IJERD – International Journal of Environmental and Rural Development (2015) 6-1

Research article
erdGolden Apple Snail as Source of Protein Diets of Fattened
Mud Crab (Scylla serrata Forskal) in Cellular BambooCages
MARIA DANESA S. RABIA
Bohol Island State University, Calape Campus, Bohol, Phillipines
Email: senillo_danesa@yahoo.com
Received 5 March 2015

Accepted 31 May 2015(*Corressponding author)

Abstract To identify feed alternative in the fattening of mud crab (Scylla serrata Forskal),
three diets were tested using a modified cellular cages. Mixed sex crabs were fed with trashfish, golden apple snail and combination of trash fish and golden apple snail at 10% bodyweight. Growth, survival, moulting and picked meat yield and quality were evaluated.
Specific growth rate and survival were highest in crabs fed with golden apple snail andcombination. Moulting was significantly affected by diet types. There was no significant
difference in the yield of picked meat and overall acceptability scores. Golden apple snail
could be a potential dietary substitute for trash fish.
Keywords mudcrab fattening, specific growth rate, bamboo cages, feed types

INTRODUCTION
Mud crab (Scylla serrata Forskal) locally known as “alimango” is considered as the biggest, fastest
growing and the most desirable aquaculture mud crab species in the country. For the past decades
aquaculture of mud crab has been intensively studied because of the high market demand of thecommodity and dwindling wild stocks. Hatchery technology was developed and adopted to answer
the problem in seed supply which was considered as the major limitation of mud crab farming in its
early stages (Keenan, 1999). Feeding management in grow out, perceived as the main bottleneck in
the advancement of mud crab aquaculture, has been carefully studied through development of
formulated diets and experimental feeding (Catacutan et al., 2003; Christensen et al., 2004).
Research has demonstrated the high feasibility and profitability of this aquaculture endeavour.
According to Keenan (1999), there are two basic forms of mud crab aquaculture, fattening ofcrabs with low flesh content and rearing of juveniles from the wild or hatcheries to market size.
Both of these approaches are usually pond based with or without mangroves. Fattening employs
intensive feeding while the later could be done without supplemental feeding that involves low
stocking in large mangrove silviculture ponds. In particular, mud crab fattening refers to the rearingof empty crabs identified at harvest from the wild or from farm stocks for a brief period of time
until weight is gained and ready to market (FAO, 2011). Empty crab also called as thin crab, water
crab or soft shell crab refers to a crab after moulting having thin and soft carapace with little flesh
for male and little ovary tissue for female. Various structures can be used to fatten mud crab for
relatively short period of time around 15-30 days that include cages, ponds or tanks. Fattening canbe held at fairly high densities provided that water quality is optimum, feeding is regular and therearing environment is free from diseases. Several studies demonstrated that mud crab fattening is a
profitable aquaculture activity (Trino and Rodriguez, 2001).
In the country crab fattening has been widely practiced but varies widely in the different
regions due to limited baseline research studies. Trino and Rodriguez (2001) studied crab fattening
in ponds and found out that it is economically feasible and production could be very high.
Technology verification done by Southeast Asian Fisheries Development Center (SEAFDEC) anda few private individuals using bamboo cages with individual cells or compartments that held one
crab per cell resulted to high survival and better weight gain. Nonetheless, the experiments only
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focused on the structures for rearing but not on feeding management which is also a very important
aspect to achieve maximum economic benefit. Fattened crabs are usually fed with a mixed diet oftrash fish and mollusk at a ration ranging from 6-10% body weight (SEAFDEC, 2011). Studies
using cheaper feed alternatives in crab fattening are limited. This study will evaluate the feasibilityof golden apple snail or locally known as “kuhol” as a substitute of the usual diet of mud crab.
OBJECTIVE
The main objective of the study was to determine the effect of experimental fattening of mud crab
(Scylla serrata Forskal) using different feed types (trash fish, golden apple snail and combinationof trash fish and golden apple snail) on the following indices:a. growth in terms of absolute growth rate, total carapace length and widthb. survival and moulting incidencec. yield and quality of picked meat
METHODOLOGY
Location and Cage Design
The experiment was conducted in BISU Calape-Calunasan Brackishwater Station. A cellular
system cage design adapted from SEAFDEC was used. The modified bamboo cage had adimension 2 m x 0.9 m x 0.3 m and divided into 15 compartments, covered with plastic screen for
feeding and sampling convenience. The cage was firmly fixed by its corners to the substrate using
bamboo stakes to prevent it from being washed away in high weather. The cage was placed in thepond canal with ¾ of its body submerged during the lowest low tide. The set up is ideal for
mudcrab culture as water exchange takes place naturally through tidal fluctuations.
Procurement of Stocks and Stocking
Mixed sex crabs with similar sizes weighing 50-100 g were purchased from local fishermen in
Calape at PhP 100.00 per kilogram. The crabs were weighed (77.78 g) and carapace length (72.47mm) and width (50.87 mm) were measured individually. Crabs were individually held in thecompartment or “cell” in the cage. A total of 15 crabs were stocked for each treatment
corresponding to the different feed types. Stocking was done late in the afternoon.
Rearing
The crabs were reared for 15 days. Water quality parameters such as salinity, temperature and pH
were monitored daily. The cages were cleaned daily by removing excess feeds and waste. Drifted
debris that clings in the cage was removed to prevent damage in the cage and to easily facilitate
water circulation. Six crabs from each treatment were weighed and carapace length and width weremeasured every three days as basis for the feed ration.
Diet Preparation and Feeding
The feeds used in the experiment were trash fish, golden apple snail and combination of trash fishand golden snail. Trash fish was bought from the local market, washed with clean water and stored
in freezer. Golden apple snails were collected in the nearby rice fields and were purged by soaking
in clean water for 24 hours. Frozen trash fish was thawed in running water and meat of the golden
apple snail was separated by breaking the shells individually and weighed based on the exact feedration. A feeding rate of 10% body weight was employed (SEAFDEC, 2011). Feeding ration wasincreased based on the body weight of the crabs measured every three days. Feeding was done
twice a day, 7 am and 4 pm.
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Sampling and Harvesting
At an interval of 5 days, all mudcrab in each cage were netted, weighted and recorded for analysis
of growth and survival. Measurements were done using a calibrated weighing scale recorded ingrams. After days, survival was assessed by counting remaining stocks in the cage. Final bodyweight, carapace length and width were measured. Survival rate, absolute growth rate, specificgrowth rate and feed conversation ratio were computed.
Picking and Sensory Evaluation
All the harvested crabs were steamed. The meat was then carefully separated from the shell andweighed. After weighing, nine panellists evaluated the sensorial attributes in terms of aroma,
texture and taste using the using the simple 9-point Hedonic Scale (9-extremely like, 8-like verymuch, 7-like moderately 6-like slightly, 5-neither like nor dislike, 4-dislike slightly, 3-dislike
moderately, 2-dislike very much, 1-dislike extremely).
Statistical Tools and Analysis
Data were statistically analyzed using descriptive statistics particularly; mean, standard, andpercentage. Mean of treatments were compared by Analysis of Variance (ANOVA) at 0.50
confidence level.
RESULTS AND DISCUSSION
Water Quality
The ranges of the water quality parameters (salinity: 25-35 parts per thousand (ppt); temperature:
25-30 oC; pH: 7.5-8.7) recorded during the experiment are within the suitable levels and the culture
period (15 days) is within the duration being practiced for mud crab fattening (Cholik and Hanafi,1992). Placing the cages in the pond canal was ideal because water was continuously flowing
maintaining optimum water quality conditions. The preliminary experiment conducted inside thepond resulted to poor growth and survival that could be attributed to poor water quality as waterexchange was limited.
Growth, Survival and Moulting Incidence
The mean final weight of the crabs after 15 days of fattening ranged from 90 g to 100 g in alltreatments (Table 1). Crabs fed with a combination of trash fish and golden apple snail had thehighest mean final body weight at 100.20 g with a total weight gain of 21.93 g. Begum et al (2009)
reported relatively lower weight gain at 10-16 g in mud crab with initial weight of 200 g fattened in
ponds for 16 days fed with tilapia. In the experimental fattening of mud crab in ponds using trash
fish by Trino and Rodriguez (2001), weight gain was relatively higher ranging from 150-200 g withinitial weight of stocks at 260-280 g. The lower weight gain observed in the current experiment
could be attributed to the use of small stocks and possibly the thinness of the muscle of the crabs
initially used (Liong, 1993).
Specific growth rate was highest in mud crab fed with golden apple snails and combination oftrash fish and golden apple snails (Fig. 4) at both 1.54% day-1. Specific growth rate of mud crab in
all the treatments were comparable to that of mixed sex mud crab reared in ponds fed with trash
fish for 20 days with specific growth rate of 0.8+ 0.12% day-1 (Trino and Rodriguez, 2001).

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Table 1 Mean initial and final body weight, weight gain and carapace width and length ofcrabs after 15 days of fattening using different feed types
Treatment

Initial wt (g)Final wt (g)Wt gain (g)Carapacewidth (mm)Carapace length(mm)Trash fish
Golden apple
snail
Trash
fish+Golden
apple snail

77.73

90.71

12.98

50.93

72.29

77.33

97.53

20.20

51.07

70.87

78.27

100.20

21.93

52.07

74.53

Survival was highest in crabs fed with golden apple snail and combination of trash fish andgolden apple snail at 100% (Table 2). The result was relatively higher compared to that of Begum
et al. (2009) wherein survival rate of crabs reared in cages was only 93.75%. High survival wasattributed to the use of cellular cage system. Crabs were held individually to prevent cannibalismand as well as to provide optimal environment for growth.
Another primary use of the cellular cage is the production of soft-shell crabs or newly moulted
crabs (FAO, 2011). In this kind of system, small mud crabs are reared in isolation a few weeks
until they moult. Soft-shell crabs command higher price and farmers have focused on soft-shell
production to maximize profit. In the present study, moulting incidence was observed as an effectof the dietary treatment. It was found out that moulting was significantly affected by diet types;
20% of the crabs fed with golden apple snail and combination of trash fish and golden apple snail
moulted during the experiment while none of the crabs moulted in the group fed only with trashfish. The use of golden apple snail could have accelerated moulting incidence. High calcium
content of the diet (from the shells of the golden apple snail) could possibly induced moulting ofstocks but this needs to be further investigated.
Table 2 Survival, occurrence of moulting and production of mud crab using different feedtypes
Treatment
Trash fish
Golden apple snail
Trash fish+Golden apple snailSurvival (%)
93100100Moulting (%)
02020

Economic Analysis
As to stocking density, the present study following the stocking density suggested by SEAFDEC(SEAFDEC, 2011) and still yielded a comparable survival rate of >90%. Tables 3 and 4 provides
an overview on the economic analysis of different fed types for mudrab in cellular cages. Mudcrab
fed with golden apple snail constitute the high return of investment compared to the othertreatments as indicated that low expenses incurred during the conduct of the study because feeds
are readily available.
Meat Yield and Quality
There was no significant difference in the yield of picked meat (Table 5) and overall acceptability
scores in terms of taste, texture, aroma and color among the three treatments (Table 5). The meanscore among the three treatments was 8 which is equivalent to like very much in the Hedonic Scale.
The results suggested that sensory attributes of mud crab fed with golden apple snail werecomparable to that of mud crab fed with trash fish.

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Table 3 Return-on-investment of the 3 units 2 m x 0.9 m x 0.3 m cellular cages at different fedtypes
ROIParameters
Total
harvest(-ind)
AWG
Total
biomassGrossincomeLess: Total
expenses
Net income
ROI

Unit

T1

T2

Input
T3

pcs

15

15

15

g

12.98

20.20

21.93

kg

0.195

0.303

0.329

T1

40.00

T2

70.00

T3

T1

T2

Income
T3

48.75

75.75

82.75

8.75
21.88%

5.75
8.21%

7.75
10.33%

75.00*the Php 250.00-300.00 per kg was based on the actual market price of mudcrab at Calape Public Market

Table 4 Weight of the picked meat and carapace and the corresponding yield
Trash FishGolden Apple SnailTrash Fish+Golden Apple
SnailPicked Meat (g)
31.51
41.22

Carapace Weight (g)
9.46
8.85

Total (g)
40.97
50.07

% Yield
76.97
82.07

37.74

7.10

44.83

84.09

Table 5 Sensory evaluation scores of the panellist in terms of overall acceptability
Panelists123456789
Mean

Trash fish
8888887878

Golden apple snail Trash fish+Golden apple snail
97979788887889799888CONCLUSION
The growth, survival and picked meat yield and quality of mud crab fed with golden apple snails
were comparable to that of mud crab fed with trash fish. The results indicate that golden apple snail
collected from nearby rice fields could be a potential dietary substitute for trash fish in mud crab
fattening.
RECOMMENDATIONThe same experiment could be conducted using bigger stocks weighing 200 g. It is interesting toevaluate if there is a significant difference between the growth of male and female individuals.
Other fattening duration could be tried using the same dietary treatments. Changes in the proximate
composition of the mud crab before and after fattening is also very essential to determine theeffects on the nutritional state of the organism.
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ACKNOWLEDGMENT
We would like to express our sincerest gratitude to the 4th year BS Fisheries students Jeffrey
Infiesto, Francis Josol, Rinalyn Bulala, Maricris Remojo and Jomel Baobao for the assistance in theconduct of the experiment.
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Cholik, F. and Hanafi, A. 1992. A review of the status of the mud crab (Scylla serrata) fishery and culture inIndonesia. BOBP/REP, 51, 13.
FAO. 2011. Mud crab aquaculture: a practical manual. FAO Fisheries and Aquaculture Technical Paper No.
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Keenan, C.P. 1999. Aquaculture of mud crab, genus Scylla - past, present and future. In: Keenan, C.P.,
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Liong, P.C. 1993. The culture and fattening of mud crabs. Infofish Int. 3:46.
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