Wild or farmed fish

This article was originally published on The Conversation.

Fish is one of the main sources of protein in the Mediterranean diet. In Spain, fish consumption is higher in the northern and northwestern regions, where fresh fish is mainly consumed. When we go to fishmongers or supermarkets to buy these foods, we find species of both wild origin and aquaculture origin, and it is sometimes difficult to understand what implications their origin has (beyond the selling price).

Fish as food

The truth is that fish is a very interesting food from a nutritional point of view, both because of its protein and lipid content and because it contains no carbohydrates. Therefore, we should try to include it in our diet.

The protein content of fish is 15-20% (similar to the meat of land animals), and this percentage remains constant in both marine fish and freshwater species. It should be noted that fish protein provides all essential amino acids (those that our body cannot synthesize) in adequate proportions. In addition, the high digestibility of fish protein, as well as the fact that the collagen it contains gels at lower temperatures than meat protein, makes it a protein source of particular interest to children and the elderly.

As for lipids, their content is lower in so-called white fish (for example, hake, monkfish or rooster fish) and higher in blue fish (for example, anchovies, sardines or salmon). However, the interesting feature of fish lipids is not so much their quantity as their type: since the majority (two thirds of the total) are unsaturated, their proportion is significantly higher compared to meat lipids.

Among the lipids present in fish, polyunsaturated fatty acids (PUFAs) are distinguished, which can constitute up to 45% of the total. Among them, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which belong to the omega-3 family, should be noted. In fact, DHA and EPA are generally considered to be “responsible” for the cardioprotective effects associated with fatty fish consumption, promoting vasodilation and therefore helping control blood pressure, regulating the metabolism of cholesterol (mainly DHA) and triglycerides. and reducing the risk of blood clots (they are precursors to prostaglandins).

For all of these reasons, it is recommended to consume three to four servings of fish per week, trying to vary between lean types (white fish) and fatty types (blue fish), which will provide the cardioprotective effects mentioned above and promote consumption. other nutrients (such as vitamins A and D and minerals such as iodine, selenium or calcium).

Differences between wild and aquaculture fish

In addition to differences in price or availability, there are also significant differences in the nutritional composition of wild and farmed fish. These differences do not affect proteins (the proportion or type does not change) but do affect lipids.

The difference is due to the fact that feeding fish in aquaculture is aimed (logically) at achieving the greatest weight gain in the shortest possible time. For this purpose, feed is usually used, which is traditionally made, in particular, from fishmeal and fish oil. It should be noted that these ingredients are now being replaced with plant-based protein sources and oils for sustainability reasons.

In contrast, wild fish need to find food to survive. As a consequence, the fat content of aquaculture specimens is usually higher than that of wild specimens of the same species, as has been described in species such as sea bream or sea bass.

But in addition, differences in diet also influence the fat composition of wild and aquaculture fish. Thus, it has been observed that for the same fish species, the proportion of omega-3 AGPs is lower in aquacultured fish because the feed they are fed is rich in omega-6 AGPs. In fact, the percentage of linoleic acid (omega-6 LPAA) in aquaculture salmon was observed to be 20 times higher than in wild salmon.

This may cause the cardioprotective effect of consuming farmed fish to be less than that of consuming wild fish due to the former’s higher omega-6 AGP (pro-inflammatory) content.

So, what is the best fish to eat?

Taking the above into account and purely from a nutritional perspective, wild fish consumption would be more appropriate than aquaculture consumption due to the better omega-3:omega-6 AGP ratio. However, it should be noted that due to the bioaccumulation of contaminants over a very long period of time, some large wild species such as swordfish, bluefin tuna or shark have high mercury content, so it is recommended to avoid their use. use by pregnant and lactating women, as well as children from 0 to 10 years.

It should be noted that both wild and aquaculture fish have the ability to accumulate chemical pollutants (such as heavy metals, dioxins, microplastics, drugs, etc.), although they differ in the sources of pollution. For wild species, the type and concentration of contaminants present in the fish will largely depend on the quality of the water in which they live; while in the case of aquacultured fish, the quality of the feed they are fed is also important.

Price is another factor that determines the choice of wild or aquacultured fish. In this sense, purchasing seasonal and local species can promote the consumption of wild fish at more affordable prices.