Aquaculture can be a sustainable food source

Overfishing is a threat to aquatic biodiversity. The worst sceneries predict that a massive flood of fish extinctions occurs in this century, if commercial fishing is continued at its present level. This is a major problem, as it occurs at the same time that the need for animal protein in our food should change from the traditional mammals (cattle, swine and sheep) towards poikilotherms. A production of flesh kilogram requires only about 1/10 of energy in poikilotherms as compared to mammals. Because of this, they are a much preferred food source compared to traditional farm animals, when we are faced with problems with land use, climate change and biodiversity loss. Of poikilotherms fish are by far the most acceptable food – virtually everyone has eaten them, whereas the alternatives, insects, snakes, crocodiles etc. all are disliked by several people or are difficult to culture.

So, aquaculture could be a way forward to provide the world with animal protein in a sustainable fashion. However, that would not be the present way of aquaculture. There are presently many reasons why aquaculture is not sustainable. First, most cultivated fish are predators, such as salmonids. Their feed is usually fish flour-based. So, it does not decrease overfishing, the only change is that one can fish species, which would not be preferred human food.  Second, fish are cultured especially in marine net cages at high densities. Feeding therefore causes local eutrophication and the fish are not subjected to normal activity. Third, to prevent parasites and diseases in the high-density environments, a lot of medications are used. These affect the ecosystems in the vicinity of the cages. For example, one of the major parasites of salmon is salmon louse, a copepod. Its treatment affects all crustaceans in the vicinity of the net cage. Thus, lobster stocks may suffer. It should be noted that all fish diseases are favoured by the high fish densities in the net cages. finally, the fish in the net cages do not get the same amount of exercise as wild fish. Because of this, if fish are reared for stocking, their survival is likely to be reduced.

The reason why aquaculture has mainly been in sea bins is naturally the cost – the profit is maximized at the cost of the environment. However, shouldn’t we start putting environment first in order to keep the world in reasonable condition. Sustainable aquaculture is presently possible. Instead of cultivating fish in sea cages, they could be kept in tanks in dry land. In such tanks water flow can be kept directional and all the waste collected before it enters the sea, rivers or lakes. If need be, water purification similar to normal municipal wastes could be applied. Instead of the fish flour, flour made of insect maggots could be used. Maggots can be grown in bulk quantities already today.

By these means the salmonid aquaculture would be made sustainable. Increasing the number of fish species cultivated in large amounts one could also combine, e.g., rice production and aquaculture or vegetable production and aquaculture.