Livestock Research for Rural Development 30 (7) 2018 Guide for preparation of papers LRRD Newsletter

Citation of this paper

A field survey of small scale cage and pond farming of Asian Seabass (Lates calcarifer) in Cambodia

Sen Sorphea1,2, Anders Kiessling1, Andrew C Barnes3, Chau Thi Da4, Jan Erik Lindberg1 and Torbjrn Lundh1

1 Department of Animal Nutrition and Management, Swedish University of Agriculture Sciences, P O Box 7024, 75007 Uppsala, Sweden
Torbjorn.Lundh@slu.se
2 Marine Aquaculture Research and Development Center (MARDeC), Preah Sihanoukville province, Cambodia
3 School of Biological Sciences and Centre for Marine Science, The University of Queensland, Brisbane, QLD4072, Australia
4 Department of Aquaculture, Faculty of Agriculture and Natural Resources, An Giang University, Long Xuyen city, Vietnam

Abstract

A survey of small-holder cage and pond farming of Asian seabass (Lates calcarifer) was conducted in the Preah Sihanoukville, Kampot and Koh Kong provinces of the coastal region of Cambodia. Most of the fish farms used open net-cages for culturing Asian seabass. Few farmers kept the fish in brackish water ponds before final grow-out in coastal sea cages. The farmers were predominantly male and most of them owned the fish cages and ponds used for culturing. The educational level of fish farmers was low with 36 to 45% having finished only primary school. The fish farming experience varied between provinces and comprised experience gained from own practice, workshops and from neighbours. All the interviewed farmers had income from other occupations, related to aquaculture production. Hired labour was most common in Preah Sihanoukville. It was common among fish farmers in all provinces to culture Asian seabass in poly-culture with grouper (Epinephelus spp.), pompano (Trachinotus spp.), snapper (Lutjanus malabaricus) and cobia (Rachycentron canadum). A high proportion of Asian seabass fingerlings were imported from Thailand and Vietnam rather than produced in local hatcheries. Trash fish was the main feed source for the grow-out fish while commercial pellets were only used for small-sized fish. There were differences in almost all parameters investigated relating to cultivation including culture period, harvest and price between the provinces. All farmers had problems with fish diseases throughout the whole year but the competence and skills to diagnose the fish varied between fish farmers.

Keywords: aquaculture, fish feed sources, socioeconomic survey


Introduction

Fish is a highly nutritious food for humans, containing all required essential amino acids along with essential fatty acids, vitamins and minerals. In many developing countries, low-income people depend to a larger extent on fish for their nutrient supply compared to people in developed countries (FAO 2012), with small indigenous fishes and fish products providing an important source of essential micronutrients such as calcium and iron (Vilain et al 2016). However, this situation is rapidly changing with the increasing promotion of the health benefits of eating fish in wealthy nations fuelling demand. The consequent rise in fish prices is placing financial strain on low-income groups in developing countries

Cambodia is one of the poorest nations in south east Asia yet has the highest per capita consumption of fish and fish products globally (Villain et al 2016): Indeed, the per capita consumption of fresh fish was 49.7 kg/year by fishing households and 39.9 kg/year for non-fishing households according to a survey in eight freshwater fisheries provinces including 5117 households and covering 83 communes in 51 fishing districts (Ahmed et al 1999). Including processed fish, the total fish consumption by fishing-dependent communities was estimated at 75.6 kg per capita per annum. In spite of this, up to 15% of Cambodian households are considered food insecure and both wasting (-2SD below reference weight for age and gender) and stunting are reported in 10.9 and 39.9% of the population respectively ( https://www.unicef.org/infobycountry/cambodia_statistics.html). Improvement in fish supply is therefore of key importance to health and development in Cambodia.

Coastal fisheries resources in Cambodia are under stress: annual catches by licensed Thai vessels in Cambodian waters are thought to range from 26,500 – 37,500 tonnes per annum (FAO 2012). The marine fishery has seen a significant increase in the number of fishing boats (both national and foreign) resulting in an increased pressure on coastal resources. Excess fishing-associated decline in abundance of species is a serious problem for Cambodia’s marine fisheries (Gillett R. 2004). In addition, there is substantial habitat degradation brought about through destructive fishing practices (e. g. dynamiting, cyanide fishing and illegal trawling in shallow nursery areas), mangrove forest destruction (for firewood and for aquaculture), siltation and the pollution from urbanization, industrialization and increasing tourism (FAO 2012).

Marine and freshwater finfish aquaculture has been strongly promoted in Cambodia to meet the increasing domestic demand for fish and maintain a sustainable catch of wild fish. However, Cambodia has great potential for marine aquaculture with a coastline of 435 km covering an area estimated at 17,800 km distributed among the four provinces Kam Pot, Kaoh Kong, Krong Keb and Preah Sihanoukville. The offshore marine area contains 60 islands distributed among the provinces Koh Kong (23 islands), Kam Pot (2 islands), Preah Sihanoukville (22 islands) and Kep (13 islands) (Rizvi and Singer 2011). However, aquaculture development in emerging economies is often restricted by supply chain bottlenecks such as fish supply (availability of fingerlings) and cheap, readily available, nutritious animal feeds. In Cambodia at present, the demand for seed stock is partially met by import from neighbouring Thailand and Vietnam, while domestic production remains limited. But fish farmers face particular technical problems in marine finfish culture, including lack of access to quality fish seed, lack of proper culture techniques, poor management and disease outbreaks (Joffre et al 2010).

Asian sea bass (Lates calcarifer) are popular fish native to tropical and subtropical south east Asia and Oceania, including Cambodia, and are highly suitable for both marine and freshwater farming, with wide temperature tolerance (Katersky and Carter, 2007) and well-defined nutritional requirements (Glencross, 2006). Farming of sea bass in marine and brackish water occurs on a small scale in the coastal provinces of Preah Sihanoukville, Kampot and Koh Kong and has potential to supply both local demand and provide valuable export income for Cambodia through managed development of the industry, though little is known of current practice in the region. Consequently, the aim of the present study was to collect base-line data on the state of small-scale cage and pond farming of Asian seabass located in the coastal area of Cambodia and to identify factors that are limiting development. This will better inform research and policy for promotion of Cambodian aquaculture towards improved food security and poverty alleviation amongst low income households in the region.


Material and Methods

Principal Study Design and Sampling Area

The survey focused on small-scale fish farms in coastal provinces of Cambodia in January 2015 and included a written questionnaire complemented with a 15 days travel period for interviews. The survey was carried out in the provinces of Preah Sihanoukville, Kampot and Koh Kong hich are located in the coastal area of Cambodia where farming is currently practiced (Figure 1).

Figure 1. Map of study provinces marked with circles.

Preah Sihanoukville  municipality is located in the south of the gulf of Thailand with a total land area of 868 km. It comprises the largest coastal town in Cambodia with the biggest seaport in the country. Koh Kong province covers an area of 11,160 km, borders Pursat Province in the north and Kampong Speu province in the east. Kam Pot province is located in the South-western part of Cambodia with a total coastline of 73 km. The coastline stretches from the border of H Tin district in Vietnam to Koh Ses (island in Preah Sihanoukville. Kam Pot province comprises eight districts with 92 communes and 477 villages, and has around 4% of the total population (Rizvi and Singer 2011).

In Preah Sihanoukville, two districts (Steng Hav and Prey Nop), four communes (Otres, Kom Pen, Ream and Tumnob Rolok) and three villages (Pum Muoy, Ong and Pum Bei) among all districts, communes and villages were included. In Kam Pot, two districts (Tek Chu and Kompong Bay district), two communes (Preak Tnaot and Traeuy Koh) and three villages (Trapeang Ropov, Changhaon and Ta Angk) were included. In Koh Kong, two districts (Srae Ambel and Mondol Seima), three communes (Srea Ambel, Bak Khlang and Peam Krasaob) and three villages (Srea Ambel, Bak Khlang Bei and Peam Krasaob Ti Muoy) were included.

Data Collection

Primary data on farming practices was collected through a structured questionnaire, observations and informal interviews. The questionnaire included questions on (i) general characteristics of the fish culture, socioeconomic characteristics (the fish farmers’ educational level, experience of fish farming, other occupation of farmers etc.), (ii) details of fish culture practices (number of cages/ponds, source of fish seed, stocking density, technical resources, water sources, mortality, common fish diseases (symptom), cause and effect of diseases, opportunities and constraints (problems of disease, water pollution), number of workers employed etc., (iii) type of feed used, feeding and (iv) size or weigh at harvest, fish yield for the last calendar year.

All farmers in each selected province, 20 farmers in Preah Sihanoukville, 11 farmers in Kam Pot and 25 farmers in Koh Kong were then interviewed (secondary data collection) as a complement to their written response. In cases of illiterate persons, the same questions as in the questionnaire were asked during the interview, then constituting a more formal part of the oral discussion.

Statistics

The data were coded and analysed by descriptive statistics and analysis of variance using Microsoft EXCEL and SAS (Version 9.4). Differences were considered significant at level of p< 0.05.


Results

General Information on Fish Farming Practices

Most of the fish farms were established along the coastal area and used cages for culturing of Asian seabass. Floating cages were most common in Preah Sihanoukville (Kompong Som) (Figure 2a), where most of the cages are located along the dam, while stationary cages were most common in Koh Kong and Kampot province (Figure 2b and c). In some cases, ponds were used to grow smaller size fish for 1-2 months before they were moved to the cages for on-growing. For the farmers without ponds, the fingerlings were kept in open marine cages with small mesh sizes for 2-3 months before they were graded and moved to grow-out cages.

Background of Farmers

The interviewed Asian seabass farmers were predominantly male and most of them owned the fish cages used for culturing (Table 1). In addition, some farmers also owned fish ponds.

Figure 2. Example of farms culturing Asian Sea Bass in the three regions investigated. a) floating cages in Steng Hav district, Tumnob Rolok commune,
Pum 3 village (Preah Sihanoukville province), and stationary cages in b) Tek Chu district, Preak Tnaot commune, Trapeag Ropov village
(Kompot province) and in c) in Mondol Seima district, Peam Krasob commune, Peam Krasaob Ti Muoy village (Koh Kong province).

In general, the educational level of the fish farmers was poor with 9 and 20% being illiterate in Kampot and Koh Kong, respectively. Moreover, 36 to 45% of the fish farmers had finished only primary school. Preah Sihanoukville province had the highest educational level with 30% having finished high school (Table 1). From the early 20th century, the Cambodian education system was operated under the French model (primary school from grade 1-4, secondary school from grade 5-8 and high school from grade 9-12). National examinations are conducted twice, once at grade 9 (degree of secondary diploma) and second at grade 12 (degree of high school certificate) (Ministry of Education, Youth and Sport).

Amongst the surveyed farmers, fish farming experience ranged from 1 to 20 years in Preah Sihanoukville, from 2 to 16 years in Kam Pot provinces and from 1 to 32 years in Koh Kong province (Table 1). The sources of fish farming experience varied between provinces. In Preah Sihanoukville province the fish farming experience was mostly gained from their own practice (75%). In Kam Pot province the fish farming experience was gained from practice (27%) and from workshops (36%), and in Koh Kong province from their own practise (32%) and from their neighbours (48%). All the interviewed farmers were actively engaged in fish culturing at the time of the study.

In addition to farming many farmers (72 - 90%) were also engaged in related businesses, such as processing of dry shrimp, fishing and selling aquaculture products (Table 1). Some farmers (10 - 28%) had other jobs (teacher, police) or were involved in other businesses such as selling groceries, rice cultivation and taxi service. Hired labour was most common among fish farmers in Preah Sihanoukville province (60%), while fish farmers in Kampot and Koh Kong mainly perform the daily work themselves (73 and 92%, respectively) (Table 1).

Table 1. Characterization of small-scale Asian Seabass fish farmers in the surveyed provinces (% of all farmers within province)

Components

Descriptions

Provinces

Preah Sihanoukvillea

Kampotb

Koh Kongc

Educational level

Illiterate

0.0

9.0

20.0

Primary school (grade 1-5)

40.0

46.0

36.0

Secondary school (grade 6-9)

30.0

27.0

28.0

High school (grade 10-12)

30.0

18.0

16.0

Property

Cage owner

90.0

82

84

Cage owner & hired pond

10.0

18

16

Technical skill*

Own experience

75.0

27.0

32.0

Neighbours

15.0

9.0

48.0

Workshops

0.0

36.0

4.0

Middle man

5.0

0.0

4.0

Own experience & workshop

0.0

27.0

0.0

Own experience & neighbours

5.0

9.0

12.0

Other income

Aquaculture related

90.0

73.0

72.0

Other business

10.0

27.0

28.0

Labour

Own work

20.0

73

92.0

Hired staff

60.0

27

4.0

Both own and hired

20.0

0.0

4.0

Number of farmers in each provinces (an= 20), (bn=11), (cn=25)
*
Some farmer has more than one answer. Sell aquaculture product, shrimp processing , raise animal and fishing, fisherman, repairing fishing boat. Teacher, moto taxi service, owner ice factory, selling food, selling feed stuff (grocery), gold smith. policeman, rice farmer.

Characteristics of Fish Farms

The number of cages per farm and cage dimensions varied significantly between provinces (Table 2). The largest fish farms were found in Preah Sihanoukville province (P<0.0002). The cage size (P<0.0005) and cage water volume (P<0.0001) was significantly larger in Kampot and Koh Kong provinces compared with Preah Sihanoukville.

The number of ponds used by fish farmers was highest in Koh Kong province followed in descending order by Kampot and Preah Sihanoukville provinces (Table 2). Moreover, pond depth was largest in Koh Kong province followed in descending order by Kampot and Preah Sihanoukville provinces (P<0.0001). Pond size and pond water volume was highest in Koh Kong province followed in descending order by Preah Sihanoukville and Kampot provinces but there were no significant difference between the provinces.

Table 2. Characteristics of cages and ponds used in small-scale Asian Seabass farms in the surveyed provinces

Descriptions

Provinces

p -Value

SE

Preah Sihanoukvillea

Kampotb

Koh Kongc

Cages number

60 (8.0-300)

7.0 (1.0-23)

6.0 (1.0-20)

0.0002

42.8

Cage size (m2)

8.0 (3.0-16)

13.7 (4.0-36.8)

14.4 (6.3-27)

0.0005

5.3

Cage depth (m)

2.4 (2.0-3.0)

2.8 (2.0-3.5)

3.5 (2.0-5.5)

<0.0001

0.7

Ponds number

5.0 (3.0-6.0)

2.0 (2.0-2.0)

2.0 (1.0-3.0)

0.1

1.2

Pond size (m2)

5761 (576-5000)

750 (600-900)

7200 (1600-10000)

0.3

3962

Pond depth (m)

1.0 (1.0-1.5)

1.5 (1.5-1.5)

1.3 (1.0-1.5)

0.3

0.2

Number of farmers (an= 20), (b n=11), (cn=25) Number is in mean (Min – Max)



Table 3. Characteristics of stocking in small-scale Asian Seabass farms in the surveyed provinces

Description of stocking

Provinces

P-Value

SE

Preah Sihanoukvillea

Kampotb

Koh Kongc

Cage, smaller size (head/cage)

880 (100-4000)

1468 (250-800)

1782 (380-5000)

0.2

1642

Cage, larger size (head/cage)

328 (100-600)

448 (250-550)

460 (250-2000)

0.002

122

Pond, smaller size (head/pond)

964 (600-10000)

2859 (10000-10000)

1156 (5000-10000)

0.49

3487

Number of farmers (an= 20), (b n=11), (cn=25) Number is in mean (Min – Max)

The stocking density of fingerlings per cage was lower in Preah Sihanoukville province than in Kampot and Koh Kong provinces (Table 3). This resulted in a stocking density per cubic meter in Kam Pot province followed by Koh Kong and Preah Sihanoukville provinces.

This resulted in a stocking density per cubic meter cage water volume of 44-77 head/m3. After 2-3 months, the stocking per cage was reduced, which gave a stocking density of 14-20 head/m3. The stocking of fingerlings in ponds was largest in Kam Pot province followed by Koh Kong and Preah Sihanoukville provinces. The stocking density per square meter pond area ranged from 1.0 to 4.2 head in the provinces (P<0.004) (Table 3).

There were significant differences between the provinces in size (P<0.02) and price of fingerlings (P<0.024), culture period (P<0.039), harvest size (P<0.05), survival rate (P<0.0001), selling price of Asian Seabass to market (P<0.0001) and the cost per kilogram of trash fish (used as feed source) (P<0.01). However, there were no significant differences between the provinces in the total number of fingerlings used per crop (Table 4).

Table 4. General information of small-scale of Asian Seabass farming

Descriptions

Provinces

P-Value

SE

Preah Sihanoukvillea

Kampotb

Koh Kongc

Experience (year)

9.7 (1-20)

5.6 (2-16)

6.6 (1-32)

0.2

6.4

Size of fingerlings (cm)

7.0 (4-12)

8.0 (6-12)

6.2 (4-7.5)

0.02

1.7

Price of fingerlings ($/head)

0.3 (0.15-0.40)

0.3 (0.15-0.33)

0.2 (0.13-0.23)

<0.0001

0.06

Culture period (month)

9 (4-12)

7 (6-10)

8 (5-12)

0.04

1.9

Harvest size (g)

877 (600-1100)

977 (750-1200)

854 (650-1100)

0.05

137.3

Selling price of fish ($/kg)

6.4 (4.0-8.0)

5.7 (5.0-7.0)

4.4 (3.2-7.0)

<0.0001

0.8

Survival rate (%)

30.8 (5-50)

49.5 (25-60)

20.2 (5-60)

<0.0001

15.0

Cost of feed (trash fish) ($/kg)

0.3 (0.18-0.31)

0.3 (0.18-0.33)

0.2 (0.16-0.33)

0.02

0.1

Fingerlings per crop (head)

400 (300-60000)

575 (400-15000)

503 (380-30000)

0.1

7912.0

Number of farmers (an= 20), (b n=11), (cn=25)  Number is expressed in mean (Min – Max)

Feeds and Feeding

Typically, fingerlings of small size were fed 3 to 4 times per day while this was reduced to 2 times feeding per day (morning and afternoon) when the fish reached larger size (larger than 7 cm). Trash fish was the most common feed type used for grow-out Asian Seabass in all provinces (Table 5), ranging from 55 to 100% of the fish farmers. The highest use of commercial dry feed which is imported from Vietnam was found in Preah Sihanoukville province (45%) followed by Kam Pot province (18%), while fish farmers in Koh Kong did not use any commercial feed. Some farmers fed commercial dry pellets to fingerlings of smaller size (5 to 7 cm length) for 1 to 1.5 months during the culture period.

Between 20 and 45% of the fish farmers surveyed would like to change from feeding trash fish to feed dry pellets, while 55-80% intended to continue using trash fish (Table 5). Some farmers claimed that Asian seabass fed trash fish had tastier flesh than fish fed commercial dry pellets. There were no fish farmers that used homemade feed in their culture mainly because some ingredients are expensive and difficult to find (need to import from Vietnam), but also due to limited knowledge on how to produce homemade feed.

Table 5. General information on feeding and feed used by small-scale Asian seabass farmers in the surveyed provinces

Components as %

Descriptions

Provinces

Preah Sihanoukvillea

Kampotb

Koh Kongc

Feed type

Trash fish

55

82

100

Commercial dry pellet & trash fish

45

18

0

Feeding frequency

1 time/day

75

20

5

2 times/day

18

82

-

Depend on trash fish available

50

21

19

Changing to pelleted feed

Yes (would like to change)

40

45

20

No (don’t want to change)

60

55

80

Source of fingerlings

Local

10

0

0

Thailand

30

0

72

Vietnam

20

0

0

Middleman

0

0

12

Local & Vietnam

20

0

0

Local & Thailand

10

82

0

Local, Thailand & Vietnam

5

0

0

Local & middleman

0

9

0

Thailand & Vietnam

5

0

0

Thailand & middleman

0

9

16

Cultured species

Only Seabass

20

45

32

Seabass, Grouper, Snapper & Pompano

80

55

68

Number of farmers (an= 20), (b n=11), (cn=25)

Fish species under culture

It was common among the fish farmers in all provinces to culture Asian seabass in poly-culture with Grouper (Epinephelus eoioides and Plectropomus leopardus), Pompano (Trachinotus spp ) Silver pomfret, (Pampus argenteus) Snapper (Lutjanus argentimaculatus) and Cobia ( Rachycentron canadum). The highest frequency of poly-culture was found in Preah Sihanoukville province (80%) followed by Koh Kong provide (68%) and Kam Pot province (55%).

Fingerlings were sourced from many sources in the surveyed provinces (Table 5), but the highest proportion of fingerlings were imported from Thailand and Vietnam, while locally produced fingerlings comprised a small proportion of the fish supply (Table 5).

Farm operating costs

There were significant differences between the provinces in the total cost of fingerlings per crop (P=0.02), total cost of trash fish (P=0.04) and total cost of labour (P=0.005) (Table 6). However, there were no significant differences between the provinces in total harvest (kg) and total income from selling fish per crop (culture cycle).

Table 6. The expenditure and income

Descriptions

Provinces

P-Value

SE

Preah Sihanoukvillea

Kampotb

Koh Kongc

Total cost of fingerling ($/crop)

3049 (75-13650)

996 (130-4875)

1468 (74.10-5850)

0.02

2172.6

Total cost of trash fish ($/day)

41.9 (1.2-300)

8.9 (1.75-48.75)

9.8 (0.81-58.5)

0.04

42.8

Total cost of labor ($/month)

200 (70-700)

150 (100-200)

200 (200-200)

0.09

151.6

Total harvest (kg)

969 (40-5000)

251.8 (33-1000)

482.5 (75-4500)

0.2

967.5

Total income from selling($/cycle)

5127.9 (240-29250)

1509.0 (165-6000)

2181.4 (244-20475)

0.16

5849.8

Number of farmers (an= 20), (b n=11), (cn=25), The significant differences between provinces. are significantly different (P<0.05)

Fish mortality and potential causes

Farmers had problems with fish mortality throughout the whole year (Table 7). However, they had different opinionson what to observe on the fish to diagnose disease during the culture period.

Table 7. General information on the fish mortality symptom

Descriptions as %

Provinces

Preah
Sihanoukvillea

Kampotb

Koh
Kongc

Change colour to dark & swim surface

-

27

8

Drop scale

55

9

60

Bulging abdomen

-

18

24

Bulging eyes

15

-

-

Opaque/cloudy eyes

-

9

-

Body lesion

20

-

-

Broken tail

5

-

4

Blind eyes

5

-

8

Haemorrhagic skin

5

-

-

Skin lesion

20

9

28

Leech (white & dark colour leech)

20

27

40

Lost appetite

-

-

4

Lost mucus

-

-

4

Red eyes

15

-

-

Red belly

5

9

8

White sport

5

9

12

Not observe (not sure)

10

27

12

Number of farmers (an= 20), (b n=11), (cn=25)
One farmer has more than one answer about the symptom of fish mortality in each province

In addition, the competence and skills to diagnose the fish varied between fish farmers. The general belief was that change of colour from bright to dark, swimming on the surface and loss of appetite are the first symptoms of disease. However, some fish farmers were unable to observe these symptoms and could not provide clear answers to link symptoms to fish death.


Discussion

Fish farmers established along the coastal area of Cambodia were predominately male and most of them owned the net-cages used for fish culturing. The use of cage culture in open-water offers a low-investment opportunity for fishermen to change from catching wild fish to culture fish for sale (Sowles et al 1994). However, the use of net-cage culturing in open-water impose an increased risk of disease occurrence within the cage reared fish and the potential risk of transfer of diseases to (and from) the natural fish population (Nash et al 2001). Fish farmers in all the surveyed provinces experienced problems with diseases and fish mortality throughout the year. However, the competence and skills to identify symptoms of disease and to diagnose a specific disease varied among the fish farmers despite long-time experience of fish farming. This may be related to lack of specific training and the poor educational level in general. Moreover, most fish farmers had other occupations in addition to fish culturing, which may result in less time to look for relevant information and to spend on the culturing activities.

The use of net-cage culturing in open-water may also impose an increased risk of fish escapes from cages and consequent potential impact (negative and/or positive) on wild fish populations, including potential genetic, ecological and social impact (FAO 2006; Fleming et al 2000). This concern is heightened by the import of non-native strains or varieties of fish for culture from neighboring countries. Open cage culture may also impact the surrounding aquatic environment and ecosystem from bio-deposits beneath the net-cages due to accumulation of uneaten feed and excreta from the fish. This can impact the benthic communities by eutrophication and anoxia in the sediments and may increase the risk of toxic algae blooms enhanced by the dissolved inorganic waste in the water column around the cage. Indeed, results from various studies on benthic impact show that 23% of C, 21% of N, and 53% if P from feed wastage, fish excretion, faeces and respiration is accumulated in the bottom sediments (Wu 1995).However, the significant impact resulting from high nutrient loading in culture system is generally confined within 1 km of the culture area.

The stocking density of fingerlings varied significantly between provinces. In ponds, where farmers kept smaller fingerlings (length <10 cm) before transfer to cages for grow-out, the average stocking density ranged between 1.0 and 4.2 head per square meter. The stocking density for fingerlings was lower than reported by Kungvankij et al (1985), while it was in the range recommended for Asian seabass culturing by FAO (2006).

It was common among fish farmers in all provinces to culture Asian seabass in poly-culture with Grouper, Pumpano, Snapper and Cobia. This is common practise in Asian seabass farming in South East Asia (FAO 2006) as a means of reducing disease pressure, stabilise income from fish production over time from the cages and to make better use of feed provided.

Trash fish was the main feed source used for grow-out of Asian seabass in all provinces. However, some farmers fed commercial dry pelleted feed for smaller fingerlings before transfer to grow-out net cages. Asian seabass are opportunistic predators that feed on crustaceans and fish, with an ontogenetic dietary progression from micro-crustacean to macro-crustacean to fish (Davis 1985). Wild juvenile seabass (1-10 cm) are omnivorous with their diet comprising some plankton but dominated by invertebrates, crustaceans and fish, while the diet of wild fish of larger size (>20 cm) is almost exclusively comprised of crustaceans and fish (Kungvankij et al 1985). Thus, trash fish is likely to be well-utilized by animals that are adapted as aquatic carnivores. Trash fish was used fresh without preservation by freezing and was bought, or caught, and fed on the farm the same day. Trash fish was prepared by cutting into small pieces then fed directly to caged fish. However, there are numerous sustainability issues associated with trash fish use in aquaculture (Rosenthal 1994; Wu 1995). These include lower feed efficiency and increased excreted nitrogen compared to pelleted feed (Hansen et al 1990).

We investigated the drivers of the low use of commercial dry pellets in Asian seabass culture in the surveyed provinces and found that uptake of synthetic diets was mainly constrained by high price. The price of commercial dry pellets for Asian seabass was estimated to be around 2.3USD per kg compared with around 0.2 – 0.3 USD per kg for trash fish. In addition to cost, many fish farmers preferred to use trash fish as it easier to obtain than multiple feed ingredients. There was also limited knowledge amongst fish farmers on how to prepare pelleted fish feed on-farm from dry ingredients. Moreover, farmers who are also fisherman can catch and collect the trash fish by themselves giving them control over supply. Another driver of trash fish use was (perceived) end-product quality with many farmers claiming that Asian seabass feed trash fish had tastier flesh than those fed commercial dry pellets. It is probable that the supply of protein, fat and minerals differs when fish are fed trash fish compared with commercial dry pellets. Indeed, free amino acids, peptides, organic acids, quaternary ammonium bases and minerals have been identified as taste-active compounds in fish (Haard 1992). In addition, fatty acids, in particular the unsaturated phospholipid fatty acids are important for the meat flavor development (i. e. production of volatile, odorous, lipid oxidation products) (Wood et al 2003). Williams et al (2003a) found that the taste Asian Seabass was affected when meat meal was used to replace fish meal in extruded diets. Asian Seabass appears to have limited capacity to use lipids as a primary energy source and will thus deposit body fat when diet lipid content is increasing (Williams et al 2003b). Fat content in trash fish varies between species and was reported to be in the range 2 to 10% in head, viscera and muscle (Xie et al 2007). In contrast, the recommended fat content in dry pelleted feed for grower Asian seabass is in the range 12 to 20% (Catacutan et al 1995). Thus, it is reasonable to assume that the intake of protein and fat in cultured Asian seabass will differ depending on the choice of feeding strategy and is perhaps supportive of the surveyed farmers’ perceptions reported here.

Mortality amongst farmed fish is still the major limiting factor in most aquaculture industries globally. Cage systems in marine or fresh water system can facilitate pathogen exchange between farmed and wild population (Johansen et al 2011), leading to pathogen spillover (Krkosek et al 2006) or spillback (Kelly et al 2009).

In the present survey, all farmers reported varying issues with mortality but generally lacked the expertise to identify causes. Symptoms mostly included loss of appetite, darkening and lethargy, which are characteristic of a number of diseases prevalent in the region including marine white spot disease (Yanong 2009) and steptococcosis (Agnew and Barnes 2007). A more comprehensive veterinary epidemiological survey amongst coastal farms in Cambodia may be timely to facilitate education on disease prevention as the industry develops.


Conclusions

Feed and disease are the main problems for Asian seabass culture in Cambodia. Because of the high cost of the commercial dry pellet, farmers predominantly use the trash fish as the feed source, which is unlikely to be sustainable for the future development of aquaculture in Cambodia. Locally available, low cost alternative feed ingredients such as brewer’s yeast, coupled with education of local farmers or feed producers in small-medium scale fish feed manufacture may be required to encourage increased use of dry feeds as the industry grows.


Acknowledgment

The authors thank to the Sida/SAREC MEKARN (Mekong Basin Animal Research Network) project for funding the research and my PhD scholarship and to all supervisors for their help, support and assistance during this study. Thanks to my director and my college for their kindly cooperate.


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Received 7 June 2018; Accepted 21 June 2018; Published 3 July 2018

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