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The Interesting Dollar Sunfish, Pet and Laboratory Specimen


Garold Sneegas - http://gwsphotos.com
By Neil Hinckley

Common Name: Dollar Sunfish

Latin Name: Lepomis marginatus

Origin: North America

Temperature: 60 - 80F (15.5 - 27C)

Ease Of Keeping: Moderately easy

Aggressivness: Semi-aggressive

Lighting: Dim to bright.

Adult Size: Up to about 4 - 5" (10 - 12.5cm)

Minimum Tank Size: 20 Gallon

Feeding: Will eat most things, but prefers live food. It may take some time for wild caught specimens to accept processed food.

Spawning Method: They should be fed a rich diet of mostly live and frozen foods. They also like cooling period. The male defends the young, and can kill the female if the aquarium is not large enough or provide enough hiding spots. The female is typically removed after spawning.


Click to enlarge in a new window
Garold Sneegas - http://gwsphotos.com

Click to enlarge in a new window
Garold Sneegas - http://gwsphotos.com

In the aquarium hobby there has always been, and will likely always be, the easy to care for, beautiful, compatible, but still almost unbuyable fish. The dollar sunfish (Lepomis marginatus) is one of these fish. It is not a new discovery, or a fish of extraordinary rarity, in fact it is fairly common in much of the United States, but it is still not very common in the aquarium trade. Even in the scientific community it has only rarely been studied alone, seeming instead to prefer to be included in genus wide studies. However, Lepomis marginatus has many characteristics that make it desirable in these fields. It is a medium sized, hardy, egg laying species with a wide variety of desirable behavioral and aesthetic virtues, making it very compatible with the aquarium trade. It is also of interest to the scientific community for some of those same reasons, as well as for its ready ability to hybridize with other species in its genus.

One of the most important aspects of a fish when it is being considered for its ability to be kept in an aquarium is the adult size of the fish. This is necessary for a few reasons. The first is that tank busters become very hard to place when they get close to a foot in length.


Tankbuster:
Fish that get very large. Generally any solitary fish that approaches a foot in length or more, or a schooling fish that grows to about 6 inches or more.
The second is that in almost every case the aquarium is going to be smaller than the fish's natural habitat, and so limits the fish to the smaller end of the fishy size spectrum. A third reason is for compatibility aspects, as in almost every case a fish will eat any other fish that happens to fit in its mouth. Luckily for the Dollar Sunfish, it fits comfortably into the medium size of fish, reaching somewh! ere between 4 and 5 inches in length a,b. This means that it can be kept with a wide variety of other fish as it is not too likely to eat or be eaten by other fish. Also, because of its relatively small mouth it is able to be kept with smaller fish than would be normal for a fish of its size.

However, size is not all that the dollar sunfish has going for it. After all, what benefit is there in having a nicely sized fish if it is so sensitive to water conditions that it is impossible to keep in the aquarium? Again Lepomis marginatus gives a good showing in terms of its hardiness. It can live in a wide variety of water temperatures, varying from lower than 60 degrees F up to about 80 degrees F before the fish begins to get stressed a. A temperature of about 74 degrees F seems to be optimal as the fish will breed almost continuously a at it.

In addition to its hardiness and size compatibility, the Dollar Sunfish is a gorgeous fish. Its coloration is similar to the awe inspiring Jewel cichlid,


Jewel Chichlid:
Hemichromis bimaculatus. A cichlid found in rivers in Africa and, noted for its extraordinary coloration and extreme aggressiveness.
and depending on the strain c the males of the species can rival even the most beautiful Jewel, with a deep red and orange background speckled with bright blue iridescent dots.

This fish still has one more thing that adds to its desirability, and that is its behavior. Overall, the behavior of this fish is very like a cichlid, both in terms of its aggressiveness and its spawning behavior. This sunfish is not shy


Chichlid:
"Cichlids are secondary freshwater fish and inhabit most of the Paleotropics (Africa) and the Neotropics..."
-Wikipedia
about showing off its colors in the home aquarium and has been shown to adapt to aquarium life in as little as a week, something that is remarkable for any medium sized fish. It is a moderately aggressive fish, and like the cichlids shows its most aggressive behavior when the males are breeding or when they are guarding the eggs or newly hatched fry. And, yes, they can be bred in the aquarium, another plus for the aquarist.

The aquarium hobby is not all that Lepomis marginatus is good for though. It has also been studied by scientists, almost always as a result of its and the other fish's in its genus' breeding behavior. One of the early studiesd that included this fish was looking at what it is that determines if something is a separate species or a strain of an already described species. In order to do this the scientists compared what proteins various species of the genus Lepomis produced, as well as looking at the actual genes of the fish. The reason that the genus Lepomis was chosen is that it is a species that has a well documented ability to hybridize and produce fertile offspring. In fact, at the time that the paper was published there were 21 crosses that were known to have occurred in nature, out of 55 that are possible. In order to determine if this ability was a result of an unusual closeness of genetics as manifested by the pr! oteins that the species produce. In the end they discovered that a great genetic closeness is not necessary for species to hybridize, and so speciation is not determined by being unable to produce fertile offspring, but is instead determined by significant genetic differentiation compared to the known differentiation throughout the range of the species.

In another study e, again using the entire Lepomis genus, the fish were used to help define which evolutionary theory is most likely correct, punctuated equilibria as it was originally proposed, or the longer standing theory of phyletic gradualism. In order to


Punctuated Equilibria:
Also called the rectangular theory of evolution, after the shapes that it forms on evolutionary charts. This theory states that the majority of genetic changes take place when speciation occurs, with very little changing most of the time.
Phyletic Gradualism:
Also called gradual evolution. This is the more traditional theory of evolution, where there is a smooth slope in charts of evolution. It is based on the "slow but steady" principle, saying that small changes are happening frequently.
get evidence to support one or the other theory, the researchers gathered species of two different genera that had a large difference in the number of species that they contain, in order to see if they could observe differences in the rate of genetic change in the different genera. The genus that they chose to represent the species heavy genera was that of the American minnow, Notropis, a genus made up of well over 100 species. Lepomis is obviously the genus chosen to represent the species poor genera, and is a good choice as it only has 11 species. In the end, their observations point toward the phyletic gradualism theory, as the amount of change in the off! spring of the two genera is essentially the same. The researches do state that they are hesitant to apply this observation to other genera as there are possible errors in the experiment, such as that both genera undergo the same rectangular evolution patterns but that the new Lepomis species go extinct at a higher rate than the Notropis species.

In a more recent study f, Lepomis marginatus gets more individual attention as the researches look at a behavior that has resulted in a new strain in other species in the Lepomis genus. This behavior is that of nest parasitism, where a male other than the nest guardian fertilizes some of the eggs in a nest during the mating of the male and various females. In the species of Lepomis where this


Bourgeois Males:
"Normal" males. These males actively pursue females and guard their nesting site against intruders.
is most common there is a strain of male that is significantly different in morphology from the bourgeois males. This strain has some specific differences that make it identifiable. They are smaller bodied, and lack the bright coloration that he bourgeois males possess. They also become sexua! lly mature at a much faster rate, and have a much larger ratio of their body weight invested genital tissue. The species where these males are most apparent is the bluegill, and it is this trait that this study was looking for in Lepomis marginatus. In order to determine if this trait existed in the dollar sunfish the researchers collected males and eggs from their nest, and then looked at the DNA in order to determine if the nest guardian was also the father of the eggs in the nest. They also collected a random sample of males that were not guarding a nest in order to see if a strain of parasitic males could be found. The study resulted in the conclusion that there is no such strain in the marginatus species. Out of all the males that they collected, only one had an abnormal genital to body mass ratio, and it was still much closer to the norm than the strain in Bluegill. Out of all the young that were compared with their guardians, 94-96% of them were deemed to be t! he offspring of their nests guardians. The majority of those that were n't the offspring of their nests guardian were in one nest and matched the guardian of a nest about one and a half meters away, suggesting that they may have been displaced in a dispute of some kind.

So, although the dollar sunfish is perhaps not the most scientifically interesting fish to be found, it, and the other members of its genus, have some interesting traits and have been used in a significant number of evolutionary studies, witnessing to their usefulness. They are also a very interesting fish for the hobbyist, with the possibility of incurring much more interest in this area than in the fields of science. Hopefully in the future the good traits of this and other native fishes of North America will come under closer scrutiny and their value will be more fully appreciated.

Some of the different variations of Lepomis marginatus



Photos Mark Binkley. Coutesty of jonahsaquarium.com, Click the thumbnails for a larger picture.




a. Robert Rice. "The Dollar Sunfish (Lepomis marginatus) as an Aquarium Species." Native Fish Conservancy. 28 March 2005.

b. Geologic Survey of Alabama. "Dollar Sunfish" Outdoor Alabama. 28 March 2005.

c. R. W. Wolff. "Dollar Sunfish: Spawning Two Varieties of Lepomis marginatus." The Native Fish Conservancy. 28 March 2005.

d. Avise, John C.; Smith, Michael H.. "Biochemical Genetics of Sunfish. II. Genic Similarity between Hybridizing Species." The American Naturalist Vol. 108, No. 962 (Jul1974): pp. 458-472

e. Douglas, Michael Edward; Avise, John C.. "Speciation Rates and Morphological Divergence in Fishes: Tests of Gradual Versus Rectangular Modes of Evolutionary Change." Evolution Vol. 36, No. 2 (Mar1982): pp. 224-232

f. MacKiewicz, M.; Fletcher, D. E.; Wilkins, S. D.; DeWoody, J. A.; Avise, J. C.. "A genetic assessment of parentage in a natural population of dollar sunfish (Lepomis marginatus ) based on microsatellite markers." Molecular Ecology , Vol. 11 Issue 9 (Sep2002)



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