1918.] T. Southwell & B. Phashad : Indian Fish Parasites. '343 



5. General covsideratior'S. — A summary of the history of this disease 

 amongst fishes, and the literature relating thereto, has ah'eady been 

 given by one of us (2) and need not therefore be recapitulated. These 

 tumours do not occur in fishes living under natural conditions. They 

 only arise when fish are placed under artificial surroundings, such as 

 occur in aquariums and hatcheries. These artificial conditions react on 

 the fish in such a way that anomalous tissue, of thyroid nature, arises, 

 either as a single tumour (as in trout), or a series of tumours (as in the 

 climbing-perch). It is impossible to say whether these tumours are 

 derived directly from the cells of the thyroid gland or not. A specific 

 organism is suspected, but as yet no such organism has been isolated. 



The tumours from the climbing-perch described above differ in cer- 

 tain respects from similar tumours described by other writers from 

 other species of fish. 



The colloid carcinomas recorded up to the present are rounded 

 structures with smooth surfaces. Ours, as we have pointed out, may 

 present the appearance of a series of closely approximated nodules, 

 attached to each other, and to the body of the fish, by a short stalk. 

 In other cases the surface of the tumour is rugose and the nodulai 

 appearance is less distinct. Quite young tumours are flatfish or mush- 

 room shaped. 



The colloid carcinoma described by one of us (2) from a trout caught 

 in the Punjab was enclosed in a tough fibrous capsule or cyst. The 

 ones described from the climbing-perch are not encapsuled but mereh' 

 covered with epithelium. It is clear, therefore, that the tumours ma}' 

 either be encapsuled or not, in accordance probably with their point oi 

 origin. Gaylord and Marsh (1) in discussing anomalous deposits of thyroid 

 nature in fishes state that : " as the thyroid is a somewhat diffuse organ 

 one might expect to find instances of remotely placed deposits. We are 

 therefore surprised to find the sharp delimitation to the region already 

 described which appears to exist in our wild specimens, with one marked 

 exception, i.e., the jugular pit to which reference has already been made. 

 It has been assumed by some writers that aberrant thyroid deposits in 

 some region might be frequently expected. This has been due to the 

 development of tumour nodules in regions beyond the normal and usual 

 seat of distribution, such as the low^er mouth parts and gill arch region. 

 The only outlying tumours of this sort which may be inferred with 

 certainty to arise from original deposits of thyroid are the so-called pit- 

 tumours." 



The observations made on the tumors found in the climbing-perch 

 show that thyroid deposits may occur anywhere in the fish, as internal 

 or external growths. It is, however, impossible to decide at present 

 whether such thyroid deposits are original or secondary. 



It will be obvious that in the climbing-perch, the tumors being 

 disposed as masses of tissue over the surface of the body, it is not im- 

 possible in some cases for the fish to remove them by rubbing the affected 

 part against a solid substance. The tumors are, however, somewhat 

 firmly attached. Whether removal in this manner would invariably 

 result in spontaneous recovery may be doubted, since the tumours in 

 question have a deep-seated origin. 



h2 



