Most betta enthusiasts start as betta hobbyists. Over time, they become enchanted with the fish, learn how to breed them, discover the huge diversity of body forms and colors, and eventually select some fish with which to work for a long period.
Pretty much all hobbyists eventually begin experimenting with crossbreeding their fish in an attempt to produce some new color or form.
Although many people have tried to create new color combinations and tail forms, one area that has scope for development is the form of the betta fish’s dorsal fin.
Dorsal Fin Basics
The dorsal fin is the uppermost fin on the betta fish.
When viewed in cross-section, dorsal fins are circular with short, inflexible spines that do not branch. Following the bony rays, there is a variable number of some flexible rays, known as lepidotrichia. Those rays are formed of short, hemispherical bone segments that enclose the nerves and blood vessels that supply the fin with oxygen and enable it to be raised and lowered.
The segmented design of the fin allows the rays to flex. Typically, betta fish dorsals have either one or two spines and anywhere between seven to ten flexible rays, depending on the variety of fish.
Modern short-finned plakats or fighters, typical long-finned show bettas, and fancy (show) plakats all display ray numbers that are only slightly higher than those of wild betta fish. However, from a breeder’s perspective, it should be noted that fin rays are more liable to branching in both long-finned show fish and fancy plakats.
The Effect Of Doubletail
It’s well-known to betta breeders that they can breed bettas with a much larger number of fin rays by using fish that carry the doubletail gene.
The doubletail belongs to a class of mutated genes that are recognized by geneticists as producing mirror-image duplications. In a typical single-tail fish, the dorsal fin will be much different in shape and size to the anal fin.
Doubletail fish show a duplication of the caudal (tail) fin, as well as a replacement of the dorsal (top) fin with an identical anal (bottom) fin. If you picture a plane that runs from the fish’s head to the base of his caudal fin, the fins on the opposite sides of the imaginary plane will present as mirror images of one another.
The doubletail trait is controlled by one gene that behaves as a simple Mendelian recessive gene. Every gene comes in two copies. One gene comes from the mother betta and one from the father. Those copies are called alleles. Two classes of alleles are recognized as the doubletail gene; the wild type allele (+), and the mutant (dt) allele.
So, that means that a fish that bears two copies of the wild type allele, i.e., a ++ animal, will be a single-tail. A fish with copies of the mutant allele, i.e., a dtdt animal, will be a doubletail.
A fish that carries both a mutant and wild type allele (=dt) (heterozygote) will also be a single-tail. However, the dorsal fins on these fish usually have a broader base and will support a larger number of fin rays than seen in homozygous (++) fish.
Preferred IBC Form
The dorsal designs that you see today in modern betta fish are partly due to the genetic legacy that modern breeders have inherited from their predecessors, and it’s also part of a function of the goals that modern breeders are trying to achieve. The latter being set by the International Betta Congress (IBC) in their “Judging Standards.”
According to section 2 of the Judge’s Manual standards, the betta’s dorsal fin should ideally be:
“shaped as a wide-based, elongated teardrop …” The judging standards go on to say that “width and fullness is important, with maximum fin area a goal …”
It is immediately apparent that the latter requirement can be achieved relatively easily by using the doubletail gene. That’s because of the area and width of the dorsal fin increase along with the greater numbers of fin rays. So, the number of enhanced-ray fish that carry a single doubletail allele guarantees that outcome.
A second criterion under the IBC standards applies to all fins and states that:
“fin ray should be straight and grow parallel …”
That rule is often interpreted by judges as meaning that dorsal fin rays must be uniformly long with the first flexible ray being the same length as the second, the second as long as the third, etc. The doubletail dorsal delivers that effect, as the fin rays of the anal fin are all of virtually the same length.
The International Betta Congress’ judging ideals for dorsal fins clearly encourage the use of the doubletail gene. For betta breeders, producing the dorsal fin is pretty straightforward; you just need to produce fish that carry a single doubletail gene, and you are sure to create a specimen with a dorsal fin of far superior quality than a dorsal in a fish that does not have a copy of that gene.
The Next New Thing
Because the IBC standards are so easily accommodated by a single gene, breeders have not yet had an incentive to work on developing the dorsal fin. Experienced breeders anticipate that progress can be made in enhancing the symmetry of the dorsal fin and in the extent of the branching of the fin rays.
One approach to that is to ask what cannot be achieved by the exclusive use of a doubletail. Fish that carry doubletail genes rarely have branched dorsal fins. When branching does occur, it is generally restricted to a few posterior fin rays, and almost all the branches are merely simple junctions. Multiple branching, such as that seen in the half-moon caudal, is rarely seen in dorsal fins.
Another feature that is lacking in the doubletail dorsal fin is that of radial symmetry — using a doubletail causes a rectangular shape in a fish that is usually shaped quite differently.
Typically, maximal length of the fin doesn’t occur at its mid-point, but slightly farther back. However, the amount of webbing between the rays is greater at the back than it is in the front, as is the branching. So, the overall effect creates a half-circle shape.
It’s easy to envisage a dorsal fin that has rays that are similar in length, which form a perfect half-circle, but where each ray has extensive branches. No such dorsal fin currently exists. However, it is nonetheless a goal that might be achievable through selective breeding.
To create the next new thing takes not only a well-conceived goal but also requires that certain biological prerequisites are in place. The most important of these is the requirement for a variation to exist in the trait that you wish to enhance.
That means if you want the symmetry of the dorsal fin to be that of a half-circle, rather than a rectangle, you will need to find fish that have a more circular and less boxy fin shape and breed them to one another. Similarly, if you want to produce a dorsal fin that has extensive branching, you must use a fish that has at least some degree of branching in the dorsal fins.
Therefore, the key to enhancing a trait is to use breeding stock with forms that are close to the goal that you are seeking to achieve and to continue that process through multiple generations until you succeed.
However, just using variation is not sufficient. The variants that you use must be of a very particular type. Variation can have two components, environmental and genetic. An example of an environmental variation is the observation that the background against which the fish is reared will have a bearing on the intensity of its color.
For example, a black fish that is reared against a black background will come out as a darker black than a black fish that’s reared against a lighter background.
However, mating fish and rearing them against a dark background does not guarantee that your line of black fish will improve in the long term. Once those fish are shown against a light background, they will be shown to be no lighter in color than their predecessors. For variation to provide improvement within the line, the variation must be hereditary, as only genetically-based variations are relevant.
In some cases, genetic variation may simply not exist. For example, if you try to produce a betta with two dorsal fins, you will most likely never succeed, purely because you will never find a fish that has a genetic variation for fin number.
So, how do you know whether the goal that you have in mind is attainable?
Unfortunately, biologists do not have any coherent theory of the possibility. However, a reasonable rule of thumb is available. If you know that the fish is able to produce a structure, it is generally the case that you can modify that structure. For example, if you know that a flexible fin ray is capable of branching, genetic variation for less or more branching is likely possible.
That rule of thumb should not be considered as a guarantee, although more often than not, selection is effective in creating more or less of a form that already exists.
From Here to There
So, returning to the goal of creating a half-moon dorsal, there is a reason for optimism, as variations of the desired sort abound. When you begin your breeding project, you will need to complete two tasks. First of all, you need to move away from the parallel, boxy, anal-fin-like dorsal rays of the doubletail toward a more circular dorsal outline.
The modern show Plakat provides the desired profile. You can expect to make rapid progress in producing the desired circular form by crossbreeding to Plakats. However, the task of creating long straight edge rays will most likely be no simpler in the dorsal fin than breeders of half-moon bettas found it to be in the caudal.
Your second task will be to improve fin ray branching. That may be the greater challenge, although there are several half-moon lines that produce fish with extensive dorsal branching
So, will the doubletail gene play a pivotal role in the achievement of the imagined half-moon dorsal? That appears likely. Although the doubletail gene does produce some less desirable effects on branching and symmetry, a substantial increase in the number of fin rays is unlikely to be achieved without its use.
Betta breeders are continually working on their stock to try to create some fantastic new color or form combinations. Whether anyone ever creates the dorsal form we’ve envisaged in this article is immaterial.
What is certain is that hobbyists working in their basement fish rooms or farms will continue to recognize that novelty matters. Breeders will take a look at these amazing fish and imagine what could be done with them, perform selective crosses, and once again surprise and delight enthusiasts around the world with the seemingly limitless variation that this species seems to be capable of expressing.
To find out more about how betta genetics works before you dip a toe into the murky waters of betta breeding, check out this article on the fascinating world of betta color genetics, and this piece that looks more closely at the genetics of form in Crowntail betta fish.