WEIGHT GAIN AND REPRODUCTION OF Pomacea canaliculata (Lamarck, 1822) (Gastropoda, Ampullariidae).

*Nara R. Terra1 & Alois Schäfer2

1Fundação Estadual de Proteção Ambiental Henrique Roessler, RS - Divisão de Biologia - Porto Alegre - RS - Brasil.

2Fachrichtung Biogeographie - Zentrum für Umweltforschung - Universität des Saarlandes - Saarbrücken - Deutshland

*Mailing address: FEPAM - Divisão de Biologia - Rua Dr. Salvador França, 1707. CEP: 90690 000 Porto Alegre, RS, Brasil. E.mail: labbiofepam@pro.via-rs.com.br



Weight gain and reproduction in 40 molluscs, beginning at 86 days of age, were observed during 373 days. The molluscs were kept in aquaria, with reconstituted water. They were weighed once a week and at the beginning of reproductive activity, and egg laying and hatching were followed daily. The Variation Coefficient as compared with weight gain is as much as 113%, and the females are larger and heavier than the males. There is no correlation between the size of the individuals and sexual maturity. The females suffer progressive decalcification as they lay eggs. The individuals die after completing their reproductive activity. Observations indicate that this species is appropriate for toxicological trials, because it is easy to breed in laboratory and costs little to maintain.

Key words: Pomacea canaliculata, reproduction, growth, South America



Pomacea canaliculata (Lamarck, 1822) is a species that is widely distributed throughout the Neotropical region, and occurs all the way from the Amazon basin in Brazil, to the Province of Buenos Aires, in Argentina. It is also found in Bolivia, Paraguay and Uruguay (6). In Rio Grande do Sul the species is found in Passo Fundo, Marau, Camaquã (PINEDA, personal communication), in the coastal lagoons (8,12,13), Caxias do Sul, Montenegro, Gravataí, Porto Alegre and Viamão.

P. canaliculata was introduced for food purposes initially in China, and extended to Japan, the Philippines, Korea, Malaysia, Indonesia and Thailand (17).



The habit of living and feeding in the riparian area, makes P. canaliculata an important species to provide information regarding changes in the quality of the aquatic environment.

P. canaliculata was found on Eupatorium sp., Ludwigia sp., Chara sp. (6) Scirpus californicus (7). The clutches are constituted by groups of red, spherical, calcareous eggs (9) and are rarely laid in the water (5,10,16).

Aspects of the biology of P. canaliculata are referred to by LOPES (14), BACHMANN (1) and CASTELLANOS & FERNANDEZ (5).

Many species of molluscs have been used in bioassays with heavy metals, insecticides, herbicides and other xenobiotics, supplying good results in long-term tests (2,4,11,19,20). P. canaliculata was used also in acute tests with heavy metals (8).

The purpose of this study is to provide the biological foundations for the use of P.canaliculata in screening tests with toxic substances (TERRA & SCHÄFER, in preparation).


The development of P.canaliculata was observed based on eggs collected at the end of September at Águas Belas Reservoir in the County of Viamão (30o02’20"S51o 01’17"W ), RS, Brazil. The molluscs hatched in the lab were called paternal generation, and their first generation descendants(F1).

Weight gain, survival and reproduction were observed for 373 days (between the 86th and 459th day), in 40 molluscs, distributed in four aquaria, containing ten specimens each.

The difference between males and females was established only between adult individuals, when the egg mass becomes visible in females, and the developed penis in the males.

The molluscs were distributed in the aquaria and shelves with the help of the random numbers table, based on a lot with 300 individuals. The aquaria (15 cm wide x 30 cm long x 20 cm high) were cleaned with running water and detergent and rinsed, and were later washed with 50% nitric acid, rinsed again with running water, and then with deionized water. The aquaria were kept covered with a glass plate.

Reconstituted water was placed in the aquaria; it was prepared daily using deionized water filtered through activated carbon. Water reconstitution was based on CABRIDENC (3) and adapted to the hardness found at the site where clutches were collected (40mgCaCO3). Water was renewed every 24h, from the birth of individuals until the end of observations. The water was removed from the aquaria by siphoning. A PVC cylinder, measuring 10cm in diameter by 20 cm in length, closed at the lower extremity by a glass slide, with holes 0.5 cm in diameter over its length, was used to introduce the water.

The molluscs were fed lettuce ad libitum.

The environmental temperature was maintained at 22oC ± 1.5oC.



The values of pH, temperature, specific electric conductivity and oxygen saturation in water were controlled by daily potentiometric measures before changing the water.

The individuals of the paternal generation were weighed weekly on a semianalytical balance (precision of 0.01g), totalizing 2,120 items of data. Before weighing, the shells were dried with filter paper. The survival of individuals was observed every 24 h.

The weight of five males and five females found copulating in the aquaria was measured to find out whether there is a relationship of size between sexes for this activity.

The development of 1,000 F1 individuals was followed up to the 75th day of life, when they were weighed and discarded. The F1 individuals were grouped according to day of birth, in containers with 100 ml of reconstituted water.

After the clutch hatched, the non-viable eggs were removed and counted. The survival of the young was followed by stereoscopic microscopy, by observing heartbeats.

In order to determine the best fitting function to the growth data of P. canaliculata , the method described by RICKLEFS (18) was adopted, using the weight of the organism as a function of time, based on the von Bertallanfy equation.

The variation coefficient (VC) was used to determine weight variability in individuals.

The individuals not selected randomly for observation were kept in the laboratory for a two-year period, with the same system for feeding and medium changes, but were not observed periodically for weight change.


The mean weight gain curve shows two different stages: the first is described by an almost linear increase, up to approximately the 18th week of life (February), when the weight gain difference between males and females begins; the second extends to close to the 63rd week of life (January), when weight gain follows a sigmoid. During the 48th week of life (September), an impulse in weight gain is observed, coinciding with the higher weight gain of females, due to the beginning of the maturation phase of the eggs (Fig. 1).

Figure 1. Mean weight gain curves of males and females P. canaliculata during 52 weeks, beginning in the 12th week of life at 22±1.50C.

The VC increases until approximately the 41st week of life (August), and remains stable until the 48th week which corresponds to the pre-reproductive period. After this, up to the 62nd week of life (December) weight loss occurs, coinciding with the reproductive period, and a new stabilization follows, but with values lower than the first, identifying the period during which individuals that have reproduced themselves die. (Fig. 2).

Figure 2. Variation coefficient of weights in P. canaliculata, during 52 weeks, beginning in the 12th week of life, at 22±1.5°C.

During the observations, the VC ranged from 29% at the beginning of the experiment to 113% at the time of maximum weight variation, which corresponded to the 49th week of life (September). The VC was higher than 100% for a 13-week period, between the 39th and 52nd week of life (July to October ).

Utilizing the von Bertallanfy equation to transform the data ( mean of the weights of 40 individuals), it was observed that they are described by a straight line ( r=0.99; n=40) up to 52 weeks of life. Beginning at that age, the weight gain rose sharply, due to the maturation of the female gonads and egg formation. During the development phase, when the individuals are mature, the conspicuous pink color of the gonads stands out in the female, giving even the


shell a reddish tint. In males, the penis is seen to be quite well developed in this phase, like a whitish formation throughout its length, except in individuals that have intense sexual activity, when this organ presents a pinkish tip. During the reproductive period, the females are larger and heavier than the males. In only a single pair was it observed that the weight and size of the male were greater than those of the female. This occurred among the exemplars that did not mature during the first year of life but were kept under the same conditions as those under observation.

The weight of mature individuals, taking into account only the males found copulating or with a pinkish tip of the penis, and females with a visible egg mass, is presented in Table 1.

Table 1. Absolute weight (grams) of tem females and six males of P.canaliculata, visibly mature, observed during weighing. The individuals were not copulating.



The weight of males and females copulating in the laboratory does not present a correlation (r = 0.54; n = 5), suggestingthat there is no relationship of size among copulating individuals (Figure 3).

This study showed the need to stimulate the male sexually in order for eggs to be laid, thus sterile eggs occur due to the lack of egg fertilization, and not due to lack of copulation. This behavior was observed when there were only females in one aquarium, and only males in the other, when no laying activity occurred in the aquarium containing females. Copulation occurred less than 30 minutes after five males were transferred to the aquarium in which there were only females, and five females to the aquarium in which there were only males. The first laying occurred less than 24 hours after copulation. The individuals were redistributed at 11 am one day, and, at 8 am the next, there were already clutches that hatched after 23 days.

The laying activity begins when the individuals are approximately one year old, and they die after the reproductive period. Among individuals who do not mature during the first year, only a few lay eggs a few times during the second year, and die immediately after this. Most of these eggs were non-viable.

During observations in the laboratory, the eggs hatched at between 19 and 36 days, and 68% of them were viable.

It was observed that the retardation of weight gain in P. canaliculata coincides with the smallest daily photoperiod.

The clutches laid in water did not hatch.

During the reproductive period, the P.canaliculata females suffer progressive decalcification as the clutches are laid, making the shells fragile.

The mean number of eggs laid per female was six, with an average of 82 eggs per clutch. The survival determined for F1 individuals up to 75 days of life is 38.6% under controlled laboratory conditions. The mean weight of individuals at 75 days of life is around 0.06 g, under the same conditions.





As to the time of year when reproduction began and ended, September and February, the results are different from those mentioned in literature. This difference may be related to the different latitudes where other studies were carried out (1, 14). It is observed that some organisms lay eggs throughout the reproductive period, while others begin this activity later or end it earlier (1, 14). Genus reproduction time is variable, with a few individuals maturing at the beginning of October, laying eggs until the end of February, while others mature later (1). The same author observed sporadic laying around September 15 (North of Santa Fé at 32o C) and July 17, (Upper Paraguay at 10o S).In the same study, that author mentions that sterile clutches do not change color, but does not specify whether he performed a test to look at the content of those eggs. In observations performed in the state of Rio de Janeiro, it was reported that adult individuals of genus Pomacea lay eggs from February to March, with renewed rare laying at the beginning of July. However, the latter were not viable (14).

There must be sexual stimulus to enable laying eggs. These mature, within 24 days on average. Approximately 68% of the eggs were viable. Of the individuals born in a laboratory, 61.4% died before 75 days of age.

Between the first copulation and the egg-laying, 24 hours can elapse. This disagrees with the statement that some specimens copulate once or twice, laying eggs or not, with others lay their eggs at short intervals of three days to one week, which is the normal time between copulation and egg-laying (1) The observations performed in this study disagree with the bibliography with states that, in the natural habitat, P. canaliculata lives from three to four years, but agree that the individuals die after reproduction (5) This sequence of laying causes decalcification in the females of P. canaliculata. Calcium mobility was also observed for Pila virens (Lamarck) in which the calcium content of the gut gland during hibernation is 13.2% of the sum total of calcium in the organism, diminishing to 6.5% during the egg-laying season (15).

Molluscs of the same age, kept in the laboratory under uniform conditions, present great variation in size (22), as observed in this experiment.

Laboratory observations identified two more sensitive phases in the life cycle of individuals: between September and February ( reproductive period ) and between October and April ( hatching).

The reproductive frequency of the females is variable, as is the period required for hatching. The females are larger and heavier than the males. The ontogenic cycle of P. canaliculata is completed in slightly over one year.

The information on reproduction , weight gain, egg viability and survival rate of F1 is essential to become acquainted with the species for use in toxicological tests. Due to the easy maintenance in the laboratory and reproductive viability, P. canaliculata is appropriate for use in this kind of test.


To Dr. Rosane Lanzer, for reading critiqueing and making suggestions for the manuscript, to J.O. Menegheti MSc., for statistical advice, to Dr. Maria Cristina Pons da Silva for species identification , to Dr. M. Dolores S. Pineda, to biologists Rita Semeraro, Eliete Göepfert and Eunice N. M. Kertész for their help in laboratory activities.



Ganho de peso e reprodução em Pomacea canaliculata (Lamarck, 1822) (Gastropoda, Ampullariidae). Foi observado durante 373 dias, o ganho de peso e a reprodução em 40 moluscos, a partir de 86 dias de vida. Os moluscos foram mantidos em aquários com água reconstituída. foram pesados semanalmente e no início da atividade de reprodução, acompanhou-se diariamente a realização das posturas e a eclosão dos ovos. O coeficiente de variação em relação ao ganho de peso alcança 113%, sendo as fêmeas maiores e mais pesadas que os machos. Não há correlação entre o tamanho dos indivíduos e a maturidade sexual. As fêmeas sofrem descalcificação progressiva a medida que efetuam as posturas. Os indivíduos morrem após cumprida a atividade reprodutiva. As observações indicaram que esta espécie é apropriada para realização de ensaios toxicológicos, devido a facilidade de criação em laboratório e o baixo custo de manutenção.



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