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Aquaculture: reproduction in captivity

Aquaculture is expanding at an accelerating pace globally, but the big step forward will come when the sector is able to produce intensively in small spaces, optimize facilities, reduce the ecological impact of the activity, and control the waste products generated. In addition to producing food, aquaculture is expected to supply other markets in the future.

Aquaculture is the farming of aquatic organisms—including fish, crustaceans, mollusks, reptiles, amphibians, and aquatic plants—in their natural medium. It implies human intervention in reproduction, feeding, and in protecting organisms from predators.

According to the Food and Agriculture Organization (FAO) of the United Nations, aquaculture is the fastest growing food-producing sector (7.4% annual rate) and the one that is diversifying most. Global aquaculture production for human consumption (fish, crustaceans, mollusks, and other aquatic animals) went from 47.4 million metric tons in 2006 to 52.2 metric tons in 2008. In the case of aquatic plants (mostly seaweeds)—cultured for human consumption as well as non-food uses—production increased from 14 million metric tons in 2006 to 15.8 million metric tons in 2008.

At the global scale, the figures show that aquaculture has expanded very rapidly, but an analysis of the situation around the world reveals that the sector has experienced a degree of stagnation in Europe. “The key to changing the growth trend for the sector in Europe, particularly in the Mediterranean region, is to make aquaculture compatible with other coastal activities and ensure that it respects the coastal environment,” says Joan Oca, director of the Barcelona School of Agricultural Engineering (ESAB), and a researcher with the Aquaculture and Aquatic Product Quality (AQUAL) research group.

To tackle this major future challenge it is essential to implement much more intensive aquaculture systems that deliver high yields in small areas.

Aquaculture activities also need to be carried out in a way that effectively controls the waste products generated in order to avoid the discharge of uneaten feed, feces, and all the metabolic excretions fish produce. “We need to develop efficient water recirculation systems, systems that make it possible to collect very small volumes of water and do extensive water treatment on land. We should even look for some application for waste materials. The goal is to ensure that the water returned to the sea is of high quality,” says Joan Oca.

Another measure being considered to minimize the ecological impact of aquaculture facilities is the use of multi-trophic production systems, which have long been used in Asia. These systems combine various levels of the trophic chain (carnivorous and herbivorous species) to obtain a neutral end waste. The waste byproducts of one aquatic species serve as inputs for the next one in the chain.

According to Lourdes Reig, a researcher with the AQUAL group, “the main objective for the sector is to optimize and improve facilities. Technologies that are fully developed for the production of other animal species have not yet been deployed in the aquaculture sector. A lot of work remains to be done because processes are not as standardized.”


aqüiculturaThis is precisely the area the AQUAL research group’s work is concerned with. “Our research is aimed at developing highly intensive land-based systems, with maximum control of environmental parameters, and we focus primarily on flatfish. We study behavioral responses: we want to determine species preferences in terms of substrate types, zones within the culture tank, and speed of flow or water turbulence. We then design facilities based on these preferences,” says Joan Oca.

This approach bridges the gap that often exists between engineering and biology. “Our group is mixed because we know that when you're working on a production process involving living organisms you can't treat these fields as if they were independent of each other. If the goal is to standardize processes, we need to observe the effects of any technology on the end product, which is the fish,” he adds.

In recent years, AQUAL conducted part of its research within the framework of the European Raceways project, which was aimed at optimizing raceways, the long tanks used for rearing fish in land-based facilities. In the second stage of the project, dubbed Compaqua, a compact system for intensive production will be developed to optimize use of resources.

AQUAL is also looking at ways to optimize the design of culture tanks as part of a project to improve the facilities and technology used in the Mediterranean region with the aim of facilitating intensification and growth in the aquaculture sector. The group's contribution to the project, financed by the Spanish Ministry of Science and Innovation, focuses on designing tanks with different geometries that provide good hydraulic conditions, are self-cleaning, and help ensure that water quality is relatively uniform so space is used as efficiently as possible and there are not tank areas that the fish do not use.

Dangers and uses of aquaculture
At present over 100 million metric tons of fish are caught in the world’s oceans each year, but not all this yield ends up on our dinner plates. More than a third of wild-caught fish is used to make fish meal and fish oil, and about 60% of fish meal and 90% of oil goes into the production of feed for cultured fish.

In a market where the strongest demand is for carnivorous species that are fed fish meal, the future of aquaculture depends on finding an alternative. “For now the approach is to progressively substitute plant protein for fish meal,” says Lourdes Reig.

Apart from improving nutrition, achieving sustainable development in the sector requires improvements with respect to reproduction. This means getting to the point where all species can reproduce in captivity. "If this can be done,” says Reig, “aquaculture will become an activity that doesn’t depend on catches of wild fish.”

Currently the main aim of aquaculture is to produce food products for human consumption. Nevertheless, the researchers believe aquaculture needs to be able to supply products to many other sectors in order to take a major step forward. The products in question will be nutrition-related. Apart from vitamins and mineral salts, which are already on the market, researchers are looking at products with the potential to have beneficial effects on diseases like osteoarthritis, cancer and fibromyalgia.

Aquaculture could also supply products of pharmacological interest, obtained from algae, and products of technological interest for use in industries such as biofuel production. Aquaculture can also supply markets in sectors such as aquariology and provide plants and animals to repopulate species in the aquatic environment.

Consumer distrust
At a time when we do not always know exactly what we are eating, another big challenge for aquaculture is to convince consumers that cultured fish is healthy and tastes good. Experts say a lot of work remains to be done to educate the public and combat the belief that there are differences between wild and farmed fish.

Contrary to what many believe, differences are hard to detect because wild and farmed fish have practically the same characteristics and quality. Aquacultured fish are the offspring of wild fish; they have grown on a fish farm but their genetic makeup is practically identical to that of their wild cousins. For example, they contain the same omega-3 polyunsaturated fatty acids, which are regarded as particularly valuable for a healthy diet. Moreover, they are subject to an exhaustive range of health-control measures designed to ensure the health of both fish and consumers.

Perhaps the biggest difference consumers may note between farmed and wild fish is that the former are fattier because they are better fed. This is a characteristic people tend to dislike, so an effort is being made to bring to market fish products with the characteristics consumers demand.

Another problem to be addressed is that cultured fish is an undifferentiated product. In the future fish farmers are likely to differentiate products according to their use and the consumer segments targeted.

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