Genetics/Crosses by Tom Allen

Simple Genetics 

Guppies, like humans, have 23 chromosomes.  Lined up on these 23 chromosomes are thousands of genes which determine traits that the fish will exhibit.  During a mating, genes (one from the male and one from the female in positional order) combine to form the visible and invisible traits that the parents will pass to their offspring.  Some traits take the combining of only 1 gene.  Others, like the excellent  red color in guppies we all work toward, take as many as 4 genes to complete.  If your fish have only 1 or 2 or 3 of these needed red genes, you will never produce young which exhibit the super red color without crossing to another unrelated red strain.

There are two terms in genetic theory that it would be appropriate to define at this point: (1) phenotype which is the appearance of the fish and (2) genotype which is the genetics of the fish.  When entering your fish in an IFGA show (or any other show for that matter), it is the appearance of the fish that the judges are concerned about.  If it is a “gold,” it should look like a “gold.”  If it doesn’t look (phenotype) gold, even though it comes from a gold strain (genotype), it is likely to be disqualified.

Here are some simple genetic illustrations:

GOLD is defined as a fish (male or female) that has at least 25% yellow gold color in the body (like a gold wedding band).  The caudal can be any color.  To obtain 100% genetic golds in a dropping, both male and female must carry the gold gene.  It is positional and always appears in the same location on the same chromosome in guppies.  That means that you can cross two different gold strains and be assured of always getting 100% gold babies in each dropping.  Since there are so many other genes that play into making a quality fish, you may get gold but they may not be good golds.  If you outcross a gold with a non-gold, 100% of the dropping will show the non-gold trait in the f-1 generation.  However, all of the fish in the dropping will carry the gold gene (its recessive).  Crossing brother x sister from this drop of young will produce an f-2 generation with (on average) 25% of the fish being gold in appearance and 75% will be non-gold.  Two-thirds of these non-golds, are recessive gold but they all appear as non-gold.

BRONZE is a fish (male or female) that has an “old gold” background color in the body with, at least, 25% of scales with dark edges.  Some grey strains have the scale edging but would be disqualified because they lack the background color.  You can substitute BRONZE into the GOLD write-up above and it will ring true.  Bronze, like GOLD, can have any color(s) in the caudal.

ALBINO is any fish (male or female) that has red or pink eyes regardless of body color.  There are presently 2 IFGA classes for albinos: (1) red albinos and (2) AOC (all other colors) albinos.  Like GOLD and BRONZE, albinos follow an identical genetic pattern with the gene for albinism being located in the same position on the same chromosome in every albino strain.  Thus, cross any two albino strains and you will always get albinos.

The genes for GOLD, BRONZE and ALBINO, while positional on the chromosomes, are at different locations meaning that if you cross a GOLD and an ALBINO, you should get 100% non-gold, non-albino young in the f-1 generation.

SNAKESKIN, by definition, is any male guppy that has an unbroken rosetta pattern covering at least 60% of the body.  Females show no snakeskin pattern.  The gene for the snakeskin trait can be on the y-chromosome (passed from father to sons) or on the x-chromosome (passed from mother to sons).  The only way to determine where the gene lies is to outcross to a non-snakeskin strain and check the f-1 males for the pattern.

HALF-BLACK is any male or female that has a black (any shade) coloration from the edge of the dorsal to the peduncle area with at least 50% coverage.  The gene for half-black can be y-linked, x-linked or passed from both parents.  The IFGA currently recognizes 7 caudal colors in male half-blacks (red, blue, green, yellow, pastel, purple and aoc) and 2 caudal colors in female half-blacks (red and aoc).

SWORDTAIL is defined as any male having a sword-like extension of the caudal.  There are single swordtails (upper or lower) and double swordtails.  Females show nothing that would hint that she is from a swordtail strain.  Both male and female must carry the swordtail gene to get swordtail young in a mating.

Crosses That Work

If you notice that your current strain is showing some weakness (small size, poor color, bad finnage shape, no resistance to disease, etc.) often to only way to introduce improvement is to outcross to a “compatible” strain.  Recall that 85% plus of all outcrosses produce fry that are inferior to their parents.  Because there are so many different guppy strains in the hobby, there are literally millions of options open to you but here are some crosses that have produced excellent hybrids in the f-1…

1) another strain of the same color.  It makes sense that if you want reds, don’t     introduce another color into the mix.

2) red albinos and reds

3) red and h/b red, blue and h/b blue, green and h/b green, etc.

4) purples and greens

5) h/b pastels and pastels (white aoc’s)

6) h/b pastel and blues (to produce h/b aoc’s)

7) solid color and yellow verigated snake females (to produce bicolors)

Note that not every possible cross like those listed above will produce quality young.  Unless the parent strains are “compatible,” there is no telling what the f-1 generation will turn out to be.  Likewise, there are probably other crosses that are not listed here that will work to produce excellent hybrid young.


Taking Young, Record Keeping & Culling. by Tom Allen

Taking Young 

The most successful guppy breeders all follow a common practice when taking young…they isolate the pregnant female in a small nursery tank (along with some floating plants or some other type of cover) and allow her to drop her young without the interference of other guppies.  Once it is determined that she is finished, the female can be returned to her breeding tank or disposed of.  Keeping all the young from the same dropping together during their growth period (say up to 6 months) allows you to compare males/females against one another making it easier to select the stunted or mis-colored males and eliminate them from any future breeding setup.

Those of you who choose to participate in IFGA shows on a regular basis will need to have fish available whenever a show is scheduled (typically, April through October/November).  To assure that you have show-quality guppies when you need them, it is imperative that you schedule when you take young.  Let me cite an example of a simple scheduling plan.  Let’s assume that there are shows scheduled for April 1st, May 15th, July 30th and the Annual show on October 1st.  Let’s also assume that you know that your Blues take 6 months to grow into show prime.  Wouldn’t it be great if you could have a full dropping come into prime at the exact time each show is scheduled?  If you want fish for April 1st, you have to take a dropping on October 1st of the prior year (6 months growth cycle).  You would take your second dropping on November 15th, third dropping on February 1st.  Taking a dropping on April 1st should set you up for the Annual show later in the year.  Now, it is altogether possible that your show fish will live beyond 1 show but you shouldn’t depend on it.  There is no worse feeling than to lose a class championship because you didn’t have enough good males available for the shows.   

Remember, no breeder can possibly keep all the young that guppies can produce which is why they got the nicknamed the “millions” fish.  Keep in mind that “the best carpenter is not the one with the biggest pile of sawdust under the tablesaw!”



Think about checking young from an outcross you made earlier, say 4 months into their growth cycle, and seeing super sized and super colored fish.  You’ve decided that these are guppies that, in your mind, are every bit as good in quality as those you’ve seen win in IFGA Best-of-Show competition.  Wouldn’t it be a shame, then,  if you could not recreate the outcross because you couldn’t remember which male and which female were the parents of the potential BOS young?  Since some of you are just starting out with guppies, you may not see this as a problem in your breeding program.  However, as you accumulate droppings of gups and, particularly, when you maintain multiple lines of a color strain, it would be great if you could reproduce, time and again, the outcross which produced these super gups.  Every breeder keeps info at differing detail levels so you will have to choose “how much” and “what” information you need to keep for your breeding program.  Here are some suggestions:

Dropping Number – a number, assigned to each dropping or each new fish/trio, which   can be written on a tank with corresponding background information in a strain           folder.  The dropping number is like your SSN…it’s simply a pointer to more   detailed information held somewhere else.

Color Strain Code – a 2 or 3 character code which highlights the color strain (ALB,  PUR, GRN, HBP, etc.).  If you want, you can also add a 1-digit numerical value to highlight which line of the strain these fish represent (ALB1, ALB2, etc.)

Date acquired – date of birth for a dropping or date of acquisition for a new trio

Crossing information – Color strain codes & Dropping numbers of fish crossed

Genetic background – any pertinent information about the genetics of the fish (i.e. Greens   originally gotten from Lach, etc.)

Generation code – P-0 (parent),  F-1 (first filial generation),  F-2 (second gen),  etc.

Strain description – possibly tied in with Genetic Background since it could help you in making better breeding choices in the future (good size, short dorsals, poor            caudal color, etc.)



If there is any segment of our hobby that often gets overlooked, it is culling.  Culling is the science (art??) of keeping only those guppies that will be used as future breeders or those that will be grown out to be entered in future IFGA (or local) shows.  There are breeders who do not cull because they cannot stomach disposing of a fish.    Typically they raise “mountains” of mediocre fish and find themselves without quality entries whenever good fish are needed to enter into shows.  Obviously, this is not a habit that is encouraged.  If you have a problem of disposing of culls, set up a cull tank and let them live out their lives in this environment.  Better yet, find a shop that will buy, trade or just take your culls and move them out whenever you get a bag full.   

The key to successful culling is to keep an entire dropping of young together as they age and grow.  In this way, you can more easily determine which of the fry just don’t meet the breeding standard that you are trying to establish.  First to go should be guppies that are deformed.  Often you can find another hobbyist who has an Oscar that will be grateful to get your culls.  If you are breeding for males, there will be fish in each dropping that don’t quite match up to the color criteria that you have set for your show fish.  These are often saleable or tradeable at your local fish shop.  Since many droppings contain 50% males and 50% females, you can easily reduce the number of females and allow your males to reach their full potential with more tank space and food.