Survival Rates Of Snails Research Articles

Effects of Calcium Levels in Artificial Pellet Feed on the Growth and Survival Rate of Black Apple Snails (Pila polita)

The present study was conducted to evaluate the effects of different dietary calcium levels on the growth and survival rate of black apple snails (Pila polita) in the grow-out period. There were 3 replicates for each treatment and the snails were fed with five calcium levels (% dry matter) in diet as follows: 1% (Ca1), 3% (Ca3), 5% (Ca5), 7% (Ca7), and 9% (Ca9). Two-month-old juveniles with an average initial body weight of 2.13g, shell height of 21.71mm, and shell width of 16.35mm were reared in tarpaulin tanks (1 × 1 × 1m; 40cm water depth) at the density of 100 individuals per tank. After 4 months of the rearing period, the average body weight, shell height, and shell width of the snails reached the highest values in the Ca5 treatment (28.43 g, 54.97 mm, and 40.09mm, respectively) and these values were significantly different compared to the remaining calcium contents (Ca1, Ca3, Ca7, and Ca9). The survival rate of the snails in Ca3 (75.7%) was higher than in Ca1 and Ca7 (74.7%), Ca5 (73.7%), and Ca9 (71.7%). However, the survival rate was not significantly different among the treatments. Snails in Ca5 obtained the highest productivity (2.88 kg m-2) and this value was significantly different from Ca1 (2.55 kg m-2) and Ca9 (2.35 kg m-2). The results of this study showed that the growth rate and productivity of black apple snails were highest when they consumed a diet containing 5% calcium. The optimum requirement of calcium for the black apple snails in the grow-out period was 4.51%.

Dynamic change of population structure of Oncomelania hupensis

Objective To understand the successive dynamic change of population structure of Oncomelania hupensis during a one-year period, so as to provide the evidence for snail control. Methods A river beach and a ditch infested with O. hupensis snails were selected and longitudinally investigated in the midmonth during one year. The snail survey indices included the survival status, gender, number of whorls, length and width of shell, and gonad development status (measured by the color depth of gonad and the length ratio of gonad to liver), and the monthly snail eggs in the soil were collected and counted simultaneously. In addition, the temperature and humidity of the soil and the daily data of air temperature and precipitation were measured or collected during the study period (every month). Results Both survival rate of snails and live snail density at the two environments were positively correlated with the temperatures of air and soil. With a slight bimodal distribution, the snail survival rate peaked from May to June, and in September. The living snail densities got the highest level in July and September in the river beach, and from April to May in the ditch. The regression equations of snail length (L) and width (W) were Lbeach = 2.355 + 1.678W (F = 2 989.43, P < 0.01) and Lditch = 0.478 + 2.091W (F = 2.989.43, P < 0.01), respectively. The snails were the ones with 4.07-11.81 mm in the length (8.98 ± 0.92) mm in the river beach, and the snails were the ones with 3.63-9.92 mm in the length (7.03 ± 0.82) mm in the ditch. The main snails were the ones with five to eight whorls of shell in the river beach and four to seven whorls of shell in the ditch. The proportions of snails with less than or equal to five whorls (in the river beach) and four (in the ditch) were the highest in May and September, about 20%. The ratios of male and female snails were 1.66 in the river beach and 1.22 in the ditch, respectively. The gonad development status of male and female snails was basically synchronous and had a bimodal abundance period - from April to May and September to October. The numbers of snail eggs in the soil among months were significantly different, reaching the highest in June in the river beach (100.8/0.1 m2), and May in the ditch (82.5/ 0.1 m2). Conclusion The principal periods of breeding and alternation of generations of snails are April-May and SeptemberOctober every year, which should also be the optimal time for mollusciciding in schistosomiasis susceptible zones.

The role of spotted green pufferfish Tetraodon nigroviridis in controlling golden apple snail Pomacea canaliculata: an effective biological control approach involving a new agent

ABSTRACTThe golden apple snail Pomacea canaliculata is invasive in South China and poses serious harm to agricultural production and aquatic ecosystems. In the present study, we investigated the predatory potential of the spotted green pufferfish Tetraodon nigroviridis (50 mm in body length) on snails of various sizes in fresh and brackish water (4.5 ppt salinity). The survival and damage rates of 50 snails were estimated at 1, 3, 5 and 7 days. The survival rate of snails, including 10 adult snails (20–35 mm shell height), decreased less than 25% in the presence of pufferfish, and this decrease was more profound in brackish than in fresh water. Approximately 98% of the snails died in brackish water in the presence of only four pufferfish. The pufferfish also inflicted a high rate of snail injury resulting from attacks involving bites. In addition, the pufferfish affected the behaviour of the snails, with more than 95% of snails exhibiting tightly closed opercula. Thus, the results of this study suggest that pufferfish are effective for the biological control of golden apple snails.

Total antioxidative status and the activity of peroxidase and superoxide dismutase in the haemolymph of Lymnaea stagnalis (L.) naturally infected with digenean trematodes

Indicators in the antioxidative system of snails naturally infected with three species of trematodes (Plagiorchis elegans, Paryphostomum radiatum and Echinoparyphium aconiatum) were compared. The total antioxidative status (TAS) and activities of peroxidase (POX) and superoxide dismutase (SOD) in the haemolymph of sexually mature individuals of wild-caught Lymnaea stagnalis, maintained at 19 8 Ci n the laboratory, were tested. No significant differences were detected in TAS between P. radiatum snails uninfected and infected, with the exception of the 20th day. In the case of snails infected with P. elegans TAS was higher than in controls only at the beginning of the experiment, while in those infected with E. aconiatum it was always lower than in the control group. In all infected snails the activ- ity of POX was higher than in uninfected snails. The changes in activity of SOD in the infected snails differed depending on the species of trematodes. Among the tested host -parasite systems, the survival rate of snails infected with E. aconiatum was the lowest. We suggest that the TAS of snails can be used as an indicator of trematode virulence.

Susceptibility of Biomphalaria spp. to infection with Schistosoma mansoni in sympatric and allopatric combinations with observations on the genetic variability between snails

This investigation was carried out to study the susceptibility of Saudi Biomphalaria arabica to Egyptian Schistosoma mansoni in comparison with the susceptibility of Egyptian Biomphalaria alexandrina to the same parasite. This was in order to know the possibility that the parasite might be able to spread into Saudi Arabia and to determine the genetic variability between Egyptian B. alexandrina and Saudi Biomphalaria arabica snails. Lab bred Egyptian B. alexandrina and Saudi B. arabica snails were exposed individually to 10 freshly hatched Egyptian S. mansoni miracidia/snail. The mortality rate, infection rate, prepatent period, duration of cercarial shedding and cercariae production per snail were recorded in both the sympatric couple (Egyptian B. alexandrina and Egyptian S. mansoni) and in the allopatric combination (Saudi B. arabica and Egyptian S. mansoni). The results revealed that, the survival rate of snails exposed to Egyptian S. mansoni miracidia at 34th day post-exposure (at first cercarial shedding) was higher in B. arabica than in B. alexandrina. After shedding, the mortality rate was higher in the B. arabica, compared to B. alexandrina. The infection rate was higher in B. arabica than B. alexandrina; the mean of prepatent period was shorter in the B. arabica than in the B. alexandrina. However, the duration of cercarial shedding was longer in the Egyptian snails and the cercarial production per snail was higher in B. alexandrina snails than in B. arabica. To study the genetic variability between B. alexandrina and B. arabica, RAPD-PCR on the genomic DNA of snails was done. RAPD-PCR revealed significant variation between the two snail species. In conclusion, the results suggest that B. arabica can play a role in the transmission of Egyptian S. mansoni in Saudi Arabia and therefore this parasite might be able to spread into the Kingdom. In addition, the RAPD-PCR results demonstrated genetic variability between the two species which may be related to the differences in susceptibility of both Saudi and Egyptian Biomphalaria snails to Egyptian S. mansoni infection.

Complex species interaction in tropical backreef communities

A complex interaction between the sea urchin, Tripneustes ventricosus, and snail, Cerithium litteratum, has emerged in lagoonal backreefs of Jamaica. These two species are spatially correlated in most of the habitats that were examined. In field and laboratory observations, urchins pick up and cover their tests with as many as 40 live snails continuously for up to two days. I examined whether urchins cover to avoid predation, and whether growth and survival of snails is negatively affected by this behavior. The presence of predators prompted urchins to collect ten times as many snails, which gained 47% less tissue weight and 75% less shell lip thickness than snails unassociated with urchins. However, the survival rate of snails positioned on urchins was three times greater than that of free snails on sandy backreef substratum. Results of this study imply a biomass gain versus survival trade-off, and provide insights into complex interactions.

Effects of predation on the exotic freshwater snail Pomacea canaliculata (Caenogastropoda: Ampullariidae) by the indigenous turtle Chinemys reevesii (Testudines: Geoemydidae)

We studied the predatory potential of the turtle Chinemys reevesii on the apple snail Pomacea canaliculata using two series of experiments. First, we investigated the relationship between turtle body size and the maximum size of snails consumed over a period of 3 days within 0.37 m2 containers. The maximum snail size consumed was positively related with turtle size. Secondly, we investigated the predation of snails by turtles over a period of 8 weeks. We released 200 snails (10–30 mm shell height) and an adult turtle (155–183 mm carapace length) into each of two 2.08 m2 plots with soil and rice plants. Subsequently, snail density was monitored every week and 200 snails were added to low density plots up to twice a week. Two control plots with the same initial density of snails but without turtles were also monitored. The density and survival rate of snails were lower in plots with a turtle than in control plots. We estimated that a single turtle consumed >2,000 snails in 8 weeks. In addition, the biomass of duckweed (given as food for snails) was greater in turtle plots than in control plots, suggesting that the presence of turtles had an indirect effect on weed.

Schistosoma haematobium: comparative studies on the characteristics of infection in three populations of Planorbarius metidjensis from the Agadir province in South Morocco.

Planorbarius metidjensis measuring 2 or 3 mm in diameter and originating from three populations in the Agadir province (Ida Ou Gnidif, Imouzzer, and Sidi Belkacem) were experimentally infected with Schistosoma haematobium to determine if the complete larval development of the parasite might be ensured by any snail population of the Agadir province and to compare the general characteristics of infection. No significant difference between the three populations was noted in the survival rates of snails when the first shedding occurred or in the prevalence of infection. The mean duration of the shedding period was significantly higher in the Imouzzer population (111 days versus 53-58 days). The total number of cercariae shed per mollusc was significantly lower in the Ida Ou Gnidif planorbids (1,398/snail versus 3,346 and 3,343/snail in the other 2 groups). The same rhythm in daily cercarial production was noted in the three snail groups, with the periodicity being 18-20 days. Despite some differences in parasite development between the three snail populations, the different populations of P. metidjensis can ensure the complete development of S. haematobium and maintain local transmission in the South of Morocco.