156 
BULLETIN OF THE BUREAU OF FISHERIES 
subject for consideration, even were they not, in one respect at least, useful agents 
in the larger rivers. 
It may surprise most people to be told that the gar serves any useful purpose, 
but the interrelations of nature give frequent occasion for surprise. Within compara- 
tively recent years it has been learned that the gar serves as the host of the parasitic 
young (glochidia) of the most valuable of all fresh-water mussels. (Howard, 1914.) 
The yellow sand shell ( Lampsilis anodontides ) yields a shell that for form, texture, 
and luster compares most nearly, of all fresh-water shells, with the marine “mother 
of pearl.” It is useful not only for the manufacture of buttons of superior grade 
but also for the preparation of pearl handles for knives and for other novelties. From 
extended investigation, it appears that all species of gar may function as hosts of 
this mussel, and that no other fish will answer. Without the presence of gars in our 
rivers we could not have a fishery resource that has considerable present value and 
doubtless greater future value, unless this mussel can be maintained by artificial 
means. 
The most striking feature of change in the fauna of the upper Mississippi in 
the last dozen years is the great increase in the numbers of yellow sand shells. From 
being a very infrequent shell culled out in small quantities to be exported for the 
production of novelties, it has now become a standard shell for use in button manu- 
facture, yielding a high price because its elongate form, relatively uniform thickness, 
and good cutting qualities permit a high-quantity production of buttons. To a 
considerable extent it now replaces the niggerhead mussel, once the standard shell 
for button manufacture. The clammers of the river are now beginning to hold the 
gar in higher esteem. 
Some notes regarding the habits of the gars will establish more clearly their 
place in the biological economy of the river. 
More than other fishes, the gar is commonly in evidence, owing to its habit of 
swimming at the surface. Equipped with a cellular air bladder, which functions in 
part as a lung, the gar frequently “breaks” the surface, protruding it head and long 
snout, turning partly on its side, emitting a bubble of exhausted air, and gulping in 
a new supply. “The movements are very rapid and almost convulsive, as if the 
fish were suddenly oppressed by something and hastened to remove it.” (Wilder, 
1877, p. 7.) Garman found that when a gar was restrained below the surface air 
bubbles were allowed to escape and the fish became evidently very uneasy, “moved 
rapidly to and fro, turned and twisted and lashed its tail,” until it was permitted to 
rise to the surface, when it apparently gulped in a large volume of air. After this it 
descended and remained quiet for the usual period. Mark (1890) concluded from his 
experiments that only oxygen exchange with the atmosphere was effected in this way, 
the respiration of C0 2 being effected in some other way; but Potter (1927) has recently 
shown that both oxygen and C0 2 exchanges take place through the swim bladder. 
Furthermore, Potter gives evidence to indicate that “the capacity of the swim bladder 
and the rate of inhalation are great enough to supply sufficient air for the needs of the 
body.” It appears that gar pikes have alternate modes of respiration — by gills or 
by the swim bladder functioning as lungs — and that they will live for days when forced 
to depend exclusively upon either the one or the other. 
“The manner of feeding is also unlike that of fishes and resembles that of reptiles. 
Other fishes take their food with open mouth and swallow it at once; but this one 
approaches its prey slyly, sidewise, and, suddenly seizing it, holds it in its jaws until 
