Inheritance of Long Fins in Ornamental Koi Carp

Abstract

Inheritance of long fins in ornamental koi carp Cyprinus carpio was studied. Fish segregations with regard to the presence or absence of long fins in two progenies were recorded and analyzed. In progeny 1, produced by crossing a long‐fin koi female with a short‐fin (wild‐type) koi male, the observed segregation of long‐fin fish : short‐fin fish did not differ significantly from the 1:1 Mendelian ratio. In progeny 2, produced by crossing the same long‐fin female with a long‐fin male, the observed segregation of long‐fin fish : short‐fin fish did not differ significantly from the 3:1 Mendelian ratio. Based on these data, it was concluded that the appearance of long fins in koi is under the control of a dominant mutation of one gene ( Lf/lf ). Fish with genotypes LfLf and Lflf have long fins, while fish with genotype lflf do not have this trait. Since the appearance of long fins in koi is controlled by a dominant mutation, the development of a true‐bred, long‐fin line could be achieved only by identifying heterozygotes Lflf by means of test crosses and removing them from the stock.
Received April 14, 2010; accepted June 16, 2010

Full text

North American Journal of Aquaculture 73:49–52, 2011
C

American Fisheries Society 2011
ISSN: 1522-2055 print / 1548-8454 online
DOI: 10.1080/15222055.2011.544942
COMMUNICATION
Inheritance of Long Fins in Ornamental Koi Carp
Boris Gomelsky,* Kyle J. Schneider, and Ahmed S. Alsaqufi
Aquaculture Research Center, Kentucky State University, Frankfort, Kentucky 40601, USA
Abstract
Inheritance of long fins in ornamental koi carp Cyprinus carpio
was studied. Fish segregations with regard to the presence or ab-
sence of long fins in two progenies were recorded and analyzed. In
progeny 1, produced by crossing a long-fin koi female with a short-
fin (wild-type) koi male, the observed segregation of long-fin fish :
short-fin fish did not differ significantly from the 1:1 Mendelian
ratio. In progeny 2, produced by crossing the same long-fin female
with a long-fin male, the observed segregation of long-fin fish :
short-fin fish did not differ significantly from the 3:1 Mendelian
ratio. Based on these data, it was concluded that the appearance
of long fins in koi is under the control of a dominant mutation of
onegene(Lf/lf ). Fish with genotypes LfLf and Lflf have long fins,
while fish with genotype lflf do not have this trait. Since the ap-
pearance of long fins in koi is controlled by a dominant mutation,
the development of a true-bred, long-fin line could be achieved
only by identifying heterozygotes Lflf by means of test crosses and
removing them from the stock.
The Japanese ornamental koi carp Cyprinus carpio is one
of the most popular decorative fish in many countries all over
the world, including the United States. Koi were developed ap-
proximately two centuries ago in Japan (Kuroki 1981; Davies
1989). The long-fin variety of koi, also called butterfly koi,
is a relatively new morph that has been developed in the last
several decades. In the United States, long-fin koi have been
developed at Blue Ridge Fish Hatchery (North Carolina) from
the middle 1980s by crossing of normal short-fin koi with the
long-fin common carp of Asian origin (LeFever 1991, 2010).
This long-fin carp apparently originated from Indonesia, where
a local long-fin strain of common carp (also called “kumpay”)
has been described (Kirpichnikov 1981; Sumantadinata 1995;
Emmawati et al. 2005). Long-fin common carp has also been
found in the southwestern part of China (Wang and Li 2004).
There is information (Anonymous 1988) that the long-fin morph
of koi was obtained in Japan in the early 1980s by crossing koi
with Indonesian long-fin carp. In Japan, long-fin koi are not al-
lowed to be demonstrated at koi competitive shows (Anonymous
*Corresponding author: boris.gomelsky@kysu.edu
Received April 14, 2010; accepted June 16, 2010
Published online February 2, 2011
1988; Christensen 1999). Therefore, their popularity in Japan
and some other countries is relatively low. However, long-fin
koi are very popular in the United States, and many fish farms
cultivate them for sale.
Publications on the origin and characteristics of long-fin koi
(LeFever 1991, 2010) do not contain any information on the
inheritance of this trait, and no data on this subject are available.
The present study reveals the mode of inheritance of long fins
in koi.
METHODS
The experiments were conducted at the Aquaculture Re-
search Center, Kentucky State University (KSU), Frankfort.
Two progenies were produced, and fish segregations with re-
gards to presence or absence of long fins in these progenies
were recorded and analyzed.
Progeny 1 was produced by crossing a long-fin, white-red koi
female with a short-fin (wild-type), white-red koi male. Progeny
2 was produced by crossing of the same long-fin, white-red fe-
male with a long-fin, white-red-black male. Long-fin and short-
fin fish parents used in crosses were chosen from broodstock
without any previous knowledge of their genotypes because no
preliminary crosses were performed. To induce final oocyte mat-
uration in female and spermiation in males, fish parents were
injected with carp pituitary extract (Sigma Chemical, St Louis,
Missouri) at 3 mg/kg of body weight. Eggs were artificially in-
seminated in plastic bowls and were treated with a water–cow
milk mixture (volumetric ratio = 8:1) to remove adhesiveness.
Embryos were incubated in McDonald’s jars. Approximately
3,000 swim-up larvae from each progeny group (quantities were
evaluated by volumetric method) were stocked into two separate
20-m
3
outdoor tanks for rearing. Tanks were supplied with water
from a 0.2-ha reservoir. During 5.5 months of rearing, fish were
fed an artificial diet; fish also consumed zooplankton and ben-
thic organisms that were developed in tanks and flowed in with
the reservoir water. Two months after stocking, several hundred
49
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50 GOMELSKY ET AL.
FIGURE 1. Long-fin (left) and short-fin (right) fish from progeny 2; bar = 2cm.
fry were randomly removed from each tank to decrease fish
density and provide better growth conditions for the remaining
fish.
After 5.5 months of rearing, tanks were drained and all
fish were collected and analyzed. Fin type (long-fin or short-
fin) and color of each collected fish were recorded. Sam-
ples of long-fin and short-fin fish from progenies were taken
for individual measuring; fish total length (TL) and standard
length (SL) were measured. Based on length measurements,
the percentage index “relative tail length” (RTL) was cal-
culated for each fish in samples (according to the formula
[TL—SL] × 100/SL). The typical numbers of fish in samples
taken for measurements were 21 or 24. However, 100 long-
fin fish from progeny 2 were measured since the distribution
of fish in this category with regard to RTL was obtained and
analyzed.
Segregations of fish in progenies with regard to both
fin and color types were compared using a chi-square test
(Zar 1999). Differences in mean RTL values between differ-
ent groups of fish were evaluated by a Student’s t-test (Zar
1999). Distribution of long-fin fish from progeny 2 with re-
gard to the RTL index was compared with normal distribu-
tion by means of a Kolmogorov–Smirnov goodness-of-fit test
(Zar 1999).
RESULTS
Numbers of fish analyzed and segregations of long-fin fish :
short-fin fish in progenies 1 and 2 are given in Table 1. As an
illustration, a photograph of several fish from progeny 2 is pre-
sented in Figure 1. In progeny 1, the observed segregation of
long-fin fish : short-fin fish did not differ significantly (P > 0.05)
from the 1:1 Mendelian ratio. In progeny 2, the observed segre-
gation of long-fin fish : short-fin fish did not differ significantly
from the 3:1 Mendelian ratio (P > 0.05).
In progeny 1, the mean ± SD SL and TL of short-fin fish were
5.65 ± 0.88 cm and 6.87 ± 1.03 cm (n = 21), respectively, while
those of long-fin fish were 5.79 ± 0.68 cm and 8.18 ± 0.97 cm
(n = 24), respectively. In progeny 2, the mean ± SD SL and TL
of short-fin fish were 7.83 ± 1.36 cm and 9.48 ± 1.63 cm (n =
24), respectively, while those of long-fin fish were 6.92 ± 1.17
cm and 9.93 ± 1.55 cm (n = 100), respectively. The mean ±
SD RTL indices were 21.73 ± 2.61% and 40.98 ± 3.42% for
short-fin and long-fin fish and 21.23 ± 2.27% and 43.91 ±
4.30% in progenies 1 and 2, respectively. In both progenies, the
differences in mean RTL indices between short-fin and long-fin
fish were statistically significant (P < 0.001). Long-fin fish had
a 1.89 and 2.07 times larger mean RTL index than short-fin
fish in progenies 1 and 2, respectively. Distribution of long-
fin fish in progeny 2 with regard to the RTL index is given in
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COMMUNICATION 51
TABLE 1. Characteristics of progenies and segregation of fish with regard to fin length.
Segregation (%)
Progeny Female Male Number of
Proposed type Proposed theoretical
number phenotype phenotype fish analyzed Long fin Short fin of cross segregation
1 Long fin Short fin 377 49.6
a
50.4
a
Lflf × lflf 1:1
2 Long fin Long fin 222 72.1
b
27.9
b
Lflf × Lflf 3:1
a
Not significantly different from 1:1 (P > 0.05).
b
Not significantly different from 3:1 (P > 0.05).
Figure 2. This distribution did not differ significantly (P > 0.05)
from normal.
DISCUSSION
Long-fin and short-fin fish segregations in progenies 1 and
2 did not differ significantly from Mendelian ratios of 1:1 and
3:1, respectively. Based on these data, it may be concluded that
appearance of long fins in koi is under the control of a dominant
mutation of one gene (Lf/lf ). Fish with genotypes LfLf and Lflf
have long fins, while fish with genotype lflf do not have this trait.
Proposed genotypes of fish parents used in crosses are shown
in Table 1. These are the first reported data on inheritance of
long fins in koi. Earlier, Tan and Phang (1994) revealed that
elongation of fins in zebrafish Danio rerio, which belong to the
same Cyprinidae family as koi, is also caused by a dominant
mutation of one gene.
Long-fin koi are characterized by elongation of both paired
and unpaired fins. In order to characterize the rate of fin elonga-
tion quantitatively, we calculated and compared the RTL index.
In both progenies, the mean RTL index is approximately two
times larger in long-fin fish compared with short-fin fish.
Since the phenotypic ratio of fish with long and short fins in
progeny 2 was close to 3:1, the category of long-fin fish should
consist of heterozygotes Lflf and homozygotes LfLf with a ratio
of 2:1. Distribution of long-fin fish in progeny with regard to
0
5
10
15
20
25
30
34.0-
37.0
37.1-
40.0
40.1-
43.0
43.1-
46.0
46.1-
49.0
49.1-
52.0
52.1-
55.0
Relative Tail Length (% )
%
FIGURE 2. Distribution of long-fin fish in progeny 2 with regard to the relative
tail length index.
RTL index did not differ significantly from a unimodal normal
distribution. This indicates that the Lf allele is characterized by
complete dominance. If incomplete dominance for this allele
occurred, the difference between fish with genotypes Lflf and
LfLf would have resulted in a bimodal distribution of fish with
regard to RTL index.
In both analyzed progenies, short-fin and long-fin fish did
not differ significantly with regard to color segregations (data
not presented). This indicates that mutation causing elongation
of fins is not associated with color traits.
The results of the present study should be taken into account
by producers of long-fin koi who are interested in developing
a true-bred, long-fin line of koi (giving only long-fin fish in
consecutive generations). Since appearance of long fins is con-
trolled by a dominant mutation, it would be relatively difficult
to develop a true-bred, long-fin line since the crossing of two
heterozygotes (Lflf ) gives the mixed progeny. Development of
a true-bred, long-fin line could be achieved only by identify-
ing heterozygotes Lflf by means of test crosses and removing
them from the stock. For identification of fish genotypes, long-
fin fish should be test crossed with short-fin fish (lflf ): crosses
of homozygous fish LfLf will produce only long-fin fish (Lflf ),
while crosses of heterozygous fish Lflf will result in progenies
consisting of long-fin fish and short-fin fish with the 1:1 ratio.
ACKNOWLEDGMENTS
Support for this study was provided by Kentucky’s Regional
University Trust Fund to the Aquaculture Program as KSU’s
Program of Distinction. The authors thank Robert Durborow for
valuable suggestions and Sid Dasgupta for advice on statistical
treatment of the obtained data. Special thanks to Andrei and
Lena Bukin for advising on literature sources on the subject in
koi literature and providing copies of some articles.
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