450 EEPOET OF COMMISSIONER OF FISH AND FISHERIES. [18] 



be thus stored or removed without materially changing the volume of 

 the tissue, the above simple explanation would, to one ignorant of his- 

 tology, seem very natural. 



I have been struck by this mutual replacement of fat and water in . 

 looking through a column of analyses of the flesh of fish and of other 

 animals. In a colored diagram it is especially striking, though it is 

 very weU brought out in Table XI. If we leave out, on the one hand, 

 a few of the most watery sorts of fish, as flounder, and, on the other, 

 some of the fattest flesh of mammals, we have in the remaining fish and 

 in the flesh of animals, an almost uniform content of protein, the chief 

 variations being in the fat and th« water, of which one increases as the 

 other decreases, and vice versa. 



CLASSIFICATION OF SPECIMENS OF FISH ON THE BASIS OF THE 

 AMOUNTS OF FAT IN THE FLESH. 



On the whole, perhaps, as appropriate a general classification as any 

 for our present purpose would be based upon the proportions of fat in 

 the flesh. The subjoined grouping, for instance, seems to be a tolerably 

 satisfactory one. 



1. Very fat fish ; flesh containing over 10 per cent, of fat. 



2. Moderately fat fish; flesh containing between 5 and 10 per cent, 

 of fat. 



3. Bather lean fish ; flesh containing between 2 and 5 per cent, of 

 fat. 



4. Very lean fish, flesh containing less than 2 per cent, of fat. 



I append a list of the specimens coming within each of the above 

 categories, giving their approximate composition. 



1. Fish whose Jlesh contained over 10 per cent, of fat {very fat). — Lam- 

 prey eel, * salmon, salmon trout, butter fish, herring. Composition of 

 flesh : Water, 69 to 71 per cent. ; water-free substance (nutrients), 30 to 

 37 per cent.; protein 18 to 23 per cent.; fats, 11 to 13 percent.; mineral 

 matters, 1.1 to 1.5 per cent. 



2. Fish whose flesh contained between 10 and 5 per cent, of fat {mod- 

 erately fat). — Shad, Spanish mackerel, eel, pompano, mackerel, whitefish, 

 alewife, halibut, porgy. Composition of flesh : Water, 68 to 75 per 

 cent. ; water-free substance (nutrients), 25 to 32 per cent. ; protein, 18 to 

 22 per cent.; fats, 5 to 10 per cent. ; mineral matters, 1.0 to 1.6 per cent. 



3. Fish whose flesh contained between 5 and 2 per cent, of fat {rather 

 lean). — Mullet, white perch, sheepshead, Cisco, striped bass, masca- 

 longe, weakfish, buffalo-fish, brook trout. Composition of flesh : Water, 

 75 to 79, average, 77 per cent. ; water-free substance (nutrients), 21 to 

 25, average, 23 per cent. ; protein, 17 to 20, average, 19 per cent. ; fats, 

 2 to 5, average, 3 per cent. ; mineral matters, 1.2 to 1.6, average, 1.3 per 

 cent. 



* The composition of the specimen of lamprey eel was somewhat anomalous, having 

 only 15 i)er cent, of protein and 0.7 per cent, of ash. 



