COMPARATIVE STUDY BETWEEN MONO AND POLYCULTURE SYSTEMS ON THE PRODUCTION OF PRAWN AND MILKFISH IN BRACKISHWATER PONDS

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COMPARATIVE STUDY BETWEEN MONO AND POLYCULTURE SYSTEMS ON THE PRODUCTION OF PRAWN AND MILKFISH IN BRACKISHWATER PONDS

Kuntiyo*
Dan Baliao**

ABSTRACT

The growth, survival, production and economic feasibility of milkfish and prawn grown singly and in combination are described. Stocking density combination involved 20,000 prawn jv/ha with 2,000 milkfish fingerlings/ha for polyculture; 20,000 prawn juv/ha in monoculture; and 2,000 milkfish fingerlings/ha in monoculture. After 109 culture days, results showed no significant difference (p<0.05) on growth and survival rates of both commodities in two culture schemes. Mean weight gain was 30.88 g for prawn and 263.33 g for milkfish in monoculture and 31.85 g and 210.57 g for prawn and milkfish, respectively, in the polyculture system. Mean survival rates were 94.03 percent for prawn and 99.0 percent for milkfish in polyculture; and 82.13 percent for prawn and 92.33 percent for milk-fish for the polyculture system. Net aggregate production, however, was highly significant in polyculture, attaining 923.50 kg/ha/crop. Economic feasibility revealed encouraging results for polyculture over monoculture, with return on investment (ROI) valued at 45 percent for polyculture.

INTRODUCTION

Culture of tiger prawn (Penaeus monodon Fabricius) and milkfish (Chanos chanos Forskal) either in mono or polyculture system has long been practiced in some Asian countries. At present, milkfish culture is largely considered an industry and considerably high production has been attained with the development of rearing techniques. In the Philippines, milkfish production reached 211,506 tons valued at 1.9 billion pesos, with a national average yield of 870 kg/ha/year in 1981 (Samson, 1983). In Indonesia, milkfish has been produced at 51,922 tons valued at US$31.7 million in 1980 (Chong et. al., 1983). Taiwan has produced milkfish of 27,000 and 32,000 tons/year from 1965 to 1982 and production per hectare increased from 1765 kg in 1965 to 2078 in 1979, then declined to 1080 kg in 1982 (Lee, 1983).

* Staff member, Brackishwater Aquaculture Development Center, Jepara, Indonesia

** Former Research Associate, SEAFDEC AQD, Leganes Research Station, Leganes, Iloilo, Philippines

At the moment, tiger prawn is considered one of the fastest growing species among penaeids tested and cultured in ponds (Kungvankij, 1983; Baliao, 1986). Its culture is also fast-developing as an industry today. In Asia, with intensive culture system, the production pf prawn is usually over 3000 kg/ha (Hirasawa, 1983). With supplemental feeding, Thailand has obtained a yield equivalent to 5 tons/ha/year (Kungvankij et. al., 1976), while production in Taiwan has reached 10 tons/ha/year with artificial feeding and aeration system (Liao, 1977). The above results notwithstanding, polyculture of prawn with milk-fish still remains a good prospect for developing countries -with either milkfish alone as main crop and prawn as secondary crop or vice versa.

Trials on prawn with milkfish in the polyculture system have been conducted by researchers in some countries. Pudadera (1980) showed that competition between prawn and milkfish is negligible and that relatively high production could be attained in the polyculture system. Gunderman and Propper (1977) said that P. monodon, is the most desirable species of three (P. merguiensis, P. monodon, P. japonicus) although the other two can also be successfully reared together with fish in properly managed ponds. Lopez and Ranoemihardjo (1978) noted that culturing milkfish could increase the production from 300 to 1000 kg/ha/year.

This study was conducted with the hope to further:

1. Compare the growth, survival rate and production of prawn in polyculture and monoculture systems.

2. Determine the economic feasibility of the aforesaid culture system.

MATERIALS AND METHODS

Experimental Set-Up

This study was implemented in the Southeast Asian Fisheries Development Center, Aquaculture Department, using the facilities of the Leganes Research Station from 21 July to 7 November 1986. Eight ponds (size 500 sq. meters), earthen, were utilized. Ponds 1, 2 and 6 were used for rearing milkfish and prawn in polyculture; Ponds 4, 5 and 7 for prawn in monoculture; and Ponds 3 and 8 for rearing milkfish in monoculture system.

Each pond was provided with two 12-cm diameter PVC standpipe gates installed at the opposite ends of the pond serving as water inlet and outlet. Nylon net enclosures were provided in all gate systems to prevent the entrance of unwanted species and escape of stock. Diagonal canals 2 m wide and 20 cm deep, sloping or gradually deepening towards the outlet pipes, were also constructed. Twigs were installed across the pond bottom to increase surface area for attachment of fishpond organisms. Feeding trays and depth gauges were also installed in each compartment.

Experimental Design and Treatment

The experiments were randomly distributed in the eight 500 sq. m. ponds, with treatment combinations as follows:

Management Procedure

1. Pond preparation

   This was initiated with the repair of all damaged or leaking dikes and gates followed by draining and levelling of the pond bottom. Soil samples within the upper 15 cm layers were rendomly taken. The samples were airdried for about 15 days, followed by analyses of organic matter content, pH, available nitrogen, phosphorus, iron, and acetate soluble sulfate.

   To prevent unwanted species from entering the ponds, semi-circular nylon screens were installed in front of the gates.

   For controlling or eradicating unwanted species that remained in the pond, a mixture of hydrated-lime (Cao) and ammonium sulfate (21-0-0) was applied at a 5:1 ratio. For eradicating snails, 1 kg/ha of Brestan was applied.

   Chicken manure at the rate of 2 tons/ha was applied by broadcast method. Thereafter (2–3 days), urea (46-0-0) and di-ammonium phosphate (16–20-0) were applied at the rate of 22 kg/ha and 50 kg/ha, respectively, where the water depth was 15 cm.

   Water was admitted gradually by gravity at 5 cm at a time until stocking depth of 30 cm was reached in about 3 to 4 weeks.

2. Rearing Period

   Stocking. Two-month-old fingerlings averaging 6 g and one-month-old juveniles averaging. 45 g reared in adjacent nursery ponds were used. Release of juveniles and fingerlings was preceded by acclimation indoors done by equalizing temperature and salinity of water in ponds and transport plastic bags. Stocking was done in the early morning (0600–0800 hrs) of 21 July and 22 July 1986.

   Feeding. Two to 3 days after stocking, chopped trash fish as supplemental feeding for prawn was given both by broadcast and feeding tray methods. Feeding rate was 10, 8 and 6 percent of body weight per day (Baliao, 1985) adjusted monthly at an estimated 100, 90 and 80 percent survival, respectively.

   Monitoring of water parameters/stock sampling. Monitoring of water parameters to determine water pH, temperature, dissolved oxygen, water transparency and depths was done two times weekly (every Tuesday and Friday) at 0700 to 0900 hrs. (in the morning). Monitoring of biological parameters was done monthly to determine individual body weight and length increases, The number of samples taken using cast net were 30 pcs for prawn and 15 pcs for milkfish.

   Limnological/biological parameters. The following equipment were used:

   a.	Chemical parameters	Horiba Water Checker
   	1) pH	-do-
   	2) Temperature	-do-
   	3) Dissolved oxygen	-do-
   	4) Conductivity	-do-
   	5) Salinity	Refractometer
   b.	Physical parameters
   	1) Transparency	Sechi discs
   	2) Depth	Depth gauge
   c.	Biological parameters
   	1) Body weight/length	Ruler with mm scale and Triple beam balance

   Fertilization and water management. To maintain natural food (lablab/plankton), application by broodstock method of either urea (46-0-0) at the rate of 18 kg.ha or diammonium phosphate (16–20-0) at the rate of 50 kg/ha was subsequently done every 15 days after water management. Water management was conducted 3 to 4 days every spring tide by gravity, replenishing about one-thirds of the pond water.

3. Harvest

   After 109 days culture period, prawn and milkfish were harvested by current, draining and manual picking. Soil samples were again taken. The prawns were sold to AA Export. Import Market through the local buying station and milkfish were sold to SEAFDEC AQD employees.

RESULTS AND RECOMMENDATIONS

A. Physico-Chemical Parameters

Water parameters in all treatments appeared to have similar trends during the course of the experiment. Salinity values ranged from 5 to 29 ppt (Fig. 1). Dramatic fluctuations were observed during the months starting from July to September. However, there was no adverse effect observed on stock except on the disintegration of natural food (lablab) which eventually settled on the pond bottom, caused by heavy rain. In the last month of the culture period, the salinity values narrowed down to 23 ppt in all treatments.

Water transparency was recorded at 24 to 39 cm (Fig. 8) while water depth ranged from 40 to 75 cm (Fig. 9).

Soil analysis after the culture period indicated no relative differences among treatments with pH, organic matter content, available PO₄, available NO₂, values of 6.78, 5.43, 5.83, 0.1083, respectively. Compared to the initial analysis, the general trend shows reduction in values after the culture period. This could be explained apparently by the dissociation of nutrients that were converted eventually into fish.

B. Growth, Survival and Production Rates

1. Prawn

   Growth and survival rates of prawns, stocked singly or in combination with milkfish, showed no significant difference (P<0.05) among treatment means. At harvest, mean body weight of prawn was 31.50 g and 31.95 g for mono and polyculture system, respectively. The average survival rate was 82.13 percent for polyculture and 94.03 percent for monoculture,

   Figures 1 and 2 show the growth curve of prawn exposed to different treatments. Prawn production was not significantly affected by stocking rates and/or culture scheme, although yield was slightly higher in monoculture (29.50 kg/500 m²) compared to polyculture with milkfish (26.24 kg/500 m²).

2. Milkfish

   Similar trend with the prawn growth and survival rates of milkfish showed no significant difference (P<0.05) among treatment means (Table 2). The final average body weight of milkfish was 217.33 and 271.00 g for mono and polyculture system, respectively. Production, however, was significantly higher for milkfish grown in monoculture (26.25 kg/ 500 m²) than in polyculture (19.94 kg/500 m²).

   Figures 2 and 3 indicate the growth curve of milkfish stocked singly or in combination with prawn. Mean survival rate was 92.33 and 99.0 percent for Treatments 1 and 3, respectively.

The computation of the costs and returns for Treatment 2 (Polyculture of Prawn and Milkfish) showed higher annual profitability levels of 62,705.90 net income after tax; 45.20 percent return on investment (ROI) and payback period of 2.21 years as against Treatment 1 (Monoculture of Prawn), having annual profitability levels of 53,213.26 net income after tax, 38.69 percent ROI and 2.49 years payback period. Both treatments have the same stocking rate of prawns at 20,000 fry/hectare. Using marginal analysis, the incremental annual cost of 4,062 comprised of milkfish fry (3,800), miscellaneous expenses (360) and interest expense (102) for Treatment 1 resulted to an incremental net profit after tax of 9,492.64. The positive marginal difference between the marginal profit and the marginal cost resulted to higher profitability levels mentioned above. Thus, polyculture of milkfish and prawn results to an additional economic advantage to the farmer.

Treatment 3 (Monoculture of Milkfish) is a losing proposition as shown in Table 5. This is primarily due to the high investment requirement in acquiring fishponds (100,000/ha) to produce low-value species such as milkfish. This condition will prevent investors from going into milkfish monoculture. The present milkfish growers have owned their lands for a long time and are not required high investment for pond acquisition. Profitability level can be attained by proper control of variable cost or cost of input with minimal fixed costs.

On the basis of the data obtained (no significant difference on growth and survival), prawn and milkfish stocked singly or in combination indicated their culture efficiency even with different stocking combinations. With supplementary feeding, the total crop became independent or not entirely dependent on primary productivity level, thus increasing the stock and likewise increasing the total crop as implied by Prowse (1968) and Tang (1972). This was also supported by the report of Pudadera (1980), indicating that competition between prawn and milkfish is negligible and that relatively high production could be attained in the polyculture system/

However, the extent of stocking combinations that will give an efficient polyculture of prawn and milkfish under different culture techniques needs further study.

Table 1. Mean weight gain and relative growth increment of prawn and milkfish in mono and polyculture system.

^1/ Treatment means with the same superscript are not significantly different (P<0.05)

Table 2. Mean final weight, survival and production of prawn and milkfish in mono and polyculture system.

¹ Treatment means with the same superscript are not significantly different (P<0.05)

Table 3

Cost and Return of Polyculture of Prawn with Milkfish
Per Hectare

A.	SALES
	Item	Production (kg)	Price (P)/kg	Sub-total Value
	1. Prawn	524.73 kg	90.00/kg	47,225.70
	2. Milkfish	398.91 kg	25.00/kg	9,972.75
			Total Value	57,190.45
B.	VARIABLE COST
	Item	Quantity	Cost/Unit	Total Value
	1. Fry
	a. Prawn	20,000 pcs	0.40/pc	8,000.00
	b. Milkfish	2,000 pcs	0.60/pc	1,200.00
	2. Fertilizer
	a. Chicken Manure	2 tons	668.00/ton	1,336.00
	b. Ammonium Sulfate	0.5 bag	225.00/bag	112.50
	c. Ammonium Phosphate	4 bags (200 kg)	180.00/bag	720.00
	d. Urea	1.5 bags (75 kgs)	140.00/bag	210.00
	3. Lime	2 tons	720.00/tons	1,440.00
	4. Brestan	1 kg	600.00/kg	600.00
	5. Coconut fronds	500 pcs	0.50/pc	250.00
	6. Feed
	a. Trash fish	3,100 kg	3.00/kg	9,300.00
	7. Ice	2 blocks	70.00/block	140.00
	8. Styrofoam	10 pcs	140.00/pc	1,400.00
	9. Casual labor
	a. Caretaker	1 person	400.00/mo.	1,400.00
	b. Hireman	4 men/day	30.00/day	120.00
	10. Miscellaneous	10%		2,622.85
		Total variable		28,851.35
C.	FIXED COST
	1. Depreciation			666.66
	2. Interest			4,628.37
	3. Salary			1,050.00
		Total Fixed Cost		6,345.03
		Total Cost		35,196.38
D.	NET PROFIT BEFORE TAX			22,002.07
	Income Tax (5% × Net Profit Before Tax)			1,100.10
	Net Income After Tax Per Crop			20,901.97
	Net Income After Tax Per Year			62,705.90
E.	ECONOMIC PARAMETERS
	1. Return of Investment			0.452
	2. Pay back Period			2.21
F.	INVESTMENT REQUIREMENT			-
	1. Pond Equisition			100,000.00
	2. Pond Development			10,000.00
	3. Operating Capital			28,851.35
		Total Investment		138,851.35
G.	EQUIPMENT
	Source of Funds
	1. Equity 50%			69,425.68
	2. Loan 50%, 20%/year			69,425.68
	3. Interest/year			13,885.13
	4. Interest/crop			4,628.37

Table 4

Cost and Return of Monoculture of Prawn
Per Hectare

A.	SALES
	Item	Production (kg)	Price ()/kg	Total Value
	1. Prawn	589.93	90.00/kg	53,903.70
	2. Milkfish	-	-	-
B.	VARIABLE COST
	Item	Quantity	Cost/Unit	Total Value
	1. Fry
	a. Prawn	20,000/ha	0.40/pc.	8,000.00
	b. Milkfish	-	-	-
	2. Fertilizer
	a. Chicken Manure	2 tons/ha	668.00/ton	1,336.00
	b. Ammonium Sulfate	0.5 bags	225.00/bag	112.50
	c. Ammonium phosphate	4 bags (200 kgs)	180.00/bag	720.00
	d. Urea	1.5 bags (75 kgs)	140.00/bag	210.00
	3. Lime	2 tons	720.00/ton	1,440.00
	4. Brestan	1 kg	600.00/kg	600.00
	5. Coconut fronds	500 pcs	0.50/pc	250.00
	6. Feed
	a. Trash Fish	3,100 kg	3.00/kg	9,300.00
	7. Ice	2 blocks	70.00/block	140.00
	8. Styrofoam	10 pcs	140.00/pc	1,400.00
	9. Casual Labor
	a. Caretaker	1 person	400.00/month	1,400.00
	b. Hireman	4 men/day	30.00/day	120.00
	10. Miscellaneous	10%		2,502.85
				27,531.35
C	FIXED COST
	1. Depreciation			666.66
	2. Interest			4,584.37
	3. Salary			1,050.00
		Total Fixed Cost		6,301.03
		Total Cost		33,832.38
D.	NET PROFIT BEFORE TAX			18,671.32
	Income Tax (5% × Net Profit Before Tax)			933.57
	Net Income After Tax Per Crop			17,737.75
	Net Income After Tax Per Year			53,213.26
E.	ECONOMIC PARAMETERS
	1. Return of Investment			=38:69%
	2. Pay back Period			= 2.49
F.	INVESTMENT REQUIREMENT
	1. Pond Equisition			100,000.00
	2. Pond Development			10,000.00
	3. Operating Capital			27,531.35
		Total Investment		137,531.35
G.	EQUIPMENT
	Source of Funds
	1. Equity 50%			68,765.68
	2. Loan 50%, 20%/year			68,765.68
	3. Interest/year			13,753.13
	4. Interest/crop			4,584.37
	Cost Production/kg			57.907
	Profit/kg (90.00 -56.907			32.909

Table 5

Cost and Return of Monoculture of Milkfish
Per Hectare

A.	SALES
	Item	Production (kg)	Price ()/kg	Total Value
	1. Prawn	-	-	-
	2. Milkfish	536.22	25.00/kg	13,405.50
B.	VARIABLE COST
	Item	Quantity	Cost/Unit	Total Value
	1. Fry
	a. Prawn	-	-	-
	b. Milkfish	2,000 pcs/ha	0.60/pc	1,200.00
	2. Fertilizer
	a. Chicken Manure	2 tons/ha	668.00/ton	1,336.50
	b. Ammonium Sulfate	0.5 bags	225.00/bag	112.50
	c. Ammonium Phosphate	4 bags (200 kgs)	180.00/bag	720.00
	d. Urea	1.5 bags (75 kgs)	140.00/bag	210.00
	3. Lime	2 tons	700.00/ton	1,440.00
	4. Brestan	1 kg	600.00/kg	600.00
	5. Coconut fronds	500 pcs	0.50/pc	250.00
	6. Feed
	a. Trash fish	-	-	-
	7. Ice	2 blocks	70.00/block	140.00
	8. Styrofoam	10 pcs	140.00/pc	1,400.00
	9. Casual labor
	a. Caretaker	1 person	400.00/month	1,400.00
	b. Hireman	4 men/day	30.00/day	120.00
	10. Miscellaneous	10%		892.85
			Total variable	9,821.35
C.	FIXED COST
	1. Depreciation			666.66
	2. Interest			3,994.01
	3. Salary			2,450.00
		Total Fixed Cost		7,110.67
		Total Cost		16,932.02
D.	NET PROFIT BEFORE TAX
	Income Tax (5% × Net Profit Before Tax)			3,526.52
	Net Income After Tax Per Crop
	Net Income After Tax Per Year
E	ECONOMIC PARAMETERS
	1. Return of Investment
	2. Pay back Period			-
F.	INVESTMENT REQUIREMENT
	1. Pond Equisition			100,000.00
	2. Pond Development			10,000.00
	3. Operating Capital			9,821.35
		Total Investment		119,821.35
G.	EQUIPMENT
	Source of Funds
	1. Equity 50%			59,910.68
	2. Loan 50%, 20%/year			59,910.68
	3. Interest/year			11,982.13
	4. Interest/crop			3,994.01

Fig. 1. Growth curve of prawn and milkfish in polyculture system.

Fig. 2. Growth curve of prawn in monoculture system.

Fig. 3, Growth curve of milkfish un monoculture system

Fig. 4. Salinity profile of ponds stocked with milkfish and prawn in mono and polyculture system.

Fig. 5. Temperature profile of ponds stocked with milkfish and prawn in mono and polyculture system.

Fig. 6. Water pH profile of ponds stocked with milkfish and prawn in mono and polyculture system.

Fig. 7. Water D.O. profile of ponds stocked with milkfish and prawn in mono and polyculture system.

Fig. 8. Water transparency profile of ponds stocked with milkfish and prawn in mono and polyculture system.

Fig. 9. Water depth profile of ponds stocked with milkfish and prawn in mono and polyculture system.

REFERENCES

1. Baliao, D. 1986. Mono and Polyculture of Milkfish and Prawn in Modular Pond System.

2. Chong, Poernomo and Kasryono, 1983. Economic and Technological Aspects of the Indonesian Milkfish Industry. Advances in Milkfish Biology and Culture. p. 199–214.

3. Gunderman, N. and Propper, D., 1977. Comparative Study of the Species of Penaeid Prawn and their Suitability for Polyculture with Fish in the Fiji Islands. Aquaculture, 11: 63–64.

4. Kungvankij, 1983. Overview of Penaeid Shrimp Culture in Asia. Proceeding of the First International Conference on the Culture of Penaeid Prawns/Shrimps. p. 11–22.

5. Hirasawa, 1983. Economic of Shrimp Culture in Asia. Proceeding of the First International Conference on the Culture of Penaeid/Shrimps. p. 131–150.

6. Lee, 1983. The Milkfish Industry in Taiwan. Advances in Milkfish Biology and Culture. p. 183–198.

7. Liao, I. C., 1977. Aquaculture Study on Prawn (Penaeus monodon) in Taiwan - the Patterns, Problems and the Prospects. J. Fish Soc. Taiwan, (2): 11–29.

8. Lopez, J.V., Ranoemihardjo, B.S., 1970. Polyculture of milkfish (Chanos-chanos) and Shrimp (Penaeus monodon) to increase productions in ponds. Bull. Brackishwater Aqua. Dev. Cent., 4 (142), 1978: 268–277.

9. Prowse, G.A., 1968. Some Basic Concept of Fish Culture. Indo Pacific Fish Council Oceanimal. p. 12.

10. Samson, 1983. The Milkfish Industry in the Philippines. Advances in Milkfish Biology and Culture. p. 215–228.

11. Tang, Y.A. 1972. Stock Manipulation of Coastal Fish ..... In: T. V. R. ..........Coastal Aquaculture. In the Indo Pacific Region F.A.O., Roma, Italy. pp. 438 – 453.

12. Pudadera, B., Jr., 1980. Growth and Survival of Milkfish (Chanos-chanos Forsskal) and Shrimps (Penaeus monodon Fabricius). Masteral Thesis. University of the Philippines. p.34.

ACKNOWLEDGMENTS

This study was partly funded by FAO-NACA under the Secondment Programme of Junior Scientists to the SEAFDEC Aquaculture Department. Acknowledgments are due Messrs. Romulo Ticar, Nicolas Guanzon, Uldarico Derotas, Research Assistants; and Mr. Bienvenido Dalde, Technician, for their significant contributions to the conduct of these experiments.

Appreciation is hereby expressed to Mr. Renato Agbayani, for his assistance in the economic analysis portion of this study. Likewise, the authors are indebted to Dr. Felicitas Pascual for reading and editing this paper.