6 V. >S. BUREAU OF FISHERIES. 



Doubtless under the agitation of continued wave action manv, if 

 not all, oils and oily substances will emulsify or mix to a considerable 

 extent and so coat the <j;ills 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 typically floating. In many 

 cases, at least, the larvae for a time are also floating. This fact ren- 

 ders the possibility of grave danger to the great sea fisheries a very 

 striking o!ie, for it can scarcely be thought that eggs can hatch and 

 young normally develop in a medium of oil. The eggs and larvas 

 of oysters and other shellfish are not surface floathig, 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 larvae (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 ni 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 is 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,. 



