Mustard Gas Betta: Yellow Bicolor Betta Fish

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These days, the term Mustard Gas (or “MG”) is used, incorrectly as it happens, to describe any bicolored fish that possesses a green, blue, or steel blue body and yellow or orange fins. This particular color combination has, in fact, been in existence about as long as the Non-Red gene itself, since it is fairly easy to breed an iridescent betta to a Non-Red betta and get iridescent/yellow bicolors by the 2nd generation.

The “Original” Mustard Gas

The term “Mustard Gas” was originally coined by breeder/hobbyist Jude Als to describe his particular line of multicolored bettas. The original Mustard Gas bettas were green-bodied fish with variegated bands of blue or green, yellow, and black. In 1999, Als added a band of white as well, developing certain specimens of Mustard Gas into a four-banded butterfly, the colors of which were never clearly separated, but rather run together, creating an effect that looked like gas to its creator.

In the late 90’s, Als sold some of his Mustard Gas fish to other breeders, some of whom outcrossed the line, but retained the strain name. Therefore, the modern Mustard Gas fish is, today, so far removed from Als’ original vision as to be a completely different color/pattern combination.

One of the most intriguing aspects of the Mustard Gas strain name was the controversy it caused among breeders and hobbyists all over the world who were able to acquire fish from Als’ strain and, once having spawned them, were at a loss for what to call them. Als was very protective of his Mustard Gas name, and felt that once the pure line was outcrossed in any way, the resulting fish could no longer be called “Mustard Gas”. He rallied hard to get others to stop using his strain name, even to the point of securing a trademark for the name in 2002.

Mustard Gas Betta Yellow

The primary focus of his campaign was Marianne Lewis, to whom he had given 1 pure Mustard Gas fish, a male. Lewis bred that male to several female fish in her fishroom from different lines, and many fish came off a result of those matings that looked, to her eyes, identical to the Mustard Gas fish she obtained from Als. She bred and sold these “Mustard Gas” fish until Als asked her to quit, at which point she changed the name to “Salamander”. This added to the confusion since people started equating Mustard Gas outcrosses with Salamander, and any red bicolor fish they bred that came from a yellow bicolor outcross was named “Salamander”. (It should be noted, however, that Lewis’ Salamanders are actually yellow bicolors that resemble the Mustard Gas, and since the creator of the term (Lewis) does not even use the strain name anymore, all those “Salamanders” you see out there are probably as fake as the “MG’s”.)

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Mustard Gas Genetics – Cracking the Code

Als has stated that The MG is a formula that took 15 years’ worth of work. That being said, There could be as few as 4 genes directly responsible for it.

Si+/SiSi (Spread iridescence) (Mutant gene that causes the normal green pigment in a betta to be increased in density and distribution so that it covers the entire fish)

BlBl (green)

nrnr (non-red)

(Vf+/VfVf) Variegated fin (BF)

However, and this is interesting…the results of another breeder, named Foo Hong, suggests that the original MG line may carry melano as well. Foo Hong was able to acquire a pair of fish from Jude, a true MG STM, and a red/multi STF that was from the MG line, but we can only assume was one of Jude’s outcrosses, since he already stated that pure MG x MG gives 100% MG with no red. When Foo Hong spawned this pair he got MG, red multis, and even solid blacks! I don’t know if they were melanos or a marble based black, but it would be interesting if the pure MG strain carries melano. This line from Foo also eventually created a purple-bodied/orange-finned type. Many other breeders have managed to produce a version of yellow bicolor that has a distinctly purple body.

So, clearly, there’s something there that’s making some of the fish purple. Jude says he has produced the pure MG in purple (he calls it Purple Gas), and someone else was working a line they called “Purple Haze” that was from a pair of purple MG from Als. They couldn’t get the purple to reproduce, so finally they crossed it to steel blue, and these purple/royals were the result. I’m not sure if they got 100% purple/royal, or more like 50/50 purple/royal and steel, which would be my guess.

In the last several months I’ve been of the opinion that it is not layering blue/red that makes a fish appear purple, but using blue/non-red. Let me explain. My own line of Purple/yellow bettas have true, solid purple bodies and yellow fins. When a purple/yellow is crossed to a purple/yellow, you get steel/yellows, purple/yellows, blue/yellows, and turquoise/yellows. steel/yellow to turquoise/yellow will produce 100% blue/yellow and purple/yellow, proving that the color behaves exactly like pure iridescent royal blue. I am beginning to believe that the secret to true, solid purple bettas lies with the non-red gene, and my experiments lately have reflected that belief. In my theory is correct, having a solid purple line that breeds true (meaning, produces 100% according to type) will never be possible; you will always have the 3-4 color combinations with any spawning of purple x purple.

Mustard Gas Betta Yellow Bicolor Betta Fish

Now, let’s talk about the yellow in the MG, because that has always been the most distinguishing feature of this type, whether it is pure MG or one of the common yellow bicolors. The common yellow bicolor acts just exactly like a typical Non Red; that is, the yellow color behaves as a recessive, meaning both parents have to carry the Non-Red gene for it to show as yellow. If one parent doesn’t carry Non-Red, it will show as red instead of yellow in the first generation.

However, I’m curious as to whether the original MG carried the NR2 gene as opposed to the NR gene. After talking to Dr. Lucas, we have a better understanding of the NR2 gene. Although he used it to originally describe a pale orange phenotype, it was obviously different from the oranges we see nowadays, which behave as normal NRs. The first group of fish Lucas termed “NR2” behaved as dominants instead of recessives, and he couldn’t say why that was the case. Now if Jude has been working the true MG for 15-20 years now, it is entirely plausible that he had access to some of these NR2’s, and could theoretically have used them in the creation of the Mustard Gas strain. When one looks at the tendency of the true MG strain to throw orange bicolors right along with yellow bicolors, it is easy to speculate that the strain is heterozygous for both types of Non-Red.

The Ongoing Appeal of the Yellow Bicolor

The sharp contrast of colors on a dark-bodied betta with yellow fins makes them an ongoing favorite for breeders and hobbyists. The fish tend to look better when seen in person than they do on film and provide many challenges for improvement. One could try to reduce the iridescence on the fins, for instance, or to increase the brightness of the yellow. They also represent an almost limitless possibility for pattern, and versions of the yellow bicolor betta exist in marble, butterfly, and even grizzled.

Genetically, he body color of the yellow bicolor betta seems to work similarly to the three normal iridescent colors:

  • Blue/yellow x blue/yellow = 50% blue/yellow, 25% turquoise/yellow, 24% steel/yellow
  • Steel/yellow x steel/yellow = 100% steel/yellow
  • Turquoise/yellow x turquoise/yellow = 100% turquoise/yellow
  • Turquoise/yellow x steel/yellow = 100% blue/yellow
  • Blue/yellow x steel/yellow = 50% blue/yellow, 50% steel/yellow
  • Blue/yellow x turquoise/yellow = 50% blue/yellow, 50% turquoise/yellow

There are even black/yellow versions available:

  • Black/yellow x steel/yellow = 50% black/yellow, 50% steel/yellow
  • Black/yellow x black/yellow = 100% black/yellow

Two types of black/yellow exist; the melano type and the marble type. Females of pure melano type black/yellow are infertile.

Like any Non-Red, crossing a yellow bicolor with any color that does not carry Non-Red will result in red bicolors and multicolors in the first filial generation.

Mustard Gas Betta: Yellow Bicolor Betta Fish

So, although the true Mustard Gas betta may be all but lost today, the happy news is that the Yellow Bicolor many of you have fallen in love with that was mislabeled “MG” is still going strong. They are available in plakat, HM, DT, Crowntail, and even metallic. So go find a nice pair…do some experimenting. Perhaps someday you’ll create something completely your own. Make sure to tip your hat to Mr. Als and his controversial Mustard Gas strain!

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