6 U. S. BUREAU OF FISHERIES. 
Doubtless under the agitation of continued wave action many, if 
not all, oils and oily substances will emulsify or mix to a considerable 
extent and so coat the gills of fish or other forms, or have a poisonous 
effect which their insolubility would otherwise prevent. According 
to Weigelt, ulcerations and attacks of disease have been found to 
follow the irritating action of petroleum products. 
The eggs of sea fishes which do not seek fresh, brackish, or shore 
waters in which to spawn differ from the eggs of all these and of 
fresh-water species in that they are ty ically floating. In many 
cases, at least, the larvae for a time are aso floating. This fact ren- 
ders the possibility of grave danger to the great sea fisheries a very 
striking one, for it can scarcely be thought that eggs can hatch and 
young normally develop in a medium of oil. The eggs and larve 
of oysters and other shellfish are not surface floating, but are carried 
up and down by the current, sometimes to the surface. A special 
danger to them lies in the fact that both oil and larvee (and eggs) 
are prone to collect in eddies. 
PREVENTION OF AERATION OF THE WATER. 
The question of aeration prevention by an oil film is a very impor- 
tant one. Butterfield and Thomas have questioned considerable 
prevention, Butterfield on the supposition that mineral oil is similar 
to water in its oxygen absorption, and Thomas apparently on the 
theory that incomplete rather than complete films tend to form. 
There need be no question that extensive films do form. Further- 
more it seems established by Adeney, especially in salt water and 
any water of considerable mineral content, that streaming, with the 
consequent distribution of the air saturated surface water, is largely 
dependent upon evaporation and increased density at the surface. 
If this is the case it must follow that an oil film, by preventing 
evaporation, greatly checks aeration. Danger from this seems. 
chiefly to center in harbors where, because of general pollution, 
particularly sewage pollution, the oxygen consumption is greatest and 
where, because of gas plants and shipping and the great number of 
automobiles, the discharge of oil is also extreme. These are the 
same harbors which are the gateways to the great natural spawning 
areas of the anadromous fishes. 
In connection with the prevention of aeration, oxygen loss by the 
absorption of dissolved oxygen, by fatty acids and other substances. 
present in oils and tars, should be taken into consideration. 
DESTRUCTION OF FISH FOOD. 
Indirect action of oils and tars may consist of poisonous action on 
food organisms. Prawns appear very susceptible to tar poisons, and 
in English streams it has appeared that tarred road washings are 
even more destructive of insect life than of trout directly. It can 
scarcely be doubted that the susceptibility of minute forms is at 
least of the same order as that of fish. With a number of micro-- 
scopic forms, particularly diatoms, it 1s known that their suscepti- 
bility to a number of poisons is greater than that of fish (Whipple, 
Moore, and Kellerman). Destruction may, of course, be secondary,. 
