Improved efficiency in aquaculture

The improvements now evident in European fish farming also illustrate how increased efficiency can reduce production costs.  In 1985, the average production cost for Norwegian salmon was 46 NOK/kg.  By 1997, this had reduced to 16.6 NOK/kg and is still falling.  In reality, farmed fish is now both a cheaper and a healthier option for the consumer than any other meat produced by the most modern efficient agricultural techniques. These trends are reflected throughout European aquaculture and further afield.

Ideally the whole cultured stock should be able to eat to satiation and consume all the feed supplied.  This optimum number of individuals is expressed as X in the following figure.  With an increase in the number of individuals above the optimal number X, the retained energy decreases.  Energy retention reaches zero when the population reaches 4X.

Profitable production is dependent on the willingness of the consumer to pay for production costs plus a reasonable profit.  To reduce costs and to reach maximum efficiency in animal production, the number of individuals cultured should be kept at or below the level where it is possible to feed to satiation. 

According to this principle, management is likely to be easier in a monoculture (single species) system, or in sequenced, integrated single species systems than in traditional polyculture (multiple species) operations, where the outcomes are harder to predict.

It is somewhat ironic to find that traditional extensive fish farms, producing low-cost fish products, require a high-level understanding of complex biological systems than modern intensive aquaculture systems.  This situation is not helped by the fact that such extensive techniques are practised in regions lacking the funding for appropriate teaching, development and research into the operation and control.

Combining the best from extensive and intensive aquaculture methodologies.

Is it possible to improve or better control aquaculture production efficiency by combining advantages of modern intensive, controlled aquaculture with traditional extensive or semi-intensive polyculture concepts?

One answer may lie in the culture of one of more than one species, in an integrated approach, using separated, sequential production steps, rather than mixing species together, as practised in traditional polyculture.

Such a system for marine aquaculture has been tested in Israel where a marine fish, in the first production step, retained 26% of the protein nitrogen fed.  The effluent from this process was then passed through a bivalve (shellfish) production & filtration unit, where a further 15% of the original nitrogen input was retained as growth.  Finally, the effluent passed through a seaweed production unit, which retained 22% of the original nitrogen input.  This system therefore resulted in an overall retention of 63% of the protein nitrogen supplied in the culture products.  Production of another shellfish (abalone - Haliotis tuberculata), which can feed on the seaweed cultured in this integrated system, could be added as a further step to increase overall protein retention.

Such an integrated sequential approach could therefore be an effective means of optimising the utilisation of viable protein resources.  Work on the modelling of such systems will be very important if this kind of aquaculture becomes more common in the future; within this process of "ecological management", a higher -level of biological competence will be crucial.