Marsh. — Food and Thyroid Tumor 15 



Through control of the feeding of trout it is likely that 

 practically all of the enlargement of the thyroid gland 

 which is entitled to be considered a disease can be pre- 

 vented. It is a matter of a properly balanced ration, and 

 exactly what is effective and at the same time cheap 

 enough and procurable in quantity sufficient to meet fish 

 cultural requirements I think no one is yet in a position 

 to say. It is probable that such a food might contain a 

 considerable proportion of meat (liver, heart or lungs, 

 etc.), but that to this should be added a vegetable food 

 (flour), and a smaller portion of fish. With little doubt 

 such a mixture would then be greatly improved by a 

 necessarily small addition of either shrimp, mussels, 

 maggots or insects, or similar animals. In Germany, for 

 instance, one hatchery uses a food consisting of about 

 one-third shrimp and two-thirds fish. Since the fish 

 cost less than a cent and a half per pound and the shrimp 

 about four cents, this is understandable. But in this 

 country shrimp are regarded as a luxury and not usually 

 as an available fish food. However, you will recall that 

 in a paper before the Fourth International Fishery Con- 

 gress convened in this city in 1908, Mr. Worth set forth 

 the abundance and availability of the fresh water shrimp 

 (Palaemonetes) as a fish food and even proposed its 

 culture for this purpose. I imagine that when this re- 

 source is properly exploited it will be found that it can 

 be harvested, or cultivated, or both, in quantities ade- 

 quate for practical use. 



Having thus a rather complex mixture of foodstuffs 

 the whole mess should be cooked or at least heated 

 through to the boiling point. I think the basis or start- 

 ing point of cooking food for trout in Germany was to 

 kill the parasites so largely harbored by the fishes which 

 constitute the food, and which thus add to the danger of 

 the live trout becoming infested. The German Fisheries 

 Research Station constantly advises the hatcheries to 

 cook the food as a general precaution against fish para- 

 sites, since the trout have difficulty enough getting away 

 from the direct attacks of parasites without swallowing 



