356 MARINE FISHERIES OF NORTH CAROLINA 



from blood, and a great many others, as well as lard, suet, brains, liver, 

 heart, kidneys, sweetbreads, etc., used for food. 



Finfish are vertebrate animals, though not mammals. Their bodies are 

 cold. They have glands, liver, and viscera which produce hormones, enzymes, 

 etc., but we know relatively little about these substances in detail. Fishes 

 have thyroid glands, their stomachs and intestines produce digestive enzymes 

 which are active at very low temperatures, and we know that at least some 

 fishes produce insulin. It is a common error, however, to speak of fish 

 broadly in such way as this, as if all fishes were physiologically alike. They 

 are probably as diverse physiologically as they are anatomically. 



Glandular and other biological products of fishes, some possibly of great 

 value, have so far been commercially unavailable (except the liver oils) 

 because individual specimens are too small and numerous for economical 

 recovery of the glands. It is quite practicable to pluck out of hogs on a 

 conveyor line the pancreas, kidneys, liver, etc. The corresponding organs 

 in fishes are too small and too difficult to find. Even the vitamin-bearing 

 liver oil widely prevalent in fishes is economically produced only from 

 certain large fishes whose livers are very rich, such as cod, halibut, tunas, 

 swordfish and sharks. The organs of fishes (except, to a small extent, the 

 roes) are not even used as food. 



The by-products so far recovered from fish are relatively few, and 

 mostly crude and low priced. Among the high priced items are exceptionally 

 rich vitamin liver oils from certain species, and pearl essence, a minor 

 product made from the silvery epidermis on herring scales. The glue industry 

 based on cod skins is successful and well established, as is the shark-skin 

 leather industry on a small scale, but the tanning of other fish skins has 

 made little progress. Isinglass formerly made from the air bladders of cod 

 and hake has been supplanted by other clarifiers of beer and wine, and the 

 industry based on it has disappeared. It may be that amino acids or protein 

 hydrolysates made from fish can be something of permanent value, but 

 they must compete with proteins from animals and especially with skim 

 milk and yeast, from the latter of which most of the present production is 

 derived. Just now, one of the amino acids, methionine, of great nutritive 

 value, found especially in fish muscle, is attracting attention.^'' Protamines, 

 used in medicine to retard the effect of insulin, have been made from the 

 milt of salmon. The livers of the tile-fish contain what appears to be an 

 exceptionally powerful fat-splitting enzyme which might be of commercial 

 value, but it has not been studied scientifically. Seaweeds yield agar, alginic 

 acid, carrageenin and other gels and mucilages of importance. In short, the 

 sea offers a tantalizing assortment of possibilities of fine chemicals and 

 biologicals, but under the handicap of small size of individual fish, irregularity 



26. The synthetic product is (Sept. 1947) on the market at $11.00 per pound. 



