Fry Patterns in the South-American Catfish Genus Corydoras
ABSTRACT: The fry pattern of aquarium-bred species
of the South-American catfish genus Corydoras,
contribute to discriminate between species of the
so-called 'acutus'- group, showing a greyish adult
Identifying many of the Corydoras species
can be extremely difficult and none more so than
the long-snouted members in, the sosh adult colour
patterns. Although there are about twenty species
within this group, seven species were successfully
bred under controlled aquarium conditions. It is
demonstrated that the colour patterns change during
the fry's three to four month period to adulthood
and maturity. It was thought that juvenile colour
patterns might be an additional character with which
to differentiate between the different species.
This was demonstrated earlier with two of the short-snouted
species of Corydoras: C. rabauti (La
Monte, 1941) and C. zygatus (Eigenmann &
Allen, 1942). They were considered as one species
by many authors, until breeding experiments by the
author (Fuller, 1983a) revealed that these two species
possessed totally different body colour patterns
during their larval stages.
The seven species involved are: C. acutus
(Cope, 1872): 4 males-2 females, C. blochi blochi
(Nijssen, 1971): 2 males-4 females, C. septentrionalis
(Gosline, 1940): 3 males-2 females, C. treitlii
(Steindachner, 1906): 2 males-2 females, C. amapaensis
(Nijssen, 1972): 3 males-i female, C. ellisae
(Gosline, 1940): 3 males-3 females, and C. stenocephalus
(Eigenmann & Allen, 1942): 2 males-2 females,
all obtained from aquarium fish importers. The fry
colour patterns are recorded in line drawing form,
and were made when the fry had reached the age seven
days and twenty-eight days respectively, and at
the time when they reached the pattern of an adult
female. The adult female pattern was chosen as the
datum point at which fry are deemed to have reached
their adult coloration. (Figs. 1-7).
1 - 7. Adult females of seven long-snouted species
of Corydoras: C. acutus, C. blochi blochi,
C. septentrionalis, C. treitlii, C. amapaensis,
C. ellisae, C. stenocephalus.
Water conditions of
the tanks during the time of spawning of seven
pH (Pondus hydrogenii) = acidity! alkalinity;
neutral measurement = 7.
GH (General hardness = total hardness, measured
in degrees dH) is a measure of all dissolved
salts. 0-5 = soft, 6–10 = medium, 11-20
= medium hard = medium hard.
KR (Carbonate hardness) a measure of (bi)carbonates.
Temperature recorded in degrees Celsius
All seven species were bred in aquariums of similar
size (length 45cm, width 35cm, height 30cm), with
similar furnishings. All seven species spawned in
a very similar way following a pre-determined sequence
of events.The sexual activity starts with a male
of the species actively pursuing one of the females
until she submits to his attentions, at which point
she reverses rolls and pursues the male. The male
then takes on a quivering arched sideways stance,
allowing the female to push headfirst into the side
of his body, at a point just above and slightly
in front of the ventral fins. At the moment of contact
the male grips the female by clamping across her
barbels with his pectoral fin spine, holding her
firmly against the side of his body. The grip is
maintained until the male has stopped quivering,
this grip being referred to as the 'mating clinch'.
Both fish then separate with the female actively
cleaning various sites around the aquarium before
depositing her eggs, the male being in close attendance
all the time and ready to mate. During the mating
clinch which may take place at all levels in the
aquarium from the substrate, in amongst the plants
and spawning mops to mid water, the female will
deposit her eggs into a pouch made by pressing her
ventral fins together. When a pair of fish mate
in mid water and after the male has stopped quivering,
they drift to the substrate where they may rest
for several seconds before separating. No method
has yet been devised to successfully determine how
and at what point the eggs are fertilised.
In each of the seven species spawning activities
the none participating fish were left in the aquariums
with the spawning pairs and in all seven cases the
none participating females showed no interest at
all. The males however persisted with their attempts
to mate with the active female, in all seven cases
the first male selected by the female made sure
that he was always between her and the other pursuing
males. With all seven species after spawning activity
had ceased the adult fish were removed.
None of the seven species (Table I) showed preference
as to the level at which to deposit their eggs,
with eggs being deposited close to the substrate
and to within twenty millimetres of the surface.
The fry of all seven species take from between eighty-five
to one hundred hours to hatch (Table II) depending
on the water temperature. Although the temperature
is not a controlling factor it does have a slight
bearing on the developing embryos. For example,
C. acutus that spawned at 21,1 deg C. and
took between ninety and one hundred hours for all
of the fry to emerge. When spawned at 23,9 deg C.
they would hatch in eighty-five to ninety five hours,
but at 26,5 deg C. they still take between eighty-five
and ninety five hours to hatch. Of the seven species
(Table II) bred five, C. acutus, C. ellisae,
C. septentrionalis, C. stenocephalus,
and C. treitiii, preferred to deposit their
eggs in either Java Moss or the woollen spawning
mops. The remaining two, C. amapaensis, and
C. blochi blochi divided their eggs evenly
between the tank sides and the clumps of Java Moss.
The growth rates shown inTable
Ill are an average taken from ten specimens to the
nearest 0.5 mm.
Details of egg production of seven Corydoras
species. Per column: total number of eggs, diameter,
number of eggs laid at a time, adhesion, and time
to hatch. The adhesion (how well they stick) is a
value of personal rating out of 10.
laid at a time
Figs. 8 - 14. Aged 7 days;
seven long - snouted species of Corydoras:C.
acutus, C. blochi blochi, C. septentrionalis, C.
treitlii, C. amapaensis, C. ellisae, C. stenocephalus.
Fry growth rates of seven Corydoras species,
showing their total lengths per period of time.
colour reached in
- 10 weeks
- 8 weeks
- 9 weeks
- 10 weeks
- 10 weeks
By the seventh day after hatching the fry of all the
seven species have developed their own distinctive
colour patterns. (Figs. 8-14). Five of the species
(C. acutus, C. amapaensis, C. blochi blochi C.
septentrionalis and C. stenocephalus) show patterns
that are rather similar to each other. C. ellisae
and C. treitili have exactly the same patterns
as each other, differing from the other live species
by having no markings along the sides of the body.
As the fry of the seven species grow and develop,
their colour patterns are constantly changing and
reach a maximum intensity by the time they are four
to six weeks old. The pigmentation forms into irregular
markings that cover most of the fishes body, giving
all seven species a dark blotchy appearance especially
when viewed from above, as shown in Figs. 15-21. From
six weeks onward the ever changing colour patterns
of the fry, start to develop into the more recognisable
patterns of the adult female.
By the time the fry of all seven species are aged
between eight and ten weeks old, they will all have
attained the colour pattern shown by adult females,
as demonstrated in Figs. 1-7.
The effect of water temperature on all the fry's growth
rates, is very much the same as on egg development.
More importantly water quality does have a positive
effect on growth rates. Water quality that had been
allowed to deteriorate through contamination from
excess build up of the fry's waste matter effectively
retarded growth, it is thought that permanent growth
damage would occur if conditions were allowed to prevail
for any length of time. To maintain maximum fry growth
rates daily 30% water changes were made.
Figs. 15 - 21. Aged one month:
seven long - snouted species of Corydoras:C. acutus,
C. blochi blochi, C. septentrionalis, C. treitlii,
C. amapaensis, C. ellisae, C. stenocephalus.
Adult female coloration was chosen as the time at
which fry were deemed to have reached adulthood. This
was because with other species of Corydoras e.g.
C. barbatus (Quoy & Gaimard, 1824) that
have been bred - where there are known colour differences
between the sexes - the males of some of these species
can take a further eight or even as long as twelve
weeks to mature and develop their adult colours. (Fuller,
With the seven species so far bred from the 'acutus'
group there were no discerning colour differences
between the sexes that could be readily recognised.
The first visual signs of maturing males are in the
fin spines, the pectoral and ventral fins being the
most prominent; becoming thicker and more elongated.
In mature males of the seven species spawned the ventral
fins are possibly the most reliable indicator of sex,
as these become elongated and pointed compared to
the rounded tan shaped fins of the temales.
As with most animals, growth rates can vary tremendously.
Corydoras fry are no exception, and caused
some concern when one or two of the faster growing
quicker developing males became dominant and were
observed chasing and bullying smaller less mature
specimens. The aggression became so intense preventing
the smaller fry from feeding altogether.
To further assist and improve the survival rate of
the smaller male fry, large clumps of Java Moss were
placed in all the fry rearing tanks. This had the
effect of giving all the fry a secure refuge, and
enabled the smaller males to avoid the bullying by
the larger ones. It also had the effect of reducing
the amount of squabbling between males of equal size,
enabling the majority to reach adulthood (between
sixty and seventy percent of the fry of all seven
species reached adulthood).
Long-term observations have shown that female Corydoras
fry grow at a faster rate than males, as twenty percent.
With the seven species bred from the 'acutus'
group there is a difference of between ten and fifteen
percent in standard length after ten months. Despite
growth variation within each of the sexes, after ten
to twelve week's males and females can be separated
with relative ease:
1983a. Lookalikes unmasked. Practical Fishkeeping
January: 32-33. Fuller, I. 1983b. Spawning Corydoras
barbatus. Freshwater and marine aquarium 6 (12):
24-25, 67-68. Nijssen, H. & I.J.H. lsbrücker,
1980. A review of the genus Corydoras Lacepede,
1803 (Pisces, Siluriformes, Callichthyidae) Bijdr.
Dierk. 50(1): 190-220.