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Although there are thousands of species of fish in the sea, only around 150 types are commonly eaten around the world. They can be broadly categorised into white-fleshed fish; for example cod and haddock, or oily fish; for example salmon, mackerel and sardines. It is commonly recommended that fish should be included as part of a healthy diet. It is rich in vitamins and minerals, especially vitamin D and iodine, of which many people have insufficient intake, and oily fish in particular are abundant in the omega 3 essential fatty acids EPA and DHA which are also insufficient in many peoples' diets.
The white-fleshed fish store their fat in their liver, so the flesh is very low in fat. Oily fish, on the other hand, store their fat in their muscle tissue and skin. As the fat in our food carries most flavours, they have a much stronger taste. Not everyone likes the taste of oily fish, but it is these varieties where the omega 3 fatty acids are found, so consequently the government recommendation is to include at least one portion of oily fish in our diet every week, although it is only a small minority of people who do so.
Fish such as cod and haddock were severely overfished in the last half of the twentieth century and as a result stocks dwindled to dangerously low levels. Concerns about fish stocks have become part of our public consciousness since the early 1990s when Canada's Grand Banks cod fishery collapsed in 1992 due to insufficient fish stocks. In response to consumer pressure, conscientious food suppliers ensure that the fish they sell is sustainably caught. In the UK, the Marine Stewardship Council certifies fish from sustainable sources, so consumers can look for the blue MSC label for guidance.
But what does sustainability actually mean? The oceans are divided into areas known as fisheries, where certain species of food fish are found and caught. For a fishery to be considered sustainable, the first criterion is that stocks must not be overfished: there needs to be enough of the breed left in that area of the sea to reproduce and keep stocks at healthy levels. Secondly, the fishing methods used must not damage the local ecosystem. There are several common methods of catching fish, for example, purse seine fishing, pelagic trawl or pole and line. Whether or not it can be considered sustainable depends on the area and type of fish being targeted. There is not one ideal method, but it is important in each area that damage to the sea bed is minimal, juvenile fish are able to escape (in order to keep future stocks healthy), and by-catch (i.e. the gathering of non-targeted species) is minimised. Thirdly, the fishery must be well-planned and necessary changes must be made to ongoing fluctuations in fish stocks. Also, respect must be given to the livelihoods of those working in the industry, and a fishery must comply with local and international legislation. Particularly relevant is the impact of climate change, which has meant that fish are migrating to different areas, and fisheries have to be managed in a way which responds rapidly to these changes. It is important that consumers look for a sustainable label on the fish they buy, because sadly there are still many fisheries in the world that continue to work in a non-sustainable way.
With concerns over depleting fish stocks and fishing methods, it would seem that fish farming would be a good way forward. This is true of some farmed shellfish, such as mussels, which filter the surrounding water and leave it clean. Unfortunately, this is not the case with all farmed fish, as it has often been shown in many instances to be more detrimental to the ecosystem than the fishing of wild stocks.
Many fish farms operate in areas that are extremely small for the number of fish they contain, which means fish are overcrowded. As a result, disease can spread rapidly. Particularly among farmed salmon, infestations of sea lice are common, and low-dose antibiotics are given to the fish to prevent outbreaks of bacterial infection in the same way they are given to land animals bred for food. Additionally, farmed fish often escape which has led to breeding with wild fish of the same type, and the spread of disease to the wild population. The huge concentration of fish in one area is also extremely damaging to the surrounding area: the sea water in the area around fish farms is highly polluted, and over time the sea floor beneath the confined space in which farmed fish are kept is completely destroyed due to the pollution and toxic chemicals sinking downwards. Furthermore, there have been issues of fish stocks in one area becoming depleted (such as sardines around Morocco) due to them being caught to feed the fish in the farms. This has impacted on sardine stocks for human consumption and has also had a knock-on effect on the stocks of predatory fish in the same area that normally feed on them. As well as wild-caught fish, farmed fish are fed pellets of food which are not part of their natural diet, leading to a change in their nutrient profile, including a reduction in natural antioxidant pigments and omega 3 fatty acids. Needless to say, kept in cramped conditions and fed an artificial diet, farmed fish are less healthy than wild fish, and are less healthy for us too.
Of further concern is the contamination of fish with toxic pollutants such as PCB's and methyl mercury, which are generally higher in farmed rather than wild fish (most notably in salmon). As well as the issues around sustainability, the contaminants in fish have become of great concern, and larger and long-lived species of fish, for example, marlin, shark, swordfish and albacore tuna, have accumulated high levels of heavy metals and toxic substances that over the years have polluted our oceans. Chemicals used in industry eventually end up in the ocean as they have nowhere else to go. They are then ingested by fish in the food they eat. As larger fish feed on smaller fish and also have a longer lifespan, these toxins become increasingly concentrated as fish store them in their flesh, in particularly in their fatty tissue. For this reason, it is recommended that we keep our consumption of these large predatory fish low. Pregnant women (for whom mercury is of particular concern due to the damage it can do to the developing foetus) are advised to avoid these species of fish altogether. However, it is possible to include fish in the diet while keeping contaminants to a minimum by choosing fish that have been caught in (relatively) unpolluted waters – for example, Alaskan salmon – and also eating fish whose diet is plant-based, such as sardines. These smaller fish also have a naturally shorter lifespan, so will have accumulated less toxic substances in their flesh.
So what is the best fish to eat, taking account of the environmental concerns as well as enjoyment and health?
Truly fresh fish, caught that day from nearby oceans, with attention paid to sustainability issues would obviously be the best choice from a gastronomic perspective as well as being eco-friendly and with a low carbon footprint in terms of distance of travel. However, despite being an island, it is surprisingly difficult to buy truly fresh fish in this country unless you are buying from a local supplier directly from a seaside location. Supermarket fish, although sold as fresh has often been previously frozen, and even in its defrosted state has often been sat on ice for several days. Supermarket fish that is pre-packaged has sometimes been defrosted for over a week before it is sold – hardly what anyone would call fresh!
Paradoxically, fish is often "fresher" when bought frozen. Large fishing boats have the facilities to process and flash-freeze seafood on board. It does mean that for some types of fish, particularly oily fish which have a very short shelf-life due to the oils they contain, last much longer if it is possible to buy and keep them frozen until they are needed. It is easier to buy MSC certified fish which is purchased frozen, and there is likely to be less wastage than with fish bought defrosted or fresh. It is often less expensive too. The downside to buying frozen fish is that there is some loss of texture when cooked, and also there is considerable energy needed to keep them frozen through the whole food supply chain.
The most sustainable type of fish to eat depends on the fishery and current stock levels, so consequently changes all the time. Fish such as coley and pollock have been used in processed fish products such as fish fingers for a number of years, due to the depletion of cod in the oceans, although in some areas cod stocks have recovered well. Unless the consumer wants to spend hours researching each fish they buy, the easiest way to ensure what you choose is sustainable is to ensure it is certified as such.
So other than looking for an MSC label, what is the best way to buy fish? Although it is often seen (perhaps unfairly) as a second-rate choice, MSC-certified canned fish is the optimal choice in many ways, particularly for oily fish, which is the most nutritious type. Why is this?
- It is the least expensive way to buy fish.
- Consumers can be confident that it is sustainably sourced.
- The carbon footprint of tinned fish is very low as it is canned at source and then shipped.
- The shelf-life is almost indefinite which means there is less wastage.
- Contaminants are lowest in wild-caught, small-species fish which are the most available canned type.
- Although canned food is often seen as nutritionally inferior to fresh or frozen, with fish this is usually not the case. Fish such as salmon, sardines and mackerel are sealed in the can free of oxygen, so the fragile oils they contain are preserved, and the bones of tinned salmon and sardines are usually consumed too, which provides an excellent source of calcium and the accessory nutrients such as vitamin D and phosphorous needed to absorb the calcium are also present. The only exception to this is canned tuna, which is cooked outside the can and the oils drain away. This means that canned tuna, while being rich in many minerals such as selenium, is not a good source of omega 3 fatty acids.
New Year is often a time for people to try to make healthier food choices which can be difficult when also suffering from post-Christmas budget constraints! True Food sells MSC certified canned fish, so why not buy a few tins when you are next in the shop. In this issue of Pulse, Diana gives us some recipe ideas to help you to include this flavourful and inexpensive nutritional powerhouse into your diet.