216 Ross F. NiGRELLI 



and protein metabolism are glycogen storage comparable to 

 von Girke's disease in man, cloudy swelling (albuminous 

 degeneration), hydropic degeneration and amyloidosis of the 

 liver and kidney, to mention a few. The development of 

 melanosis, a common disturbance in fishes generally, certainly 

 indicates profound changes in metabolism involving the 

 amino acids phenylalanine and tyrosine, and the excessive 

 accumulation of guanine crystals in the tissues of certain 

 marine species in captivity is indicative of disturbance in 

 purine metabolism. 



Further, it should also be emphasized that fishes are sus- 

 ceptible to neoplasia (Nigrelli, 1952, 1954a). With the possible 

 exception of typical leukaemias, all types of tumours and 

 cancers, benign and malignant, occur in fish. The same 

 basic tissues as in mammals are involved, with tumours of 

 mesenchymal origin predominating. Although we do not have 

 definite age statistics, there is ample evidence that such 

 abnormal growths occur more frequently in older fish. This is 

 especially true for sarcomas and lymphomas, basic tumour 

 types that appear more frequently in young persons. This 

 finding, together with the fact that tumours in fish are usually 

 slow-growing, may have some physiological and phylogenetic 

 significance. 



It serves no purpose here to extend the list of metabolic 

 diseases that we have found in fishes in captivity. The 

 vertebrate fish is no different from vertebrate man in these 

 respects. It is sufficient to say that we have ample evidence 

 that some of the metabolic diseases may be hereditary or 

 congenital in origin, or that, in older fishes at least, they may 

 result from nutritional disturbances and hormonal imbalances. 

 The pathological changes are generally similar to those found 

 in warm-blooded vertebrates; in extreme cases they include 

 hyperaemia, anaemia, haemorrhage, inflammation, sclerosis, 

 atrophy, hypertrophy, hyperplasia, oedema, ascites and 

 necrosis. Basically, such conditions result in disturbances in 

 the electrolyte balance, thus affecting homeostasis. 



