ON THE FOOD OF THE MENHADEN. 121 



of this interesting food and something of the form of its varied constituents. Nor 

 has a detailed account of the systematic identification of all the organisms been 

 attempted, but it is hoped that enough has been given to indicate to those who may 

 be interested some of the more important elements of the protozoan and protophytan 

 life in brackish and inshore waters. The main object of this paper is to show the 

 importance of those groups to the life-history of the fish in question. Three otber 

 localities of similar characters (in the same coast belt of this region) were periodically 

 studied during the greater part of the summer, in which the same general character 

 of surface material was found and in which menhaden were feeding. In all cases, 

 also, the same results were obtained as have been heretofore descrided, i. e., the 

 material from the alimentary tract of the fish was entirely comparable to that of the 

 organic filtrate from the surface water. Such then is the general character of the 

 food of these fish, and some of its differences according to littoral localities. It varies 

 in amount also, as has been shown, but any of the coast waters contain an abundance 

 of this microorganic life for their sustenance, as may be determined by testing a few 

 liters of the water. 



If now the mouth of an average menhaden be opened as in its natural position 

 when feeding, its outline will form an ellipse, of which the area will be about 1.1 inches; 

 and if his rate of progress through the water when feeding be 2 feet per second (as I 

 have estimated from watching the habits of a small school confined in a large pool), 

 then the fish feeding continuously would be able to strain a column of water 1,440 

 inches iu length of the size of the fish's mouth — i. e., 1.1 inches — each minute, which 

 column of water at the surface of the Acushnet River would in July contain 6.8 gal- 

 lons of water and about 3.4 cubic centimeters of the organic filtrate, such as is found 

 in the stomach of the average fish. The average amount of food material in the 

 stomach of the fish feeding at that time is about 3 cubic centimeters, which, accord- 

 ing to this estimate, would be obtained from less than 7 gallons of water, and which 

 the fish could, therefore, extract in about one minute. Of course these quantities are 

 only estimates; the menhaden does not feed continuously, and it may be that all the 

 water does not pass through the gill-rakers at the rate the fish swims, so that the 

 amount of water actually filtered is doubtless considerably less; many of the smaller 

 organisms also may escape through the meshes of the gill-rakers, so that it may take 

 the animal longer to extract the given amount of material from the surrounding 

 medium, while my estimate of the average amount of food in a normal fish stomach is 

 very low for this particular locality. On the other hand, the animal swimming with 

 widely-open mouth against the water brings some pressure to bear, and so aids in the 

 rapidity with which the water passes backward through the pharynx — so that the 

 above low- estimated -amount filtered in a given time is by no means unreasonable for 

 such a time as the fish does really feed. 



But the estimates of the quantity of organic matter actually present in the water 

 are certainly reliable; and allowing for all shortcomings on the estimated capacity 

 and movements of the fish, there is still a wide margin in favor of its ability to gather 

 a great amount of food iu a short time. 



The passage of the food through the alimentary tract is, however, probably very 

 rapid, and a large quantity of this kind of food must be needed by the fish ; in favora- 

 ble localities the whole intestinal canal is gorged with this material. The quantity of 

 such food, moreover, is illimitable, each cubic foot of water is charged with it, and 

 rapidity of increase of the unicellular organisms in a geometrical ratio — their life- 



