Floating cage aquaculture production in Indonesia: Assessment of opportunities and challenges in Lake Maninjau

: Aquaculture in floating cages in Lake Maninjau has recorded significant growth, even as the largest contributor to total annual aquacultural production in West Sumatra Province. In this study, we assessed the output of floating net cages in Lake Maninjau, Indonesia. We analyzed the characteristics of fish farming, fish fry, feed supply, and production, and the challenges and opportunities for increasing aquacultural production in the future. We used purposive sampling in this study with an interview questionnaire to obtain information from 80 fish-cultivating households in Lake Maninjau. We then used descriptive statistical methods of data analysis. The results showed that in 2018, there were 17596 floating net cages. The majority (n = 33, 41.25%) of fish farmers have 20 to 40 floating net cages per household, and 67.5% (n = 54) are used for tilapia cultivation. We recorded that 77.5% (n = 62) of fingerlings were sourced from private hatcheries. Six companies supply commercial feed pellets in an amount of 2000 tons per month for aquaculture activities. Japfa Comfeed Indonesia Ltd. provides 35% of the feed. The fish species cultivated were Nile tilapia, common carp, giant gourami, Clarias


Introduction
Aquaculture is responsible for a supply of fish for human consumption; for this reason, aquaculture continues to grow faster than other major food production sectors [1].Indonesia is rich in natural water resources that can be utilized for aquaculture development in the future [2][3][4].In 2016, aquaculture in Indonesia occupied 1201275 ha in total, consisting of 250640 ha (20.86%) of inland area, 674135 ha (56.12%) of coastal area, and 276500 ha (23.02%) of marine area [5].These data show that the aquaculture sector plays an important economic role in Indonesia [4,6,7].Recently, the freshwater aquaculture commodities developed in Indonesia include Clarias catfish, Pangasius catfish, common carp, and Nile tilapia [8].These species have contributed as much as 14.0%, 11.0%, 13.4%, and 22.7% to Indonesian aquaculture production, respectively [2], and are derived from ponds, floating net cages, and paddy fish integrated farming [5].
Aquaculture activities in floating net cages in Lake Maninjau date back to 1992, when Yulinus Farm Limited successfully harvested fish from floating net cages constructed for their farm.At that time, the fish species being cultured was common carp (Cyprinus carpio).Nile tilapia was more dominant in the last ten years, and other species, such as giant gourami and Clarias pangasius were also farmed [9,10].In 2015, in Lake Maninjau, as many as 16608 floating net cages were recorded, compared to only 16 nets recorded in 1992 [11].However, the number of floating net cages and other supporting industries is increasing in Lake Maninjau.Therefore, a strategy is required to guide investment based on "sustainability", i.e., the practice of cultivating floating net cages to grow sustainably.At the same time, negative environmental impacts must be reduced significantly [12,13].
Previously, we did not have recorded information on the characteristics of floating net cages, sociodemographic indicators, or the number of floating net cages in each village in Lake Maninjau.Our study includes the fish cultivated, fingerling sources, and activities related to commercial feed provision and feed supply companies.Therefore, this study evaluates the characteristics and sociodemographic indicators of farms, such as the number of cages in each village, species of fish cultivated, feed supply companies, and harvested production.Apart from these data, we also analyzed the opportunities for and challenges of floating net cages in Lake Maninjau.These data are fundamental to future sustainable fish farming activities with floating net cages.

Study area
This study was conducted in Lake Maninjau, Tanjung Raya subdistrict, Agam District, West Sumatera Province, Indonesia.This lake is categorized as teptovolcanic.It is located at longitudes of E: 0012'26.63''-S:0025'02.80''and E: 100007'43.74''-E:100016'22.48'',at an altitude of 461.50 m above sea level, approximately 150 km southwest of Padang City.The biophysical characteristics of Lake Maninjau are presented in Table 1.The Tanjung Raya subdistrict has a population of 35309 [14]; the community's main activities in Lake Maninjau are floating net cage fish farming and tilapia hatcheries on the lake border.

Study design
In this study, we used the purposive sampling method.Interviews were conducted by questionnaire to obtain information on 80 fish farmers' households characteristics (10 households per village) from 850 fish farmer households in eight villages in the Tanjung Raya subdistrict [16].The eight vilages were Koto Malintang, Tanjungsani, Sungai Batang, Maninjau, Bayur, Dou Koto, Koto Kaciek, and Anam Koto.We conducted this survey in the Tanjung Raya District of Danau Maninjau from March-July 2018.Primary data collection included the total number of floating cages in each village, the number of operators of floating net cages, fish feed supply, fish fingerling availability, and harvested production.Then, we analyzed the challenges faced by fish farmers working with floating net cages.We obtained additional relevant information about fish farming activities in floating net cages from the managers of the feed companies, and from field observations.Before we collected primary data, a questionnaire was designed, and a pretest was run with several floating net cage farmers in each village.Changes in the questionnaire form were made according to the data requirements.The final questionnaires were improved, rearranged, and modified based on responses from the pretested questionnaires.In addition to primary data, we also collected secondary data, including a dataset of the number of floating net cages from 2001 to 2018 from the Department of Fisheries, Agam District, West Sumatera Province.Mapping involved georeferencing the number of floating net cages in each village based on GPS locations established for floating net cages in Lake Maninjau using ArcGIS 10.0 (Esri Canada).

Data analysis
The data collected were organized into charts, tables, and graphs in Microsoft Excel and then all answers were coded and transferred to the Statistical Package for Social Scientists (SPSS) version 17.0.

Characteristics and sociodemographic indicators
Fish farming households in Lake Maninjau have practiced production methods and the single floating net cage system for economic reasons.A production unit consists of an iron frame coated with anti-rust material (iron paint) supporting four floating net cages of 75 m 3 (5 x 5 x 3 m) constructed of 10 mm mesh.The units are used in combination with other equipment (i.e., a float, feeding station, and cage pathway).Floats are plastic drums of a double ring type, with a body diameter of 58 cm, a total height of 93 cm, a product weight of 8.6 kg, and a full volume of 200 L. In contrast, in Lake Victoria, Kenya, fish farmers used cages ranging from 8 to 125 m 3 , and the sizes of the pens were related to differences in financial resources [17].
The number of floating net cages increased exponentially between 2001 and 2018 and increased by 90.14% in the last five years (Figure 1) [14].Interest is growing for the floating net cage business.Table 2 shows the number of floating net cages in each village around Lake Maninjau.Tanjung Sani village had the highest number of floating net cages (n = 4364, 24.80%) out of a total of 17596 cages in Lake Maninjau.Koto Gadang village and Duo Koto had the lowest numbers of floating net cages (n = 660, 3.75% and n = 653, 3.71%, respectively).The difference in the number of floating net cages in each village was mainly due to the length of coastline owned by each village.
For example, floating net cages in Bayur Village are shown in Figure 2. Most of the floating net cages (n = 45, 56.26%) were located 300 m from the shore.Farmers prefer that zone due to its better water quality and protection from potentially damaging winds and currents.However, mapping showed that there were also floating net cages placed around the weir zone of the hydroelectric power plant.Several areas (<100 m) of each village were "Rasau Rindu Wisata" zones that function as fish breeding zones and are protected from fishing, thereby affecting natural fish populations.
This survey involved 80 fish farmers' households from a sample of 850 fish cultivating households.Overall, we recorded 2274 floating net cages from 80 respondents.The respondents were classified as full-time fish farmers (n = 54, 67.5%), part-time fish farmers (n = 10, 12.5%), fisherman and fish farmers (n = 13, 16.25%) or other (n = 3, 3.75%).In this case, other referred to persons who owned cages but were neither full-time fish farmers, nor part-time fish farmers, nor fishermen.These individuals could have been village office clerks, teachers, shopkeepers, or individuals earning civil servant pensions.The average income of respondent's household was USD 172.41 per month, with the majority of respondents living in the Maninjau Lake area (n = 75, 93.75%).This income is lower than the income of cage fish farmers in Lake Victoria, Kenya (USD 2832 per month).At the same time, 82% of those fish farmers live in rural areas of the Lake Victoria region [13].

Species cultured and stocking densities
The fish species cultured were Nile tilapia (Oreochromis niloticus), common carp (Cyprinus carpio), Clarias catfish (Clarias sp), Pangasius catfish (Pangasius hypophthalmus), and giant gourami (Osphronemus goramy).Other researchers have reported that Nile tilapia is the predominant species cultured in cages [13,18,19].In this study, the majority (67.5%) of the floating net cages were used for cultured Nile tilapia, 18.75% were used for common carp, 5.00% were used for Clarias catfish, 3.75% were used for Pangasius catfish, and 5.0% were used for giant gourami (Figure 5).Clarias catfish and Pangasius catfish are cultured because the production cycle is short.They can be fed feed dead tilapia, which come from the floating net cages in this area, and are resistant to poor water quality.At the same time, although the growth rate of giant gourami is slow, this species is resistant to poor water quality and has a high market price.The average stocking density of Nile tilapia fingerlings was 100 fish/m 3 (7500 fish per net), the average stocking density of common carp and giant gourami was 66 fish/m 3 (5000 fish per net), and the average stocking density of Clarias catfish and Pangasius catfish was 133 fish/m 3 (10000 fish pernet).In this study, tilapia fingerlings for cage culture were sourced from private fish hatcheries and individual hatcheries, and caught in Lake Maninjau (Figure 6).The fingerlings of common carp, Clarias catfish, and giant gourami were obtained from private companies in Luak District, Lima Puluh Kota Regency, West Sumatra Province, which is 75 km from Lake Maninjau.We collected catfish fingerlings from Kampar Regency, Riau Province, 120 km from Lake Maninjau.

Fish feed
This study revealed that fish farmers in Lake Maninjau carried out aquaculture activities for 60 to 180 days per production cycle to achieve market sizes.Most fish farmers fed the fish twice a day, from 09:00 to 10:00 AM and 4:00 to 5:00 PM.Fish were hand-fed at a 3% body weight rate per day until study termination.According to Thongprajukaew et al. [20], tilapia operations with a twice daily feeding (09.00 PM and 6.00 PM) are optimal for feed management.Conversely, feeding fish improperly can be a problem for fish farmers in developing countries [21].In this study, we noted that the feed used was floating and sinking commercial feed, however, cage fish farmers in Lake Victoria used floating, sinking, slow sinking, and other feed types [13].
In this study, we also noted that the feed used to produce floating net cage fish was supplied from a feed company in North Sumatra Province, Indonesia.Currently, the feed supplied to Lake Maninjau, Tanjung Raya District, averages 2000 tons per month.Commercial feed was supplied by seven companies, namely, Japfa Comfeed Indonesia Ltd., Central Proteina Prima Ltd., Mabar Feed Indonesia Ltd., Malindo Feedmill Ltd., Sinta Prima Feedmill Ltd., Universal Agri Bisnisindo Ltd., and Cargill Feed and Nutrition Ltd. (Figure 7).Feed was transported by truck; the distance from the location of the animal feed company to Lake Maninjau was 650 km.The feed used by fish farmers was 60% best quality feed, 30% good quality feed, and 10% relatively poor-quality feed.In Lake Kariba, Zambia, the feed supplied by two companies ranged between 50 and 100 tons per day [19].In contrast, Aura et al. [13] stated that cage farmers obtained feed from nine companies in Lake Victoria, Kenya.

Harvested fish
Based on the records of fish farmers, tilapia and gourami were given commercial feed every day from 09.00 to 10.00 and from 16.00 to 18.00.The amount of feed given ranged between 3% and 5% of body mass.Meanwhile, Clarias and Pangasius catfish were not fed commercial feed but were given dead tilapia from the surrounding cage culture.The tilapia and common carp were reared in floating net cages for each production cycle, with an average of 120 days, whereas giant gourami was reared for 170 days.Conversely, Clarias catfish and pangasius catfish were raised for 60 and 75 days.The average harvested weight of tilapia and giant gourami were 200 and 300 g/fish, respectively, and the gross yield of tilapia was 12 kg/m 3 /cycle and that of giant gourami was 10.4 kg/m 3 /cycle.The feed conversion ratio (FCR) for tilapia was 1.68, and that of giant gourami was 1.65.The average harvested weight of Clarias catfish was 125 g/fish, and that of Pangasius catfish was 150 g/fish.The gross yields of Clarias catfish and pangasius catfish ranged from 7.88 to 8.89 kg/m 3 /cycle, respectively.We did not record the FCR for Clarias and pangasius catfish because these fish are not fed commercial feed by fish farmers.

Significant challenges in aquaculture
First challenge In this study, we found several challenges in the development of tilapia aquaculture in Lake Maninjau.Most fish farmers face the challenge of mass mortality of fry in the early period of their cultivation activities due to poor water quality.In recent years, the water of Lake Maninjau has been heavily polluted, and the lake has a hypereutrophic status [22].According to [23], cyanobacteria dominate eutrophic lakes, and cyanobacteria produce cyanotoxins [24,25] reported that mass mortality of fish was associated with toxins from cyanobacteria.Meanwhile, the main challenge for tilapia cultivation worldwide is the disease Streptococcus agalactiae, which causes huge losses for tilapia farmers [26,27].In comparison, Ferguson et al. [28] stated that Tilapia Lake Virus (TiLV) was found together with well-known pathogenic bacteria such as Aeromonas spp., which negatively impacted the survival of tilapia fish.Whether TiLV lives in Lake Maninjau and negatively affects the survival rate of tilapia was not examined in this study.However, TiLV infection can decrease tilapia production and can cause serious socioeconomic impacts [28][29][30][31][32].

Second challenge
The price of commercial feed pellets (IDR 12000/kg) is the second challenge for tilapia aquaculture in Lake Maninjau because the selling price of fish is not proportional to the cost of feed.Tilapia is a target species with local market prices of IDR 19000/kg and higher production levels (approximately 85% of total production).The price of common carp is IDR 22000/kg, the price of giant gourami is IDR 40000/kg, the price of Clarias catfish is IDR 15000/kg, and the price of Pangasius catfish is IDR 14000/kg.The cost of feed contributes to approximately 60% of the operating expenses in the aquaculture system in Lake Maninjau.Furthermore, most farmers have experienced challenges in estimating the right amount of feed to provide, so the FCR varies between 1.6 and 1.8.Similar to the findings of Ali et al. [33] and Thongprajukaew et al. [20], who stated that feed was the most significant component of operating costs in an intensive aquaculture system, we found that optimum feeding without waste would determine the system's economic viability.Therefore, feeding fish according to their needs can improve productivity, help to reduce feed loss, and maintain a suitable aquaculture environment [34].At the same time, other critical challenges in fish farming are theft and predators such as birds and crocodiles [19].However, in this study, we found that theft and predators did not become a challenge for fish farmers in Lake Maninjau because farmers run their fish farming activity around their residence.

Third challence
Based on Agam Regency Government Regulation Number 5, of 2014, concerning the management of Maninjau Lake, the number of floating net cages allowed for cultivation activities, based on carrying capacity, is 6000 nets.In this study, fish farmers did not implement the above government regulations.Most aquaculture producers (58.34%) stated that the law prevented them from increasing their production and reducing their income.Meanwhile, few agricultural activities can be carried out around lakes due to the narrow, hilly, and rocky land areas [16].However, David et al. [35] stated that water bodies must be used rationally, based on the ecological carrying capacity, to sustain aquaculture production.For example, in Lakes Victoria, Kariba, Malawi, and Taihu, fish farmers have complied with the best regulations to promote sustainable aquaculture [36][37][38].In addition, government regulations have been applied along the Norwegian coast to determine the spatial distribution of salmoncages, their size, and the structure of cage ownership [39].
Furthermore, continued water damage is the third challenge for fish farmers wanting to increase fish production.Other researchers found that lake damage was caused by nitrogen and phosphorus in the water bodies [35,40].According to Syandri et al. [41], the availability of nitrogen, phosphorous and total organic matter in the water was significantly higher after fish mass mortalities harmed the water quality of Lake Maninjau.Releasing nutrients from cage aquaculture in the aquatic environment affects water quality and conflicts with multiple users.However, it also exerts a negative feedback effect on the cage operations themselves [35,40,42,43].
Table 3 shows that poor water quality, fish mass mortality, and uncertainty regarding operational aquaculture law were the main challenges in fish aquaculture activities in Lake Maninjau.On the other hand, biophysical variables such as disease, pollution, and lack of an

Figure 1 .
Figure 1.The number of fish cages established between 2001 and 2018 in Lake Maninjau, Indonesia.

Figure 2 .
Figure 2. Map of floating net cage locations in Bayur Village, Lake Maninjau, Indonesia.

Figure 3 .
Figure 3. Owners of floating net cages in Lake Maninjau.

Figure 4 .
Figure 4. Ownership of floating cages per fish farmer household in Lake Maninjau.

Figure 5 .
Figure 5.The proportion of fish farmers' households by fish species kept in Lake Maninjau.

Figure 6 .
Figure 6.Sources of tilapia fingerlings for aquaculture activities.

Figure 7 .
Figure 7. Fish feed supplied by each company to Lake Maninjau.

Table 2 .
Distribution of floating net cages in eight villages in Lake Maninjau, Indonesia.