Fasciola hepatica in Snails Collected from Water-Dropwort Fields using PCR

Fasciola hepatica is a trematode that causes zoonosis mainly in cattle and sheep and occasionally in humans. Fascioliasis has been reported in Korea; however, determining F. hepatica infection in snails has not been done recently. Thus, using PCR, we evaluated the prevalence of F. hepatica infection in snails at 4 large water-dropwort fields. Among 349 examined snails, F. hepatica-specific internal transcribed space 1 (ITS-1) and/or ITS-2 markers were detected in 12 snails and confirmed using sequence analysis. Morphologically, 213 of 349 collected snails were dextral shelled, which is the same aperture as the lymnaeid snail, the vectorial host for F. hepatica. Among the 12 F. hepatica-infected snails, 6 were known first intermediate hosts in Korea (Lymnaea viridis and L. ollula) and the remaining 6 (Lymnaea sp.) were potentially a new first intermediate host in Korea. It has been shown that the overall prevalence of the snails contaminated with F. hepatica in water-dropwort fields was 3.4%; however, the prevalence varied among the fields. This is the first study to estimate the prevalence of F. hepatica infection using the vectorial capacity of the snails in Korea.

Individual growth of Drepanotrema cimex (Pulmonata: Planorbidae) from Arenalcito pond, Natural Reserve Multiple Uses Martin García Island, Buenos Aires, Argentina / Crescimento individual de Drepanotrema cimex (Moricand, 1839) (Pulmonata, Planorbidae) de Arenalcito, Reserva Natural de Usos Múltiples Isla Martín García, Argentina

The species of the genus Drepanotrema, most of them endemic to the Neotropical region, belong to the Planorbidae. Of the nine species of this genus, six are found in Argentina. The present investigation analysed the individual growth of Drepanotrema cimex in Arenalcito pond (34°11 S, 58°15 W), Martín García Island Natural Reserve of Multiple Uses, Buenos Aires Province, Argentina. A total of 14 samples were collected (n = 1931) from February 2006 to June 2007. Five environmental variables were measured: water temperature, dissolved oxygen (mg L1), electrical conductivity (µS cm1), total dissolved solids, and pH. The individual growth of the species was analysed mathematically by means of the von Bertalanffy equation, where: Lt = 5,6(1-e2,0592 (t0,293)). The parameter L was estimated by the Ford-Walford Method. The population of D. cimex was characterised by a complex and dynamic size structure throughout the annual cycle. The analysis of the curves revealed unimodal (2006) and polymodal (April to June 2007) distributions, which pattern served to identify the existence of cohorts within the population studied.

As espécies do gênero Drepanotrema, a maioria delas endêmicas da região Neotropical, pertencem ao Planorbidae. Das nove espécies desta família, seis são encontradas na Argentina. Este artigo analisa o crescimento individual de Drepanotrema cimex na lagoa de Arenalcito, Reserva Natural de Usos Múltiples Ilha Martín García, Buenos Aires, Argentina (34°11 S - 58°15 W). A amostragem foi realizada entre fevereiro de 2006 e junho de 2007. Durante o curso das campanhas foram obtidas 14 amostras (n = 1931). Cinco variáveis ambientais foram medidas: temperatura da água, oxigênio dissolvido (mg L1), condutividade elétrica (uS cm1), sólidos dissolvidos e pH. O crescimento individual das espécies foi analisada matematicamente por meio da equação de von Bertalanffy em que: Lt = 5,6 (1-e2, 0592 (t0, 293)). O paràmetro L foi estimada pe lo método de Ford-Walford. A população de D.cimex foi caracterizada por uma estrutura complexa e dinâmica de tamanho ao longo do ciclo anual. A análise das curvas mostrou distribuições unimodais (2006) e polimodais (abril-junho 2007), identificando a existência de coortes na população estudada.

A study of chlorophyll-like and phycobilin pigments in the C endosymbiont of the apple- snail Pomacea canaliculata

Pigments present in the brown-greenish C morph of an intracellular endosymbiont of Pomacea canaliculata were investigated. Acetone extracts of the endosymbiotic corpuscles showed an absorption spectrum similar to that of chlorophylls. Three fractions obtained from silica gel column chromatography of the acetone extracts (C I, C II and C III), were studied by positive ion fast atom bombardment-mass spectrometry (FAB-MS) and hydrogen-nuclear magnetic resonance (H-NMR). Results indicated the presence of (1) a sterol in the yellow colored C I fraction; (2) a mixture of pheophorbides a and b in the major green fraction, C II; and (3) a modified pheophorbide a in the smaller green fraction, C III. Aqueous extracts of the C endosymbiont did not show evidence of the occurrence of C-phycocyanin, allophycocyanin or phycoerithrin (light absorption, fluorescence emission, and electrophoresis of the protein moieties) while cyanobacterial cells (Nostoc sp.) showed evidence of C-phycocyanin and allophycocyanin. The possible phylogenetic and functional significance of the pigments present in the C endosymbiont is discussed.

Life history of the land snail Habroconus semenlini (Stylommatophora: Euconulidae) under laboratory conditions

Habroconus semenlini is a micro-terrestrial gastropod native to South America. There are no previous studies on its biology. We studied its pattern of growth, fertility and lifespan under laboratory conditions. For this purpose, 80 snails were either grouped or kept isolated (40 animals in each condition) during their lifetime. Growth is indeterminate and the species is capable of self-fertilization with high reproductive success. Grouped snails had lower fecundity than the animals that were kept in isolation. This species has a short lifespan and only one reproductive period, which characterizes the occurrence of semelparity. Rev. Biol. Trop. 57 (4): 1217-1222. Epub 2009 December 01.

Habroconus semenlini es un gastrópodo micro-terrestre nativo de América del Sur. Actualmente se carece de estudios sobre su biología. Este estudio tuvo como objetivo verificar el patrón de crecimiento, la fecundidad y la esperanza de vida de esta especie en condiciones de laboratorio. Con este fin, 80 caracoles fueron mantenidos aislados o agrupados (40 animales en cada condición) durante su ciclo de vida. La especie tiene crecimiento indeterminado y es capaz de auto-fertilización con alto grado de éxito reproductivo. Los caracoles agrupados tuvieron menor fecundidad que los que se mantuvieron en aislamiento. Esta especie tiene una vida útil corta, y sólo un período reproductivo, lo que caracteriza la semelparidad.

Do climate variables and human density affect Achatina fulica (Bowditch) (Gastropoda: Pulmonata) shell length, total weight and condition factor? / Variáveis ambientais e humanas afetam o comprimento da concha, peso total e fator de condição de Achatina fulica (Gastropoda: Pulmonata)?

The length-weight relationship and condition factor have been broadly investigated in snails to obtain the index of physical condition of populations and evaluate habitat quality. Herein, our goal was to describe the best predictors that explain Achatina fulica biometrical parameters and well being in a recently introduced population. From November 2001 to November 2002, monthly snail samples were collected in Lauro de Freitas City, Bahia, Brazil. Shell length and total weight were measured in the laboratory and the potential curve and condition factor were calculated. Five environmental variables were considered: temperature range, mean temperature, humidity, precipitation and human density. Multiple regressions were used to generate models including multiple predictors, via model selection approach, and then ranked with AIC criteria. Partial regressions were used to obtain the separated coefficients of determination of climate and human density models. A total of 1.460 individuals were collected, presenting a shell length range between 4.8 to 102.5 mm (mean: 42.18 mm). The relationship between total length and total weight revealed that Achatina fulica presented a negative allometric growth. Simple regression indicated that humidity has a significant influence on A. fulica total length and weight. Temperature range was the main variable that influenced the condition factor. Multiple regressions showed that climatic and human variables explain a small proportion of the variance in shell length and total weight, but may explain up to 55.7 percent of the condition factor variance. Consequently, we believe that the well being and biometric parameters of A. fulica can be influenced by climatic and human density factors.

A relação peso comprimento e o fator de condição têm sido bastante explorados em pesquisas envolvendo caracóis para obter o índice de condição física em populações e avaliar a condição do habitat. Neste trabalho, nosso objetivo foi descrever que variáveis influenciam os parâmteros biométricos e o bem estar de Achatina fulica em uma recente introdução. De novembro de 2001 a novembro de 2002, amostras mensais desses caracóis foram coletadas na cidade de Lauro de Freitas (Bahia), Brasil. Em seguida, os caracóis foram acondicionados em laboratório e foram obtidos o tamanho da concha e o seu peso. A partir desses dados a curva potencial e o fator de condição foram calculados. Cinco variáveis ambientais foram consideradas: amplitude de temperatura, temperatura média, humidade, precipitação e densidade humana. Regressões múltiplas foram usadas para gerar modelos preditivos através do critério de seleção e logo foram ordenados utilizando o critério de Akaíke. Regressões parciais foram usadas para obter os coeficientes de determinação do clima e fatores humanos. Um total de 1460 indivíduos foram coletados, apresentando uma amplitude de crescimento de concha entre 4,9 a 102,5 mm (média 42,18 mm). A relação entre o crescimento total e o peso revelou que A. fulica apresentou um crescimento alométrico negativo. Regressões simples indicaram que a umidade teve uma influencia significativa sobre o tamanho total e o peso. A amplitude de temperatura foi a variável que mais influenciou o fator de condição. Os modelos de regressão múltipla indicaram que os fatores climáticos e humanos explicaram uma pequena porção da variança, no entanto explicou 55,8 por cento da variância do fator de condição. Consequentemente, acreditamos que o bem estar e os parâmetros biométricos de A. Fulica podem ser influenciados por fatores climáticos e humanos.

Effects of dietary calcium on growth and oviposition of the African land snail Limicolaria flammea (Pulmonata: Achatinidae)

In an attempt to elucidate the role of calcium in the life of the edible Achatinid snail, Limicolaria flammea (Miller) I investigated short and long term effects of calcium added to the food. The short term experiments lasted for 18, 30 and 32 weeks respectively, while the long term experiment to determine life time utilization of calcium carbonate lasted for 15 months. In the short term experiments, hatchlings were divided into densities of one, ten and 50 snails. In the 10 snail group, there was a positive correlation between calcium provision, body weight (t test, p < 0.01; r = 0.96, p < 0.0001) and shell length (t test, p < 0.01; r = 0.96, p < 0.00001). There was also a positive correlation between increase in shell length and availability of calcium in the 1 snail group (t test, p< 0.01; r = 0.99, p < 0.00001). In the 50-snail group, the correlation was positive for shell length of the snails (t test, p < 0.05; r = 0.99, p < 0.0001) and body weight (t-test, p < 0.05; r = 99, p < 0.00001). Mortality was very high in the snails deprived of calcium and they did not produce eggs. In the long term experiment, there were three feeding peaks in L. flammea. In the first feeding peak, amount of food and calcium ingested by the snails increased in the first three months of life. The second feeding peak occurred at six months of age, while the last occurred at 10 months of age. The amount of calcium ingested during the second peak decreased gradually in the 4th and 5th month. The amount of calcium ingested was lowest during the 3rd feeding peak. The period of highest weight gained by the snails was between the 1st and 6th month and then dropped at between six and 12 months of age which corresponds to the period of egg production. There were also three peaks of egg production; the first was between six and eight months (535 eggs), the second at between 10 and 11 months (350 eggs) and the third at 13 to 14 months (310 eggs) respectively.

Estudié el efecto de agregar calcio al alimento sobre el desarrollo del caracol pulmonado africano Limicolaria flammea (Müller). La cantidad de calcio tuvo una correlación positiva con el peso corporal (T de Student, p < 0.01; r = 0.96, p < 0.0001) y la longitud de concha (T de Student, p < 0.01; r = 0.96, p < 0.00001). Los caracoles que no recibieron calcio murieron en gran cantidad y no produjeron huevos. En un experimento a largo plazo, hubo picos de consumo del calcio y el mayor aumento de peso fue en los seis meses iniciales. Los picos de producción de huevos fueron entre los seis y los ocho meses (535 huevos), entre los diez y once meses (350 huevos) y en los meses 13 y 14 (310 huevos).

Biological and biochemical studies on Biomphalaria Alexandrina snails showing overgrowth and their infection with Schistosoma mansoni

The growth, egg-laying capacity, susceptibility to infection with Schistosoma mansoni and some biochemical parameters were-determined for Biomphalaria alexandrina snails which showing overgrowth compared to those of the same age having normal growth. During the period of 14 weeks, the growth rate of snails with overgrowth was significantly higher than those with the normal size. At the first week of observation the mean shell diameter of overgrowth snails was 5.75 +/- 0.8 mm and reaching 9.03 +/- 0.6 mm by the end of the 14[th] week, compared to 2.9 +/- 0.6 mm and 7.2 +/- 0.7mm for snails with normal size. The rate of increasing growth [relative to snails with the normal size] in the overgrowth snails was comparatively very high during the 1[st] week [ranged between 64.5% and 98.3%]. It was found that B. alexandrina snails with overgrowth laid higher number of eggs than those with the normal size. Their onset of egg-laying was at the first week of observation [1.42 eggs/snail/week] until reaching to the highest peak at the 15[th] week [18.7egg/snail/week]. Comparing with snails of the same age and normal size, the egg-laying started at the 5[th] week with a very low number of eggs [0.5 eggs/snail /week], reaching to 4.3 eggs/snail/week at the 15[th] week. There was a very highly significant reduction [p< 0.001] in the infection rate of snails with overgrowth [ranged between 5.0% and 8.3%] compared to those of snails with normal size [ranged between 52.4% and 52.9%]. The hemolymph glucose concentration of B. alexandrina with overgrowth was significantly [P<0.05] and highly significant [p<0.01 and p<0.001] higher than those of the corresponding snails with the normal size in Set I [snails from egg-masses of individual snails], Set II [snails from individual egg-masses] and Set III [snails from groups of egg-masses of groups of snails]. The total protein concentrations in hemolymph of snails which showing overgrowth were increased than those of normal size of Sets I and II, but urea concentrations were decreased in Sets I and III

Growth rate fitting using the von Bertalanffy model: analysis of natural populations of Drepanotrema spp. snails (Gastropoda: Planorbidae)

The genus Drepanotrema includes six species in Argentina. The life cycle in natural systems of Drepanotrema depressissimum, and D. lucidum has been little studied, except for some casual observations. The aim of this study is to analyze main population trends (age structures, recruitment periods, life span and curves of individual growth) in Paiva pond, Argentina. We explored growth model fitting and comparison methodologies between species and environments in Paiva pond and Isla Martín García (IMG), to determine interspecific patterns. Theoretical curves of von Bertalanffy’s model for each population were contrasted with samplings using the χ2 test. Expected sizes were transformed into a percentage of maximum size and cohorts started from zero time, which allowed them to be independent of the real or estimated starting date and a comparison was possible. A similar time scale was used, because the k values proved to be sensitive to time scale. Maximum size reached by D. lucidum was 6.9 mm and by D. depressissimum 9.38 mm. Growth rates (k) fluctuated from 1.302 to 1.368 in the first and 1.339 to 1.509 in the second species. No statistically significant differences were found in growth curves among species inhabiting the Paiva pond and in the different IMG water bodies independent of the beginning of each cohort and maximum size. In general, no winter cohorts were observed, except in one population of D. kermatoides (IMG). Comparing circannual and biannual growth rhythms most of the species reached 60 % of their development during their first year, and 85 % or more during their second year. Rev. Biol. Trop. 55 (2): 559-567. Epub 2007 June, 29.

En Argentina se encuentran seis especies del género Drepanotrema. El ciclo de vida en sistemas naturales de Drepanotrema depressissimu y D. lucidum ha sido muy poco estudiado, excepto por algunas observaciones aisladas. El objetivo de este estudio es analizar las principales tendencias de la población en la Laguna Paiva, Argentina. Usamos modelos de crecimiento y metodologías comparativas entre las especies y los ambientes en Paiva y la isla Martín García (IMG). Además, las curvas teóricas del modelo de von Bertalanffy para cada población fueron contrastadas con las muestras utilizando la prueba χ². Los tamaños esperados fueron transformados en porcentajes de tamaño máximo y las cohortes se iniciaron a partir del tiempo cero, lo cual les permitió ser independientes de la fecha inicial real o estimada y con ello ser comparables. Se utilizó una escala de tiempo similar debido a que los valores de k demostraron ser sensibles a la escala de tiempo. El tamaño máximo alcanzado por D. lucidum fue de 6.9 mm y por D. depressissimun fue de 9.38 mm. Las tasas de crecimiento (k) fluctuaron de 1.302-1.368 en la primera especie y 1.339-1.509 para la segunda especie. No fueron encontradas diferencias significativas en las curvas de crecimiento entre las especies que habitaban en Paiva ni en los diferentes cuerpos de agua de IMG, independientes del inicio de cada cohorte y del tamaño máximo. En general no se observaron cohortes de invierno, excepto en una población de D. kermatoides (IMG). Al comparar los ritmos de crecimiento anuales y semestrales, la mayoría de las especies alcanzaron el 60 % de su desarrollo durante el primer año y el 85 % ó más durante su segundo año.

Obtención de masas ovígeras del caracol lancetilla, Strombus pugilis (Mesogastropoda: Strombidae) en condiciones de laboratorio / Obtaining of egg masses of the snail, Strombus pugilis (Mesogastropoda: Strombidae) under laboratory conditions

The survival, reproduction and embryonic development of Strombus pugilis, were determined during a period of ten months under laboratory conditions. Seven progenitors were collected in Contoy Island, Quintana Roo, Mexico and later transferred to the laboratory, where they were placed in aquarium with 80 1 of sea water and fed with "pellets". A total of 30 egg masses were collected, one on September and the other on April. The estimated total length of one egg mass was 11.24 m; the mean number of embryos obtained per 2 cm was 264, obtaining an estimated total of 157 500 embryos in the egg mass. The means of the physical-chemical parameters during the study were: salinity 37.6 +/- 0.5% per hundred, pH 7.5 +/- 0.5 and temperature 28 +/- 0.2 degrees C. The maintenance and water recirculation system used to sustain the breading stock is excellent both for reproduction of the organism and for obtaining egg masses under controlled conditions.

Effect of non target snails on some biological of lymnaea natalensis snails and their infection to fasciola gigantica

The influence of non-target freshwater snails [Melanoides tuberculata and planorbis planorbis] on the capacity of Fas-ciola egg production F. gigantica miracidia to infect Lymnaea natalensis and their affect on mortality and growth rates showed that the snails exhibited a competitive ability against L. natalen-sis The mortality rate existed in mixed cultures with snails was greatly increased, and increased with increase of snails number. The egg production and growth rate were negatively affected by the presence of M. tuberculata and p. planorbis which was more pronounced when snails were at higher ratio 1L:10D.Also, the snails showed significant degree of reduction in infection rate of L. natalensis with F.gigantica miracidia.

Desarrollo embrionario de Strombus pugilis (Mesogastropoda: Strombidae) en el laboratorio / Embrionary development of Strombus pugilis (Mesogastropoda: Strombidae) in the laboratory

Stages from oviposition to veliger hatching are described for Strombus pugilis under laboratory conditions. Two egg masses from Playa Seyba, México, (20 degrees 45' N, 91 degrees 45' W) were used (three sub-samples per mass). Each sub-sample was immersed in a 11 container at 29 +/- 1 degrees C. This description is based on stages known from Strombus gigas, which include number of: fertilized eggs, morulae, gastrulae, trochophore larvae with slow movements, larvae with primordium foot, larvae with eyes, larvae with statocyst and veliger larvae. Eggs with first division appeared five hours after oviposition in the three replicates of each mass, although in greatest number in one of the egg masses. Trochophore larvae with slow movements appear after 50-54 hours and veligers hatch after 90 hours.

Diferentes fontes de cálcio na dieta do escargot gigante africano (Achatina fulica) e seu efeito no crescimento e rendimento de carcaça / Different calcium sources and their effect on the carcass of the snail Achatina fulica

Avaliou-se a eficiência do emprego de diferentes fontes de cálcio e o seu efeito sobre a carcaça do escargot Achatina fulica. Montou-se um ensaio, em delineamento inteiramente casualizado, com 4 tratamentos, com 10 animais/repetiçöes, com tamanho semelhante, aos 45 dias de idade, com duraçäo de 120 dias, utilizando a Dieta Base proposta por CUELLAR et al (1986) como padräo. Os tratamentos aplicados por kg de D.B foram: T1(250g/de calcário calcinado), T2(250g/ de farinha de concha de escargot); T3(250g/de osso calcinado) e T4(D.B. c/ 25 por cento de carbonato de cálcio). Ao término do ensaio, os animais foram submetidos a jejum de 7 dias e em seguida abatidos, e individualmente, pesados, mensurados e a carcaça fracionada em: concha, carne, hepatopâncreas, genitália/epifragma e líquidos (sangue, muco e água).

Effect of the plant azole pinnate on survival, growth rate fecundity and hatchability of egg-masses of Biomphalaria alexandrina snails

Data indicated that Azolla pinnata plants variously reduce the growth rate of Biomphalaria alexandrina snails expressed as net increase in shell diameter [direct or indirect exposure]. The plant density plays an important role in this respect. The higher the plant density, the lower the growth rate and vice versa. Indirect exposure of newly hatched B. alexandrina resulted from exposed treated eggs reduced the growth rate of these snails. Data revealed that direct and/or indirect exposure to the abnormal high density [50,000 plants/L] resulted in complete killing of B. alexandrina snails after 2 weeks from continuous exposure. Snails exposed directly to Azolla at 50,000 and 25,0000 plants/L failed to lay eggs. On the other hand, snails exposed to 10,000 plants/L laid few eggs, resulted in low reproductive rate [57.94] compared with unexposed ones [110.6]. The same results were recorded with hatchability of Biomphalaria eggs

Cultivo de Pomacea sordida (Swainson, 1823) em Cativeiro / Culture of Pomacea sordida (Swaison, 1823) in Captivity

Estabelecidas as condições necessárias para a reprodução e o desenvolvimento em laboratório de Pomacea sordida (Swainson, 1823), apresentamos os dados relativos à criação intensiva deste molusco. Estudos de alimentação demonstraram as preferências dos animais jovens (3, 6 e 9 mm). No estabelecimento de curvas de crescimento, foram utilizados alface e rami, por serem estes os alimentos mais bem aceitos pelos animais menores. A conversão média foi de 6g de alimento por grama de crescimento. Gráficos relativos ao consumo de oxigênio indicam que a densidade populacional aceitável foi de 1.000 animais por m2 com 10 mm (4cm2 de superfície de tanque por animal). A continuação deste estudo se faz necessário a fim de determinar a viabilidade econômica do processo e a natureza química do produto.

The growth conditions for Pomacea sordida in the laboratory were established. Various sources of feeding were tested and lettuce proved to be the best for the young mollusks. To the bigger ornes than 6 mm rami was an inexpensive foodstuff. Results related to the oxygem consumption indicated that the available density was 1.000 animais per m² and the best body length for the specimens should be 10mm. Our results suggest thar this animal could be raised as a source of animal protein for animal feeding. A continuation of study is necessary in order to determine the economical viability of the process and the chemical composition of the product.

Moluscos aquáticos do Estado de Rondônia (Brasil), com especial referência ao gênero Biomphalaria preston, 1910 (Pulmonata, Planorbidae) / Freshwater mollusks of the state of Rondonia (Brazil), with special reference to the genera Biomphalaria Preston, 1910 (Pulmonata, Planorbidae)

Foi realizado no Estado de Rondônia, Brasil, levantamento malacológico com o objetivo de estabelecer a distribuiçäo geográfica dos moluscos aquáticos, com ênfase especial no gênero Biomphalaria. Foram pesquisados 11 municípios ao longo da rodovia BR-364, totalizando 162 ecossistemas límnicos, dos quais 77 (48%) apresentaram-se positivos para, pelo menos, uma espécie de molusco. As seguintes espécies foram encontradas: Gastropoda, Planorbidae: Biomphalaria sp., B. amazonica, B. occidentalis, Drepanotrema cimex, D. anatinum, D. lucidum e D. depressissimum; Physidae: Stenophysa marmorata; Ancylidad: Gundlachia sp.; Thiaridae: Aylacostoma sp.; Ampullaridae: Pomocea sp.; Pelecypoda, Sphaeriidae: Eupera primei e Pisidium sp. Säo apresentados dados de distribuiçäo geográfica e discutida a importância epidemiológica dos achados

Avaliaçäo de populaçöes de planorbídeos, em habitats naturais, pelo método de perfuraçäo da concha / Evaluation of planorbid populations, in natural habitats, by the method of perforation of the shell

Propöe-se um novo método de marcaçäo de planorbídeos para determinaçäo de densidade e de outros parâmetros pertinentes ao estudo de dinâmica de populaçäo, como capacidade de migraçäo, taxas de crescimento e potencial biótico nos habitats naturais. Consiste em marcaçäo através de dois furos de cerca de 2 mm de diâmetro de cada lado da concha em sua extremidade anterior, usando-se um estilete metálico. Após a marcaçäo os caramujos säo imediatamente reintroduzidos no habitat, em local correspondente ao da captura processada poucos minutos antes. Nos experimentos realizados, as taxas de caramujos marcados, recapturados uma semana após a marcaçäo, variaram de 14 a 18% e permitiram calcular a populaçäo total de B. glabrata, de 5 mm de diâmetro ou mais. O método permite estimar também a populaçäo de jovens com menos de 5 mm e fazer marcaçöes múltiplas. É muito simples, de fácil manejo, näo exige equipamentos nem pessoal especializados e provoca menos impacto no ambiente do que outros métodos

Biology of Robertsiella kaporensis snails and Malaysian Schistosoma.

Studies on the bionomics and host-parasite relationship of Robertsiella kaporensis and Malaysian Schistosoma were investigated. The study was divided into 4 parts: cultivation of snails, R. kaporensis, and maintenance of Malaysian Schistosoma life cycle, daily cercarial shedding cycle in R. kaporensis, miracidial load and cercarial shedding pattern and the infectivity of Malaysian Schistosoma cercariae. R. kaporensis were cultured in the laboratory with the use of plastic container provided with fine sand. The snails were fed with diatoms and Saraca leaves. The development period for the snail eggs was about 20-30 days, the young grew to maturity in 14-15 weeks, and the average growth rate of snails was 0.23 mm per week. The daily cercarial shedding cycle of snails had shown that the peak emergence of cercariae of Malaysian Schistosoma occurred at night, between 6-10 pm. The miracidial load which yielded the best results in terms of percentage infection rates of snails and cercarial output was the miracidial concentration of 8 miracidia per snail. The study on infectivity of Malaysian Schistosoma cercariae has shown that there was a decrease in infectivity of the cercariae to mammalian hosts as the cercariae increased in age. The percentage infection rate of mice and numbers of worms recovered were highest in mice infected with cercariae of 0-1/2 hr. old. Infection of cercariae fell rapidly after the cercariae were 16 hr. old.