Fish food for thought

Fish food for thought

Pilchards Farmed fish are a renewable resource – but the same isn’t necessarily true for their diet. Salmon, cod, sea bass and sea bream are fed fishmeal pellets made from edible wild species such as sardines, pilchard and blue whiting. It can take more than three kilos of fish to produce a kilo of salmon (known as the conversion rate), so this equation represents a greater loss of wild fish than if people simply ate the mackerel, sardines and other small fish. Salmon farmers claim there’s no market for most of the fish caught to produce fishmeal and fish oil for feed, though feeding them to farmed fish is depriving wild fish such as cod of a food source. Nevertheless they are looking into ways of improving the conversion rate, and at alternative feeds based on soya, for example. However carnivorous fish will never be able to survive only on plant-based feeds. Advocates of aquaculture also point out that salmon are more efficient at converting their feed into protein than many land animals are. It takes far more feed to produce a kilo of beef, for example, than a kilo of salmon. (BBC, 2009)


Posted in food
2 comments on “Fish food for thought
  1. empetersson says:

    A little more info on the topic of aquaponics that I mentioned earlier in class.

    The benefits of aquaponics has been researched in Canada for a number of years now, and is basically a marriage of aquaculture (raising farmed fish for consumption) and hydroponics (growing plants in a water bed, without using soil). As fish waste builds up it becomes toxic to the fish, yet this “dirty” water is full of nutrients which can be useful for plants – which in turn filter the water for the fish. Therefore water is not wasted through flushing the system to clean the tanks, and additional fertilizers are not needed for the plants. In the closed cycle, additional water is only needed to replace evaporation and absorption by the plants.

    It is primarily a hobby farm sort of activity right now, as commercial use has proven complicated due to balancing the concentrations of waste/nutrients, the scale required, and the need to have two specialties. However, the research has shown that once the system is fully running the microbiology is more efficient than inorganic hydroponics (

    For more info, please see:

  2. jeremy says:

    Interesting post and equally interesting comment. Seems to me a bit of ecological economic efficiency analysis wouldn’t go amiss here.

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