored sperm, so I had to carefully pick out progeny that were truly F1 hybrids. Good thing, because the first, early batches were mixed (hybrids and non-hybrids).

For the Endler male X female guppy cross (Photo), I picked out young female progeny with clear tails, a distinguishing feature of Endler females. So I was able to collect 5 nice virgin females from mating Endler males to a top Rainbow female.

**Top Rainbow female guppy with young male Santa Maria Endlers.** (This Endler strain is itself an Endler/guppy hybrid.)

For a reverse cross, I mated my best Rainbow males to Endler females (Photo). I identified hybrid females as Rainbow-sired by their darker, pigmented tails.

**Top Rainbow male with Santa Maria Endler female.**

This is a long-term project. So far, I am pleased with the progress. When I began, I was not sure how to identify hybrid females. But now I have 5 very fine virgins from each of the 2 outcrosses. I plan to mate them to my best young Rainbow males.

Selling My Guppies

Since 2017, I have been writing about breeding guppies. Finally, I have a stock of select older breeders from 4 different “families” that are producing progeny worth selling. Members of the families are from different matings. To avoid inbreeding, none of the pairings are between full siblings. These guppies have a lifespan 2-3 times better than when I started, and in my humble opinion, are gorgeous. Granted, it is easy to talk about how great your guppies are, but will they do okay in the hands of others?? After selling my guppies to a local aquarium store, the owner praised them with the following comment, “Your guppies don’t die.” Below is a video of one breeder family (4 females and 3 males).

My Rainbow guppies in a 10 gal with no filter or aeration. Just plants. These guppies are breeders selected for their beauty and longevity.

Outcrossing Guppies: The Rare Male Advantage

My new article ‘Outcrossing: The Rare Male Advantage’ discusses how the female guppy’s decided preference for novel males can help in outcrossing. Females quickly turn over paternity to new males rather than stored sperm from familiar males. Article discusses my successful outcrosses and the impressive scientific and experimental basis for the ‘The Rare Male Advantage’ in guppies. This subject has widespread implications for evolution, speciation, and maintaining genetic heterozygosity in natural populations.

**Lyretail Males crossed with a Blue Grass female. Article shows results!**

Guppy Genetics

Revision of 2020 Guppy Genetics Article

I revised my 2020 article ‘Breeding Guppies: Genetic Pitfalls and Successes‘. Revision contains april-18_2018-1 same basic material, but I simplified article. I spent more time discussing popular mutations that can perplex beginners. And I down-sized a complicated discussion on the genetics of swordtail guppies. It was not that relevant in successfully outcrossing my beautiful delta-tail females (Photo) with male swordtail guppies. These outcrosses were wildly successful and I had no trouble breeding out the swordtail trait.

Guppy Longevity

My article Guppy Longevity (10 pages) answers the question of why fancy guppies don’t live that long. It puts much of the blame for guppy fragility onto the common practice of using only young fish as breeders. The long-term result is detrimental genetic changes. Since I started using only older fish as breeders, I’ve increased the longevity of my fish from ~6 months to over 12 months. Photo shows a 15-month old male and female. Still room for improvement, but this is progress.