Fish culture in rainfed rice fields of northeast Thailand

Adoption of rice-fish culture by farmers in the rainfed areas of northeast Thailand is examined with reference to recent field research and extension in the region. The practice is placed in perspective with the development of aquaculture per se and the human and agricultural ecology of this heterogeneous region. Rice-fish culture is a recent activity in the region and has been promoted by government and non-government agencies with variable success among small-scale farmers. The widespread availability of private hatchery-produced fish seed and perceived decline in wild fish have been important stimuli. Rainfed rice fields are marginal agricultural environments and lack of water constrains both rice and fish production. Wild swamp fish are tolerant of these conditions and traditional systems for their management and capture have expanded greatly in recent years. In much of the region ‘trap’ ponds are used more for catching wild fish than as refuge sumps or ponds for fish culture per se; wild fish typically constitute between 20 and 80% of the total yields in stocked systems. Widespread availability of fish seed allows more farmers to try rice-fish culture but the small size of seed at purchase is still a problem particularly where carnivorous, wild fish are prevalent. Appropriate on-farm nursery techniques may improve success and adoption of hapa nursing has been high in some parts of the region. Species ratio and density of fish stocked depends mainly on their availability from fry traders; the major species stocked in rice fields are the silver barb (Puntius gonionotus), common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus).

Farmers adapt rice fields for fish culture as part of their whole farm strategy; benefits to rice, vegetable and fruit and livestock may be considered more important than fish yields. The high value attached to even small quantities of fresh fish is a major incentive for rice-fish culture, but women who are decision makers in terms of changes to rice fields and household consumption have often not been fully considered during promotion of rice-fish.

The relatively small areas of riceland that farmers can stock and harvest fish, low yields per unit area and high consumption of fish reduces the importance of rice-fish culture in many rural households. The analysis suggests that stocking fish in rice fields in areas with poor access to wild fish supplies from community water bodies would have most impact.

Although rice-fish culture can contribute to subsistence requirements, the high labour demand often means that intensified capture of wild fish or pond-based culture of fish are more attractive for poorer and better off farmers, respectively.     

Aquaculture information sources for small-scale fish farmers: the case of Ghana

The Ghana ministry of fisheries and the ministry of Agriculture provide free extension services and other technical services to fish farmers in Ghana, e.g. producing fingerlings at government-operated fish hatcheries for sale to farmers. Non-governmental organizations and universities have also provided some technical assistance to fish farmers in efforts towards the development of aquaculture in Ghana. The study identified the various sources of aquaculture information to Ghanaian fish farmers and examined the factors that affected their decision to utilize these alternative sources of information. Using choice modelling techniques, the study found that the probability of farmers seeking information on aquaculture from the Ghana government increases with literacy by about 43% more than with illiteracy and by about 34% with an increase in total size of ponds. The probability that a literate farmer will choose to obtain aquaculture information from a non-governmental organization decreased by about 10% compared with an illiterate farmer. The probability of choosing 'other sources' for aquaculture information increased by about 27% for farmers residing in Ashanti region compared with farmers in the Brong-Ahafo region but the probability of farmers seeking information from 'other sources' decreased with literacy and number of years farming.     

Current status of freshwater prawn culture in Vietnam and the development and transfer of seed production technology

ABSTRACT:   In Vietnam, the giant freshwater prawn Macrobrachium rosenbergii is becoming an increasingly important targeted species, as its culture, especially in rice fields, is considered to have the potential to raise income among impoverished farmers. The production of M. rosenbergii based on aquaculture reached over 10 000 tons per year in 2002, having increased from about 2500 tons since the 1990s. Until recently, lack of a stable supply of seed had been an important obstacle to the further expansion and development of M. rosenbergii culture, but cumulative research on larval rearing, especially in the 1990s, has led to the development of new seed production technology based on the 'modified stagnant green water system'. Following its dissemination by the efforts of provincial authorities, hatchery operators, and farmers, the freshwater prawn seed production industry developed rapidly in the Mekong Delta with over 90 hatcheries producing 76.5 million postlarvae in 2003. This is considered to have affected the expansion of rice–prawn farming in the Mekong Delta, leading to increased aquacultural production in the region. This paper reviews the current status of freshwater prawn culture in Vietnam and background history, and presents a socioeconomic evaluation of seed production technology implementation.     

EFFICIENCY OF RESOURCE USE AMONG POND FISH FARMERS IN CENTRAL UGANDA: A STOCHASTIC FRONTIER PRODUCTION FUNCTION APPROACH

This article presents the use of a stochastic frontier production function to examine the efficiency of resource utilization in pond fish farming in Uganda. The study draws on data from a field survey administered to 200 small-scale fish farmers in three major fish farming districts in Central Uganda: Mukono, Mpigi and Wakiso. The districts were part of a large aquaculture development project funded by the United States Agency for International Development-Aquaculture and Fisheries Collaborative Research Support Program. Productive efficiency was analyzed using stochastic frontier analysis with a translog production function while assuming a truncated-normal distribution for the inefficiency term. The output variable was total quantity of fish produced, while input variables were quantity or value of inputs used in the production process, namely labor, pond size, stocking density, capital and feeds. The estimated index of resource-use efficiency revealed that small-scale farmers were inefficient in resource allocation by over-utilizing labor with an estimated allocative efficiency index of ?0.94 and grossly under-utilized pond size, feeds and fingerlings with allocative efficient indices of 1.15, 1.64, 3.71, respectively. The results suggest that there is considerable scope to expand output and also productivity by increasing production efficiency at the relatively inefficient farms and sustaining the efficiency of those operating at or closer to the frontier.     

Molecular tracing confirms that infection with infectious pancreatic necrosis virus follows the smolt from hatchery to grow‐out farm

Infectious pancreatic necrosis (IPN) is an important restraint to production of salmonids in aquaculture globally. In order to implement efficacious mitigation strategies for control of this disease, it is important to understand infection routes under current production systems. IPN virus has been shown to be transmitted vertically in Rainbow trout, from broodstock to fingerlings in hatcheries, and there is circumstantial evidence suggesting that vertical transmission can also occur in Atlantic salmon, in addition to horizontal transmission between grow‐out fish in farms. In this study, we show that the smolt carries infection with IPN from hatchery to the marine farm. We do this by comparing sequences from fish groups taken both in hatcheries and on corresponding marine grow‐out farms. We use statistical analysis to prove that sequences obtained from the same fish group in both hatchery and marine farm are more similar than sequences obtained from random fish groups on hatcheries and marine farms.     

Effects of photoperiod and the duration of conditioning on gametogenesis and spawning of the mussel Mytilus galloprovincialis (Lamarck)

The mussel industry in Europe is facing two major problems: scarcity in wild seed supply in some regions and loss of commercial quality during the spawning season in other areas. The solution to these problems could be seed production in hatcheries. In addition, seed production in hatcheries would also allow the production of triploid individuals, with consequent benefits for the producer. This requires broodstock conditioning, to obtain mussel seed outside the natural season. In this study, the effects of photoperiod and the duration of the conditioning period were examined on the gametogenesis and spawning of the mussel Mytilus galloprovincialis (Lamarck) in a hatchery. The results obtained indicate that the conditioning of this mussel is possible in a hatchery by supplying a sufficient amount of food and increasing the water temperature. It was shown that gametogenesis of conditioned mussels was dependent on the duration of the conditioning period. Spawning, besides being dependent on the duration of the conditioning period, also appears to be dependent on photoperiod, although these results are not clear enough. This supports the hypothesis that gametogenesis and spawning are regulated by different physiological mechanisms.     

A comparison of traditional and modified inland artisanal aquaculture systems

Traditional artisanal aquaculture systems are commonly assumed to be mainly for subsistence, to use predominantly on-farm inputs, and to have been developed by farmers themselves. Such systems with a long history in South East Asia exist mainly in northern Lao PDR, northern Vietnam and in West Java. In most other areas the traditional fish supply, wild fish, has declined only relatively recently, providing a stimulus for growth of aquaculture over the past few decades. An overview of artisanal aquaculture so defined in the South East Asian region is presented from a systems context considering social and economic aspects (micro- and macro-level perspectives), production technology (rice fields, ponds, cages), and environmental aspects (fitting into the local resource base without adverse environmental impact). Most artisanal aquaculture systems are integrated with crops and livestock but generally resource-poor farms constrain production. Rising expectations mean that productivity must be enhanced by off-farm inputs for aquaculture to contribute significantly to the farm household livelihood system. It is proposed that the term ‘small-scale’ be used rather than ‘artisanal’ because of increasing farmer interest in income rather than subsistence, because of increasing use of off-farm inputs, and because of the increasingly important role of science in the promotion of such systems.     

Improving spawning synchrony in the Nile tilapia, Oreochromis niloticus (L.)

Abstract. The development stage and number of seed (eggs and fry) removed from individual incubating Oreochromis niloticus (L.) broodfish at 10-day interharvest intervals (IHI) was compared with the harvest of free-swimming fry from undisturbed fish held in a tank within the same system. Spawning synchrony and productivity were compared for (1) total exchange of females for ‘conditioned’ females after each harvest, (2) exchange of only spawned females, and (3) return of females back into the spawning tank. Improved synchrony and seed production were positively related to removal of eggs and fry from incubating females and could have important implications for broodstock management in commercial hatcheries. Allowing fish to remain undisturbed in clear water tanks may lead to inhibition of spawning activity related to the formation of hierarchies. Individual weight loss by females during incubation was correlated with stage of seed harvested and thus with timing of spawning during the interharvest interval.     

Production risk of pangas (Pangasius hypophthalmus) fish farming

Pangas is a relatively new and fast-growing fish species that has great potential for production and export growth in Bangladesh. However, production variability exists from farm to farm and location to location, which indicates that production risk may be a problem in pangas farming. Research on production risk is therefore of great importance, especially for small-scale farming systems in developing countries, where farmers are more vulnerable to risk. This study investigates the production risk of pangas farming in selected areas of Bangladesh. A Just–Pope stochastic production function is chosen to estimate the mean and risk functions. The test result shows that significant production risk exists in pangas farming, and that the risk differs between small and large farms.     

The Cost of Production of Giant Clam Seed Tridacna gigas

The costs of providing giant clam seed in Australia are examined for alternative annual volumes of production. Considerable economies of scale in production are available, both in relation to labor costs and non-labor costs (mostly capital costs). The fall in per-unit cost of producing giant clam seed is considerable when annual production is expanded from 100,000 to 500,000 seed clams per year. At 10% rate of interest, the unit cost per clam seed falls from $1.43–$2.04 at a production level of 100,000 to $0.41–$0.55 at a production level of 500,000. Per-unit operating costs also fall. They decline from $1.01–$1.22 to $0.29–$0.35. This suggests that there are likely to be cost economies in having large centralized hatcheries.     

Development and evaluation of a stress challenge testing methodology for assessment of Nile tilapia (Oreochromis niloticus, Linn.) fry quality

A decline in the quality of the freshwater fish seed available to small-scale farmers in Asia has been identified as an important constraint on the development of aquaculture in the region. There is a need for simple and reliable methods of determining the quality of seed at the farm gate or hatchery. The present study was carried out, in the field, to develop and evaluate a stress challenge test for Nile tilapia (Oreochromis niloticus, Linn.) fry as the effects of stress on fish performance have been well documented and similar tests are used elsewhere in the sector. Formalin and iodized salt were used as reference toxicants. LC₅₀ values were estimated using mortality figures resulting from exposure of marketable-sized fry to saline and formalin solutions. The two test concentrations, 24 ppt for saline and 500 p.p.m. for formalin, were used as reference toxicants in acute, static bioassays to challenge fry reared under different conditions during the post sex-reversal, nursery period. Using existing farm practice as controls the conditions were: 50% increased stocking density, formalin treatment, 40% reduction in feed rate and no supplementary feed. Fry length proved to be a very significant co-variable; adjusted means showed no significant difference between treatments. The importance of only marketing tilapia fry weighing over 0.2 g was emphasized. It was recommended that the challenge testing approach could be modified, but that it was vulnerable to unquantifiable and uncontrollable factors arising from management and the environment, which may have altered responses to the stressor.     

Production of Atlantic salmon smolts in Europe—Current characteristics and future trends

The production of Atlantic salmon smolts in Europe is close to 250 million per year with Norway and Scotland as the dominating producers. At present, more than 90% of the production takes place in land-based, single-pass flow-through farms, but conversion to recirculating aquaculture systems (RAS) is being considered by many producers. About 18 million smolts are annually produced in cage-based farms in Scottish lochs.Over the last decade, the annual production at Norwegian hatcheries has increased 3–4 times. Introduction of efficient oxygenation both of inlet water and within the fish tanks is a key factor allowing a reduced specific water flow. Most water sources in coastal regions are characterised by very soft water. Insufficient carbon dioxide control is considered a major reason for disease outbreaks and reduced growth in hatcheries. Commonly applied water treatment attempts in hatcheries are ozonation and UV irradiation, CO₂ stripping and addition of seawater. Only a few existing hatcheries in Norway and Scotland are presently utilising RAS. Modern RAS for smolt production are mainly large farms, e.g. a RAS farm on the Faeroe Islands which produces 6 million smolts annually.     

史氏鲟和达氏鳇养殖亲鱼群体遗传多样性分析

利用线粒体控制区序列片段(史氏鲟,425bp,达氏鳇,434bp)分析检测了两个养殖场留做后备亲鱼的史氏鲟和达氏鳇的遗传多样性。在所检测的养殖史氏鲟后备亲鱼4个年龄群体共34个体中,发现5个单倍型,共有11个多态位点,占碱基总数的2.6%,无简约信息位点。不同单倍型之间有1～10个变异位点,占碱基总数的0.2%～2.4%。各单倍型之间的遗传距离为0.002～0.024。单倍型多样性Hd=0.768,平均核苷酸差异数k=4.367,核苷酸多样性Pi=0.011。而分别来自2个养殖场的2个达氏鳇养殖群体都是1个群体仅1个单倍型,2个单倍型之间仅有2个碱基差异,遗传距离为0.005,遗传变异极度缺乏。结果提示在利用史氏鲟和达氏鳇后备亲鱼进行繁殖育苗时要充分注意近交的影响。     

'No-mucus skin disease' of rainbow trout, Oncorhynchus mykiss (Walbaum): a case report

Abstract A skin disease of intensively reared salmonids in Ontario hatcheries, known to the farmers as'no-mucus skin disease', is reported for the first time. It was characterized by erosive and ulcerative lesions found mainly on the flanks of fingerlings, which resulted in exposure of the tips of the scales. Associated with these lesions were colonies of bacteria seen in the SEM to be clustered round the mucous cell pores and under-running the margins of epithelial cells. The cause of this condition is unknown, although the response of fish to formalin treatment, and the presence of bacilli seen in skin scrapings and in the SEM, suggest that bacteria are responsible.     

Economic contribution of fish culture to farm income in Southeast Vietnam

Rural aquaculture is the farming of aquatic organisms with extensive and semi-intensive husbandry practised by small-scale rural households for their consumption and income. From a field survey in Southeast Vietnam, using enterprise budget analysis and nonparametric tests with indices of change, adoption, and agreement, this study justifies that rural aquaculture is a good option for rural development, making an important contribution to farm income with a high adoption rate among poor farmers. Fish farmers have gained an increased level of satisfaction by means of fish culture production growth along with corresponding economic gains. This enterprise continues to play an increasing important role in their livelihoods and has potential to develop further in the area.     

An evaluation of fish health‐management practices and occupational health hazards associated with Pangasius catfish (Pangasianodon hypophthalmus) aquaculture in the Mekong Delta,Vietnam

This study aimed to evaluate the current status on the use of probiotics, disinfectants and antimicrobials in hatcheries, nurseries and grow‐out farms producing Pangasius catfish (Pangasianodon hypophthalmus) in the Mekong Delta, Vietnam. Semi‐structured interviews were conducted with 83 aquaculture enterprises (15 hatcheries, 32 nurseries and 36 grow‐out farms). Farmers reported use of a total of 24 different antimicrobials, e.g. for treatment of bacillary necrosis and motile aeromonad septicaemia, and a variety of disinfectants, probiotics and nutritional supplements. In contrast to small‐scale farmers, all large‐scale grow‐out farmers studied were certified and therefore had higher levels of formal education and specialized aquaculture training to diagnose and treat diseases. All farmers prepared their own medicated feed with a high risk of treatment failure, negative environmental impact from released antimicrobials and resistance development. Small‐scale farmers were at particular occupational health risks when handling antimicrobials and other chemicals, e.g. mixing medicated feed with bare hands. There is an urgent need to improve knowledge and use innovative approaches, e.g. private‐public partnerships, to assure a prudent use of chemicals, to improve capacity and access to disease diagnosis, particularly for small‐scale grow‐out farmers and nurseries. Efforts to control use of antimicrobials in aquaculture should be coordinated with the livestock and human health sectors taking an One‐Health approach.     

An assessment of alternative strategies for the integration of pond aquaculture into the small‐scale farming system of North‐east Thailand

Abstract

This paper uses a linear programming model to examine the economic viability of four fish production strategies in the context of rainfed farming systems in the north‐eastern region of Thailand. The four systems are rice bran feeding system, pond fertilization using buffalo manure, fish production recommendations developed by the Asian Institute of Technology (AIT) Recommendations and an integrated duck/fish production system. These systems have been introduced into North‐eastern Thailand where the main obstacles to fish production are the lack of indigenous knowledge offish culture and a shortage of water. While technical feasibility studies are needed to evaluate the practical viability of aquaculture technologies, economic assessment is required to assess their commercial viability. The objective of this paper is to examine whether or not these fish production systems can contribute to, and integrate with, the prevailing farm system in the North‐east of Thailand. The linear programming model is used to determine the optimum on farm product mix that maximizes net returns under each of the four production systems. Among different resources, labour requirement in the fish‐stocking month appeared to be the first binding resource, while capital requirement was not a constraint for an average farming household of the region. A sensitivity analysis is presented to show how each of the fish production systems operates with different levels of pond size, labour and capital availability. The results of the study show that these aquaculture systems are economically attractive and can contribute significantly to the livelihood of the small‐scale farmers of North‐east Thailand.     

Infectious pancreatic necrosis virus in the environment: relationship to effluent from aquaculture facilities

Effluents from three fish hatcheries were monitored for the discharge and subsequent downstream distribution of infectious pancreatic necrosis virus (IPNV). Samples of springwater and surface water, and tissues from salmonid and non-salmonid fish were assayed for IPNV. Water samples were processed to recover virus by adsorption to an electropositive, microporous filter matrix. No IPNV was detected in surface water collected above fish hatcheries or in hatchery springwater supplies. The virus could be detected for at least 19.3 km below the point of effluent discharge from hatcheries and the prevalence of IPNV infection in stream-resident fish was 2.8%.     

Assessment of the impact of dissemination of genetically improved Abbassa Nile tilapia strain (GIANT‐G9) versus commercial strains in some Egyptian governorates

WorldFish initiated a selective breeding program in Abbassa—Egypt to develop and produce the genetically improved Nile tilapia strain known as “Genetically Improved Abbassa Nile tilapia (GIANT)”, adopting the same technology used for the Genetically Improved Farmed Tilapia (GIFT), in Asia. WorldFish provided the Ninth Generation (G9) broodstock of the GIANT to 11 Broodstock Multiplication Centers (BMC’s) in five governorates; these centres then disseminated improved mixed‐sex fry to 160 tilapia hatcheries which supplied all‐male fry to 1,500 fish farms in 2017. We present results of an impact assessment of the G9 of GIANT in 83 of these fish farms in four Egyptian governorates (Kafr El‐Sheikh, Fayoum, Behera and Alexandria). Results indicate that the use of GIANT in all governorates achieved significantly higher (18.8%) fish yields (12.3%–26.4%) and 15.7% lower FCR (feed conversion ratio), reflecting a positive impact on their net profits compared with those who used commercial strains. Overall, fish farmers who stocked GIANT had significantly higher average fish sales (5,567 US$/ha) than those who stocked non‐improved commercial strains (5,192 US$/ha) in all governorates. However, when comparing within governorates, the difference was significant only in Fayoum and Alexandria noting a mixed performance of the GIANT strain. The mixed performance indicates that some hatcheries may have crossed the different strains, which lowered the performance differences. To get an objective analysis of the performance of the GIANT, it is recommended that similar assessment be undertaken with new generations of the strain supported by on‐farm performance trials.