QUESTION: This week will continue our look at aquaculture, and specifically the issue of the feeding of aquacultural species. Previously, Sinjan from Johannesburg asked:
“A few years ago I read that aquaculture was the answer to the problems associated with commercial fishing, but lately I have been hearing differently. What has happened?”
ANSWER: As we stated in the last issue of Ask Deep Blue, aquacultural development faces a few tough challenges. But it is important to remember that fish farming is really still very much in its infancy. And even if we look at something like say sheep domestication – which has been around since 11000 BC or so – we see things never do really reach a “finished state” (any biological system resists stasis).
According to professor Carlos M. Duarte, about 430 (97%) of the aquatic species presently in culture have been domesticated only since the start of the 20th century, with an estimated 106 of those species having been domesticated only in the past decade . This is actually a bit exciting as we all can take part in improving processes, if by no other means than by staying informed and using our purchasing power to support good systems.
But one particular concern regarding aquaculture, one which has seen a great deal of publicity, is that some species naturally consume other fish – usually in processed form – in their feed. In general, industrial fish, a term loosely denoting species targeted specifically for use in feed preparation, are caught and processed into fishmeal and fish oil. The extruded oils and solids are mixed in with other substances, like plant matter, to formulate aquacultural feeds. So while eating a farm-raised, carnivorous fish does mean you are taking pressure off of wild stocks in one regard, a wild fish somewhere was caught and centrifuged to feed it.
One must remember that ratios of the fishmeal and oil used in a particular feed vary. Some fish grow better with a higher proportion of fishmeal and oil. Too, the life cycle period of the farmed species affects these ratios. The simplistic language here belies the complexity of the process. Much effort goes into examining these processes and adjusting them for maximum benefit at best price.
And here is an important point; feed producers and fish farmers actually want to use the absolute minimum amounts of fishmeal and oil in their feeds. Why? Because the stuff is not cheap, not at all. There is a point where the growth-related benefits of the proportion of fishmeal and fish oil in feeds begins to trail off. It doesn’t hurt the fish to have an excess of fish-derived protein in its feed, but no extra benefit, or a proportionally lessened benefit, is realized. It’s the old Law of Diminishing Returns scenario. So the object is to find the “sweet spot” (and it changes all the time) where maximum benefit is derived from least resource.
Additionally, great effort is being made by scientific institutes and feed manufacturers to find a suitable replacement for meals and oils derived from marine species. The person (or company) who figures it out will be immediately filthy rich, and can give up mucking about with fish and lay in the sun with a cold margarita.
But what we are finding out is that marine-derived sources hold qualities that replacement sources cannot match. For instance, the type of Omega 3 fatty acid produced from the oily fishes normally targeted as industrial fishes is head and shoulders above plant derived sources. (Keep that in mind, because these Omega 3’s are also the best for human consumption too!) But again, the financial prize is considerable, so we will keep trying. In all likelihood – and this is our opinion – there probably never will be a completely suitable replacement. However, what probably will happen is that some sort of replacement will be developed that when used in concert with marine-derived proteins and oils can give very similar developmental benefits.
We must also note that these same issues apply in a similar way to feeds used for land-based animals which utilize fishmeals and oils. The benefits again are well documented, but as with aquacultural feeds, they do put pressure on the stocks of fishes used to derive the proteins and oils.
But here might be a good place to tout the extraordinary nature of industrial fish species. They are not like sharks or tunas or other top-of-the-food-chain species; they reproduce rapidly, respond readily to corrective measures and are almost unilaterally harvested in ways that are not harmful to the physical marine environment or other marine species.
But what are we to do? If aquaculture continues to expand – and it will – what can we do to make sure industrial fish are not over-harvested? And here are your “simple answers to complex questions”. We must first give greater support to those trying to find suitable replacements. Again it may very well be that a complete replacement will never be found, but a partial substitution will work wonders. Secondly, we can all adopt lower carbon lifestyles and pressure policy makers at all levels to provide the kinds of systems that will allow us to adopt these lifestyles with greatest ease. Industrial fish are affected by water temperature changes and to shifts in established currents, both of which arise from Global Warming.
Another suggestion is that we can begin to augment our seafood consumption with species not as reliant on industrial fish for feed. Mussels, for instance, are just about nature’s perfect marine protein source. If you haven’t tried mussels over linguine (with a bit of white wine, garlic and olive oil) you are missing one of life’s great pleasures. Sardines are very good grilled, and anchovies can add an extremely nice robustness to any sauce. We can still eat more fish, but by just expanding our culinary repertoire, we can relieve pressure from industrial stocks – and get the Omega 3 benefit directly from the source.
Again, the feed question is not by any means the only challenges facing aquacultural development. We will be focusing our next few Ask Deep Blues on some of the other concerns including; how the physical environment is affected by aquacultural establishments, genetic modification of farmed species, the ethics of fish farming (animal rights), and disease outbreaks in the population of farmed species (and surrounding wild stocks). Check back soon!