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Dorsal Designs

Sherolyn-Basement Bettas

Figure #1: A schematic representation of a flexible fin ray. (From Laforest, L., et al. 1998. Development 125:4175-4184).

Figure #2: Tracing of dorsal fins from (A) a wild Betta splendens, (B) a short-finned fighter, (C) a show plakat, and (D) the long- finned show Betta.
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Figure #3: Tracing of dorsal fins from long-finned show Betta illustrating the effect of the doubletail gene on the dorsal fin. Tracings refer to fish bearing (A) zero, (B) one, and (C) two copies of the doubletail allele.

Most Betta enthusiasts follow a well-trodden road. They become enchanted with the animal, learn to breed them, discover the diversity of the available colors and body forms, and eventually settle on some line of fish with which they work for an extended period. Virtually all breeders who follow this progression succumb to the temptation to experiment in an attempt to develop novel forms and colors. 

Foremost amongst the success stories must be Gene Lucas' discovery of the opaque factor and the use of this gene to establish the White Betta. Notable recent achievements are Gilbert Limhengco's development of the orange color and, as recounted in my last column, the development of the halfmoon finnage.

Progress toward new colors or forms requires that a breeder has a goal in mind, that the necessary biological prerequisites are in place and, finally, that one possesses the focus and devotion necessary to bring the project to fruition. I would venture to guess that at any given time there are scores of such projects ongoing. To my mind, one area where considerable improvement is possible is in the form of the dorsal fin. 

Dorsal Fin Basics

The dorsal, or topmost fin, is characterized by two distinct kinds of fin rays. The first few rays are spines, or bony rays. Circular in cross-section, spines are short, inflexible, and do not branch. Following the bony rays are a variable number of flexible rays, the so-called lepidotrichia. These rays are built from short hemispherical segments of bone that enclose blood vessels and nerves (Figure #1: A schematic representation of a flexible fin ray. From Laforest, L., et al. 1998. Development 125:4175-4184). The segmental design allows the fin ray to flex. Unlike the bony rays, flexible rays may dichotomously branch to generate new secondary, tertiary or even quaternary rays. By convention, scientists refer to the number of bony rays by Roman numerals and the number of flexible rays with Arabic numerals. Thus, in his original description of Betta splendens, C. T. Reagan (1909. The Asiatic fishes of the family Anabantidae. Proc. Zool. Soc. Lond. 767-787) reports the dorsal of the species as I-II/7-10, meaning he observed specimens have either one or two spines and anywhere from 7 to 10 flexible rays. 

While hardly a substitute for a proper quantitative study, one might get a rough sense of modern ray counts from the images displayed in Figure 2. A tracing of a dorsal from a wild caught fish attributed to Betta splendens shows numbers comparable to the original description (I/8, Figure 2A). Modern short-finned fighters or plakats (II/11, Figure 2B), fancy (show) plakats (II/10, Figure 2C), and typical long-finned show Betta (II/10, Figure 2D) display ray numbers that only slightly exceed the numbers in the wild populations. Note, however, that fins rays are more prone to branch in both the fancy plakats and in long-finned show fish. 
Figure #2: Tracing of dorsal fins from (A) a wild Betta splendens, (B) a short-finned fighter, (C) a show plakat, and (D) the long- finned show Betta.

The Effect Of Doubletail

It is well known to breeders that dorsal fins with substantially greater number of fin rays can be readily achieved with the use of the doubletail gene. Doubletail is representative of a class of mutations well known to geneticists, those causing mirror image duplications. In a typical singletail fish, the dorsal fin is appreciably different in size and shape from the anal fin. Doubletails display a duplication of the caudal (tail) fin, accompanied by a replacement of the dorsal (top) fin with a duplicate anal (bottom) fin. If you imagine a plane running from the head of the animal to the base of the caudal, the fins on opposite sides of the plane would appear as mirror images of one another. 

Gene Lucas first provided evidence that the doubletail trait was controlled by a single gene which behaved as a simple Mendelian recessive (1968. A study of variation in the Siamese fighting fish Betta splendens, with emphasis on color mutants and the problem of sex determination. Ph.D. thesis, Iowa State University). I remind readers that each gene comes in two copies, one from the mother and one from the father. These copies are called alleles. Two classes of alleles are known as the doubletail gene, the wild-type allele (+) and the mutant (dt) allele. A fish that carries two copies of the wild type allele, that is a ++ animal, will be a singletail, whereas a fish with two copies of the mutant allele, that is a dtdt animal, will be a doubletail. The heterozygote animal, that is a fish with both a wild type and a mutant allele (+dt) will also be singletail, although the dorsal fins on such animals typically have a broader base and support a greater number of fin rays than do homozygous (++) animals. 

Preferred IBC Form

The form of dorsals that we see today is, in part, a function of the genetic legacy which modern breeders have inherited from their predecessors and, in part, a function of the goals breeders are currently seeking to achieve. The latter have been set by the 'Judging Standards' of the International Betta Congress (IBC). A look at the IBC standards regarding dorsal fins is instructive.

According to the standards, the dorsal is 'ideally to be shaped as a wide based, elongated teardrop...' The judging rules go on to state that 'width and fullness is important, with maximum fin area a goal..' (Section 2, Judge's Manual, Chapter 5, General Standards, p17). It is immediately apparent that this latter requirement is easily achieved by use of the doubletail gene. Specifically, the width and area of the dorsal necessarily increases with greater numbers of fin rays, so the enhanced ray number of fish carrying a single doubletail allele guarantees this result. 

A second criterion, which applies to all fins, is that 'fin rays should be straight and grow parallel...' (Chapter 5, Condition Rating Area, p. 18). This rule is frequently interpreted by judges to call for dorsal fin rays to be uniformly long, so that the first flexible ray of the dorsal is as long as the second, the second as long as the third, and so on. The doubletail dorsal similarly delivers this effect, since the fin rays of the anal fin are all of nearly equal length. Compare, for example, the fish in Figure 2A-C with that in Figure 3B. The anal fin is shaped like a rectangle with fin rays largely unbranched and parallel. That the doubletail gene intercalates parallel rays into the dorsal is readily apparent in Figure 3B. 

The IBC judging standards for dorsal fins are clearly cast in a fashion that encourages the use of the doubletail gene. For breeders, the dorsal fin is, in effect, easy; one needs only produce animals carrying one copy of the doubletail gene and one is essentially guaranteed a dorsal fin that exceeds the quality of any dorsal in a fish lacking a copy of the gene. 

Blois, France, 2001

I have been thinking of the shape of the dorsal since the fall of 2001, when I accompanied the renowned Swiss breeder Rajiv Masillamoni to judge the annual show in Blois, France. Readers may recall from my last column the central role Rajiv played in developing the halfmoon Betta; others may know him through his excellent books (Masillamoni, R. and Schmidt, J. 1998. Schleierkampffische. Bede-Verlag; Gonella, H. and Masillamoni, R. 1997. Kampffische. Bede-Verlag). Amongst the magnificent fish at this show were those of a guppy breeder, Alan Genet, who had recently turned his attention to Betta. Rajiv and I were both struck by the dorsals on his fish, in particular, by way in which the fin, when flared, snapped open like a Japanese fan. Alan made Rajiv a gift of some of these fish and indeed some of these very fish are an appreciable part of the genetic background of the line I maintain today. 

On the long drive back from the show to Rajiv's place in Switzerland, we talked about these fish. After they had a chance to settle down in Rajiv's fishroom we finally had the chance to take a leisurely look at them. While the fish were young, it was apparent that Genet's fish had an unusual degree of branching in the dorsal and that their dorsals had a roughly circular outline. It got me thinking, as no doubt many other Betta breeders have before me, about what might be done by tinkering with the dorsal fin.

The Next New Thing

The fact that IBC standards are so easily met by a single gene effect means that breeders have not had incentive to work on development of the dorsal fin. Following the thinking begun in Rajiv's fishroom, I suspect progress could readily be made in the symmetry of the dorsal and in the extent to which the fin ray branches. 

One way to think about this is to ask what is not achieved via the exclusive use of doubletail. Dorsal fin rays in fish carrying doubletail are rarely branched (e.g., see Figure 3B). Branching, when it occurs is largely restricted to a small number of posterior fin rays and virtually all branches are simple bifurcations. Multiple branching, where each branch branches and then branches yet again, such as those that characterize the halfmoon caudal, are rarely seen in dorsal fins. 

Another feature lacking in the doubletail dorsal is radial symmetry. Use of doubletail induces a rectangular shape to a fish that is normally shaped quite differently. Consider the shape of dorsal in a modern show plakat (Figure 2C). Inspection of these fins shows that the length of fin rays progressively increases to some maximum, then progressively decreases. Typically the fin of maximal length is not at the mid-point of the fin, but slightly posterior. The amount of webbing between rays, however, is greater in the back than in the front, as is the branching so the overall effect is one in which the shape is one of a half-circle. 

I can easily imagine a dorsal fin that is a perfect half-circle, where each ray is of comparable length, but each displays extensive branching. I am thinking of a fish with a dorsal that looks something like that shown in Figure 4. No such dorsal fin exists at present; this drawing is simply a figment of my imagination. It is nonetheless a goal that I suspect might be achieved by selective breeding if one set one's mind to it. 

Biological Prerequisites

Generating the next new thing requires not only a well-thought out goal, but that certain biological prerequisites are in place. Foremost amongst these is the requirement that variation exists in the trait one wishes to enhance. Specifically, if we want the symmetry of the dorsal to be that of a half-circle and less that of a rectangle, then we need to be able to find fish that have more circular and less boxy fin shapes to breed to one another. Likewise, if we wish to produce dorsal with more extensive branching, there must be fish available with at least some branching in the dorsals. The key to enhancing a trait is to choose as breeders those forms closest to the goal that you seek to attain and continue this process generation after generation until the goal is realized. 

The existence of variation is not alone sufficient. The variation must be of a very particular sort. Variation may have two components, genetic and environmental. An example of environmental variation is the observation that the background against which a fish is reared will affect the intensity of its color. A black fish reared on a black background will appear a darker black than a fish on lighter background. Yet, mating fish reared on a dark background will not guarantee that your line of black fish will improve over time. As soon as these fish are shown against a white background, they will be revealed to be no more improved in color than their predecessors. For variation to lead to improvement in the line, one requires that that variation can be inherited. Only genetically based variation is germane.

Genetic variation may simply not be available. For example, if you want to produce a Betta that possessed two dorsal fins, you will likely never succeed simply because you will likely never find a fish with genetic variation for fin number. How does one know whether the goal one has in mind is attainable, that is, how does one know that genetic variation exists to select upon? Unfortunately, professional biologists lack any coherent 'theory of the possible.' A reasonable rule-of-thumb, however, is available. If you know that the animal has the ability to produce a structure in the first place, it is often the case that it will be possible to modify that structure. For example, if you know a flexible fin ray can branch, it is likely that genetic variation for more (or less) branching will be possible. This rule of thumb should emphatically not be considered a guarantee, but more often than not selection is effective in producing more or less of something that is already present.

From Here To There

Returning to the goal I have in mind - that of a halfmoon dorsal - there is reason for optimism. Variation of the desired sort abounds. At the outset, two tasks seem necessary. First, one needs to move away from the boxy, parallel, anal fin-like rays of doubletail dorsals towards a more circular dorsal outline. The modern show plakat readily provide the desired profile. One may expect rapid progress in producing the desired circular outline by crosses to plakats, although the task of achieving long straight edge rays will likely be no simpler in the dorsal than halfmoon breeders found it to be in the caudal. 

The second task will be to improve fin ray branching. This may seem the larger challenge, but several halfmoon lines throw fish with substantial dorsal branching. Figure 5 (Tracing of dorsal fins from (A) Sean Mahabir's and (B) my own halfmoon lines. Note extensive branching in the fin rays shown.) shows two dorsal fins, each with only a few fin rays outlined. The first is a tracing of a pastel fish from the Colorado breeder Sean Mahabir and the other is from my own line of black lace-red butterflies. Both show extensive (quaternary) branching. While variation for branching is clearly available, the task of producing symmetrical branching around some tangent to the body axis is quite likely to prove challenging. 

Will the doubletail gene play a role in achieving the imagined halfmoon dorsal? I strongly suspect so. While doubletail has some undesirable effects on symmetry and branching, a substantial increase in number of fin rays will likely never be achieved without its use. The best combination, after all, would be to have the desired circular form from plakats; the branching hinted at in the fish in Figure 5, and the fin ray counts offered by the doubletail gene. 

Betta breeders are constantly working their stock to achieve some new form or color combination. Whether the dorsal form imagined here will ever be realized is immaterial. What we can be certain of is that hobbyists working on their farms or in their basement fishrooms will continue to recognize novelty, imagine what might be done with it, perform selective crosses, and once again surprise the rest of us with the seemingly endless variation that this animal seems capable of expressing.  that each gene comes in two copies, one from the mother and one from the father. These copies are called alleles. Two classes of alleles are known as the doubletail gene, the wild-type allele (+) and the mutant (dt) allele. A fish that carries two copies of the wild type allele, that is a ++ animal, will be a singletail, whereas a fish with two copies of the mutant allele, that is a dtdt animal, will be a doubletail. The heterozygote animal, that is a fish with both a wild type and a mutant allele (+dt) will also be singletail, although the dorsal fins on such animals typically have a broader base and support a greater number of fin rays than do homozygous (++) animals. 

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