Monday, October 31, 2016

The nutrition and sustainability of farmed fish

In 2005 the late Professor Tony McMichael and I published, in the American Journal of Preventive Medicine, an invited commentary called "Fish, health and sustainability"

In it, we wrote: "The widespread practice of feeding wild-caught fish to farmed piscivorous (fish eating) fish increases production of some high-value species, but decreases the availability of fish for direct human consumption, on a per capita basis. To meet consumer demand for such fish, and at the same time to reduce the pressure on wild fish stocks, aquaculturalists are increasingly turning to land-based plants, such as grain, soybeans, lupins, and blended vegetable oils as staple fish food. However, because several of these crops are comparatively low in desirable long-chain fatty acids (especially n-3 PUFAs), the n-3 PUFA concentration of fish raised this way is likely to be lower than in their wild-caught cousins. Consequently, the n-3/n-6 PUFA ratio is also lower than what is thought to be optimum."

In other words, feeding fish foods which is derived from the land rather than a marine or riverine ecosystem is likely to change their nutritional quality, probably adversely. But we did not then speculate that fishfeed would soon include land based animal foods. 

However, in 2016 the leading Australian television investigative programme Four Corners presented "Big Fish", an investigation into the sustainability of aquaculture in Tasmania. It mentioned (as a comparatively minor point) that fishfeed used in Tasmania now includes "ruminant protein" (ie from sheep, cattle, goats or other digastric mammals). There is a theoretical risk that the feeding of ruminant protein to fish could increase the risk of transmissable encephalopathy (especially if such ruminant material is imported to Australia), but a larger risk that this practice will reduce the nutritional value of farmed fish which consume such protein. Additionally, artificially coloured fish (eg salmon) may also have reduced nutrition, compared to wild fish. This is plausible even if the dyes that are used to artificially colour farmed fish such as salmon are entirely benign. This is because the natural process that leads to a pink colour in salmon are not being reproduced in farmed fish that are dyed - if they were, then the artificial colour would not be needed.

As far as I know, the studies which have shown health benefits of ingesting fish do not discriminate between whether the food ingested is farmed or wild. They should.