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Effect of Diet and Stocking Densities on Life History Traits of Clea helena (Philippi 1847) Reared in Captivity

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Abstract

The freshwater gastropod Clea helena has recently been targeted by the freshwater ornamental industry due to its predation abilities on other snail species. This work describes for the first time some life history traits of this species, including reproduction, growth and development under laboratory conditions. Additionally, appropriate stocking densities were studied in order to assess the production viability of healthy snails in close-circuits systems. The species is dioecious and breeds under laboratory conditions but fertility rates presented were low. Hatching occur 52 ± 6 days after oviposition, at 25.0°C. Development is direct and juveniles hatch at shell length SL=3.1 ± 0.3mm (n=20) and resemble the adults in shell shape and color. Growth rates during a maximum period of 60 days were compared between snails fed on three different diets and results showed they were influenced by the different diets treatments (P<0.05). Growth performance experiments at three stocking densities (5, 10, 20 snails/L) with three replicates per treatment were also performed. During the first month, individuals stocked at 5 snails/L had significantly faster growth rates than those stocked at 20 snails/L. No significant growth responses were found during the second month among all densities and overall growth rates for this experiment also revealed no density-dependent growth responses.
Open Access
Volume 4 • Issue 5 • 1000187
J Aquac Res Development
ISSN: 2155-9546 JARD, an open access journal
Research Article Open Access
Coelho et al., J Aquac Res Development 2013, 4:5
http://dx.doi.org/10.4172/2155-9546.1000187
Research Article Open Access
Aquaculture
Research & Development
Keywords: Gastropoda; Freshwater; Carnivore; Diet; Stocking
density; Ornamental; aquaculture
Introduction
e family Buccinidae (Gastropoda: Neogastropoda), commonly
known as true whelks, presents a worldwide distribution, with the
larger species occurring at the subtidal zones of both northern and
southern temperate and cold seas. Clea helena (Philippi, 1847) is one
of very few whelks that lives its entire life in freshwater habitats and
can be natively found in Tropical Indo-West Pacic regions like China,
ailand and Indonesia [1].
Most Clea species live in clean, fast-owing streams where they can
be found in sandy or muddy substrates. C. helena is exceptional in being
found in ponds and ditches too, and its tolerance for a wider range of
water conditions is probably why this one particular species does so
well in captivity.
Adult individuals present a typical ovate-conical thick shell (Mean
Shell Length=24.3 ± 3.6 mm; n=35) with brown and yellow lateral
bands. e shell presents ve to six whorls spiral with lateral ridges
and an operculum. e body is yellowish with grey speckles all over.
e mantle forms a foldable tube, while the siphon is equipped with
chemoreceptors, that like in other predators or scavenger species, Clea
uses to perceive water and locate food. ere is no apparent sexual
dimorphism in the shell structure. Virtually nothing is known about
this species’ natural life traits. However this poorly studied freshwater
snail has recently been targeted by the freshwater ornamental industry,
due to its predation abilities on other snail species that frequently
became aquarium pests. For this reason it is commonly called “Assassin
Snail” in the trade.
Despite its growing popularity, studies concerning this species’
biology and developmental growth patterns are absent. is basic
information is essential in order to develop an optimal rearing protocol
and improve production systems. From an aquaculture production
point of view, the culture system is one of the most inuential factors
for growth and survival of various commercial species, but such
information does not exist for C. helena.
e objective of this work was to describe for the rst time C.
helena life history traits, including collecting breeding, growth and
development data under laboratory conditions as well as to determine
appropriate stocking densities in order to assess the production viability
of healthy snails in close-circuits systems.
Material and Methods
is study was conducted over a period of 17 months.
Broodstock and experimental setup
e broodstock (Mean Shell Length=25 ± 2.3 mm; n=20) was
obtained from an online Portuguese pet store. e animals were
maintained in one aquarium (100 L) containing a substratum composed
of a 4 cm layer of sterilized beach sand, and equipped with a lter (Rena®
Filstar XP2) and aeration system, maintained under a natural daylight
with no articial ilumination. Tropical freshwater large leaf plants, PVC
pipes and plastic net pieces were added to the tank to provide spawning
surfaces for the snails. e snail density was 0.2 individuals L-1.
During the study, water quality was monitored daily for temperature
and pH, and weekly for nitrites, nitrates and phosphates. Water
*Corresponding author: Ana Rita Coelho, Instituto Português de Malacologia,
Zoomarine, EN125 Km65 Guia, 8201-864 Albufeira, Portugal, Tel: +351965690096;
E-mail: rita.coelho@gmail.com
Received January 20, 2013; Accepted March 25, 2013; Published April 05, 2013
Citation: Coelho AR, Dinis MT, Reis J (2013) Effect of Diet and Stocking Densities
on Life History Traits of Clea helena (Philippi 1847) Reared in Captivity. J Aquac
Res Development 4: 187 doi:10.4172/2155-9546.1000187
Copyright: © 2013 Coelho AR, et al. This is an open-access article distributed
under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the
original author and source are credited.
Abstract
The freshwater gastropod Clea helena has recently been targeted by the freshwater ornamental industry due
to its predation abilities on other snail species. This work describes for the rst time some life history traits of
this species, including reproduction, growth and development under laboratory conditions. Additionally, appropriate
stocking densities were studied in order to assess the production viability of healthy snails in close-circuits systems.
The species is dioecious and breeds under laboratory conditions but fertility rates presented were low. Hatching
occur 52 ± 6 days after oviposition, at 25.0°C. Development is direct and juveniles hatch at shell length SL=3.1
± 0.3mm (n=20) and resemble the adults in shell shape and color. Growth rates during a maximum period of 60
days were compared between snails fed on three different diets and results showed they were inuenced by the
different diets treatments (P<0.05). Growth performance experiments at three stocking densities (5, 10, 20 snails/L)
with three replicates per treatment were also performed. During the rst month, individuals stocked at 5 snails/L
had signicantly faster growth rates than those stocked at 20 snails/L. No signicant growth responses were found
during the second month among all densities and overall growth rates for this experiment also revealed no density-
dependent growth responses.
Effect of Diet and Stocking Densities on Life History Traits of
Clea helena
(Philippi 1847) Reared in Captivity
Ana Rita Coelho1,2,3*, Maria Teresa Dinis1 and Joaquim Reis2
1Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
2Instituto Português de Malacologia, Zoomarine, EN125 Km65 Guia, 8201-864 Albufeira, Portugal
3Zoomarine, EN125, Km65 Guia, 8201-864 Albufeira, Portugal
Citation: Coelho AR, Dinis M T, Reis J (2013) Effect of Diet and Stocking Densities on Life History Traits of Clea helena (Philippi 1847) Reared in
Captivity. J Aquac Res Development 4: 187 doi:10.4172/2155-9546.1000187
Page 2 of 4
Volume 4 • Issue 5 • 1000187
J Aquac Res Development
ISSN: 2155-9546 JARD, an open access journal
temperature was maintained approximately constant at 25 ± 1°C using
an aquarium heater (RenaCal Basic 150W). Two times per week, 15-
20% water changes were performed to improve water quality.
Specimens were fed with a combined maintenance diet of dry food
supply like catsh pellets (Nutran© Sinking tablets) and live prey
such as Physella acuta (Draparnaud 1805) and Melanoides tuberculata
(Müller 1774), ad libitum.
Reproductive behavior
Clea helena is dioecious and sexual dimorphism is absent, therefore
total broodstock acquired (20 individuals) were stocked together in
order to assure that the group could be sexually heterogenic. Notes
on reproductive behavior (presence/absence copulation; copulation
position and duration) were taken twice a day (10:00 am and 4:00 pm).
Aer spawning was nished, females were measured with callipers
(Figure 1) for mean shell length (SL; measured from the top of the
spire to the base of the aperture). Egg sacs’ length was measured on the
attached edge. Objects with recently laid eggs were carefully transferred
to sh oating incubation devices inside the broodstock tank till
hatching occurred.
Juveniles-diet and growth
is experiment was conducted in a recirculating 250 L glass
aquarium system, with no substratum and lled with oxygenated,
ltered, freshwater, maintained under a natural photoperiod. C. helena
juveniles (Mean Shell Length=9.5 ± 31.5 mm; n=20) selected from
the stock population, were held individually in oating plastic sh-
breeding boxes (Hagen© Marina multibreeder: length 20.32 cm, width
9.16 cm, height 10.79 cm), aer removing the bottom compartment.
Ten replicates for each of 3 dierent diet treatments were placed
in the tank. e experiment tank contained thus a total of 30 semi-
submerged oating devices, each containing one juvenile snail. e
snail density was 0.12 individuals L-1.
e fact that all cage devices were housed in the same tank ensured
homogeneous conditions for all experiments. Water conditions were
kept similar to those described in Broodstock and breeding setup
section.
Prior to any feeding experiment, juveniles were fed ad libidum for
ve days and then fast (no food provided) for two days to standardize the
hunger levels. Growth rates during a maximum period of 60 days were
compared between snails fed on three dierent diets: A-Catsh pellets,
B-live prey, C-combined dry and live food (broodstock maintenance
diet). Juvenile snails were fed to excess every two days. Treatments were
randomly allocated within the system.
Growth performance was measured as an increase in shell length
(from apex to the base of the spire) using a calibrated micrometer under
a stereomicroscope (Nikon SMZ800) or with callipers to the nearest
0.05 mm, according to individual size. Shell length, as opposed to shell
weight, was monitored because it is thought to be a more important
factor for reaching sexual maturity (Hanning, 1979). Individuals were
measured in regular periods (15, 30, 45 and 60 days). Average weekly
growth increment (G) was calculated using the following equation:
10
10
WW
G
tt
=
Where W0 and W1=shell length at times t0 and t1, respectively [2].
Eventual casualties were recorded and removed from each tank as
soon as detected to prevent water fouling and cannibalism.
Eect of stocking density
Laboratory raised C. helena juveniles (standard lengths=8-11mm)
were randomly selected and stocked in similar plastic oating cages used
for growth performance experiments at one of three stocking densities
(5, 10, 20 snails/L) with three replicates per treatment. Treatments were
randomly allocated to the location within the tank. To perform this
experiment, snails were fed combined maintenance diet of dry food and
live prey described in Broodstock and rearing setup section.
Shell length was determined using the same methodology
described in Growth performance experiment with individuals being
measured in regular periods (15, 30, 45 and 60 days). is experiment
was conducted for a period of eight weeks.
Statistical analysis
e statistical signicance of the eects of dierent diet treatments
on growth rates of the juvenile snails was evaluated by one-way ANOVA
[3] for data obtained at four dierent times (15, 30, 45, and 60 days).
Signicance of dierences among treatments was tested with a
Tukey’s post-hoc test. Dierences among treatments were considered
signicant for P<0.05. Data were tested for homogeneity of variances
using a Shapiro-Wilk test and were found to be normally distributed.
All statistic analyses were performed using Statistica 6.0 (Statso Inc.).
Results
Breeding and early development
Twelve days aer broodstock accommodation started, mating
behaviors were recorded, with males climbing over females shell. For
a period of 20-30 minutes male stayed rmly attached to the female
shell but no copulatory attempt could be seen. Aerwards, male slightly
slides towards female right side and starts grasping with his penial
sheath searching for genital aperture.
Copulation would usually last for 3 h 40 min ± 45 min (n=7).
Spawning process was dicult to observe because this is mainly a
nocturnal behavior. Eggs were laid individually in transparent sac
deposits in solid smooth surfaces, like PVC pipes or plant leafs, but
were frequently seen in aquarium walls too.
Eggs were 1.3 ± 0.4 mm in length and egg sacs 3.7 ± 0.6 mm in
length on the attached edge (Figure 2). Each female deposits between
1 to 4 eggs per clutch in a straight line, separated from each other by 5
mm approximately. Eggs were frequently seen in aquarium walls too.
Hatching occurred 52 ± 6 (n=25) days aer oviposition; the range
Figure 1: Measurement of C. helena shell length.
Citation: Coelho AR, Dinis M T, Reis J (2013) Effect of Diet and Stocking Densities on Life History Traits of Clea helena (Philippi 1847) Reared in
Captivity. J Aquac Res Development 4: 187 doi:10.4172/2155-9546.1000187
Page 3 of 4
Volume 4 • Issue 5 • 1000187
J Aquac Res Development
ISSN: 2155-9546 JARD, an open access journal
was 46-58 days at 25.0°C (n=25). Egg cases were found empty with
open holes that provide evidence of successful hatches (Figure 3).
Newly hatched juveniles (Figure 4), measured SL=3.1 ± 0.3 mm
(n=20) and resembled the adults in shell shape and color although
typical shell stripes were not clearly marked.
Diets and growth
Growth rates of C. helena juveniles, estimated by shell length, were
inuenced by the dierent diets treatments (P<0.05) (Figure 5).
Juveniles reared with Diet 3 (dry food and live prey combined diet)
presented signicantly higher growth rates than those presented by
both other diets (ANOVA; F=4.30; P<0.05; post-hoc Tukey, p<0.05). No
signicant dierences were found between the use of Diet 1 and Diet
2 (P>0.05). Growth pattern was similar to all three diets and juveniles
fed with combined diet (dry food and live prey) presenting the highest
growth rate during the entire test duration.
Stocking density experiment
e mean shell length (SL) at stocking was 9.6 ± 1.5 mm (n=105)
and there were no signicant dierences in initial SL among densities
(P>0.05).
Average weekly growth rates of C. helena juveniles, tended to
slightly decline with increased stocking density during the rst month
and were indistinguishable among densities during the second month
(Figure 6).
During the rst month, individuals stocked at 5 snails/L had
signicantly faster growth rates than those stocked at 20 snails/L
(p=0.031). No signicant growth responses were found during the
second month among all densities and overall growth rates for this
experiment also revealed no density-dependent growth responses.
Survival ranged from 97-100% among individual replicates with no
signicant dierences among treatments (p=0.691).
Discussion
Like the other members of the family Buccinidae, C. helena is
gonochoristic and fertilization is internal. ere is no visible sexual
dimorphism and in all copulations observed, no size dierences were
recorded between males and females. is morphological pattern
diers from those described for other Buccinidae species [4] were
Figure 2: Clea helena fertilized egg sac attached to a plant leaf.
Figure 3: Clea helena recently hatched egg.
Figure 4: Clea helena newly hatched juvenile.
10.83
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70
Shell length (mm)
Age (days)
Dry food
diet
Live Prey
diet
Combined
diet
Figure 5: Mean (mm, ± Standard deviation, N=5) of Clea helena juveniles
shell length reared at three different diets.
ab b
c
0
1
2
3
4
5
6
5 snails/20L10 snails/20L20 snails/20L
Mean Growth rate (mm/Wk)
1st Month
2nd Month
Overall
Figure 6: Mean Weekly growth rate (mm/WK ± <SD) of juvenile Clea Helena
stocked at three different densities over an 8 weeks period. Signicant
pairwise differences between densities are shown by letter and were found
only during the rst month.
Citation: Coelho AR, Dinis M T, Reis J (2013) Effect of Diet and Stocking Densities on Life History Traits of Clea helena (Philippi 1847) Reared in
Captivity. J Aquac Res Development 4: 187 doi:10.4172/2155-9546.1000187
Page 4 of 4
Volume 4 • Issue 5 • 1000187
J Aquac Res Development
ISSN: 2155-9546 JARD, an open access journal
sexual dimorphism was clearly registered, although no data is available
on other Clea species.
To our best knowledge, no data on wild specimens’ spawning
season is available either, but results from the present study indicate
that, under laboratory environmental controlled conditions, C. helena
is able to breed all the year through.
Unlike other Buccinidae family members female, C. helena
individuals lay only 3-4 eggs per clutch. Even under controlled
conditions and ad libitum food availability, this species presented a very
low fertility rate and a very high survival rate through the entire study
[5].
Research on diet and growth clearly showed that a combined diet
(dry food and live prey) produces signicantly better results than those
presented by other simpler diets used. at comes in line with the
knowledge that this species is a very eective and non-specic snail
predator, which results in a naturally diverse and enriched protein
food intake. is is also consistent with reports for other invertebrate
species [6], that diets which contain a mixture of two or more proteins
are better utilized by the animals. We hypothesize that during the
feeding experiments using a combination diet, the energy consumed
by the snails while preying could easily be compensated by the dry food
simultaneously available. e absence of signicant dierences among
both other diets might also be related to the ratio between food intake
Vs energy spent acquiring it.
Choosing an appropriate diet is crucial for maintaining successful
snail stock cultures in laboratory. In order to fulll the optimum
growth rate possible for this species, further studies would have to be
undertaken in order to nd an articial protein source that fullls the
dietary needs with inexpensive cost and ease of use that might suit an
intensive production management.
Natural densities of C. helena are unknown, so comparisons with
other freshwater snails (Pomacea and Marisa genera), marine snails
(Babylonia genus) and land snails (Helix genus) stocking densities
studies were considered. Average weekly growth pattern during the rst
month, with increased stocking density tended to decline slightly during
the rst month which is concordant with similar studies performed on
Pomacea genus [7,8], Marisa cornuarietis [9], Babylonia areolata [10]
and various land snail species [11-13].
In the present study, individuals stocked at 5 snails/L had signicantly
faster growth rates than those stocked at the upper limit tested (20
snails/L). is is also consistent with experiments performed with other
previously referred genera and is likely to be related with competition
for space and prey among individuals. No signicant growth responses
were found during the second month among all densities, which could
possibly indicate that the amount of metabolites wastes accumulated in
the water, that are usually considered detrimental to juvenile’s growth,
doesn’t seem to inuence our test responses.
Survival rates obtained allow us to consider C. helena a robust
specie, which is an important feature when considering ornamental
market issues, like shipping and wholesale stocking.
Conclusions
Besides the overall contribution to a systematic knowledge of
C. helena life history important traits like breeding, growth and
development data under laboratory conditions this study also
demonstrates that it is feasible to culture healthy marketable size snails
in a re-circulating system. Nevertheless, further studies are encouraged
namely focusing in nding a dietary articial protein source substitute
and trying to raise the extremely low fertility rate presented which can
be impairments to a prospectus commercial farming of this species.
Acknowledements
Ana Rita Coelho holds a grant from the Fundação para a Ciência e Tecnologia,
Portugal (BDE 15577/2005).
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Citation: Coelho AR, Dinis MT, Reis J (2013) Effect of Diet and Stocking Densities on Life
History Traits of Clea helena (Philippi 1847) Reared in Captivity. J Aquac Res Development 4:
187 doi:10.4172/2155-9546.1000187
... Freshwater snails of the genus Clea are one of very few groups of whelks that live their entire life in freshwater habitats and can be natively found in the Tropical Indo-West Pacific regions of China, Indonesia and Thailand (Trew, 1990;Coelho et al, 2013). They are found in ponds, small streams, waterfalls and ditches, and has a tolerance for a wide range of water conditions (Krailas et al, 2012;Coelho et al, 2013). ...
... Freshwater snails of the genus Clea are one of very few groups of whelks that live their entire life in freshwater habitats and can be natively found in the Tropical Indo-West Pacific regions of China, Indonesia and Thailand (Trew, 1990;Coelho et al, 2013). They are found in ponds, small streams, waterfalls and ditches, and has a tolerance for a wide range of water conditions (Krailas et al, 2012;Coelho et al, 2013). Colloquially they are known as the assassin snail and snail-eating snail. ...
... This snail feeds on worms and gastropods due to its predation abilities. It is known to feed on other snail species that frequently became aquarium pests (Coelho et al, 2013). They were reported as the first intermediate host and second intermediate host of intestinal flukes in Thailand (Krailas et al, 2012;Chantima et al, 2013). ...
Conference Paper
Full-text available
Trematode infections of freshwater snails genus Clea A. Adams, 1855 were studied at 11 locations in the reservoirs of lower northeast Thailand. The aim of this study was to evaluate the natural trematode infections of Clea snails. In March 2016, the snails were collected from four provinces (Nakhon Ratchasima, Buri Ram, Surin and Si Sa Ket). Five collectors picked snails by hand for 10 minutes at each station. The collected snails were observed for trematode infections by shedding and crushing methods. The infection rate was 1.92% (6/312). Cercariae were categorized by their morphological characteristics. Three types of cercariae were found. They were Furcocercous cercariae-Brevifurcate apharyngeate cercariae (tail forked), Cotylomicrocercous cercariae-Podocotyle (Podocotyle) lepomis (cup-shaped tail with adhesive organ), and Cercariaeum cercariae-Brachylaima virginianum (tail absent). The infection rates by these parasites were 0.64%, 0.96% and 0.32% respectively. Double infections were found with Podocotyle (Podocotyle) lepomis and Brachylaima virginianum.
... Among these, Clea helena (von dem Busch, 1847) ( Fig. 1), sometimes referred to Anentome at the rank of genus or subgenus, has recently become a popular commodity in the ornamental pet industry (Ng et al., 2016a(Ng et al., , 2016b. The ability of this species to tolerate still waters (Brandt, 1974) has been a significant factor in their adaptability to captive conditions (Coelho, Dinis & Reis, 2013). Commonly known as "assassin snails" among other names for their voracious appetite for other gastropods, they are non-selective predators and scavengers of a wide variety of gastropods, including those larger than themselves, but may also feed on fish eggs and shrimp (Bogan & Hanneman, 2013). ...
... Little is known about the anatomy and biology of Clea, with much of what is to be found in the published record relating primarily to taxonomy and distribution, although interest in the life history and ecology of the genus has grown with their increasing popularity as aquarium pets (Monks, 2009;SiputKuning Journal, 2010;Coelho, Dinis & Reis, 2013). In addition, Clea nigricans A. Adams, 1855 has been used to explore the potential impact of climate change on tropical freshwater systems (Polgar et al., 2015), and Clea helena has been touted as a possible model for developmental and environmental physiology (Newel & Bourne, 2013). ...
... They are present in Nassariinae (Fretter, 1941;Johansson, 1957;deMaintenon, 2001;Strong, 2003), but are lacking in Anentominae as well as in Dorsaninae and in Buccinanopsinae (Simone, 1996;Simone & Pastorino, 2014). As in other freshwater gastropods, Anentome deposits egg capsules on firm substrates and development is nonplanktotrophic; eggs are deposited in clutches of one to four eggs from which crawling juveniles emerge (Coelho, Dinis & Reis, 2013). This reproductive strategy has important implications for limiting dispersal and gene flow, and hence for speciation via isolation by distance. ...
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The genus Clea from SE Asia is from one of only two unrelated families among the megadiverse predatory marine Neogastropoda to have successfully conquered continental waters. While little is known about their anatomy, life history and ecology, interest has grown exponentially in recent years owing to their increasing popularity as aquarium pets. However, the systematic affinities of the genus and the validity of the included species have not been robustly explored. Differences in shell, operculum and radula characters support separation of Clea as presently defined into two distinct genera: Clea , for the type species Clea nigricans and its allies, and Anentome for Clea helena and allies. A five-gene mitochondrial (COI, 16S, 12S) and nuclear (H3, 28S) gene dataset confirms the placement of Anentome as a somewhat isolated offshoot of the family Nassariidae and sister to the estuarine Nassodonta . Anatomical data corroborate this grouping and, in conjunction with their phylogenetic placement, support their recognition as a new subfamily, the Anentominae. The assassin snail Anentome helena , a popular import through the aquarium trade so named for their voracious appetite for other snails, is found to comprise a complex of at least four species. None of these likely represents true Anentome helena described from Java, including a specimen purchased through the aquarium trade under this name in the US and one that was recently found introduced in Singapore, both of which were supported as conspecific with a species from Thailand. The introduction of Anentome “ helena ” through the aquarium trade constitutes a significant threat to native aquatic snail faunas which are often already highly imperiled. Comprehensive systematic revision of this previously unrecognized species complex is urgently needed to facilitate communication and manage this emerging threat.
... Thus, the time of introduction of Anentome helena into Kranji Reservoir could not be more than five years ago. Its natural diet has not been studied in detail, but ex-situ experiments and observations by aquarists have recorded Anentome helena actively hunting and preying on smaller-sized Planorbidae, Physidae, and Thiaridae species (van Benthem Jutting 1956;Monks 2010;Coelho et al. 2013;Newel and Bourne 2013), and even larger snails in the Ampullariidae and Viviparidae (Mienis 2011;Bogan and Hanneman 2013). Thus, the other species of freshwater snails in Kranji Reservoir, including juveniles of the rare apple snails Pila scutata (see Tan et al. 2013), could be potentially at risk if the spread of Anentome helena remains unchecked. ...
... As it appears that Anentome helena has only recently been introduced into Kranji Reservoir, it is imperative that further rapid surveys be conducted to investigate the extent of its distribution in Singapore and potential impact on native fauna. Too little is known about its ecological requirements in a natural setting (Coelho et al. 2013). In any case, the popularity of Anentome helena as a form of biological control in home aquaria worldwide, could mean multiple potential sources of introduction (i.e., irresponsible aquarists). ...
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Anentome helena (von dem Busch in Philippi, 1847) is known among aquarium enthusiasts as the “assassin snail”, and is usually kept to prey on other snail species that are considered pests in home aquaria. There have been concerns that, given its prevalence in the ornamental pet trade, it is only a matter of time before this predator is introduced to the wild. We report the first occurrence of established populations of Anentome helena in a non-native habitat, and provide CO1 sequences of the species from the wild.
... For instance, the ornamental pet trade caused the first non-native establishment of C. helena in Singapore (Ng et al. 2016b) and argued as a threat to native gastropods (Mienis 2011;Bogan and Hanneman 2013). Although reported as having a medium risk of freshwater invasion (Patoka et al. 2017b), C. helena can breed well in the still-water and have adaptability even in captive conditions (Coelho et al. 2013). Many invasive species frequently establish in natural habitats, in absence of any prevention or eradication efforts as the methods are often not costeffective (Lodge et al. 2006). ...
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The carnivorous snail Clea (Anentome) helena (von dem Busch, 1847) (Gastropoda: Nassariidae), commonly called as the “assassin snail” is sold worldwide including India for aesthetics and the ability to kill pest snails in aquaria. Assuming invasion as a fair possibility, the predation potential of C. helena on seven native freshwater snails was assessed. The exotic predator consumed all the native snail species provided in the experiment and prey consumption varied with the prey species identity, the prey density and the prey size class. Future colonization and establishment of C. helena in Indian freshwater ecosystems may reduce the abundance of the native gastropod snails, in absence of suitable intervention.
... Detailed knowledge of the conditions required for optimal growth, development, and nutrient allocation of BSF is necessary for implementation of large-scale production systems (Coelho et al., 2013). The effect of nutrient density of the ingested food on development, growth, and body composition of BSF in interaction with larval density has not been investigated systematically before. ...
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Performance and body composition of insect larvae depend on quality and quantity of their diet, and on biotic factors such as larval density. We investigated the effect of dietary nutrient concentration and larval rearing density on survival, development, growth, and protein and fat contents of larvae of the black soldier fly (BSF), Hermetia illucens L. (Diptera: Stratiomyidae). Neonate larvae were fed with a low (NC1), intermediate (NC2), or high nutrient concentration (NC3), and with four rearing densities (50, 100, 200, or 400 larvae per container). Two feeding regimes (FR) were tested: in FR1, the amount of diet added during the experiment was based on the visually estimated larval mass present, whereas in FR2, a fixed feeding ration of 0.6 g of food per larva was applied at the start. FR1 resulted in food limitation, resulting in significantly lower body crude protein content on diet NC1 than on NC2 at larval densities 100 and 200. Larval crude fat content was higher on diets with higher nutrient concentration and at lower larval densities. For FR2, development time was shorter on diets with higher nutrient concentration and at lower larval densities. Individual larval weight and total larval yield increased with higher nutrient concentration at all four larval densities. At lower nutrient concentration, higher larval density resulted in higher individual larval weight and total larval yield, revealing an interaction between larval density and dietary quality. Larval crude protein content was higher at lower densities and lower nutrient concentration. Larval crude fat was higher at higher larval densities and nutrient concentrations. This study indicates that larval protein content is regulated within narrow limits, whereas larval crude fat content is strongly affected by nutrient concentration and by larval density.
... Studying the effect of these factors on nutrition and development of insects is particularly important for mass-rearing insects for feed and food in order to optimise productive performance and nutritional quality. Detailed knowledge of the conditions required for optimal growth, development and nutrient allocation of BSF is necessary for implementation of large-scale production systems (Coelho et al., 2013). The effect of nutrient density of the ingested food on development, growth and body composition of BSF in interaction with larval density has not been systematically investigated before. ...
... Sebagian besar spesies ini hidup di air bersih dan sungai berarus sedang dengan substrat berpasir atau berlumpur. Spesies ini juga dapat ditemukan di kolam, saluran air, dan memiliki rentang toleransi yang lebar (Coelho et al. 2013). ...
... The present study is the first known stable-isotope analysis on Buccinidae snail, with the literature mainly having focused on its taxonomy and geographic distribution (Polgar et al. 2015). Our results showed that the snail had little overlap with d 13 C values for leaf litter or periphyton (Table 2) and the d 15 N values confirmed reports in the literature that Buccinidae is predacious (Coelho et al. 2013). ...
Article
Waterfalls have unique physical characteristics and harbour highly specialised macroinvertebrate communities, but have been the subject of very few ecological studies. There are no previous studies of trophic structure of waterfall assemblages. It was hypothesised that because of the steep gradient of waterfalls and low retention of terrestrial-based resources, the abundant basal food resources would be periphyton. In addition, because of the frequent scouring flood events, it was predicted that periphyton would be a significant source of food for filter feeders. Waterfalls in the Ulu Temburong National Park (Brunei Darussalam) were used in the present case study. Methods included stable carbon (C)- and nitrogen (N)-isotope analyses (SIA; δ¹³C and δ¹⁵N of leaf litter and periphyton) and gut-content analysis (GCA) of the most the abundant macroinvertebrates. With δ¹⁵N values ranging from –1.9 to 5.5‰, literature suggests that this indicates that herbivores (Heptageniidae and Blephariceridae), omnivores (Simuliidae and Hydropsychidae) and predators (Buccinidae) live in the waterfalls. Apart from Buccinidae, the taxa had δ¹³C signatures ranging from –33 to –26‰, with a high dependence on periphyton, which is similar to other tropical-stream biotopes. The present study suggests that despite scouring velocities, waterfalls support animals with a range of diets, based on grazing or scraping, filter feeding and predation.
... One species, Clea (Anentome) helena (Fig. 2) is found in the Mekong River in Vietnam and Thailand (Chantima et al., 2013;Thanh and Hai, 2010). The species is common in the Mekong River and is exported to Europe and Americas where it is used to control snails in hobby aquaria (Coelho et al., 2013). In the wild, it probably primarily feeds on carrion rather than seek out live prey. ...
Article
Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam.
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This nomenclator provides details on all published names in the family-, genus-, and species-group, as well as for a few infrasubspecific names introduced for, or attributed to, the family Melanopsidae. It includes nomenclaturally valid names, as well as junior homonyms, junior objective synonyms, nomina nuda, common incorrect subsequent spellings, and as far as possible discussion on the current status in taxonomy. The catalogue encompasses three family-group names, 79 genus-group names, and 1381 species-group names. All of them are given in their original combination and spelling (except mandatory corrections requested by the Code), along with their original source. For each family- and genus-group name, the original classification and the type genus and type species, respectively, are given. Data provided for species-group taxa are type locality, type horizon (for fossil taxa), and type specimens, as far as available.
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Newly hatched juvenile Buccinum undatum can be reared under laboratory conditions. Good was growth is achieved when juveniles were fed on combined diets (blue mussel, cod, and fish pellets). Juveniles reached shell heights of 33.0 4.2 mm, 26.9 3.8 mm, 23.2 2.2 mm, and 20.1 1.6 mm, after 14 months of fedding on a combined diet, blue mussel, cod, and fish pellets, respectively under ambient sea temperature and salinity. After 14 months juveniles fed blue mussel had the highest survival rates (67%) followed by those fed a combination of all other experimental diets (61%), cod waste (53%) and fish-feed pellets (46%). High mortalities were recorded in most treatments during the summer months between June and September. This species appears to have an aquaculture potential, as juveniles readily feed on artificial diets at an early age, show high survival rates and could potentially reach market size in 2 years or less. The major constraint in realising this potential at present, is the relatively low value of the species; if market values increased as a result of serious depletion of natural populations, hatchery production of juveniles for intensive aquaculture or restocking could become economically viable.
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The premier text in the field, Biometry provides both an elementary introduction to basic biostatistics as well as coverage of more advanced methods used in biological research. Students are shown how to think through research problems and understand the logic behind the different experimental situations. This book is designed to serve not only as a text to accompany a lecture course but is also a must-have reference text! NEW TO THIS EDITION • An Increased Focus on Computer-Based Statistical Methods. Computational formulas have also been replaced throughout with simpler structural formulas for ease of understanding. • Matrix methods. Matrix methods are introduced in new sections on multiple regression, general linear models, ancova, and curvilinear regression. A new appendix on matrix algebra is also included. • New Chapter on Statistical Power and Sample Size Estimation. The new edition features a new chapter that covers statistical power, measures of effect size, and the estimation of sample size required for tests and for confidence limits. • Up-to-Date Coverage of Key Developments in Biostatistics. This edition includes the most up-to-date coverage of key topics such as meta-analysis and trends in the discipline such as the use of resampling methods.
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(1) Growth-rates and activity of juveniles of the land snails Cepaea nemoralis (L.) and C. hortensis (Muller) in the laboratory were inversely related to density in the range of one to eight snails per box of 1000 cm2 internal surface area. (2) Single C. nemoralis in boxes of 125 cm2 surface area were more active, and grew faster, than eight in 1000 cm2 boxes. The influence of other snails or their products is therefore an important part of the effect. (3) Interspecific density effects for Cepaea could not be distinguished from intraspecific effects at the combination of densities investigated. (4) The activity of C. nemoralis and C. hortensis, and possibly of Helix aspersa (Muller) is reduced in boxes pretreated with mucus trails of the same species. (5) The activity of Cepaea hortensis is reduced by pretreatment with C. nemoralis mucus. Helix aspersa mucus has no effect on the activity of Cepaea. Chromatography reveals close similarity in the mucus of C. nemoralis and C. hortensis; that of Helix aspersa is distinct. (6) The possibility of growth inhibiting pheromones in snail mucus is discussed in relation to the population dynamics of the species and to the results of other studies.
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Juvenile Balea perversa were kept for 450 d at different densities on their natural substrate and food. After this period of intraspecific competition, individuals were kept singly under conditions of high food supply for the rest of their life (126-484 d; period of relaxed competition). Age and size at first reproduction as well as reproductive output, were influenced by initial experimental density; individuals kept at high density reached sexual maturity late and at a small size. In the relaxation period, reproductive rate did not differ between snails from different initial densities. Individuals initially kept at high population density lived longer during the relaxation period than ones kept at low density. Nevertheless, they did not live long enough to compensate for the earlier loss in fecundity; overall reproductive life span and lifetime fecundity decreased with increasing initial density. B. perversa initially kept at high population density responded with compensatory growth to the more favourable conditions of the later period and became equal in shell size to those kept at low population density. Some snails gave birth to larger offspring than others, but offspring size was correlated neither with the size of the mother nor with the density at which the mother was initialy kept. However, offspring size was negatively correlated with the mother's relative growth rate during the relaxation period, indicating a trade-off between offspring size and maternal growth and thus an indirect effect of initial density. -from Authors
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Six different indoor rearing densities (250 to 500 animals per m2) were tested. Three repeats were carried out for each density. The following were recorded: feed intake, weight and number of adult individuals (animals with a reflected peristome), non-adult weight at the end of the experiment, and mortality. A simplified calculation of gross margin is also presented. It was observed that, at low densities, the animals consumed more, were bigger and more of them became adults. However, the total amount of biomass produced is greater at higher densities. If the breeder merely fattens the snails, then the gross margin is maximal at a density of 250 animals per m2. If the breeder fattens and cooks his own produce, then the gross margin is maximal at high densities. Compared to the mixed rearing method currently used, the performances observed in this indoor rearing experiment could be improved further (particularly in terms of the percentage of adult animals obtained).
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There has been interest in culturing the Florida apple snail, Pomacea paludosa, for stock enhancement purposes in central and south Florida to help promote snail kite (Rostramus sociabilis) recovery. In 2007, Harbor Branch Oceanographic Institute at Florida Atlantic University began to research techniques necessary to culture Florida apple snails at a commercial scale (tens of thousands per year). This article reviews stocking density and diet experiments that have yielded a protocol for large-scale culture of Florida apple snails. The objectives of this research were to determine the stocking density that supports efficient production and to determine whether diet choice affects growth and survival and can improve captive growth rates at higher stocking densities. Juvenile apple snails were stocked at six densities (10, 20, 40, 60, 80, and 100 snails/m2) in recirculating aquaculture systems with a raised substrate. Although growth was faster in the lowest stocking density compared to the highest density during the first month, the difference subsided in the second month, and overall growth rates and final shell lengths were not statistically different. Survival was not affected by density. A second experiment testing higher densities (100, 175, and 250 snails/m2) showed that snails could be stocked as high as 250 snails/m2 and confirmed that the lowest density is optimal for first-month growth. An initial diet study examining six diets (romaine lettuce, two combination diets of plant material and catfish chow, and three ingredient-only diets) showed shell length growth rates of 3 mm/wk for snails fed the macroalgae Ulva Diet and Catfish Diet (catfish chow only) for two months. In a subsequent experiment, snails stocked at 250 snails/m2 and fed the Ulva Diet grew faster than those at the same density fed the Catfish Diet. The greatest growth occurred in snails fed the Ulva Diet and stocked at 100 snails/m2. Based on these results, it is recommended that the Florida apple snail be cultured in recirculating aquaculture systems with a raised substrate at 100 snails/m2 and an artificial diet of Ulva macroalgae mixed with catfish chow. Snails cultured in this manner are suitable for release into the wild after three months when they reach adult size (25 mm) and reproductive maturity.
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Hatchery-reared juvenile spotted babylon Babylonia areolata (mean initial shell length 12.8 mm) were cultured intensively to marketable size in three 3.0 × 2.5 × 0.7 m indoor canvas rectangular tanks. The duplicate treatments of flowthrough and semi-closed recirculating sea-water systems were compared at an initial stocking density of 300 individuals m−2 (2250 juveniles per tank). The animals were fed ad libitum with fresh carangid fish Selaroides leptolepis once daily. During 240 culture days, average growth rates in shell length and body weight were 3.86 mm month−1 and 1.47 g month−1 for the flowthrough system and 3.21 mm month−1 and 1.10 g month−1 for those in the semi-closed recirculating system. Survival in the flowthrough system (95.77%) was significantly higher than that in the semi-closed recirculating system (79.28%). Feed conversion ratios were 1.68 and 1.96 for flowthrough and semi-closed recirculating systems respectively.
Article
Penaeus monodon juveniles (average weight = 1.32 g) were kept in individual 2 l perforated plastic containers, 10 of which were placed in each of the twenty-four 50 l rectangular wooden-glass aquaria supplied with seawater filtered through a sand-gravel filter (32–34 ppt; 26.5–29.0°C; pH, 7.6–8.2) at 0.8–1.01 l/min. Eight diets were prepared containing 25–60% protein and fed at 10% of the body weight/day for the first 2 weeks and 8% for the succeeding 4 weeks.Shrimps fed the 40% protein diet produced the best growth, feed conversion ratio (FCR), protein efficiency ratio (PER) and survival rate. However, shrimps fed the 30, 35 and 45% protein diets produced comparable results. The protein content of the shrimps was directly related to the level of protein diet up to 50%; whereas fat content seemed to be inversely related up to 50% protein diet.