01 de octubre de 2014
This article reviews the tilapia pond production system conducted in nutrient-enriched green water polyculture ponds, based on a field survey of 19 farms located in central provinces of Thailand, namely, Prachinburi, Chachoengsao and Chonburi.
By Txomin Azpeitia
Thailand is the fourth largest Asian country in terms of production volume, and sixth in the world ranking. Domestic market holds over 90% of the production with the remaining 10% destined for the overseas market. It is argued that the reasons and main constraint of the low export volume is lack of a consistent product quality with no off-flavour. In response, The Thai National Bureau of Agricultural Commodities and Standards have developed a Good Aquaculture Practice (GAP) farming certification programme, including environment and disease management recommendations, to attain a product meeting high quality and safety standards, and set the basis for further export market expansion.
In Thailand, Nile tilapia, Oreochromis niloticus, is the major fish species cultured, most commonly produced in nutrient-enriched green water ponds across the country with certain provinces having significantly larger production and distinct production systems. Pond and cage production together accounted for almost the total tilapia production volume in 2011 (155,554 tons), also produced in ditches and paddies. This number accounted for 41% of total freshwater aquaculture production that year; however, tilapia production had dropped a 24% from the previous year, because of floods that hit the north and central provinces of the country.
Although there are ditch and paddy production, their contribution to production is small. Cage contribution in terms of value is larger than pond systems mainly due to a higher market price fetched by the attractively-red-colored tilapia, produced mainly in the provinces crossed by the Chao Phraya River and tributaries, in between northern and central provinces; and in the Mekong River, bordering with Lao. This monoculture production system that exploded in the 90’s, has been negatively impacted by diseases caused by intensification, overcrowding and deteriorating water quality of the rivers and reservoirs. Consequently tilapia production in cages-in-ponds has been developed to favour water quality control in enclosed systems.
In Isan region, an area comprising northeastern provinces, production is mainly of subsistence and conducted in small backyard ponds, a practice initially promoted by community development organizations. Nowadays, there are also large corporate farms that produce large volumes for export.
In the central provinces production is mainly in green water ponds, only in some cases tilapia is produced in polyculture in cages-in-shrimp-ponds. In this case, tilapias are nursed for two months and then transferred to grow-out hapas. They are fed high quality formulated feed to allow a simultaneous harvest after a relatively short grow-out cycle. Green water pond production, on the other hand, relies on locally sourced by-products such as rice bran as supplementary feed and chicken manure fertilization to enhance the natural productivity. Formulated feed is becoming popular. However, aquatic feeds are considered extremely expensive considering the low market price attained by pond-raised tilapia. For that reason farmers use livestock or catfish feeds, often only in the final stage of grow-out, as a fattening phase, to boost growth and improve flesh quality; and most importantly, to ensure the profitability of their operation.
Production system in the central region of Thailand
Finfish polyculture and tilapia-shrimp polyculture were the most common practices encountered during the survey, and only in two cases tilapia was reared in monoculture and used formulated feed. Polyculture systems rely on agricultural locally-sourced by-products such as rice bran, as supplemental feed, and chicken manure as fertilizer to enrich the water and encourage natural phytoplankton growth.
The size of tilapia farms varied with some small farms, almost of subsistence with a single pond, and some farmers running several large size ponds in separated locations. In most of the cases, Nile tilapia was the primary specie produced along with several other finfishes (polyculture) in ponds averaging 3 to 5 hectares.
Pond conditioning and fertilization
Regular water and soil quality monitoring was uncommon, and conditioning was conducted without using any chemical or commercial product, except for lime and piscicides used for control and disinfection in some cases.
Depending on the condition of the pond bottom, organic matter built up, and if the rainy season allowed, ponds were dried for a minimum of a week and up to a month after drainage. This step helps to eradicate any wild fish and also enhanced soil condition by breaking down organic matter on sediments. Farms required digging the pond bottom with heavy machinery on a continuous or annual basis in the worst of the cases.
Piscicide use is popular according to previous surveys, although none of the interviewees mentioned it. Lime was widely used during the pond preparation step has a disinfectant, killing disease-causing organisms with its pH elevation and buffering effects. Lime purchased at 0.56 USD/kg was most frequently applied product in rates ranging from 50 and 300 kg per ha, depending on the soil condition.
In some areas access to water was a limiting factor - as observed this year, delayed rains negatively impacted production, postponing fish stocking – often mentioned by farmers. Additionally, increasing water salinity was becoming a recurrent problem. Both factors negatively impact water quality and lead to a decrease in growth and survival because most farmers only exchange water when its quality drops significantly or after harvest, in a static water production system. Incoming water was generally filtered with nylon bags or hapa nets. Often water from a draining pond was reused for filling another pond, or recirculated through a reservoir prior to its re-use.
Tilapias are facultative omnivores that feed on phytoplankton, zooplankton, detritus, insects, wastes and commercial pellets. However manufactured feed is not necessary for its green water production, encouraged by fertilization. Today, the use of inorganic fertilizers is very limited and in their place locally sourced chicken manure is used. Generally, this practice is sustainable in terms of agriculture or food industry waste recycling; however, it can lead to excessive organic matter built up in the soil sediment due to poor digestibility of input used. Besides deteriorating water quality, they are also a source of pathogens, unlike inorganic fertilizers which do not show any of these adverse effects. On the side of most ponds there is usually an area covered with a canvas, engineered to offload the manure transported by farmers in pick-up trucks. The manure, depending on the source, ranged from 15-70 USD per ton. Farmers rely on their experience in monitoring water color and adjust the fertilizer application rate accordingly. Generally there was an increase in manure requirements throughout the culture period to maintain growth, for example chicken manure was applied once per week and rates between 50 and 500 kg per hectare. In contrast, requirements decreased with the use of manufactured feed which also provide nutrients in the form of N and P to the system’s food web. Although on some farms that carry out a fattening stage in the last on-growing months using formulated feed to boost growth, they continued to apply chicken manure despite this fact.
Benefits of polyculture
Production of several finfish species or finfish-shrimp in polyculture reduces risk of financial loss due to mortalities or price drops in the market, as well as increases income. Mud carp, common carp, bighead carp, silver barb, seven-striped barb, small scale barb, snakeskin gourami, pangasius, rohu, white shrimp, etc. reared together with tilapia utilize all the niches and increase the yield by feeding on all available food sources, and reduce competition.
Tilapia fingerlings are more sensitive to poor water quality and predation than juveniles, therefore nursing fry in earthen ponds or hapas-in ponds is often practiced as mitigation and reduces culture period. Providing a safe environment to the fish fry during nursing also enhances growth, although extended ongrowing in a single pond, that is, stocking fry directly in earthen ponds for ongrowing is also popular.
Locally produced all-male tilapias are the preferred choice of farmers due to its faster growth, and even size at harvest that attains a higher market value. Surprisingly, more affordable, lower performance and early breeding mixed-sex fry are still used. The stocking densities observed in nursing and ongrowing stages shown in the table are dependent on fish size, feeding method, cycle length and expected yield.
For feeding purposes, feeding stations comprised of several floating plastic baskets were placed to hold the daily provided supplementary feed. Fine rice bran is the most popular feed input among interviewed farmers, probably due to its affordable price and proximity of rice mills that often directly supply the farmers at their farm gate. In the past years, rice bran price has increased in accordance with rice prices, and as a consequence, cheap aquatic feeds, manufactured for catfish or herbivorous species, use increased as well.
Corn bran and other agricultural by-products have been used according to previous surveys but in the current case only by selective farmers. By-products from bread and fish industry are also popular, due to the farms proximity to cities or industrial states. A surprising feedstuff used in two different operations was cow skin, directly purchased at the slaughterhouse and offloaded in the pond upon arrival to avoid its rotting at the farm. Digestibility, nutritional profile and safety in terms of pathogen load are the main concerns when using alternative feedstuff with high carbohydrate and low protein contents (except for cow skin).
Ongrowing takes between half- and a year largely depending on the feeding and fertilization techniques. A fattening stage during the last ongrowing months appears to be a common practice. This practice requires the use of higher quality formulated feeds, in terms of crude protein concentration, to enhance growth. Similarly, higher quality premium pellets are used in integrated farms that produce tilapia in hapas in polyculture shrimp ponds, to boost tilapia growth in a relatively short production cycle and allow a simultaneous harvest of both species. In some cases, fish are nursed on manufactured diets, such as frog pellets to produce fishes larger than 100 gram before they are transferred to grow-out ponds.
Among shrimp farmers it is becoming a common practice to stock tilapias in water reservoirs or in shrimp ponds, because tilapia is known to improve water quality, reducing bacterial load, and thus, incidence of disease. Many interviewees conducting this practice mentioned they started rearing black tiger shrimp to then move onto white shrimp and finally tilapia. Recurrent viral disease outbreaks in shrimp were the main reason for their graduation or shift to tilapia or finfish polyculture.
Harvest is generally conducted by a contracted team that determines fish price upon arrival or, less frequently, by the farmers themselves. In semi-intensive ponds relying on by-products, production of 6 tons tilapia per hectare is considered average, while secondary species would add up 1 to 2 tons to the tilapia yield.
In Thailand over 90% of the production goes into the domestic market, provincial wholesale markets located nearby the farms. In the case of small-scale farmers that partially harvest, they may directly sell to customers visiting the farm or in local markets.
Fish market price entirely depends on fish size, color, body shape and length, even if there are some seasonal price fluctuations during festivities. Live tilapia farm-gate price ranged between 1.24 and 1.86 USD per kg, while chilled tilapia sold for 0.82 and 1.39 USD per kg. Mixed fish fetched the lowest prices.
Today access to water, flooding and their adverse effects on water quality are increasingly becoming an issue. In some areas access to water is a limiting factor and, often its increasing salinity a recurrent problem. Both negatively impact water quality resulting in a decrease in growth and survival, as many farmers only exchange water when its quality deteriorates significantly or after harvest. Excessive organic build up on sediments due to overfeeding or pond mismanagement leads to deleterious conditions such as soil acidification that negatively impacts fish welfare, especially fingerlings and juveniles.
Operators of semi-intensive farms often complain about unaffordable tilapia formulated diet prices, and used pig or herbivorous fish diets instead. The use of feed additives such as probiotics or immune-enhancers is limited to integrated systems where shrimp is produced in combination with tilapia, due to the low margin of polyculture semi-intensive tilapia production.
Disease outbreak appears to be the main concern of farmers because tilapias are susceptible to several bacterial and parasitic diseases. Streptococcus, Flavobacterium and Francisella bacterial strains are among the most prevalent causes of disease, especially during the warmer months where water temperatures soar above optimum levels. The cause of disease outbreaks are rarely diagnosed, however pond disinfection with chlorine or potassium permanganate are usually conducted on farm as a preventive measure.
Streptococcus in tilapia is caused by Streptococcus agalactiae, in contrast to other finfish that mostly are infected by S. iniae, is by far the major impact on economic terms to tilapia aquaculture. Acute streptococcosis mortalities that occur during the summer season and chronic mortalities that happen during the warmer months of the year affect tilapias of all sizes. Mortalities in larger size fish negatively impact productivity and food conversion ratios.
Unlike cage farming, in pond production the use of antibiotics is not a common practice, instead they apply preventive measures. Maintaining adequate levels of oxygen by avoiding phytoplankton overblooms, or in the case of small ponds installing paddle wheel aerators; and adjusting the stocking density according to the season, are among the measures taken.
Barriers for industry expansion and government policies
Interestingly, the argument that local authorities point out as main constraint for export market expansion, the off-flavor in tilapia fillet, was not mentioned by any farmer, probably because this does not appear to be an issue for the domestic market. Off-flavor happens in freshwater systems, caused by the absorption of metabolites produced by some species of actinomycetes and cyanobacteria which accumulates in fish flesh giving a musty and muddy flavour. Described practices in tilapia semi-intensive ongrowing such as organic fertilization and agricultural by-products use are more prone to produce off-flavors and their water quality deteriorating effect, especially in terms of dissolved oxygen in over fertilized ponds, enhance the accumulation of these metabolites.
In order to produce a product of consistent quality, Thai National Bureau of Agricultural Commodities and Standards have developed a Good Aquaculture Practice (GAP) certification programme for tilapia farming in collaboration with the Department of Fisheries (DOF) that sets the standards in terms of input safety requirements and storage, health management, farm sanitation and record keeping with a special focus on veterinary drug and residue use and limits, feed and fry input traceability and effluent water quality standards. Additional activities that include technical training and workshops, export network development, and public marketing campaigns are conducted as well. The GAP promotes fish free of drug residues and management that mitigates off-flavors in tilapia farming, harvest and post-harvesting practices, though it does not cover hatchery and nursing stages.
The GAP addresses the off-flavor issue and recommends in cases where fish taste is muddy or musty, to discontinue organic fertilizer use in the last two months prior to harvest and exchanging water in order to reduce blue-green algae. Nevertheless, cautious should be taken with manufactured feeds which when decomposed also enhance blue green algal growth. Finally, pond liming or microbial treatments are advised if off-flavor still persists.
With the United States as the first importer of tilapia worldwide, largely supplied by China, Thailand still needs to compete with the lower production costs, particularly feed and labour, of Chinese produce maintaining a standard quality fish. Nevertheless, tilapia market price should increase to allow the producers having a larger profit margin to implement the measures required to improve tilapia quality and safety for the international markets.
The information discussed in this article was collected during the field surveys from February to May 2014 as part of the SEAT project, Sustaining Ethical Aquaculture Trade (http://seatglobal.eu/), funded by the European Union 7th Framework (FP7) Program and coordinated by Stirling University.
Special thanks to Mr. Warren Turner, General Manager of Nam Sai Farms (http://www.tilapiathai.com/), a hatchery specialized in producing all-male tilapia, and his team, for their support arranging visits, translating and unconditional help, and also to Miss Janielle Wallace, Principal Investigator, for her invaluable advice and helpful discussions on the topic and this article review.
Detailed survey reports of some surveyed farms can be found in this link: http://asianaquaculture.blogspot.com/