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Mating system of the Amazonian cichlid angel fish, Pterophyllum scalare

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Abstract

The species, Pterophyllum scalare distinguishes itself by its breeding behavior, involving competition for territory, sexual partners, courtship and parental care. The purpose of this study was to identify the mating system adopted by this species of fish. Twenty males and twenty females were observed under semi-natural and experimental conditions to test the hypothesis of serial monogamy. Under semi-natural conditions, after the third breeding cycle, the couples changed mates. Under experimental conditions, the couples changed partners after the first breeding cycle. Under experimental conditions, mate recognition was investigated through the preference of the females, indicated by the time they spent with the males. The females were available or not for courtship from new males, depending on their aggressiveness or submission. The larger and more aggressive males obtained new mating opportunities while the submissive males were rejected by the females. The mated fish were aggressive towards intruders in the presence of the mate, protecting their pair bond. In the interval between breeding cycles, the couples did not display aggression towards intruders, confirming the hypothesis of serial monogamy. Best mate selection by the females and the opportunity of new matings for both sexes influenced the reproductive success of this species.
Braz. J. Biol., 67(1): 161-165, 2007
161
Mating system of the amazonian cichlid
angel fish, Pterophyllum scalare
Cacho, MSRF.
a
*, Yamamoto, ME.
a
and Chellappa, S.
b
a
Postgraduate Programme in Psychobiology, Department of Physiology, Universidade Federal do Rio Grande do Norte,
Av. Salgado Filho, 3000, Lagoa Nova, CEP 59072-970, Natal, RN, Brazil
b
Postgraduate Programme in Aquatic Bioecology, Universidade Federal do Rio Grande do Norte,
Praia de Mãe Luiza, s/n, Via Costeira, CEP 59014-100, Natal, RN, Brazil
*e-mail: socorrocacho@ufrnet.br
Received June 10, 2005 – Accepted August 24, 2005 – Distributed February 28, 2007
(With 2 figures)
Abstract
The species, Pterophyllum scalare distinguishes itself by its breeding behavior, involving competition for territory,
sexual partners, courtship and parental care. The purpose of this study was to identify the mating system adopted by
this species of fish. Twenty males and twenty females were observed under semi-natural and experimental conditions
to test the hypothesis of serial monogamy. Under semi-natural conditions, after the third breeding cycle, the couples
changed mates. Under experimental conditions, the couples changed partners after the first breeding cycle. Under ex-
perimental conditions, mate recognition was investigated through the preference of the females, indicated by the time
they spent with the males. The females were available or not for courtship from new males, depending on their aggres-
siveness or submission. The larger and more aggressive males obtained new mating opportunities while the submissive
males were rejected by the females. The mated fish were aggressive towards intruders in the presence of the mate,
protecting their pair bond. In the interval between breeding cycles, the couples did not display aggression towards in-
truders, confirming the hypothesis of serial monogamy. Best mate selection by the females and the opportunity of new
matings for both sexes influenced the reproductive success of this species.
Keywords: Cichlidae, reproductive behavior, mate selection, serial monogamy.
Sistema de acasalamento no ciclídeo amazônico, Pterophyllum scalare
Resumo
A espécie Pterophyllum scalare se destaca pela complexidade de seu comportamento reprodutivo, envolvendo com-
petição por território e parceiros sexuais, corte, acasalamento e cuidado parental. Este trabalho teve como objetivo
identificar o tipo de sistema de acasalamento adotado pelos peixes desta espécie. Vinte machos e vinte fêmeas foram
observados nas situações seminatural e experimental para testar a hipótese de monogamia serial. Em situação semina-
tural, após o terceiro ciclo reprodutivo, os casais mudaram de parceiros, enquanto que, em situação experimental, os
casais mudaram de parceiros a partir do primeiro ciclo reprodutivo. Em situação experimental foi investigado o reco-
nhecimento do parceiro, pela permanência das fêmeas que se mostraram disponíveis ou não à corte de novos machos,
em função da agressividade e submissão deles. Machos maiores e mais agressivos obtiveram novas oportunidades de
acasalamento e machos submissos foram rejeitados pelas fêmeas. Os peixes acasalados foram agressivos a intrusos na
presença do parceiro, protegendo a ligação do par. No intervalo entre os ciclos reprodutivos, os pares não mostraram
agressão a intrusos, confirmando a hipótese de monogamia serial. A escolha do melhor parceiro pelas fêmeas e a opor-
tunidade de novos acasalamentos para ambos os sexos influenciaram o sucesso reprodutivo desta espécie.
Palavras-chave: Cichlidae, comportamento reprodutivo, escolha de parceiro, monogamia serial.
1. Introduction
Monogamous animals establish short and long term
relationships during one or more successive breeding sea-
sons (Krebs and Davies, 1996). In monogamous pairs, the
male contributes to the reproductive success of the couple
by defending the territory where the female feeds or takes
care of her offspring (Wickler and Seibt, 1985).
In fish, the pair bond usually endures for just one
spawning and monogamy is maintained in only a
Cacho, MSRF., Yamamoto, ME. and Chellappa, S.
Braz. J. Biol., 67(1): 161-165, 2007
162
small number of species, since the vast majority is po-
lygamous (Takegaki and Nakazono, 1999). Among
cichlids, some species are monogamous, for example
Cichlasoma citrinellum, (Rogers, 1995) and Cichlasoma
nigrofasciatum (Lampecht and Reblan, 1997).
The angel fish, Pterophyllum scalare Lichtenstein,
1823 has distinguished itself by the complexity of its
reproductive behavior, involving competition for terri-
tory and sexual partners, courtship, mating and parental
care. In this species, the couple is greatly involved with
the offspring, mainly during the initial breeding phase
(Cacho et al., 1999).
Angel fish, P. scalare couples could be considered
monogamous, since the individuals tend to mate with a
single partner. However, it is probable that they do not
maintain a strict monogamy since the males tend to
abandon the females (Cacho et al., 1999). The females
demonstrate that they are available for courtship from
other males, often mating sequentially with new part-
ners. Thus, the objective of this study was to identify
the type of mating system adopted by these fish, testing
the hypothesis that the couples have serial monogamous
relationships, with males often deserting their partners
in search of other females for mating. Three predictions
can be made from this hypothesis: the males may aban-
don the females with their offspring after mating; after
deserting the females, the males may mate with other fe-
males; the females, when abandoned, protect their young
until independence and may accept new mating partners
in a new cycle.
2. Materials and Methods
The observations were made in the Ichthyology
Laboratory of the Department of Oceanography and
Limnology of the Federal University of Rio Grande do
Norte, Natal, Brazil in 2003 and 2004.
2.1. Acquisition and maintenance of the fish
Twenty eight-month-old males and twenty females
of the angel fish, P. scalare species from the Amazon
Basin, acquired in an ornamental fish commercial es-
tablishment, were used in the study. In the laboratory,
the fish were stocked in 1,000 L asbestos tanks. They
were maintained at a temperature of around 27 °C, pH
between 6.8 and 7.0 and dissolved oxygen ranging from
7.7 and 8.0 mg.L
-1
. Physical-chemical parameters such
as pH and temperature were checked daily. The airing
of tanks was done through a system of plastic hoses and
an aerator. The fish were examined weekly to verify
and prevent diseases. Diet corresponded to 5% of body
weight and consisted of Artemia salina Linnaeus, 1758,
and cichlid ration, fed daily ad libitum, and provided
with constant aeration. Precautions were taken to mini-
mize disturbance to the fish and the natural photoperiod
of 6 to 18 hours was maintained in the laboratory.
After a 2 month acclimatization and maintenance
period, the fish, which weighed between 9 and 30 g for
the males and between 8 and 15.7 g for the females and
total lengths ranging from 85 to 145 mm for the males
and from 80 to 128 mm for the females, were select-
ed for observation. Biometry was performed to record
weight, height and total length of the fish used. The fish
were considered small if their total length was less than
95 mm; intermediate with a total length between 95 and
120 mm and large those whose length was greater than
120 mm, in accordance with previous studies (Cacho
et al., 1999; Chellappa et al., 1999a).
2.2. Procedures
The fish were observed under semi-natural and ex-
perimental conditions by the animal focal and sequence
methods (Sabino, 1999).
2.3. Testing under semi-natural conditions
Breeding was observed in the laboratory under semi-
natural conditions, similar to those encountered in na-
ture. In their natural habitat, these fish live along river
margins in clear water with dense aquatic vegetation,
and are usually found among the roots of these plants.
In the laboratory, the fish were placed in a glass aquar-
ium (1.20 x 0.58 x 0.50 m), with a bottom of crushed
river stone and sand, adorned with different species of
Amazonian aquatic plants, with large (Anubia sp. and
Echinodorous amazonensis, Fasset) and narrow leaves,
such as Valisneria gigas, Graebener and Elodia sp.
Ten angel fish specimens were used in this test: six
males and four females of approximately 10 months of
age. A greater number of males than females were used
to stimulate mating competition.
The fish were maintained under semi-natural condi-
tions for two months (from August to September) and ob-
served for 30 days for 1 hour each day. Breeding of ran-
domly-formed pairs was observed during one breeding
cycle (a cycle of approximately 21 days, corresponding
to the period between territory occupation and independ-
ence of the offspring). At the end of the first breeding cy-
cle, the couples were marked by clipping their dorsal and
pelvic fins so that by identifying the fish individually, the
stability of the existing pair bond or the formation of new
pairs can be observed. The same fish were monitored for
five additional breeding cycles. The monitoring of the
six cycles took place over a nine-month period.
2.4. Testing under experimental conditions
To investigate the stability of the pairs under experi-
mental conditions, the fish were placed in glass aquari-
ums where tests were performed to recognize the partner
and the intruder.
2.5. Mate recognition test
Twelve males and six females were used to recog-
nize the partners by the length of time spent by the fe-
male with a male. The fish were placed in six aquariums
(70 x 40 x 40) and six tests performed, each with six
observations. Individuals that had formed pairs in a pre-
vious breeding cycle were used. In each aquarium the
male that had already mated with the female during the
Mating system of the angel fish
Braz. J. Biol., 67(1): 161-165, 2007
163
first breeding cycle was placed along with a stranger. The
males were observed under neutral conditions (a situa-
tion in which no territory had been established by either
fish). The female was introduced after 48 hours.
Previous partners of intermediate size (total length
between 95 and 120 mm) were used in these tests, along
with small male strangers (total length less than 95 mm);
previous partners with male strangers of the same size
(total length between 95 and 120 mm) and previous part-
ners with larger male strangers (total length greater than
120 mm) with N = 6 for each category. All the fish were
at an optimal breeding age of less than 1 year.
The following behavior was observed: threatening
(when the fish kept its head down, fins expanded and
floor of the mouth retracted, bending its body towards the
opponent); attacking (sudden movement towards the op-
ponent); biting (the act of compressing or injuring the op-
ponent with the teeth) retreating (when one fish distanced
itself approximately 15 cm from the other); submission
(when the fish retracted its fins, remained motionless,
keeping its head up and displaying darker coloration);
escape (when one fish stopped confronting the other
and rapidly left the area) and female preference (defined
by the time that a female remained motionless within a
10 cm radius of one of the males or swims side by side
towards the substrate to spawn (Chellappa et al., 1999b).
2.6. Intrusion test
This test was applied to test the stability of the pair
during the reproductive period and the response to in-
truders in the interval between breeding cycles. Six cou-
ples of angel fish with a previously established bond and
twelve intruders (six males and six females) were used.
Observations were performed in six glass aquariums
(70 x 40 x 40 cm), each containing one couple. To test the
stability of the bond, a male intruder was introduced and
the reaction of each couple was observed. Subsequently,
the male intruder was removed and substituted by a fe-
male intruder, with the reaction of the couple once again
observed. The intrusions were repeated three times to
investigate the behavior shown by the residents in both
situations (couple with male intruder and couple with fe-
male intruder). Later, each couple was separated and a
male intruder was introduced with the female resident,
followed by a female intruder with the male resident
in order to observe the behavior shown by the resident
animals. The introductions were repeated three times to
investigate the behavior of the residents in both situa-
tions (separated male with female intruder and separated
female with male intruder). The behavior observed was:
threatening, attacking, biting, distancing, submission, es-
cape and female preference (of the female resident with
the male resident and with the male intruder; of the male
resident with the female resident and with the female in-
truder), all previously described.
2.7. Statistical analysis
The statistical tests were performed with SAS
software (Howell, 1992), using analysis of variance
(ANOVA). Tukey’s test and Student’s t-test were used to
identify differences between the treatments used.
3. Results
3.1. Stability of the pairs under semi-natural conditions
The results obtained under semi-natural conditions
confirm the tendency of the couples to accept new mat-
ing partners. In this situation, 50% of the couples did not
maintain the pair bond after the first breeding cycle. The
remaining 50% maintained the bond during the second
and third breeding cycles. After the first breeding cycle,
50% of the males abandoned the females with their off-
spring. After the third cycle, none of the couples main-
tained the bond. All the males abandoned the females
with their offspring and mated with other females. The
females protected the larvae until they became independ-
ent and subsequently accepted new mating partners.
Under semi-natural conditions, only two of the six
males observed mated five times, one managed to mate
four times, another three times and two mated twice.
Two of the females observed mated six times, one mated
five times, another four times and two females, probably
needed longer preparation time for a new egg-laying cy-
cle, and as a result had fewer matings. The males that
had fewer matings were those that had less success when
competing for females.
3.2. Stability of the pair under experimental conditions
3.2.1. Mate recognition test
This test is not conclusive in affirming if the females
recognize their mates or not. The criteria used by the fe-
males to remain with one of the males was the aggres-
siveness or submission displayed by the males and not the
previous bond. During the test, the previous mates were
more aggressive than the strangers, only when the latter
were smaller. In this situation, aggression frequency of
the previous mates was greater than that of the strangers
with significant differences between them (ANOVA,
t-test, t = 8.08; p <0.0001). When the previous mates
and strangers were of equal size, they were equally ag-
gressive. The differences related to the aggressiveness of
the males were not significant (ANOVA, t-test, t = 0.86;
p = 0.39) However, when the previous mates were small-
er, they were significantly less aggressive than the stran-
gers (ANOVA, t-test, t = 3.34; p = 0.0019).
A significant correlation was observed between
the aggressiveness of the males and female preference
(Pearson, r
2
= 0.4876; p = 0.0001). Analyzing the com-
parisons between mean female preference for previ-
ous partners and smaller, equally sized and larger male
strangers (Figure 1), it was observed that the females
had a significantly greater mean preference for previ-
ous mates only when the male strangers were smaller
(ANOVA, previous mates: t-test: t = 15.58; p <0.0001).
When the male strangers were of equal size there were
no significant differences in female preference (ANOVA,
equal strangers: t-test, t = 0.52; p = 0.61). On the other
Cacho, MSRF., Yamamoto, ME. and Chellappa, S.
Braz. J. Biol., 67(1): 161-165, 2007
164
hand, when the strangers were larger, mean female pref-
erence for the strangers was significantly greater than
that with previous partners (ANOVA, larger strangers:
t-test = -4.83; p <0.0001).
We compared the mean frequencies of submission
behavior displayed by the males during the mate recogni-
tion test with strangers of different sizes. It was observed
that previous partners were only not submissive when the
strangers were smaller. The submissive behavior in this
case was recorded only for the strangers with significant
differences in relation to the previous partners (ANOVA,
t-test, t = -3.83; p = 0.0005). However, when the previous
mates and the strangers were of equal size, the previous
partners were more submissive than the strangers with
significant differences between them (ANOVA, t-test,
t = 2.30; p = 0.024). Moreover, when the previous part-
ners were smaller than the strangers, they were sig-
nificantly more submissive (ANOVA, t-test, t = 4.45;
p <0.0001).
Data analyses of the results of recognition tests with
smaller, equal sized and larger mates showed significant
correlation, inversely proportional between female pref-
erence and submissive behavior of the males (Pearson,
r = -0.6604; p <0.0001). The best predictor of the length
of time that a female stays away from the male was his
display of submissiveness.
3.2.2. Intruder test
The intruder test showed the reaction of the couples
to intruders during breeding. At the beginning of the re-
productive cycle, it was observed that the females stayed
a significantly longer mean period of time with their
mates than they did with intruder males (ANOVA, t-test,
t = 12.99; p <0.00001), Figure 2). The males also stayed a
significantly longer mean period of time with their mates
than they did with female intruders (ANOVA< t-test, t =
2.80; p <0.00839).
The aggressiveness of the males when faced with
intruders of either sex during the breeding cycle was
greater than that displayed by the females, with mean
values for aggressiveness equal for intruders of both
sexes (ANOVA, t-test, t = 0.3063; p = 0.7612). The fe-
males were as aggressive as the males in the presence of
other females, with mean values significantly different
from those observed in the presence of males (ANOVA,
t-test, t = -3.414; p = 0.0016). At the end of the breeding
cycle, there was no significant correlation between the
aggressiveness of couples faced with intruders (male or
female) and during the interval between the cycles the
pairs were not aggressive towards intruders of the op-
posite sex when separated.
4. Discussion
The results showed that angel fish couples adopted
serial monogamy, both under semi-natural and experi-
mental conditions. Under semi-natural conditions, the
fish mated and remained with their partners for one to
three breeding cycles. From the third cycle, the pair bond
was not maintained and both fish sought new mating
partners. Under experimental conditions, the couples did
not maintain the pair bond beyond the second breeding
cycle, acquiring new partners. In serial monogamy, as
described by Gould and Gould (1989), after investing in
the offspring, the partners seek new mating opportuni-
ties. The results of this study are in accordance with this
description.
Under semi-natural conditions, the duration of the
pair bond up to the third cycle was possibly motivated by
the presence of the offspring and by the need to protect
them. Abandoning the females must be considered as a
male strategy to increase their reproductive success, by a
greater number of matings. The females after independ-
ence of the young, also accept new courtship and mating.
However, under no circumstance was a male seen mat-
ing with more than one female or a female accepting the
courtship of more than one male.
In angel fish, the levels of aggression towards in-
truders suggest that there is a bond between the pair.
0
5
10
15
20
Small Same Larger
Size of the stranger
Mean females preference with
previous partners (min)
Figure 1. Mean and standard deviation of time (min) of fe-
males spent with the male during the recognition tests be-
tween the partner and smaller strangers: p <0.0001; of equal
size; p = 0.61 and larger: p <0.0001, using Tukey’s test.
0
5
10
15
20
25
30
Female
resident
Female
intruders
Male
resident
Male
intruders
Conditions of the males and females
Preference of the males and
females (min)
Figure 2. Preference (mean and standard deviation) of the
males and females (minutes spent with the opposite sex) in
the presence of intruders: males faced with female intrud-
ers (p = 0.00839) using Student’s t-test; females faced with
male intruders (p <0.00001), using Student’s t-test.
Mating system of the angel fish
Braz. J. Biol., 67(1): 161-165, 2007
165
However, the attributes of the male may motivate a fe-
male to substitute her partner for another more suitable
one at the end of the breeding cycle. Under experimen-
tal conditions, the females rejected their partners when
they were offered better mating opportunities. In this
case, mate choice was influenced by the body size and
aggressiveness of the males. The submissive males were
rejected by the females and consequently did not manage
to maintain the pair bond. It is likely that there is a possi-
bility of pairing with affected female breeding decisions.
A better mate choice on the part of the females must be
considered adaptative, since these mates bear genes that
may improve the viability of their descendents (Nicoleto,
1995).
Pair stability in the angel fish species was also tested
by the resident-intruder paradigm. The aggressive re-
sponse of the mated fish towards intruders at the begin-
ning of the breeding cycle may have been stimulated
by the situation of intense sexual competition and the
presence of the partner can be considered as a trigger-
ing and intensifying factor of the aggression displayed
by these fish towards intruders. These results are sup-
ported in studies by Huntingford (1979) of three-spined
stickleback, Gasterosteus aculeatus and by Walter and
Trillmich (1994) of the cichlid Lamprologus ocellatus.
Aggressiveness towards intruders at the onset of the
breeding cycle may also be understood as a protective
measure for the pair bond, maintained by the pressure
of the presence of the partner, since during the interval
between breeding cycles and when the couples were sep-
arated, there was no aggression towards intruders, con-
firming the hypothesis of serial monogamy in these fish.
The contribution of the males is important for breed-
ing success in angel fish, since these fish inhabit very
competitive environments, where it is extremely diffi-
cult for the females to protect the eggs by themselves.
Additionally, males that cooperate with parental care are
preferred by females and are thus successful in breed-
ing.
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... Pterophyllum scalare lives in groups and starts territorial defence during the reproductive season (Cacho et al., 2007;Yamamoto et al., 1999). However, in aquaria, both adults and juveniles engage in ...
... Following the cichlid reproductive pattern, P. scalare is a substrate brooder, that is, individuals choose clean surfaces as a spawning site, where adhesive eggs are laid (Bergmann, 1968;Cacho et al., 1999;Chien & Salmon, 1972;Sladden, 1937). They are serially monogamous, that is, pairs bond and biparental care takes place for each breeding; after that, male and female can bond to different partners (Cacho et al., 2007). The reproductive repertoire of P. scalare encompasses social rank organization and territory establishment, courtship, mate choice, spawning and brood care (e.g., Bergmann, 1968;Cacho et al., 1999Cacho et al., , 2006Chien, 1973;Chien & Salmon, 1972;Sladden, 1937;Yamamoto et al., 1999). ...
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... The evolution of mating systems in cichlid fishes has proceeded from monogamy with bi parental care to polygamy with maternal care, with a number of variations on these two themes. 25 In substrate brooders the parents maintain their brood on or close to the substrate until the young become independent. On the other hand, in mouth brooders the parents carry their offspring in their mouth until the young become independent. ...
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Stressors of various nature impact fish reproduction from the physiological to the behavioural levels. Seasonal changes such as drought and pluvial (rainfall) variations have a profound effect on reproduction of semiarid tropical fishes. In the semiarid tropical region of Brazil the factors that influence fish reproduction are changes in rainfall regimes and drought. These environmental changes can either stimulate or inhibit reproduction in fishes. Information on these fundamental variables on reproduction can help management and conservation of tropical fishes. Information on fish reproduction also is an important factor for understanding the freshwater ecosystems of the semiarid region. This paper is a narrative review on the effects caused by rainfall and drought on reproduction of some cichlids and an annual fish from the semiarid region of Brazil. During the breeding period cichlid fishes demonstrate aggressive behavior and dominant fishes often get priority of access to territories and mates. On the other hand, the annual fishes have rapid growth and gonadal development to complete their life cycle within a short span of time. Fishes which are subjected to varying pluvial pressures have characteristic life history patterns.
... The first, and one of the most obvious factors, is postnatal parental care, and in particular biparental care. For example, mucus feeding has often been reported in the Heroini cichlid tribe, which also display biparental care of offspring (Keenleyside 1981;Schütz and Barlow 1997;Cacho et al. 2007;Pires et al. 2015;Satoh et al. 2018). However, in contrast, in the Geophagini, maternal only parental care is the common mode of parental care, and there are no reports of mucus feeding behavior in this group (Burchard 1965;Keenleyside 1981;Rodrigues et al. 2012). ...
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Across teleost fishes, a wide range of parental care strategies have been observed. However, despite this large variation in parental care behaviors, postnatal nutritional provisioning has rarely been documented in fishes. In other taxa, anecdotal evidence suggests that nutritional provisioning of offspring via mucus secretion by parents may occur, although this phenomenon has received little attention from evolutionary biologists, especially in fishes. To address this knowledge gap, we investigate the intra- and interspecific differences, functions, and the costs and benefits of provisioning behaviors that have potentially evolved independently in different teleost clades. Furthermore, we review and discuss within an ecological and evolutionary context, the anecdotal reports and limited available empirical evidence that shows support for mucus provisioning in teleost fishes.
... Pterophyllum scalare is one of the most important ornamental Teleostei species in the aquarist trade. Although P. scalare molecular genetics (Schneider et al. 2015;Li et al. 2016), reproduction and growth (Cacho et al. 2007;Ortega-Salas et al. 2009;Kacperczyk et al. 2011;Kasiri et al. 2012) have been investigated previously, and a number of studies have been dedicated to its behavior (Gómez-Laplaza andMorgan 2003, 2005;Barreto et al. 2006;Gómez-Laplaza 2009;Agrillo et al. 2012;Gómez-Laplaza and Gerlai 2015), only one study has attempted to quantify cells in the nervous system of this species (Sakamoto et al. 1999). Thus, potential correlations between environmental changes and telencephalic cell proliferation in this Amazon species in captivity are so far unknown. ...
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Abstract Based on previous evidence that environmental enrichment is associated with telencephalic cellular proliferation and that stable visuotopic tectal circuits are essential for discrimination of placement and identity of stationary or moving objects in the visual field, differential plasticity is expected in these areas. Here we tested this hypothesis in the Angelfish (Pterophyllum scalare), a species of ornamental fish with great value in the aquarist trade. We hypothesized that total telencephalic cell number would increase under the influence of an enriched environment whereas the tectal cell number would not change. To test this hypothesis, 12 aquaria of 80 liters each were used, with six fish in each. The aquaria had either an enriched environment (EE) including stones, plants, sand and the presence of another fish from the Loricariidae family for interspecific social interaction, or an impoverished environment (IE), in which stimuli were limited to intraspecific interactions in a barren aquarium. After 62 days, six fish from each treatment were euthanized, and their brains were fixed and sectioned for Nissl staining. Then, stereological estimates of the total number of cells were performed. The fish showed no differences in weight gain, feed conversion ratio, condition factor, specific growth rate or survival. Animals kept in the enriched environment had a higher number of total telencephalic cells than animals kept in the impoverished environment (1,038,555 ± 65,357 vs. 758,331 ± 51,587, bilateral t-test, p = 0.008), but a similar number of tectal optical cells (EE 424,097 ± 29,914 vs. IE 471,409 ± 50,850, bilateral t-test, p = 0.445752). We concluded that cell proliferation in response to stimulation by the enriched environment is differentially expressed in the telencephalon and tectal areas of Pterophyllum scalare. Keywords: Pterophyllum scalare, optic tectum, telencephalon, neuroplasticity, stereology, optical fractionator.
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In this study, the larval development of Cyrtocara moorii was examined morphologically and compared with other Cichlidae species. The important morphological changes and critical developmental stages that C. moorii larvae undergo were determined during the process from hatching up to 20 days. It was observed that the larvae had a large yolk sac, transparent bodies, and undeveloped fins in the first days. Important developmental events such as eye development, mouth opening, onset of free swimming behavior, fin formation, and increased pigmentation were recorded. It was determined that the larvae started free swimming between 6-9 days, the yolk sac was completely depleted on the 10th day, and the larval development was completed, reaching the juvenile form on the 15-20th days. When the larval development of C. moorii was compared with other Cichlidae species, species-specific differences were observed as well as some similarities. It is thought that these differences may be related to the ecological adaptations, reproductive strategies, and evolutionary history of the species. It is suggested that future research should comparatively examine the larval development processes of more Cichlidae species and elucidate the mechanisms underlying this diversity.
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Induced spawning experiments on fresh water angelfish, Pterophyllum scalare was carried out for the first time using Ovaprim (sGnRH+ Domperidone). The optimum dose of Ovaprim was standardized based on three experiments, viz., fecundity (relative fecundity) at different doses, response time (hrs) at various doses and fertilization rate at different doses. Maximum fecundity (665.66) obtained at the dose of 0.35ml/kg of body weight and a significant relation was observed between doses and response time (hrs.) of spawning at 1% level. Lower breeding response time was recorded at this dose. Along with this, in different setup, appropriate environmental conditions for angel fish will be monitored.
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Conflicts of interest within and between the sexes are important processes leading to variability in mating systems. The behavioral interactions mediating conflict are little documented. We studied pairs and harems of the snail-shell inhabiting cichlid fish Lamprologus ocellatus in the laboratory. Due to their larger size, males controlled the resource that limited breeding: snail shells. Males were able to choose among females ready to spawn. Females were only accepted if they produced a clutch within a few days of settling. When several females attempted to settle simultaneously the larger female settled first. Females were least aggressive when guarding eggs. Secondary females were more likely to settle when the primary female was guarding eggs. In established harems females continued to be aggressive against each other. The male intervened in about 80% of female aggressive interactions. Male intervention activity correlated with the frequency of aggression among the females in his harem. The male usually attacked the aggressor and chased her back to her own snail shell. When a male was removed from his harem, aggression between females increased immediately and usually the secondary female was expelled by the primary female within a few days. Time to harem break-up was shorter the more mobile the primary females' young were and did not correlate with the size difference between harem females. Male L. ocellatus interfere actively in female conflict and keep the harem together against female interests. Female conflict presumably relates to the cost of sharing male parental investment and to the potential of predation by another female's large juveniles on a female's own small juveniles.
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Reproductive behavior and mate fidelity of the gobiid fish,Valenciennea longipinnis, were studied on the coral reef at Sesoko Island, Okinawa, Japan. These fish usually live in pairs, not only foraging together for benthic animals in sandy areas, but also constructing several burrows within their home range. Before spawning, both fish, although mainly the male, constructed a mound, piling up dead-coral fragments, pebbles, shells, sand and algae onto one of the burrows. After spawning an egg mass on the ceiling of the burrow, the female stayed outside and continued the construction and maintenance of the mound for 3–5 days until hatching, while the male tended the eggs inside. Mate guarding of females seemed to prevent males from monopolizing several females. Although some pairs showed mate fidelity through several spawnings, more than half of the pairs broke up after only one spawning. The pair bond was broken by mate desertion and the disappearance of each sex. Both sexes preferred larger spawning partners; larger females spawned more eggs and larger males provided better egg care. Mate desertion occurred when larger potential mates, relative to the current partner, became available. The frequency of solitary individuals was higher in males than in females, resulting in females deserting their mates more often than males. Two factors seem to have facilitated mate desertion: (1) occurrence of size mis-matched pairing and (2) overlapping home ranges.
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Conflicts of interest within and between the sexes are important processes leading to variability in mating systems. The behavioral interactions mediating conflict are little documented. We studied pairs and harems of the snail-shell inhabiting cichlid fish Lamprologus ocellatus in the laboratory. Due to their larger size, males controlled the resource that limited breeding: snail shells. Males were able to choose among females ready to spawn. Females were only accepted if they produced a clutch within a few days of settling. When several females attempted to settle simultaneously the larger female settled first. Females were least aggressive when guarding eggs. Secondary females were more likely to settle when the primary female was guarding eggs. In established harems females continued to be aggressive against each other. The male intervened in about 80% of female aggressive interactions. Male intervention activity correlated with the frequency of aggression among the females in his harem. The male usually attacked the aggressor and chased her back to her own snail shell. When a male was removed from his harem, aggression between females increased immediately and usually the secondary female was expelled by the primary female within a few days. Time to harem break-up was shorter the more mobile the primary females' young were and did not correlate with the size difference between harem females. Male L. ocellatus interfere actively in female conflict and keep the harem together against female interests. Female conflict presumably relates to the cost of sharing male parental investment and to the potential of predation by another female's large juveniles on a female's own small juveniles.
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The reactions of 34 female and 32 male three‐spined sticklebacks to a conspecific were observed in the month before the breeding season. Factor analysis indicated that the organization of the response in the two sexes was very similar; in both cases, axes labelled “aggression,” “threat,” “curiosity,” and “sex” emerged, with male fish having significantly higher scores on the first factor and females on the second. Any theory of the causes of aggression in sticklebacks should accommodate these facts.
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This study evaluated the offspring viability prediction of the condition-dependent and Fisherian models of female choice in the guppy. Families of full-sibling females were bred with the male they preferred or did not prefer in a choice experiment. The physical condition, sexual behaviour and coloration of the offspring were evaluated. There were no significant differences between offspring attributable to the type of sire. However, there were significant family and sire-type by family interactions for physical condition, male mating behaviour and coloration. These significant effects indicate that consistency within families may be due to genetic effects. Genetic analyses indicate that genetic variation probably exists for prolonged swimming performance, physical condition and display rate. The results of this study and other studies on other fish have shown that these measures of constitution are correlated with components of viability. These results are interpreted in the framework of the condition-dependent and Fisherian models of female choice.
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In isolated pairs of the biparental convict cichlid (Cichlasoma nigrofasciatum) caring for fry, pairbonds can be broken by removal of the fry. Within three hours, the mates of many pairs become so mutually aggressive that the female finally flees from her larger mate, who chases her. The pairbond is mended within seconds upon re-introduction of the fry. Yet removal of young leaves some pairs little or not at all affected. They seem to have more stable pairbonds. Multiple regression of data from 39 pairs on a quantitative measure of pairbond destruction revealed support for the so-called parity-hypothesis, which holds that a cichlid pair is compatible only when the female's aggressiveness compensates for her smaller size. The size of the female relative to the male's, and her aggressiveness relative to his in the undisturbed situation, proved positive predictors of pair stability in the fry stage. Thus the same factors which have earlier been shown to favour pair formation in other biparental cichlids seem also responsible for pair stability in a later stage of the reproductive cycle.
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Territorial interactions between pairs of size mismatched, sexually mature male angelfish Pterophyllum scalare were investigated in three different conditions: with the larger fish resident (the large resident condition), with the smaller fish resident (the small resident condition) and in a neutral territory (the neutral condition). In the two resident conditions, approximately half of the intruders had previously held territories and half had not. In all categories of fight, one fish showed submissive postures and lost the fight; eventual losers performed both attack and threat at a lower rate than eventual winners. Attack rate declined as the encounter progressed, while rate of performance of threat postures increased. In fights on neutral territories, the larger fish won all fights. In all fights with a resident-intruder asymmetry, the resident fish won the encounter, regardless of relative size. In eventual winners but not in eventual losers, levels of attack were lowest in the neutral encounters. In the small resident condition, levels of attack (corrected for activity of the resident) were lower in intruders that had previously held a breeding territory. Relative size influenced behaviour shown during fights, in that overall intensity was correlated negatively with size differential in all conditions. Thus although prior residence is the primary determinant of the outcome of territorial encounters in this species, both relative body size and prior possession of territory also influence the nature of the interaction.