236 BULLETIN OF THE UXITED STATES FISH COMMISSION. 



THE E'KOTOKOA ASfD PKOTOPBIYTES COrt^J^IDERED AS TME PRI- 



MAfieV OB IIVI>SRE(1;T ^OrJS€E OF GTEIE FOOS> OF F1SI2ES. 



By JTOMW A. RYOER. 



lu the course of observations made during tlie last few years the 

 writer has been more and more Impressed with the importance of the 

 Protozoa and Protophytes as an indirect or primary source of much of 

 the food consumed by man. This is notably true of what is known as 

 fish and shell-fish food. As very striking- instances of the truth of these 

 propositions, we need only to allude to the various edible species of 

 the herring family, the shad, herring, and sardine, the gill-rakers of 

 which are modified so as to enable them to strain the minute living or- 

 ganisms out of the water which is passed through the mouth in resjn- 

 ration; the menhaden or Brevoortia, which is of the same family and 

 swarms along our coast, and which in its turn furnishes a large propor- 

 tion of its food to the edible blueflsh, and so serves this tyrant of the 

 sea as a strainer, elaborator, and accumulator, as it were, of the minuter 

 life of the oceanic wastes which it inhabits. The oyster, in like manner, 

 subsisting, as it does, entirely u])ou Protozoa, Diatoms, minute ciliated 

 larvie, &c., reminds us forcibly that for some of the most savory lux- 

 uries of the table we are indirectly indebted to the existence of count- 

 less hosts of living marine beings, which can be rendered visible only 

 with the help of a microscope. 



Comparatively few fishes appear to be able to utilize the protozoa 

 directly as a source of food. The most remarkable exception to this 

 rule was first made known by Professor S. A. Forbes, of Illinois, who 

 found the intestiues of certain young suckers or Catostomidm packed 

 with the shells or tests of difilugian rliizopods. In the Proceedings of 

 the Academy of Natural Sciences of Philadelphia for 1881, Professor 

 Leidy states that upon examining two slides containing some of tho 

 intestinal contents of young Mijxostoma macrolepidotum and Erimyzon 

 sucetta submitted to him for exandnation by Professor Forbes he was 

 able to distinguish the shells of six distinct species of rhizo])ods or test- 

 covered amoeboid Protozoa. The habits of the fishes in question are, 

 however, mud-loving, and, since they are provided with a more or less 

 suctorial mouth, it is easy to understand how they might readily con- 

 sume large numbers of these Protozoans where the surface of the ooze 

 of the bottoms of the streams and pools inhabited by the fishes was 

 favorable to the ]iropagation and healthy existence of the former. 



In order to render the vast multitude of Protozoa available as fish- 

 food it is necessary that they be consumed by larger organisms, which 

 in their turn may be consumed bj^ the fishes. Upon investigating the 

 literature relating to the food of the smaller crustaceans, especially of 

 the Entomostraca which enter so largely into the food supplies of most 



