UTILIZATION OF DOGFISH 



127 



The following figures are selected from the tables of Atwater and Bryant, given in 

 Leach 1909, pp. 213 and 255 :— 



From this table it will be seen that the flesh' of the skate compares favourably 

 with that of the cod in nutrient value. " The dogfishes are not only palatable in the 

 fresh condition, but are as good as many other fishes when preserved by the standard 

 methods. The spiney dogfish (Squalus acanthias, the common Canadian species) 

 being in composition most like the salmon is best adapted for canning and is con- 

 sidered as good as the medium grades of salmon."^ 



(2) As to Urea and Ammonia. 



Although comparing favourably with other food fishes in nutrient value the flesh 

 of selachians contains a larger proportion of certain excretory products of the 

 organism. Most important of these are urea and ammonia. Analysis of the flesh of 

 the skate, Baja occUata, in the fresh state were made by the urease method. This 

 method consists in allowing a ferment urease to convert the urea into ammonium car- 

 bonate. The amount of ammonium carbonate formed was determined by titrating 

 against sulphuric acid before and after the ferment had been allowed to act and the 

 urea calculated from this. The results of these analyses show that the flesh of the 

 skate contains when fresh about 2 per cent of its total weight of urea. There is prob- 

 ably about the same proportion of urea in most selachians. Comparing this with meat 

 we find for example that beef contains only 0-01 -0-0:3 per eent*, which is about the 

 same as our own blood and flesh. 



There is undoubtedly very little ammonia present in the fresh skate. It is, how- 

 ever, rapidly formed as decomposition sets in.^. Under ordinary summer conditions 

 in the laboratory at St. Andrews skate may be kept overnight without giving an 

 odour of decomposition or ammonia. After forty-eight hours the ammoniacal odour 

 becomes quite strong. 



The canned product has been analysed by Dr. E. Baumann, of the Department of 

 Biological Chemistry of Toronto University, and his report is given as Appendix A 

 to this paper. Calculating the urea from the figures given in the report for urea nitro- 

 gen one obtains for the Red label, analysis I, 0-79 per cent urea, and for the Blue label, 

 analysis III, 0-34 per cent. In the latter case some of the urea had undoubtedly 

 changed into ammonia (see Appendix A). 



The amount of ammonia nitrogen in the canned samples is given in Dr. Bau- 

 rnann's report (Appendix A). Taking the Bed label I, with ammonia-N" (calculated on 

 the total weight) 0.09 per cent, the ammonia is 0.11 per cent. This amount is very 

 much greater than that found in fresh cod, which was found to be 0.017 per cent, by 

 E. D. Clark and L. H. Almy (1918). ' 



7 Field. 1910, p. 248. 



8 Leach, 1909. 



9 See statement by Dr. A. 



B. Macallum in Appendix B. 



