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379
Neotropical Ichthyology, 8(2):379-383, 2010
Copyright © 2010 Sociedade Brasileira de Ictiologia
Scientific Note
Reproductive and population parameters of discus fish Symphysodon
aequifasciatus Pellegrin, 1904 (Perciformes: Cichlidae) from Piagaçu-Purus
Sustainable Development Reserve (RDS-PP),
lower Purus River, Amazonas, Brazil
Felipe Rossoni
1
, Sidinéia Amadio
2
, Efrem Ferreira
2
and Jansen Zuanon
2
The ornamental discus fish Symphysodon aequifasciatus Pellegrin, 1904, is a popular endemic cichlid species from the Amazon
basin, however scientific information concerning biology and ecology in its natural habitat is scarce despite its importance on
the international aquarium trade. In this study we evaluated reproductive parameters of S. aequifasciatus in natural habitat in
Piagaçu-Purus Sustainable Development Reserve (RDS-PP), lower Purus River, Brazilian Amazon. Males are more frequent in
the larger size classes and this might be related to the complex breeding behavior known for S. aequifasciatus. Values of L
50
for
both sexes corresponded to more than 60% of the maximum attained length which may indicate that energy allocation for
somatic growth takes longer in S. aequifasciatus than in other species. Average fecundity for female discus was 1490, ranging
from 950 to 1892 oocytes and its correlations with standard length and total weight were very low, probably due to the highly
compressed discus´ body shape. Egg size distribution showed four types of patterns, indicating one to four modes besides the
reserve oocytes group. Our results indicate that S. aequifasciatus shows total spawning, in the beginning of flooding period,
with the peculiar capacity of releasing multiple egg batches as a strategy that potentially enhances reproductive success.
O acará-disco (Symphysodon aequifasciatus Pellegrin, 1904) é uma espécie popular de ciclídeo endêmico da bacia amazônica,
porém são poucas as informações científicas sobre biologia e ecologia em seu habitat natural, apesar de sua importância no
comércio internacional de aquário. Neste estudo avaliamos parâmetros reprodutivos de S. aequifasciatus em vida livre na
Reserva de Desenvolvimento Sustentável Piagaçu-Purus (RDS-PP), baixo rio Purus, Amazonas, Brasil. Os machos são mais
frequentes em classes de comprimento maiores, o que provavelmente está relacionado com o complexo comportamento
reprodutivo de S. aequifasciatus. Os valores de L
50,
para ambos os sexos, corresponderam a mais de 50% do comprimento total
máximo atingido para a espécie, o que pode indicar que a alocação de energia para o crescimento somático é mais prolongada
em S. aequifasciatus que em outras espécies, visto que o tamanho dos exemplares é essencial para o bom desempenho. A
fecundidade média foi de 1490 ovócitos, (950 a 1892) e sua relação com o comprimento padrão e peso total foi baixa, provavelmente
devido ao formato comprimido do corpo. Constatou-se quatro padrões na distribuição de tamanho dos ovócitos, incluindo de
1 a 4 modas, além do grupo de reserva. Symphysodon aequifasciatus apresenta desova total para o período reprodutivo, com
a peculiaridade de liberar mais de um lote de ovócitos quando necessário, como uma estratégia que possivelmente aumenta a
probabilidade de sucesso reprodutivo.
Key words: Ornamental fish, Population structure, Breeding strategy.
1
Programa Integrado de Pós-Graduação em Biologia Tropical e Recursos Naturais (PIPG-BTRN), Programa de Biologia de Água Doce e
Pesca Interior – Instituto Nacional de Pesquisas da Amazônia (INPA), Instituto Piagaçu. f_rossoni@yahoo.com.br
2
Coordenação de Pesquisas em Biologia Aquática (CPBA), Instituto Nacional de Pesquisas da Amazônia. amadio@inpa.gov.br,
efrem@inpa.gov.br, zuanon@inpa.gov.br
380
Reproductive and population parameters of discus fish Symphysodon aequifasciatus
The discus fish Symphysodon aequifasciatus Pellegrin, 1904,
an endemic cichlid from the Amazon basin, is one of the most
popular ornamental fish species in the world. Despite its historical
exploitation for the international aquarium trade there is little
information available in the scientific literature concerning biology
and ecology of this species in its natural habitat (Hildemann,
1959; Crampton, 1999, 2008; Bleher, 2006; Ready et al., 2006).
The knowledge about species biology and ecology,
especially regarding breeding, is essential to promote its
exploitation in a sustainable way, avoiding depletion of stocks.
Information about fecundity, type and time of spawning, sex-
ratio and size at sexual maturity are extremely important to
support political decisions on activities related to sustainable
exploitation of natural resources.
Chellappa et al. (2005) studied the ovarian development
of S. discus in semi-natural conditions and characterized it as
a multiple-spawner fish species. Crampton (2008), studying
S. aequifasciatus (identified as S. haraldi in his study) also
found the species to be a multiple-spawner. Câmara (2004)
doing a behavior assessment of S. discus in semi-natural
conditions verified that during the breeding season adult males
showed aggressive behavior, established territories and
defended the area against another males. The author also
found that females show preference for larger bodied males
with established territories, and was selective about the type
of substrate for spawning.
In this study we evaluated reproductive parameters of S.
aequifasciatus in natural habitat during dry/rising water
season (September to November) of 2006 and 2007. Samples
were obtained in Ayapuá Lake, Piagaçu-Purus Sustainable
Development Reserve (RDS-PP), lower Purus River, in the
Brazilian Amazon (04º53’S; 62º59’W). Fish were captured by
netting artificial fish attractors (tree branches structures,
measuring approximately 2 x 2 x 2m) and natural submerged
tree crowns (“galhadas”) and were sacrificed with a lethal
dose (varying from 2 to 5 drops per liter) of Eugenol. Fish for
fecundity determination were captured in November 2006,
during ten days interval.
Standard length (Ls, mm) and total weight (Wt, g) were
taken from each specimen. Sex and gonadal maturity stages
were identified considering texture, consistency, coloration,
size and surface vascularization of gonads (Vazzoler, 1996),
through direct macroscopic observation in the field (Table 1).
The population structure of the species was analyzed
concerning sex- ratio, which was calculated using the absolute
frequency of males and females. Biases from 1:1 sex ratio
were tested by G test (Zar, 1999).
Mean length at sexual maturity (L
50
) for both sexes was
determined from the relative frequency distribution of
young males and females (stage 1) and adults (stages 2, 3
and 4) by standard length classes (10 mm). The L
50
value
was determined by a logistic function using the expression
v
2
=1/(1+exp(-b
1
*(v
1
-b
2
))), where: v
1
= size class; v
2
=
percentage of adults in the size class; b
2
= L
50
. Males captured
during 2006 were not included in the analysis due to the initial
difficulty on identifying of males gonadal stages development.
Female fecundity was estimated as the total number of
vitelogenic oocytes produced during the reproductive
period. Ovaries of pre-spawning females (F3) were removed,
immersed in Gilson solution (Simpson, 1951) for the complete
detachment of ovarian membranes, washed and preserved
in 70% alcohol. The type of spawning was determined by
the frequency distribution of the oocyte diameter classes
(0.1 mm intervals) taken randomly from 300 oocytes of each
female (N = 23) (Vazzoler, 1996). Relationship between
fecundity and standard length or total weight for S.
aequifasciatus was analyzed using simple linear regression.
Mean fish size and mean fecundity for each spawning type
found were tested using ANOVA.
A total of 1592 specimens of S. aequifasciatus were
captured, from which 241 were dissected and sexed (128
females and 113 males). The sex-ratio was of 1:1 (G = 0.704),
similar to that found by Crampton (2008). However, the sex-
ratio analysis by size class showed significant differences
with more females in the 135-145 mm class and more males in
the 155-165 mm class (Table 2). A higher frequency of males in
the larger size classes was also observed by Crampton (2008),
indicating that males attained larger sizes than females.
Several factors of fish’s life history may affect sex-ratios
differently, and there may be variations over time. Differential
mortality and growth of males and females may influence sex-
ratio structure, resulting in the predominance of one sex or
the other throughout development stages. In many cases
Stage Characteristics
Immature
(F1/M1)
Ovaries are thin, small, and translucent without
vascularization. It is not possible to observe oocytes.
Testes are thin and translucent.
Maturing
(F2/M2)
Ovaries are large and intensively vascularized with
opaque eggs inside. Oviduct is tubular, transparent
and empty. Testes are in lobular shape and white.
Pre-spawning
(F3/M3)
Ovaries are enlarged with many orange oocytes,
occupying much of the abdominal cavity and part of
the oviduct. Testes are swollen and white.
Spent
(F4/M4)
Ovaries are flaccid, small, with scattered eggs with
hemorrhagic appearance. Testes are flaccid with
hemorrhagic appearance.
Table 1. Macroscopic description of gonadal development
stages of females (F) and males (M) of Symphysodon
aequifasciatus, based on scale suggested by Vazzoler (1996).
Table 2. G test for sex-ratio of Symphysodon aequifasciatus
from Ayapuá Lake captured between September and November
2006 and 2007, by standard length (Ls) classes. (N = number of
specimens; % = percentage;* significant for G > 3.841).
Absolute Frequency (N) Relative Frequency (%)
Ls (mm)
Females Males Females Males
G
85\95 4 1 80.00 20.00 0.82
95\105 14 7 66.66 33.34 1.73
105\115 12 13 48.00 52.00 0.04
115\125 22 12 64.70 35.30 2.41
125\135 15 15 50.00 50.00 0.03
135\145 30 13 69.76 30.24 6.09*
145\155 28 35 44.44 55.56 1.01
155\165 3 14 17.64 82.36 9.36*
165\175 0 3 0.00 100.0 -
381
F. Rossoni, S. Amadio, E. Ferreira & J. Zuanon
overall sex-ratio is 1:1, however, females can be more frequent
in larger sizes classes due to their faster growth rates (Vazzoler,
1996). Amadio & Bittencourt (2005) suggest that the
predominance of females in fishes in flooded areas in Central
Amazon may be explained by different growth and mortality
rates. Lowe-McConnell (1999), discussing differences in size
of males and females as a function of parental behavior
suggests that in egg-keeping fish species, the individual
keeper (usually the male) tend to be larger than females, and
this pattern is shown by many cichlid species. Apparently
this is not the case of the discus since this species exhibit
biparental care. Neverthess Lowe-McConnell (1999) also
suggests that in species where breeding is very frequent,
size differences tends to be more pronounced due to
bioenergetic reasons. Greater weight loss occurs during egg
production as opposed to sperm production, delaying female’s
growth in comparison to males.
Our results showed a significantly higher proportion of
males in the larger size classes. Although the number of
individuals in those classes is small, this pattern may indicate
differences in growth and/or mortality rate for males and
females. Nevertheless, mortality and growth rates for the
species were not the focus of this study and indications on
this matter have to be taken cautiously.
Cichlid species have, in general, a complex and wide range
of reproductive behavior, such as: territoriality, competition
between males, and spawning site selection. Chellappa et al.
(1999a, 1999b) and Cacho et al. (2006) suggest that male size,
aggressiveness and ability to choose and defend the territory,
are crucial factors for breeding success. Câmara (2004) shows
that female discus prefer males of larger size. These results
corroborate our findings of males being more frequent in the
larger size classes and this might be related to the complex
male breeding behavior known for S. aequifasciatus.
Relationship between standard length and total weight of
all captured specimens was highly significant (Regression
equation: Wt = -4.5545 + 3.1668 Ls, r
2
= 0.91, n = 1590 (Fig. 1).
These parameters are important to predict weight from length
and vice versa, to infer the growth of the species as well as
determine the physical condition of the specimens.
Estimated L
50
for female discus was 98.4 mm (SD +0.38),
corresponding to 63.9% of the maximum attained length for
females (154 mm) in this study. A value of 95.8 mm (SD +0.86)
for males was found, which corresponds to 61.8% of the
maximum attained length for males (155 mm).
According to Agostinho et al. (1991), tropical fish
species seem to reach sexual maturation around 40 to 50%
of their maximum attained length. The results found here
contrast with this generalization, showing values higher
than 60% for both sexes. This fact may indicate that energy
allocation for somatic growth takes longer than average in
S. aequifasciatus.
Average fecundity for female discus was 1490 oocytes
(n = 23, SD +304) ranging from 950 to 1892 oocytes, with
diameters ranging from 0.1 to 1.4 mm. Discus size ranged from
118 to 145 mm Ls (mean 134.59, SD +7.48) and from 90 to 185 g
of total weight (mean 141.22, SD +24.26). Egg size distribution
showed four types of patterns, indicating one to four modes
besides the reserve oocytes group (under 0.4 mm). It was
possible to observe a progression of modes indicating the
release of the most developed egg group from type 4 to type
1 (Fig. 2). Most females showed egg size distribution of type
3 (52%) followed by type 2 (22%) and type 4 and 1 (13%). All
types were composed by females of similar sizes (F = 0.4824,
p = 0.698) and fecundities (F = 0.0929, p = 0.963) (Table 3).
Câmara (2004) defines S. discus as a multiple spawner for
captivity breeding individuals. Under these conditions we
assume that the individuals were not exposed to a wide range
of possible environmental factors occurring in nature, such
as the floodplain pulse regime in the Amazon. Besides, Câmara
(2004) defines the type of spawning considering females in
four different stages of gonadal development while in the
present study the type of spawning was defined based on
pre-spawning female discus only, impairing a reliable
comparison between the two studies.
Crampton (2008) observed a tri-modal egg size distribution
for S. haraldi, and considered it a typical partial-spawning
fish. However, his analysis was based on a single pre-
spawning female fish with 1271 oocytes in the ovary. Foucher
& Beamish (1980) described the occurrence of a multiple modal
egg size distribution for Merluccius productus (Merlucciidae),
but with total spawning. According to the authors, only the
most developed oocyte group is released and the remaining
ones are absorbed. Similarly, Andrianov & Lisovenko (1983)
described for Merluccius gayi peruanus, a process where
Fig. 1. Length x weight plots for specimens of Symphysodon
aequifasciatus captured in Ayapuá Lake during September-
November 2006 and 2007.
Type of egg size distribution N Ls (mm) Wt (g) Fecundity
1 3 126-136 107-160 1427-1807
2 5 126-145 125-165 1034-1892
3 12 118-142 90-185 950-1861
4 3 134-138 135-170 1155-1881
Table 3. Standard length (Ls), total weight (Wt), number (N)
and fecundity range for each type of egg size distribution of
pre-spawning female of Symphysodon aequifasciatus.
382
Reproductive and population parameters of discus fish Symphysodon aequifasciatus
the most developed modal oocyte group is released only after
all groups reach full maturity, and are spawned altogether. In
both cases what seems to be a partial spawning after detailed
analysis proved to be total spawning.
Discus cichlids show complex reproductive behavior and
may be influenced by biotic parameters (such as high
predation of eggs, larvae, and young adults) and by local and
regional environmental dynamics (such as the sudden rise of
the river water level, locally known as “repiquetes”). In this
sense, it seems plausible that females discus spawn only one
egg batch at a time (the most developed one), keeping the
rest to be released later if circumstances of high predation on
eggs, larvae or fry occur. This would explain the progressive
modal shift of egg size (Fig. 2). In that way, female discus
would ensure reproductive success through the rapid
development of one or more egg batches that are still in the
ovary. In the case of reproductive success with the release of
one or two egg batches, the remaining ones would be
absorbed by the organism.
Data on the reproduction of the cichlid species Astronotus
ocellatus (Agassiz, 1831) in captivity (Paiva & Nepomuceno,
1989) showed that successive removal of larvae produced by
the parents resulted in repeated spawning. Lowe-McConnell
(1999) discusses that the number of broods produced depends
on environmental conditions, so production in tanks is higher
than in the natural environment. The author also highlights
the behavioral factor possibly involved, suggesting that the
removal of fry from the captivity in the initial phase may change
the frequency of spawning, as observed for A. ocellatus (Paiva
& Nepomuceno, 1989).
Based on what has been presented, we suggest that S.
aequifasciatus shows total spawning within the breeding
season, in the beginning of flooding period, with the peculiar
capacity of releasing multiple egg batches as a strategy that
potentially enhances reproductive success.
Correlations between fecundity and standard length and
total weight for S. aequifasciatus were very low (length: r
2
=
0.306; weight: r
2
= 0.189). There is evidence that fecundity is
more related to the length than the weight of the individual,
considering it is dependent on the size of the body cavity
(Vazzoler, 1996). It is possible that the weak relationship
observed in the present study is due to the highly compressed
discus´ body shape. In such cases, a correlation between
fecundity and body volume, rather than length would prove
to be more significant, which remains to be tested.
Acknowledgements
Thanks are due to Rodrigo Neves dos Santos for technical
support, RDS-PP fishermen and project members Mário, Assis
and Jeremias for field assistance. We are also grateful to
Marcelo Rocha and Roselis Mazurek for the English version.
This study had financial support from Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq) (MCT/
CNPq/SEAP-PR/CT-Infra no; 016/2006, process no. 408805/
2006-4 and M.Sc. scholarship), Wildlife Conservation Society
(WCS) (Andes Amazon Conservation Program – AACP) and
from Piagaçu Institute (IPI). JZ receives a productivity grant
from CNPq (process no. 307464/2009-1). FR received a M.Sc.
scholarship from CNPq.
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Accepted May 7, 2010
Published June 25, 2010
