The main input in aquaponics apart from water and energy, is fish feed. A major component of commercial fish feed is fish meal in many formulations. Feeding fish sustainably requires that we dispose of this ocean fish component in our fish feed.
Due to ocean acidification and overfishing, ocean fish may disappear in the next couple of decades. So it seems crazy that in our efforts to supply fish through sustainable fish farming, on land, with an eye to taking the pressure off ocean fish stocks, we are creating a market for more ocean fish in the form of ocean fish meal based fish feed. Our fishing practices should not involve fishing just for animal feed and fish farm feed. We should crack down on those polluters who are destroying the oceans with ocean acidification.
Ocean acidification is happening because of acid rain. This in turn is caused by our profligate burning of fossil fuels.
‘Ocean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth’s oceans, caused by the uptake of anthropogenic carbon dioxide (CO2) from the atmosphere. About a quarter of the carbon dioxide in the atmosphere goes into the oceans, where it forms carbonic acid.
As the amount of carbon has risen in the atmosphere there has been a corresponding rise of carbon going into the ocean. Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14, representing an increase of almost 30% in “acidity” (H+ ion concentration) in the world’s oceans.
This ongoing acidification of the oceans poses a threat to the oceans’ food chain.’ From Wikipedia, ‘Ocean acidification.’
In other words, many ocean creatures are going to die because our industrialized society cannot stop polluting the air and water.
Ironically, because fish waste water, used in aquaponics to grow crops, is a miracle grow fertilizer, aquaponics causes plants to grow much faster and at thicker planting densities, which gives aquaponics, if more widely used commercially, the potential to act as a carbon sink. The rapid plant growth soaks up a lot of carbon dioxide, which is a culprit in the acidification process of the oceans.
There are many other sources of high grade protein that can be used for feeding fish commercially, that do not have to be sourced from the sea and its creatures. Since ocean fish may disappear, we do not need to feed our farmed fish on them into the bargain and further hasten their demise.
Tilapia are omnivorous fish with a marked preference for green leafy vegetables. They do very well on aquatic plants that can actually be grown on the outskirts of a large commercial aquaponic operation, such as duckweed. Duckweed makes them go into a feeding frenzy from my experience. They love it! It may well be part of the way out of our own feeding frenzy on ocean fish as animal feed.
According to John W. Cross, at http://www.mobot.org/jwcross/duckweed/fish.htm, and other sources such as the permaculture aquaponic farm in Hawaii, Olomana Gardens, duckweed is an ideal food for fish and livestock. It grows in still and shallow waters and is also useful as a ‘lid’ to limit water evaporation, since it grows very densely in mats on the surface and helps to shade the water from the sun. In the wild, duckweed varieties have been used as a food source by fish in all sorts of climates and situations. It is extensively used by aquaponics hobbyists for feeding fish sustainably already. They are aware of its high nutritional value.
It is a fast-growing floating plant with few stalks, mostly all leaves. It has a very high protein content, as the above website reports as follows:
‘Much reliable analytic data is available to support the usefulness of the duckweeds as valuable food sources (Landolt and Kandeler, 1987). Most species have protein contents in the range of 15-45%, depending on the nitrogen supply, and the amino acid balance is favorable, with only TRP and MET generally limiting (Landolt and Kandeler, 1987, pp 375-377. The yearly protein yield/ha is up to tenfold higher with Lemna than with soybeans, and nearly as much better than for alfalfa (Said et al. 1979).
Recent work with Lemna paucicostata in Nigeria (Mibagwu, and Adeniji, 1988) indicates an especially high nutritional value. Their analyses of plants from three locations in the Kainji lake area showed a crude protein ranging from 26.3-45.5% of dry weight:
“The amino acid content compared favourably with that of blood, soyabean and cottonseed meals and considerably exceeded that of groundnut meal. The levels of the essential amino acids surpassed the FAO reference pattern, except for methionine which met 61.4% of the recommended value. The levels of minerals were high but should not pose any toxicity problems if incorporated into animal feeds. The levels of nitrogen in the plant are comparable to those in commercial fertilizers. The plant could be a good dietary supplement and nutrient source for humans, livestock and fish….” “With an average standing crop of 309 kg dry mass/ha and doubling time of 1.2 d, 129 kg DM/ha of dry duckweed are obtainable daily in the Kainji Lake area, which could ensure a daily supply of 59 kg of high-quality protein for poultry and fish feed formulation….”‘
Trials reported on the same site had mixed results with feeding diets of duckweed alone to tilapia. Mixed with conventional feed, however, it showed improvement in fish growth. More trials need to be done on using duckweed for feeding fish sustainably. Duckweed may also turn out to be very useful in aquaponics systems as a backup plant for sopping up excess levels of nitrates in the water.
However, there are other food sources that can be grown from vegetable waste offcuts composted at the end of the harvest cycle (which happens once a week in most commercial aquaponics systems). The first of these food sources for feeding fish comes from the soldier fly. Fish love to eat its larvae, which are very nutritious, and have the incidental advantage of being self-harvesting. Soldier fly larvae have been used in various trials for feeding fish and livestock with encouraging results, and have been used to replace menhaden fish meal quite successfully.
See Sealey et al 2011troutblacksoldierfly and A2.
A university and a non-GMO soybean company are developing a sustainable oil product to replace fish oil in fish feeds for trout, salmon, and other farmed fish. At the moment the EPA oil component in commercial fish feeds is derived almost completely from millions of tonnes of anchovies and sardines caught and fed into the fish oil processing industry’s plants. This is completely unsustainable. It takes tons of these fish to produce mere litres of oil. What is this doing to ocean ecosystems?
This company promoting sustainable aquaculture is called Imcopa and it is using microseaweeds to research ways of making this new high EPA oil as a component of its sustainable fish feed based on plant sources and not ocean fish. Ocean fish may disappear if we carry on exploiting them hand over fist as at present.
This microseaweed oil contains the right Omega 3 and 6 fatty acids that farmed fish require to maintain healthy growth. Trials are in progress to see how this oil can be used when feeding fish sustainably. It will be mixed with soybean products to produce a high fat balanced feed for farmed fish such as trout and salmon. When the research is concluded, the company hopes to market the product worldwide.
Grain amaranth has been tested on carp in an aquaculture situation with encouraging results, and has an advantage that few people realize: it can be grown in part of the aquaponics system as a prolific grain and green vegetable crop, and then fed back to the fish! See the middle parts of Samlet-rapport-amaranth from the EU-supported Mexican and Nicaraguan research on the uses of amaranth grain.
Amaranth grain has a very high nutritional value and is palatable and suitable for feeding fish sustainably. It is also a very tough crop that grows like spinach either in soil or even, like spinach, in aquaponics systems.
As you can see, there are many possibilities for feeding fish sustainably without using fish meal, fish oil, and other feed derivatives sourced from ocean fish.
If you have your own experiences with feeding fish sustainably, please do not hesitate to contact me!
If you have a lot of questions about aquaponics, there is a splendid book out by my old teacher, Dr. James Rakocy, which should help you clear up those uncertainties.