Eating live animals

The reality TV show I’m a Celebrity Get Me Out of Here is justifiably popular in the UK. Set in Australia, the contestants live in a basic camp and we viewers see edited versions of their conversations and other interactions. To boost their diet of rice and beans, selected individuals compete in “Bushtucker Trials” that involve something very unpleasant, like having large numbers of cockroaches, mealworms etc. thrown over them in a confined space (see below). Until the last series, the trials most popular with the viewing public were those involving the eating of animal body parts and also live insects. The latter torture has now been banned as it is perceived by some as being cruel; yet eating live animals is encouraged elsewhere – take the case of oysters.

Oysters are bivalve molluscs that produce a feeding current using enormous numbers of tiny hairs, or cilia, that are present on the gills. This current has a dual function as it evolved from the respiratory current, particles trapped on the surface of the gill then being transferred to the mouth by other tracts of cilia. To aid retention, oysters, like other bivalves, produce mucus, or slime, on the gills and particles captured are thus bundled up into packages from which nutritious material can be selected by an ingenious sorting mechanism using the lips (labial palps) around the mouth.

The two shell valves are joined by a hinge and a muscle runs from one shell valve to the other and this serves to close the oyster if it is exposed to the atmosphere, when attacked, or not feeling. Sea water is trapped when the shell valves are closed and this prevents damage to the soft body tissues. When we buy oysters, they have frequently been out of water for hours, so the content of the water is changed by the addition of mucus and excreta, although not at levels that poison the mollusc.

The classic way to open oysters is to shuck them and this is shown in the video [1]. Note that both the hinge and adductor muscle (between the shell valves) are cut, but no reference is made to the oyster being alive and that the water + excreta are referred to as the liquor. The flavour of the liquor is an important part of eating oysters and there are debates over whether one should chew the animals or crush them against the palate using the tongue. Fortunately, the molluscs are often served on a bed of ice so, at least, their metabolism is reduced, even if they are sometimes sprayed with dilute acid (lemon juice).

For those who do not like the idea of eating live animals, there are many recipes for cooking, and preserving, oysters and that is not a surprise, when they were such a common food, and not the luxuries that they have become today. Cooking also serves to kill bacteria that might otherwise cause intestinal disorders in those eating them: something that may have been common when oysters were collected from areas where there was a high level of pollution.

Lovell [2] gives many recipes for cooking oysters and they can be listed. Some involved rapid killing of the molluscs, others did not:

Oyster soup (7 recipes)

Oyster sauce (4 recipes)

Oyster atlets – with sweetbreads

Curried oyster atlets

Curried oysters

Stewed ousters (6 recipes)

Dutch oysters – coated in breadcrumbs and fried

Fried oysters (6 recipes)

Oyster ragout (2 recipes)

Grilled oysters

Oysters broiled the Dutch way

Roast oysters (3 recipes)

Ostras á la Pollada

Boiled oysters

Oyster sausages (2 recipes)

Minced oysters

Oyster forcemeat

Oysters and chestnuts

Oyster steak

Scalloped oysters (3 recipes)

Oyster fritters

Oyster loaf

Oysters and macaroni

Oyster pie (3 recipes)

Oyster and eel pie

Oyster and parsnip pie

Pickled oysters (4 recipes)

Oyster powder (2 recipes)

Oysters on toast (2 recipes)

Oyster ketchup

Oysters au gratin

An impressive list, and gourmets among you should refer to Lovell [2] for descriptions of how to prepare oysters for each dish. Its length is a reflection on the importance of these molluscs in the diet of many European nations (and beyond) in earlier centuries.

Arguably, the most interesting way of preparing oysters is described thus by Lovell [2]:

The oldest way of cooking an oyster, of which we have any mention, is that recorded by Evelyn, who, in the year 1672, saw Richardson, “the famous fire-eater”, perform wondrous feats, one of which was, “taking a live coal on his tongue, he put on it a raw oyster; the coal was blown on with bellows, till it flam’d and sparkl’d in his mouth, and so remained till the oyster gaped, and was quite boil’d.” Who ate the oyster thus cooked, we are not informed.

Anyone fancy trying that?

[1] https://www.youtube.com/watch?v=5GtBu8nzbA4

[2] M.S.Lovell (1884) The Edible Mollusca of Great Britain and Ireland, with Recipes for Cooking them (Second Edition). London, L.Reeve & Co.

Moules marinières

Moules marinières is one of my favourite seafood dishes and so simple to prepare. This is my version:

1. Wash recently-collected mussels under running water, clean off anything attached to the shell valves and also “beards” (called byssus threads by Biologists). Ensure that all mussels are closed tightly, or close when the shell valves are tapped with the blade of a knife.

2. Chop 3-4 shallots coarsely and sauté them in butter in a large pan until they are softened, but not coloured.

3. Add a half bottle of white wine (Muscadet works very well) and bring it to the boil. Add a little freshly-ground pepper and pour in the mussels, immediately covering the pan with a lid.

4. Turn down the heat and allow the mussels to cook for 5 minutes, shaking the pan from time to time. Pass the whole contents through a sieve, before returning the strained liquor to the pan and reducing vigorously. Keep the mussels warm.

5. Place 10-20 mussels in a deep dish and pour over some of the reduced liquor and garnish with chopped parsley. Use a shell valve as a spoon to eat the mussels and mop up the remaining juices with crusty white bread.

The rest of the white wine makes a fine accompaniment and a second bottle is usually needed if the meal is shared with others - and sometimes another bowl of mussels each, too. Fortunately, the blue mussel (Mytilus edulis) is very common on coasts and in shallow seas, and mussels are also farmed, so they are easily acquired.

Byssus threads ensure that these bivalves are attached firmly to the substratum, or to other mussels, and this provides anchorage to withstand the effect of waves and the tide when they are found in the intertidal zone. In this habitat they must also withstand exposure to the air twice a day, as this brings both the threat of drying and, during warm periods, of dangerous overheating. Drying is prevented by keeping the shell valves tightly closed by means of adductor muscles and the main one of these, the posterior adductor (A, in the photograph below), is kept contracted when the animals are not covered by water. They can keep this up for some time, as we know from looking at fishmongers’ slabs, and the mussels are thus living in their own little marine world and they can withstand quite high temperatures without harmful effects. Unfortunately, the temperature of boiling Muscadet means a quick denaturing of muscles and of proteins in other tissues, so the mussels gape open by the action of the hinge and we separate the valves (held together only by the hinge) to provide us with the spoon we use to eat the cooked animal. It is worth noting that the wonderful liquor we mop up with bread consists of wine, oil, shallots, pepper, parsley, sea water and mollusc waste products.

When living molluscs are covered by the sea, the adductor muscle is relaxed and the shell valves open by means of the elastic hinge. To grow, the mussels must feed and, perhaps surprisingly, the main organs of food capture are the gills, with two pairs on each side of the animal (visible as large translucent structures [G, in the photograph above]). The gills have many filaments and the surface of each gill is covered by millions of tiny hairs called cilia that beat with a power and recovery stroke. ¹ Cilia are ubiquitous in the Animal Kingdom and serve many functions, but the millions on the mussel gill create a current that draws water into the cavity formed between the shell valves and the water then passes between the gill filaments. Particles trapped on the gills are moved by further cilia to a food groove on each gill and yet more cilia transport the food, by now wrapped in mucus, to extensions of the mouth (the labial palps), where potential food is sorted for ingestion, the remainder being “dropped” into the exhalant current.

The anatomy of a mussel shows the evolution of extraordinary structures: the byssus threads produced from a gland on the foot; the two shell valves; the adductor muscle; the elastic hinge opening the shell valves; the gills for respiration and for feeding; the labial palps for sorting. These, in addition to the evolution of the rest of the body, with its tissues, organs and organ systems, the whole having started out somewhere in very distant time as a single cell. How did all these structures, most of which are common to all bivalve molluscs, develop? Of course, I don’t think of that question when I kill mussels in boiling wine or when I eat them, satisfying myself that they are killed rapidly. The death of oysters and scallops is different. Oysters are usually chewed, or pressed against the palate, whilst still alive and living scallops are cut up to obtain the adductor muscle, ² the commonest part that we eat. Although this is little different to the fate of these animals when attacked by a predator in natural conditions, there is something about humans eating live animals, or chopping them up while they are still alive, that makes me feel uncomfortable. Why is that? Is it because I have a sense of wonder at their extraordinary evolution and that they shouldn’t suffer this fate? I have never had a problem with dissecting live bivalves in practical classes for undergraduate students, although we were focussing on their fascinating biology. Did that overcome my apprehension?

¹ http://www.youtube.com/watch?v=P2RB2oiWwCY

² http://www.bbcgoodfood.com/technique/how-prepare-scallops