Aquaculture can be a sustainable food source

Maanantai 23.10.2023 klo 14.02 - Mikko Nikinmaa

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.

Kommentoi kirjoitusta. Avainsanat: climate change, biodiversity, fish feed

Eating fish - but wild-caught or cultivated?

Maanantai 3.4.2017 klo 13.06 - Mikko Nikinmaa

Fish is, in principle, health food, and also good in terms of climate change. As insect eating has recently been advocated as an environmentally friendly way of actually eating meat, one needs to point out that from energetic grounds fish eating is just as good. Both insects and fish are ectothermic animals, which convert feed to meat at much higher efficiency than cows or swine, because no energy needs to be wasted to maintaining body temperature.

So, it is good to eat fish, but should it be wild-caught or cultured? The world's seas are heavily overfished. The gloomiest predictions estimate that close to half of commercially fished species become extinct within the next century. Despite the overfishing, several nations and the European Union have given large funds to the development of fishing fleets, and more effective fishing gear. At the same time the same instances have pledged to maintain the biodiversity. So, the actions are in fact opposite to promises and only serve to speed up the decrease of biodiversity. In addition to fishing causing the exctinction of species, the problem with wild-caught fish is aquatic pollution. Most pollutants are taken up and remain in the bodies of fish, because they are hydrophobic, whereby their preferred site is the body and not water. Many of the pollutants further bioaccumulate along the food chain.

So, eating wild fish is, in principle, a worse alternative than eating cultured fish. However, there are several things that make the present aquaculture practises problematic for ecologically responsible fish-eater. First, most cultured fish are carnivorous, and their feed largely consists of fish flour. So, in such a case the big fishing fleets will continue to decrease the fish diversity, now not to get food for humans, but to get resources for feed factories. The only sustainable way is to replace some of the fish flour in feed with plant product. This is a direction to which several fish feed companies have recently gone to. Second, aquaculture causes local eutrophication because of the feed and faeces, which have high amounts of nutrients. The way of prevent this would be to have aquaculture facilities separated from general aquatic environment so that all the water used could be purified. One should here point out that the cultured fish do not produce more faeces than the natural populations - the difference is that they are concentrated in much smaller areas. Third, the use of antibiotics and other drugs in aquaculture facilities is high, because parasites and diseases are much more prevalent in the dense aquaculture  populations than in the natural populations. For improvement of situation with regard to this, it would also help, if the aquaculture facilities were separated from natural wateeeeer flow. Also, the use of antibiotics should be discouraged.

In conclusion, it is possible to make aquaculture environmentally friendly, but after that is done, cultured fish will not be the cheapest food that can be found. But we should be ready to use some money to use ecologically sustainable foodstuffs.

Kommentoi kirjoitusta. Avainsanat: biodiversity, water pollution, fish feed