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A. O. Meyer-Willerer, A. Santos-Soto
Temperature and light intensity affecting egg production and growth performance of the Apple Snail Pomacea
patula [Baker, 1922]
Avances en Investigación Agropecuaria, vol. 10, núm. 3, septiembre-diciembre, 2006, pp. 41-58,
Universidad de Colima
México
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Temperature and light intensity affecting egg production
and growth performance of the Apple Snail Pomacea
patula [Baker, 1922]
Efecto de la temperatura e intensidad luminosa en el crecimiento y producción
de huevos y crecimiento del caracol dulceacuícola Pomacea patula [Baker,
1922]
Meyer-Willerer,
A. O.
1
* and Santos-Soto, A.
2
1
Centro Universitario de Investigaciones Oceanológicas, Universidad de Colima, km
20 Carr. Manzanillo-Cihuatlán, Manzanillo, Col. 28860, México.
2
Facultad de Ciencias Marinas, Universidad de Colima, km 20 Carr. Manzanillo-
Cihuatlán, Manzanillo, Col. 28860, México.
* Author for correspondence: ameyer@cgic.ucol.mx
Resumen
Se efectuaron experimentos de desove del
caracol dulceacuícola [Pomacea patula Baker,
1922] en tanques exteriores durante un año. Las
observaciones incluyeron el desove de 30 hem-
bras, total de huevos depositados y la eclosión de
pequeños caracoles, todos por triplicado. Otros
experimentos en el laboratorio con 30 hembras
ovopositoras y sus respectivas masas de huevos
bajo condiciones controladas (temperatura e in-
tensidad luminosa) fueron registrados por tripli-
cado. Se comparan datos a diferentes temperatu-
ras de agua y aire, entre 20 y 32°C, y a dos
intensidades luminosas (60 y 300 lux) en los si-
tios de desove. Una tercer serie de experimentos
fueron llevados a cabo para determinar la tasa de
crecimiento con 100 caracoles recién eclosiona-
dos por experimento con temperatura controlada
(22 a 32°C) y condiciones naturales de intensi-
dad luminosa. Los resultados muestran, que el
caracol tegogolo desovó principalmente de agos-
Abstract
Outdoor experiments recording spawning of
apple snails [Pomacea patula Baker, 1922] were
recorded during one year. Observations included
spawning of 30 females with total deposited eggs
and total hatched snails, all done in triplicate.
Another series of indoor trials with 30 spawning
snails and egg masses under controlled experimen-
tal conditions (temperature and light intensity) were
recorded by triplicate. Data were compared at di-
fferent water/air temperatures, 20 to 32°C and
two light intensities, 60 and 300 lux at spawning
places. A third series of trials were aimed at deter-
mining growth performance with 100 spawned
sails per temperature trial under controlled tempe-
ratures (22-32°C) and natural light conditions.
The results show that the apple snails spawn mainly
from August to November when water temperatu-
res average 26°C or more. Hatching efficiency is
encouraged by warm air temperatures. Spawning
is also affected by light intensity, females spawn at
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Introduction
Freshwater snails are very common in the subtropics of the southeastern part of North
America and eastern coast of México [Rangel, 1988], some of them are collected in
rivers and lakes and few of them are eaten locally. Although applesnails (Pomacea spp.)
are herbivores, some large snails are suitable for culturing in fish ponds and are found
occasionally feeding on dead fish (http://www.applesnail.net/). The applesnail [Pomacea
patula catemacensis, Baker, 1922], also known in México as “tegogolo”, is strictly
endemic around the Catemaco lake in the State of Veracruz [Duipotex-Chong et al.,
2004]. This gastropod introduced intentionally in the1980’s into the States of Colima
and Jalisco (Pacific Ocean) by the governmental Secretariat of Fisheries, where
environmental conditions are similar to those of the coast of the Gulf of México
[Ontiveros, 1989]. These snails tolerate different types of climates [Osorio, 1988]
exhibiting fast growth rate and together with their herbivorous feeding, make these
snails an interesting alternative for aquaculture. Some of these snails like Pomacea
urceus exhibit a rapid growth rate in the wild (4 to 10 mm/month attaining a maximum
length of 85 mm), being a medium size snail cultured in the Americas [Lum-Kong,
1989]. This high prized snail has been over-exploited in Trinidad and Tobago, in
consequence Ramnarine [2003] developed a method to induce spawning and create
an appropriate incubation system. Little attempts have been done to culture P. patula
or to develop the husbandry that was introduced into fish ponds in Colima State.
lower temperatures in higher intense illuminated
places; at 26°C or higher, the preference reverts.
In tropical climate incubation time of larvae redu-
ces and the growth of recently hatched snails tends
to be more successful in warm weather, but their
final survival decreases.
Key words
Spawning, clutch, survival.
to a noviembre, cuando la temperatura del agua
fue de 26°C o superior. La eficiencia de eclosión
del huevo fue favorecida con temperatura media
del aire. La ovoposición fue también afectada por
la intensidad luminosa, ya que las hembras deso-
varon en lugares más intensamente iluminadas,
cuando la temperatura del aire fue más baja; a
26°C o mayor, la preferencia se invirtió. Bajo
condiciones de clima tropical, el tiempo de incu-
bación de la larva tendió a ser menor y el desarro-
llo de los caracoles pequeños hasta adultos sexual-
mente maduros fue mayor; sin embargo, la super-
vivencia de la población utilizada para dicho es-
tudio decreció.
Palabras clave
Desove, masa de huevos, supervivencia
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P. patula inhabits mainly tilapia ponds that may be entropic in certain times of the
year, even though these amphibious snails withstand low dissolved oxygen concentra-
tions in green waters aiding themselves by creeping out of water during this period.
They stay submerged during the day, hidden in the vegetation near the border and the
surface and are more active during the night leaving the water in search for green
vegetation. They also abandon the water searching for an optimal egg deposition place
guaranteeing larvae development. These snails are dioecious (i.e. sexes separate), they
present high fecundity and low mortality [Ontiveros, 1989]. Most of these snails feed
preferentially on macrophytes [Estebenet, 1995]; under controlled conditions they
accept market vegetable leftovers [Martínez, 1989], artificial diets [Mendoza et al.,
1999] and also commercial feeds [Estebenet and Cazzaniga, 1992].
Pomacea patula is a diurnal species presenting negative phototactism, thus avoi-
ding direct sunlight [Jaime, 1992]. Egg deposition is mainly done before sunrise
(Osorio, 1988). Although egg deposition is performed in complete darkness, the
whitish translucent egg masses or clutches are deposited in places that are shaded
during day. While drying, the egg mass hardens taking on a light pink color. While
maturing, these egg masses get opaque, finally light brown indicating the end of the
larva (veliger) maturation and the start of hatching time of the small snails. Breaking
the thinned shell, these small snails fall into the water. The snail reaches its maturity
after six months, growing slower after this period until arriving their maximal size of
80 mm [Jaime, 1992], showing no visible sexual dimorphism on the shells [Osorio,
1988], and consequently making sexual differentiation in live organisms practical du-
ring copulation.
P. patula snails tolerate a wide range of temperatures; during winter, the cold
northern winds in the Gulf of México may lower water temperature to 10°C and
during summer in sunny days these may be over 34°C [Ontiveros, 1989]. He also
observed that temperature affected hatching of P. patula. Other species of Pomacea
tolerate even a wider range of temperatures, like Pomacea lineata Spix, 1827. Santos
et al. [1987] made studies of these Brazilian snails in relation to their respiration
response and the dissolved oxygen observing no mortality, when snails were exposed to
temperatures as low as 5°C or as high as 40°C.
In order to understand the development of induced spawning of this species we
examine the question whether the negative phototactism of P. patula affects egg depo-
sition as a response to an external sign (e.g., no direct sunlight), or phototactism is
governed by internal cues. We also analyze the effects of temperature on egg produc-
tion under outdoor experimental conditions, egg incubation time and small snail deve-
lopment under indoor experimental conditions during shaded daytime and normal da-
ytime with an improved egg incubation system. With the spawning results, hatchery
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technology might be developed for this potential species and the produced juveniles
might be grown out in extensive aquaculture ponds.
Materials and methods
500 adult sexually mature apple snails [Pomacea patula Baker, 1922] were collec-
ted in tilapia ponds of “Potrero Grande” on the northern Pacific Coast of Colima
State, México. All collected snails were treated with methylene blue (1g/100 L) for
10 min for prophylaxis [Lázaro, 1985] and kept in a tank with a closed circulated tap
water system 20 km southeast from the capture site, exhibiting the same climate of type
aw
0
[García, 1973] as the capture place. One outdoor temperature experiment was
conducted with adult snails and another series of trials with controlled light intensity
and temperature were also performed with adult snails. Hatching observations and
growth measurements of recently hatched snails at different temperatures were also
performed.
Outdoor temperature experiment with spawning females
Field experiments have not been conducted yet, but several observations lead to a
temperature-dependent behavior. Therefore a series of experiments were conducted to
elucidate water temperature dependence. The first experiment was designed to test
natural climate conditions in an artificial medium measuring water and air temperature
in a 50% sunny and 50% shaded outdoor place (measured at midday) and feeding
with alfalfa, lettuce and tilapia starter feed. After one week of adaptation under artifi-
cial conditions, the water in the fiberglass tank turned green due to algae development.
In order to guarantee spawning, every mating pair was set apart into a separate fiber-
glass tank under same water conditions and each female was marked on the upper part
of her shell. After collecting 90 pairs of snails, they were distributed randomly in three
numbered circular fiberglass tanks (starter tanks, 1.5 m diameter, 1.0 m height) with
300 L “green” water. Each tank was initiated with “green” water and supplied with
continuous tap water flow (6 liter h
-1
) to maintain water quality. The same mixture of
food as mentioned above was provided ad libitum and every day the bottom of each
tank was siphoned. Three observations were done in each tank every day before sun-
rise and during hatching for 12 months (October 1996-September 1997): (1) coun-
ting and marking the new spawning; (2) counting hatched snails in each spawn and (3)
counting total deposited eggs per clutch once they have hatched including those that
did not hatch or were infertile. Correlation factors between (a) female weight, maxi-
mum shell length and egg number and (b) between number of egg mass depositions and
total eggs deposited, were calculated.
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Indoor controlled temperature and light intensity experiments
with spawning females
These series of experiments were designed to test spawning under controlled tem-
perature and light conditions in an artificial medium keeping water and air temperature
constant in a dark room. The 12h:12h day-night regime was regulated with the aid of
a timer-switch; two different light intensities in separate tanks were created with the aid
of light bulbs (9 W bulb measuring from 10 to 300 lux, and 60 W bulb measuring
from 20 to 900 lux light intensity on the walls of the fiberglass tank) that were placed
on the upper part (1.0 m from bottom) of the fiberglass tanks and at 30cm from the
middle of each tank assuring heterogeneous light intensity in the tank walls. Each
vertical tank wall was covered with transparent plastic foil for better handling of depo-
sited egg masses. Each light-intensity trial was done in triplicate; to maintain the right
temperature in the fiberglass tanks, these trials were done supplying the room with a
sensible thermostat air-conditioner unit. For convenience, the light/dark periods (12/
12 h) were inverted with the aid of a timer, in order to better observe egg depositions
occurring before sunrise. The light period started at 19:00 h, the dark period at
07:00 h. The snails were also fed with alfalfa, lettuce and tilapia starter feed. Water
quality was also maintained with regular siphoning of the bottom and supplying with
continuous “green” water flow (6 liter h
-1
).
Each temperature set consisted of 90 pairs of snails distributed randomly in each
of the three replicate tanks that were acclimatized during seven days; trials were com-
pleted after 30 days. Each temperature trial started with non-used, disinfected and
acclimatized snails.
“Green” water was produced in a circular fiberglass tank exposed to direct sunlig-
ht adding sufficient algae fertilizer to maintain algal densities high. Water temperatures
for the following trials were selected between the annual lowest (20°C) and highest
(32°C) measurements in Manzanillo City, State of Colima, were set at 2 ± 0.1°C
differences starting with the lowest temperature.
Indoor controlled temperature and light intensity
experiments with eggs
The eggs that were laid on an adhered plastic foil by the females in the preceding
trial were utilized for this experiment. Only those egg masses that were 60 cm from
bottom (that means 60 lux light intensity for those trials with 9 W lamp and 300 lux
light intensity for those trials with 60 W light lamp) were cut apart and incubated in an
tempered chamber with thermostat (20, 22, 24, 26, 28, 30 or 32 ± 0.1°C ) and fan.
Also light was introduced into this chamber measuring 60 or 300 lux nearby the egg
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masses, same intensities as the egg deposition sites in the tanks. Egg incubation time
was the period between egg deposition and when the first snails hatched. Achievement
in egg hatching was determined counting under a magnifying glass as live those larvae
that moved inside the egg. The others were counted as dead.
Growth of recently hatched snails in indoor controlled temperature experiments
100 recently hatched snails were placed in a plastic flask of 2 L capacity and 0.5
L of “green water”. Each trial was done in triplicate. The flasks were placed in an
incubation chamber with temperature controlled by the aid of a thermostat and fan. For
each temperature trial (22, 24, 26, 28, 30 or 32 ± 0.1°C) new small snails were
used. Light was natural indirect sunlight. The snails were also fed with first grade
grinded tilapia fingerling feed. After 4 weeks they were transferred to aquaria in the
same growth chamber. Growth of the small and juvenile snails was measured utilizing a
vernier caliper to compute the total shell length each week. Survival was also calculated
each week during 13 weeks.
Statistical analysis
For statistical analysis of the data, the software package STATISTICA/W
[StatSoft, 2000] was used. Differences in development of the various groups of egg
masses, total eggs, hatching percentage, were tested by one-way analysis of variance
(ANOVA) and between high and low light intensities and among temperature
treatments. In the case of significant differences (p<0.05), the mean values of the
different treatments were compared with the post-hoc tests (Tukey’s HSD) [Steel and
Torrie, 1980]. In order to reveal potential relationships in the development of the
different organisms, a correlation analysis was performed.
Results
Outdoor temperature experiment with spawning females
Egg deposition of snails in outdoor conditions was performed to find differences
among the months of one year. In these latitudes with tropical climate conditions all the
year round, two seasons prevail, the dry warm (December to May) and the humid hot
season (June to November). Mating lasted several hours and was observed in all tem-
peratures in the three tanks. All females that mated produced eggs. Egg deposition and
hatching of P. patula at different temperatures and light conditions is presented in
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Figures 1 to 3. Snail growth at different temperatures is presented in Figure 4, growth
per month in Table 1 and cumulative mortality in Table 2.
For comparison, data were pooled for each month accounting only 30 days for
each month (except February where only one egg mass was deposited in average per
pond). This comparison shows that the apple snails lay their eggs during the entire
year, but preferentially in the hot and humid months as Figure 1a shows (p<0.05).
The total number of eggs laid by these female snails is proportional to the egg masses
deposited (Figure 1b), but the egg hatching percentage registered significant differen-
ces (p<0.05). Hatching success was lower (average 46.25 ± 24.7% S.D.) in the
coldest months (January to April), contrasting with October, when highest hatching
percentage was achieved (hatching success average 89.2 ± 3.1% S.D.) compared to
the rest of the year (hatching success average 66.5 ± 19.6% S.D.), (Figure 1c).
The deterministic coefficient between egg mass deposited all year round and total eggs
counted in each egg deposition is 0.9545 and y = 100.6x + 1107.4 is the respective
equation that describes the straight regression line.
Table 1. Baby and juvenile snail measurements of maximum length increase per
month at different temperatures.
Table 2. Baby and juvenile snails showing cumulative mortality per month and
at different temperatures.
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Figure 1. Outdoor monthly egg depositions, numbers are average from three
tanks each with 30 pairs of snails.
(a) Bars indicate mean and the SD of means given as vertical bars of three replicates of egg depositions.
(b) Mean and SD of three replicates of total eggs deposited by the same females. (c) Bars representing
hatching percentage of all egg depositions per month, those with the same superscript are not significantly
different (p<0.05).
Indoor controlled temperature and light intensity experiments with spawning
females
The similarity factor between fresh wet weight and length of recent spawned fema-
le snails is very high (Figure 2a, R
2
= 0.9335, n = 90), revealing an extremely
significant relationship between female size and clutch size. Fresh wet weight of fema-
les and number of eggs laid per female show also a significant relationship (Figure 2b,
R
2
= 0.7899, n = 90) and also between total length and number of eggs per female
(Figure 2c, R
2
= 0.7147, n = 90).
Significant differences (p<0.05) were registered when snails deposited their egg
masses in the tanks with low or high light intensity, but also dissimilarities were detec-
ted when these eggs were laid at different temperatures (Figure 3a). Between 20 and
24°C they preferred to lay their egg masses at night in a place with more light intensity
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during day (300 lux). And when the temperature went from 26 to 32°C they laid
more egg masses during night in a place that was less illuminated during day (60 lux).
Most of the total laid egg masses (84% in average of both light intensity experiments)
females preferred to lay their egg masses in a less illuminated place between 40 and 70
cm above water level.
Figure 2. Graphs showing linear correlation between (a) wet weight after egg
depositions and maximum shell length of 90 females, (b) wet weight and
number of eggs deposited per female and (c) maximum shell length and
number of eggs. The correlation factors and the equations describing the lines
are shown.
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Indoor controlled temperature and light intensity experiments with eggs
Temperature and also light intensity affects directly the egg incubation time. When
eggs are incubated at 20°C, they need one and a half more time to hatch, than at 32°C.
At the higher light intensity (300 lux), the egg hatching time was one to two days
shorter, than at low light intensity (60 lux), being significantly different independently
from air temperature (Figure 3b). Each trial was done in triplicate. Hatching percen-
tage also is affected by temperature and light intensity; at 20°C only a fifth of the eggs
hatch, at 30 or 32°C, around nine tenths of them hatch, these percentages are slightly
but significantly higher in the trial with high light intensity, than with low light intensity
around 24 to 26°C (Figure 3c).
Figure 3. Indoor egg mass depositions from 30 “apple snails” for each trial
under controlled temperatures and two light intensities at the egg mass height,
(low intensity 60 lux, shaded bars; high intensity 300 lux, clear bars).
(a) Bars indicate mean and SD of three replicates in percentage of egg depositions by identified
females. (b) Bars representing the incubation time of eggs deposited by the same identified females. (c) Bars
representing hatching percentage; those with the same superscript are not significantly different (p<0.05).
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Growth of recently hatched snails in indoor controlled temperature experiments
Figure 4. Temperature trials measuring growth of recently hatched snail as the
maximum shell length during three months. (100 snails were held at each
controlled constant temperature and natural light.)
Baby snails presented a regular size when trial started. After one month those
grown at 30 and 32°C showed a sinusoidal growth during the first month (Figure 4)
and a higher increase in size (Table 1), but presented higher mortality (Table 2).
After 3 months of growth those held at 32°C showed the highest growth, but also the
lowest survival; those grown at 22°C showed half growth as compared to those grown
at 32°C, but survival was the maximum observed. Their growth showed significant
differences (p<0.001) when compared between temperature trials.
Discussion
Feeding was done ad libitum, therefore it is not possible to compare growth data
with other studies, although most of them were carried out with individuals of the
genus Pomacea and fed also ad libitum [Alonzo, 1984; Cazzaniga and Estebanet,
1988; Lum-Kong, 1989; Martínez, 1989; Ontiveros, 1989; Godínez, 1991; Asiain
and Olguín, 1995]. In the present essays, the selected feeding regime seemed to be
reasonably well due to high survival rates.
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The principal findings of this study is that P. patula shows a marked spawning
activity pattern dependent on the water/air temperatures and this pattern is also affec-
ted by the direct sunlight/shade presence. Although these snails deposit their egg mas-
ses during the last hours of night, coinciding with observations made by Martínez
[1989], but not with those made by Osorio [1988], who reported negative phototac-
tism during egg deposition. Pomacea patula avoids direct sunlight searching for feed in
the lower parts of the water column. It has been clearly demonstrated that egg deposi-
tion is greatest during the end of the summer, when enough algae are fixed on substrate
and weeds, and water temperature is high (30 to 32°C). But these snails can deposit
eggs during all year, mainly starting the high activity in August and ending in Decem-
ber. The highest registered egg deposition was in October with registered diurnal
water temperatures between 28 and 30°C (more than 30% of all registered egg depo-
sitions) and the lowest was accounted for February (0.4%), when water temperature
drops even lower than 18°C in Colima State coasts. These registered temperatures for
P. patula and their activity rate coincide reasonably well with those recorded for P.
canaliculata original from the Amazon Basin [http://www.applesnail.net/].
Total laid eggs show a highly positive significant correlation describing a linear
pattern proportional to egg mass depositions during all year. This suggests that any egg
mass independently from the season, thus from temperature, presents a reasonably
proportional number of total eggs, affecting temperature only egg mass depositions and
not egg quantity in the laid masses. During fall and winter, the breeding rate is at its
lowest point coinciding also with P. canaliculata [http://www.applesnail.net/]. Female
length and wet weight is also directly proportional to total eggs laid. In nature one can
find females of more than 40 g weight and 50 mm maximum shell length [Jaime,
1992], slightly smaller than those reported lengths for P. canaliculata [http://
www.applesnail.net/]. Some females can spawn three times with small intervals after a
single copulation, being the first spawn that with most hatching efficiency, declining in
the subsequent ones, observations that coincide with those made by Ontiveros [1989].
Estoy et al., [2002a] found in P. canaliculata that food availability did not affect age
at first copulation in males, whereas females at high food level started copulation and
spawning earlier than those at lower food levels. The same investigation team [Estoy et
al., 2002b] found in these apple snails, that food availability diminished spawn pro-
duction, but did not show differences between their weight-specific reproductive effor-
ts.
Eggs are laid on the shaded side of a stick or rock during day, although egg depo-
sition is done two to three hours before sunrise showing a constant circadian pattern
[Jaime, 1992]. Each clutch contained between 50 and 720 eggs with an average of
190 being different to P. canaliculata clutches with 200 to 600 per clutch [Estebenet
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and Cazzaniga, 1993; http://www.applesnail.net/]. The fact that more than 80% of
the females laid their eggs in the less illuminated part of the fiberglass tank confirms this
tendency of laying their eggs in a mostly shaded part or even in a not exposed sunlight
place at all. It seems that the ultraviolet wavelengths of sunlight are harmful for tropical
mollusks that are exposed directly [Carefoot, 1989]. Some mollusks lay their egg
masses during day and night like the sea hare Aplysia oculifera. Adams and Reeve,
1850 [Plaut, 2000]. It is possible that mollusk eggs [Carefoot et al., 1998] and
embryos [Rawlings, 1996] are protected against ultraviolet exposure by the aid of a
capsule wall. It is feasible to infer from the obtained results, that P. patula presents this
evolutionary adaptation of ultraviolet light avoidance producing a protective substance
in the capsule walls or egg shells, since they deposit their egg masses 20 to 70 cm over
the water level and therefore the probability to be exposed to direct light is superior.
Field observations during snail collection coincide with the fact that egg depositions
are placed on the shaded side produced during mid-day hours of emerged plant stems.
Significant differences were found between those trials in high or low light inten-
sities; those snails that were exposed to high light intensity and experimented tempera-
tures between 20 and 24°C, laid nine to fifteen more egg masses, than those exposed
to lower light intensity. Between 26 and 32°C this tendency reversed presenting six to
thirty more egg depositions. This behavior at these temperatures might be explained
considering that between 24 and 26°C it seems to be the maximum of egg depositions
and also the optimal growth and survival temperature for larvae. At lower temperatures
the female snail prefers places with more sun exposure; at higher ones, more shaded
places. A possible explanation could be the metabolic heat accumulation in eggs added
to direct sun irradiation that may cause temperature increase to dangerous levels.
The incubation time was one day longer when eggs were exposed to more intensive
light presenting no significant differences with respect to the shaded ones, this inde-
pendently from air temperature, except at 32°C. At lower temperatures (20 and 22°C)
hatching was less effective showing significant differences with respect to higher tem-
peratures; at higher temperatures (22 to 30°C) incubation time was gradually shorter
and those in the less illuminated trials needed one day less to hatch compared to those
with higher light intensity. These results are consistent with the observations done
above, that direct sun light may interfere with essential metabolic reactions in the eggs.
If snails are capable of producing substances that filter UV light [Carefoot et al.,
1998], it is possible, that these substances have to be produced during the first day or
days of incubation to protect eggs from direct sun irradiation and then continue with
egg development. Hatching percentage is slightly higher when exposed to higher light
intensity, but being not significant with respect to temperatures between 26 and 32°C.
Lower temperatures (20 to 22°C) decrease drastically the hatching efficiency.
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Growth of recently hatched snails was the fastest at higher temperatures, but survi-
val was inversely proportional to growth, mainly in those recently hatched and those
one-month old snails. Those kept at 22 or 24°C survived all. When the temperature
was higher, more mortality was accounted. Between first and second month, and se-
cond and third month, survival was higher also in the higher temperatures. In nature
the maximum growth is achieved in autumn when water temperatures are still over
26°C and sufficient natural food is available. The highest length achieved in these
experiments, more than 10 mm/month, was obtained with those juveniles kept at 28 or
30°C during the second month of the trial, and is far better compared to those descri-
bed by Martínez [1989], who experimented under similar conditions and P. patula
grew only 5.5 mm/month when fed with alfalfa. Other snails might grow more per
month as described by Benavides [1994], who worked with P. bridgesi feeding dead
fish growing 7.0 mm/month, or less as described by Ontiveros [1989], who fed P.
flagellata with Pistia sp. attaining a growth of 5.3 mm/month. Mendoza et al. [1999]
conducted experiments with P. bridgesi feeding balanced artificial diets with respect to
protein and energy and obtained growth rates around 14 mm/month, higher than those
reported for a wild species P. urceus registering 13.5 mm/month growths [Lum-Kong,
1989]. Ramnarine [2003] considers that an appropriate diet prior to spawning of P.
urceus might increase fecundity. With respect to the results of the present study it can
be concluded, that P. patula accepts pulverized tilapia fingerling feed in “green” water
for the first weeks and rough ground feed for their juvenile development, and it is
possible that a special balanced feed may increase their growth rate. Feeding trials for
juvenile and adult P. patula might increase fecundity and survival.
Results also show a heterogeneous growth behavior directly dependent from water
temperature: growth is faster at warm temperatures but survival decreases; in colder
water (22 to 24°C) almost all survive after three months, but growth is half slower
than in tropical temperatures. Survival is high and growth rate is also high at 26 to
28°C, those water temperatures that dominate in summer and autumn in the Pacific
Central Mexican coasts.
This research paper has clarified the advantages of culturing these commercially
edible snails in an attractive form just watching water and air temperatures and light
intensities during clutch development. This introduced species exhibits not a voracio-
us feeding behavior as the Amazonian apple snail P. canaliculata does in Asia and also
has not shown to be a biological invader and therefore an agricultural pest [Estoy et al.,
2002], since it grows only in tilapia and natural ponds. This study also contributes to
understand hatchability, growth and survival rates of young snails making these gastro-
pods an interesting extra income for tilapia aqua-culturists. Naranjo-García [2003]
emphasizes the importance of this freshwater mollusk as a food source and also as a
pollution indicator.
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From an epizootic point of view, no reports have been found about P. patula being
a potential host for the liver fluke Fasciola hepatica. This were the case of the gastro-
pod Lymnaea viridis spread out in Guam and Papua New Guinea [Boray, 1978] and
the rat lungworm Angiostrongylus cantonensis introduced with the intermediate host P.
canaliculata in Taiwan and Japan [Mochida, 1991]. This hepatic parasite was first
reported in gastropods of México by Aguirre [1939]. Mazzotti, [1955] observed
the complete reproductive cycle of this parasite in mollusks in Northern México States
and Caballero and Larios [1940] described other parasites in gastropods from the
temperate Lerma Lake, Mexico State in Central México. F. hepatica has been repor-
ted in Tabasco State, México, in relation to regional gastropods [Rangel and Gam-
boa, 2005]. In Colima State, México, some studies have been carried out with gastro-
pods as intermediate hosts of Paragonimus mexicanus [Lamothe-Argumedo et al.,
1983], and also some parasites have been detected in tilapias from a tropical lagoon,
but Fasciola hepatica has not been reported [García et al., 1993]. Sanitary observa-
tions are highly recommended for these gastropods and tilapias [Naranjo-García, 2003].
P. patula is a good fresh-water mollusk that is being over-fished in Catemaco Lake,
Veracruz State, where it is endemic [Carreón, 1999], and has good perspectives to be
cultured in Pacific Ocean States as Colima, Jalisco and Michoacán [Santos, 1999].
Conclusions
P. patula shows a marked spawning activity pattern dependent on the water —air
temperatures and this pattern is also affected by the direct sunlight— shade presence.
Snails deposited their egg masses in the tanks with low or high light intensity depen-
ding on air and water temperatures. Temperature and light intensity also affect directly
egg incubation time. Small snails present faster growth in tropical temperatures, but
survival decreases significantly. Apple snails are found in tilapia ponds and are cultu-
red extensively, since no feed is given to them and no attempts have been done so far to
reproduce P. patula artificially for mass productions. To make this product interesting
to aqua-culturists, it is crucial to increase pond population, and therefore it is neces-
sary to find optimal stocking densities, search more about reproduction strategies un-
der controlled parameters and test complementary feeds if required, when stocked in
tilapia ponds. Sanitary care should be taken in order to avoid pest infestation in fis-
hponds where this edible snail can be cultured.
Acknowledgements
This research was supported by SIMORELOS-CONACyT under the Proyect
96-01-017.
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Recibido: Diciembre 12, 2005
Aceptado: Enero 10, 2007
