BREEDING PROGRAM FOR THE DISCUS FISH ABSTRACT

Second National Congress on Genetics,
I3-l5 November 1996,
Genetics Society of Malaysia
197
BREEDING PROGRAM FOR THE DISCUS FISH
FAN, L. Q. ANDV. P. E. PHANG
School of Biological Sciences, National University of Singapore, Singapore
14
ABSTRACT
The discus fish is considered as the king ofthe aquarium fishes. Belonging to the genus Symphysodon of
the family Cichlidae, it is widely distributed throughout the Northern Amazon Basin. In general, 4 wild
local breeds are introduced, such as Heckel, Tefe Green, Blue and Brown discus. Since the early 1930's
many new colour varieties have been cultivated by artificial selection from inbreeding or crossbreeding
populations. Breeding goals of the discus fish have to cater to the market requirements to create fish
with novel colour patterns and morphological body types. Breeding strategies focus on increasing
genetic variations of colour pattern and body types as well as for growth rate and reproductivity.
Breeding methodologies include genetic parameter estimation and individual evaluation based on
individual animal model and Best Linear Unbiased Estimation (BLUE), mutagenesis and transgenesis
are being applied in recent years. These new advanced techniques can increase genetic variations and
accurately select the right individuals to establish a new line of designed variety within a family, a
inbreeding line, a pure-bred population, or hybrid population.
INTRODUCTION
The discus fish is considered as the king of the aquarium fishes. Belonging to the genus Symphysodon of the
family Cichlidae, it is widely distributed throughout the Northern Amazon Basin (Axelrod, 1986). In general,4
wild varieties are introduced, such as Heckel, Tefe Green, Blue and Brown discus. Classification of the wild
discus remains controversial (Burgess, 1991). Since the early 1930's many new colour varieties, such as Cobalt,
Turquoise, Royal Red, Pigeon, Ghost, Solid Red, Alencer Red and Super Blue with their various commercial
names, have been cultivated by artificial selection from inbreeding or crossbreeding populations (Wattley,
1985). Inheritance
of body fypes and colours, morphological
measurements, reproductive physiology and
pigment cell of discus have not been studied yet.
ln this paper, we report our resulls in discus classification, body measurelnents and reproductive physiology,
and discuss breeding strategies ofthe discus fish.
MATERIAL AND METHODS
Ninety-five mature discus fish which included the four wild forms and eight cultivated varieties collected from
various sources were used in two studies of discus classification by RAPD fingerprinting following our
preliminary study (Fan el al., 7995a, b). In these two studies, five arbitrary primers were used for the RAPD
fingerprinting. Statistical analysis was done by using the similarity index (Nei and Li, 1979) and the percent
match (Ballinger-Crabtree et al., 1992).
Two experiments with sample sizes of 49 (Fan et al., 1995c) and 63 discus fish were designed to examine
variety differences in morphological measurements among the 4 wild forms and 8 cultivated varieties and two
crosses. The measurements included angle of the head, ver{ical and horizontal scale counts, length of fish,
198
Second National Congress on Genetics, I 3- I 5 November 1996, Genetics Society of Malaysia
lengths of dorsal, ventral and caudal fins, height of fish, height of caudal fin, and body shape (coded as round,
diamond and arrow shapes). Multiple comparisons were examined by general linear hypothesis test.
The study of reproductive physiology was based on three-months reproductive records for 237 pairs of breeding
discus in a commercial discus farm and six-months records of breeding performance and behaviour for 65
breeding pairs
of
discus fish
in the
department
of Zoology of
National University
of
Singapore. Sex
determination and embryonic development of discus were also studied.
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RESULTS
Estimates of Similarity Indices (SI) and Percentage Matches (%M) using the 5 primers were relatively high for
the 4 wild and 8 cultivated varieties, from 0.65 to 0.99 and 0.72 to 0.99, respectively. The genetic distances
between two varieties were less or intermediate between those of the two varieties. The dendrograms of genetic
distances based on SI and %M showed that a 4-group classification of the cultivated discus, coded as Royal
Red, Cobalt, Turquoise and Pigeon, is generally acceptable. There were no significant differences (P > 0.05) in
body measurements among the 4 wild forms and 8 cultivated varieties when samples of each discus variety
were collected from various sources. Variations within each variety in body measurements were relatively high.
Percentage of successful pairs in total breeding pairs was 22.5Yo. The average number of eggs laid per spawn
was 180, with 43.7oh rate of fertilization, 73.7%o rate of hatching and 41.6Yo survival rate of the fry. The
hatching occurred by 2.5 days and the fry started swimming in 6 days. Sex determination were made yielding an
accuracy of 64.40/o in corresponding to the shape of the head,, 58.5%o basedqSn the shape of the fins and,5l.2%o tn
,f*,** 1 f, -,*.te
DISCUSSION
The results indicate that the 4 wild discus forms were closely related and belong to one species. Most of the
cultivated discus varieties were developed from wild Green. Variations within each variety in body
measurements indicate a potential great selection response in body type. The three methods for sex
determination suggested by discus hobbyists and farmers are not reliable and reproductivity of the discus fish is
low which is one of the main reasons for the high price in the market.
Breeding goals of the discus fish have to cater to the market requirements to increase productivity and create
fish with novel colour pattems and morphological body types. Breeding strategies focus on increasing genetic
variations of colour pattern and body types as well as for growth rate and reproductivity.
Several breeding methodologies are suggested to achieve the breeding goals. (l) Genetic parameter estimation
and individual evaluation based on individual animal model and Best Linear Unbiased Estimation (BLUE) are
very important for individual and family selection for body type, body size, growth rate and colour paftem from
a inbred or hybrid population, (2) Mutagenesis can be used to increase variations in body colour and body type
and greatly increase the possibility to create new varieties and new patterns, and (3) Transgenesis will rapidly
force a positive genetic change based on the market demand. These new advanced techniques can increase
genetic variations and accurately select the right individuals to establish a new line of designed variety within a
family, a inbreeding line, a pure-bred population, or hybrid population.
Second National Congress on Genetics, I3-15 November 1996, Genetics Society of Malaysia
199
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