David Colin Little

Aquaculture: global status and trends

Aquaculture contributed 43 per cent of aquatic animal food for human consumption in 2007 (e.g. fish, crustaceans and molluscs, but excluding mammals, reptiles and aquatic plants) and is expected to grow further to meet the future demand. It is very diverse and, contrary to many perceptions, dominated by shellfish and herbivorous and omnivorous pond fish either entirely or partly utilizing natural productivity. The rapid growth in the production of carnivorous species such as salmon, shrimp and catfish has been driven by globalizing trade and favourable economics of larger scale intensive farming. Most aquaculture systems rely on low/uncosted environmental goods and services, so a critical issue for the future is whether these are brought into company accounts and the consequent effects this would have on production economics. Failing that, increased competition for natural resources will force governments to allocate strategically or leave the market to determine their use depending on activities that can extract the highest value. Further uncertainties include the impact of climate change, future fisheries supplies (for competition and feed supply), practical limits in terms of scale and in the economics of integration and the development and acceptability of new bio-engineering technologies. In the medium term, increased output is likely to require expansion in new environments, further intensification and efficiency gains for more sustainable and cost-effective production. The trend towards enhanced intensive systems with key monocultures remains strong and, at least for the foreseeable future, will be a significant contributor to future supplies. Dependence on external feeds (including fish), water and energy are key issues. Some new species will enter production and policies that support the reduction of resource footprints and improve integration could lead to new developments as well as reversing decline in some more traditional systems.

Certify Sustainable Aquaculture

Certifications limited contribution to sustainable aquaculture should complement public and private governance. Aquaculture, the farming of aquatic organisms, provides close to 50% of the worlds supply of seafood, with a value of U.S.

The culture performance of monosex and mixed-sex new-season and overwintered fry in three strains of Nile tilapia (Oreochromis niloticus) in northern Vietnam

125 billion. It makes up 13% of the worlds animal-source protein (excluding eggs and dairy) and employs an estimated 24 million people (1). With capture (i.e., wild) fisheries production stagnating, aquaculture may help close the forecast global deficit in fish protein by 2020 (2). This so-called “blue revolution” requires addressing a range of environmental and social problems, including water pollution, degradation of ecosystems, and violation of labor standards.

Replacement of Dietary Fish Oils by Alpha-Linolenic Acid-Rich Oils Lowers Omega 3 Content in Tilapia Flesh

Two experiments (E1, E2) to evaluate the performance of new-season and overwintered fry in three strains (Viet, GIFT and Thai) of Nile tilapia (Oreochromis niloticus) were conducted at Research Institute for Aquaculture No.1 (RIA-1) in northern Vietnam. The performance of both mixed and monosex fish of the three strains was also compared. The experiments were carried out from May to November (E1) and August to November 1997 (E2) with overwintered and new-season fry, respectively. Each experiment included a comparison of production in fertilized earthen ponds (6×300 m2) and cages (18×1.2 m3) suspended within a single pond (1200 m2). In the pond trials, the three strains were stocked communally as either monosex or mixed-sex groups, whereas treatments (strain×sex) were separated into replicate cages. Individual size of fish stocked was 11.8±0.8 g (E1) and 9.4±0.4 g (E2). Floating pellets were fed at 5% (b.wt. day−1, 30% crude protein) initially, and declined to 2% by the third month of culture. Water quality and fish growth were monitored monthly. Overwintered fingerlings, both mixed and monosex, of all three strains performed well. Daily weight gain (DWG) ranged between 1.8 and 2.3 g day−1 in both ponds and cages. Among the three tilapia strains, the GIFT fish attained a significantly (P<0.01) larger individual final weight (387.7±21.0 g in ponds; 410.6±35.1 g in cages) compared to the Thai (351.6±26.1 g in ponds; 373.2±30.4 g in cages) and Viet strains (359.5±33.2 g in ponds; 350.3±33.4 g in cages). Overall, monosex fish of the three strains grew significantly faster than mixed-sex fish (P<0.05). DWG of new-season fingerlings (E2) in ponds ranged from 1.6 to 1.8 g day−1, showing slower growth compared to overwintered fingerlings. There was no significant difference in the growth between the three strains, and between mixed and monosex fish in ponds. Growth of all three strains was significantly slower in cages than ponds (overall DWG=0.8–0.9 g day−1; P<0.01). The results suggest that the performance of overwintered seed compare well with new-season fry. These results are discussed in the context of developing appropriate strategies for tilapia seed productions for northern Vietnam.

Immanent and Interventionist Inland Asian Aquaculture Development and its Outcomes

A 20-week feeding trial was conducted to determine whether increasing linolenic acid (18:3n-3) in vegetable oil (VO) based diets would lead to increased tissue deposition of 22:6n-3 in Nile tilapia (Oreochromis niloticus). Five isonitrogenous and isoenergetic diets were supplemented with 3% of either linseed oil (LO), a mixture of linseed oil with refined palm olein oil (PO) (LO–PO 2:1) and a mixture of refined palm olein oil with linseed oil (PO–LO 3:2) or with fish oil (FO) or corn oil (CO) as controls. The PO–LO, LO–PO and LO diets supplied a similar amount of 18:2n-6 (0.5% of diet by dry weight) and 0.5, 0.7 and 1.1% of 18:3n-3, respectively. Increased dietary 18:3n-3 caused commensurate increases in longer-chain n-3 PUFA and decreases in longer-chain n-6 PUFA in the muscle lipids of tilapia. However, the biosynthetic activities of fish fed the LO-based diets were not sufficient to raise the tissue concentrations of 20:5n-3, 22:5n-3 and 22:6n-3 to those of fish fed FO. The study suggests that tilapia (O. niloticus) has a limited capacity to synthesise 20:5n-3 and 22:6n-3 from dietary 18:3n-3. The replacement of FO in the diet of farmed tilapia with vegetable oils could therefore lower tissue concentrations of 20:5n-3 and 22:6n-3, and consequently produce an aquaculture product of lower lipid nutritional value for the consumer.

Is Responsible Aquaculture Sustainable Aquaculture? WWF and the Eco-Certification of Tilapia

Aquaculture is equated with the reduction of poverty by intergovernmental agencies such as the FAO, which advocate the promotion of small‐scale aquaculture through project‐based interventions. There is a lack of convincing empirical evidence to support the efficacy of this type of intervention, however. Meanwhile, commercial cultured freshwater fish production has increased hugely throughout Asia, despite limited direct donor or government support. Its impact with respect to poverty also remains ambiguous, however. This article critically evaluates the developmental impacts of both immanent and interventionist forms of aquaculture and advances finely nuanced interpretations of both.

Does Size Matter? Reassessing the Relationship between Aquaculture and Poverty in Bangladesh

Public awareness of possible environmental impacts of seafood consumption is growing. The seafood industry and environmental pressure groups have begun to certify fish and other aquatic products produced to sustainable standards. Representations of sustainability advanced by both groups in relation to tilapia converge around limited definitions related primarily to technical parameters. Such an approach does not adequately represent the complexity of sustainable aquaculture and may be counterproductive. This is illustrated by a comparing assumptions embedded in the text of the World Wide Fund for Natures “tilapia aquaculture dialogue” with empirical findings from a study assessing the sustainability of tilapia farming systems in Central Thailand. Building on these findings, representations of sustainable tilapia aquaculture produced by the “tilapia aquaculture dialogue” are criticized, and it is argued that new approaches are required if sustainable aquaculture is to be meaningfully understood and implemented.

Advanced nursing of mixed-sex and mono-sex tilapia (Oreochromis niloticus) fry,and its impact on subsequent growth in fertilized ponds

Abstract Aquaculture has long been promoted by development institutions in Bangladesh on the understanding that it can alleviate poverty. Most of this attention has focused on forms of the activity commonly referred to as ‘small-scale’. This article draws on concepts from the literature on agricultural growth and elaborates a typology of aquaculture based on relations of production which suggests that, in Bangladesh, quasi-capitalist forms of aquaculture may possess greater potential to reduce poverty and enhance food security than the quasi-peasant modes of production generally assumed to do so. The implications of this conclusion are explored.

Laboratory toxicity test and post-exposure feeding inhibition using the giant freshwater prawn Macrobrachium rosenbergii

Abstract A 168-day grow-out trial was conducted using mono-sex and mixed-sex tilapia ( Oreochromis niloticus ) fries nursed for 2, 4 or 6 months to investigate the comparative effects of advanced nursing on subsequent growth and survival. Fingerlings were kept in nylon hapas and fed at 5% biomass day −1 during advanced nursing (4 or 6 months) before stocking at 3 fishes m −2 in 18 fertilized earthen ponds (200 m 2 ). Survival rates of mono-sex and mixed-sex tilapia during advanced nursing were comparable (>70%). During the subsequent grow-out phase, survival of both mono-sex and mixed-sex tilapia increased linearly with duration of nursing ( y =36.12+4.93 x , n =9, r 2 =0.56, P y =21.38+8.45 x , n =9, P P P >0.05) between mono-sex and mixed-sex tilapia. A decreasing trend in daily weight gain, specific growth rate and individual harvested size of the stocked fishes was observed with increase in nursing period in mixed-sex tilapia due to reproduction. It was concluded that the duration of nursing was critical to producing homogeneous mixed-sex fish, and that prolonged nursing may be a useful strategy for production of mono-sex tilapias.

Passing the Panda Standard: A TAD Off the Mark?

A bioassay was developed using post-larvae of freshwater prawn Macrobrachium rosenbergii (length 9-10 mm) in order to determine the toxicity of profenofos, dimethoate, chlorpyrifos, carbendazim and zinc. This was the first study in the tropics with M. rosenbergii, particularly at the post-larvae stage (9-10 mm) on lethal (LC(50)) and sublethal (EC(50)) effects of toxic substances using post-exposure feeding rate as end point. Median lethal concentrations (LC(50) at 24 and 48 h) were respectively estimated as 11.6 and 9.8 microg L(-1) for profenofos, 142.1 and 102.7 microg L(-1) for dimethoate, 0.7 and 0.3 microg L(-1) for chlorpyrifos, and 439.7 and 329 microg L(-1) for zinc. Effects of carbendazim could not be estimated because carbendazim exposure needs more than 24h exposure period to produce observable effects at the concentrations used. The EC(50) using post-exposure feeding rates determined for profenofos, dimethoate, chlorpyrifos and zinc were 6.023, 269.3, 0.293 and 109.01 microg L(-1), respectively, at 24 h of exposure. Only chlorpyrifos and zinc had LC(50) concentrations greater than the post-exposure feeding EC(50) concentrations. This study demonstrated that the M. rosenbergii could also be used as a test animal to detect the effects of different chemical contaminants in aquatic environments.