The chemistry of growth and the food value of the common eel ( Anguilla anguilla (L.))

Abstract

As an article of diet the eel must have a literature dating back for centuries, and although its scientific history cannot claim to go back quite so far, it is nevertheless full of interest. Its life cycle has been shown to include two of the most remarkable migrations known to man. Many excellent investigations, beginning with the famous ones of Paul Bert, have been devoted to the way in which it regulates its osmotic presure during its passage from inland waters to the sea. A few scattered but, on the whole, incomplete data are available on its composition at maturity and during growth. No study of the kind now to be described appears, however, to have been made. METHODS The eels were obtained through the Freshwater Biological Association of the British Empire and were all caught in the north of England. The elvers, which were obtained in 1943 and 1944, had been kept in fresh water for a few weeks before they were sent to Cambridge. The 'snigs', i.e. the smanl yellow eels weighing about 10 g. apiece, were taken in the years 1943 and 1944 in the river Wyre, Lancs. The yellow eels were caught in 1943 on lines in the Windermere catchment area, and the silver eels in the same year on migration from this area to the sea. The eels were sent to Cambridge packed in grass or weed and the majority were alive on arrival. Yellow eels and the snig eels were obtained in the early summer and again in the autumn, but the elvers and silver eels only when they were migrating. On arrival at Cambridge the eels were measured and weighed. Elvers and one batch of snigs were analyzed whole, but the second and third batches of snigs, and all the larger eels were skinned and disected with stainless steel knives and scissors. The soft parts were then cut up into small enough pieces to allow duplicate samples, generally of 50 g., to be weighed out for mineral analysis. The remainder was usually minced to facilitate the sampling for nitrogen and fat. At first only muscular tissue was analyzed, although the skins, and the head and guts, were weighed: later the skins, heads and organs were also analyzed so that the composition ofthe whole fish might be computed. It was, however, impossible to sample the heads and bony parts without mincing them, and hence without running a very serious risk of contaminating them with iron.