PROGRESS IN BIOLOGICAL INQUIRIES 27 



ECOLOGICAL AND OCEANOGRAPHIC STUDIES 

 CONTROL OF MOSQUITOES BY MEANS OF FISH 



Investigations relative to the use of fish for controlling mosquito 

 breeding were continued at Greenwood. Miss., in cooperation with the 

 United States Public Health Service. This work was under the 

 supervision of Dr. Samuel F. Hildebrand and in immediate charge of 

 Irving L. Towers. The season was favorable until the latter part 

 of September, when heavy and continuous rains set in and the work 

 was abandoned for the season. 



Gambusia continues to give better results than any other fish. 

 In fact it no longer seems worth while to give consideration to any 

 other species in connection with mosquito control in regions where 

 Gambusia is common. In general, Gambusia provides mosquito con- 

 trol just to the extent that it is able to reach the larva?. Complete 

 control is rarely possible, but the presence of this fish always brings 

 about a very large reduction in mosquito production. 



OCEANOGRAPHY 



At the request of the New York Zoological Society, two members of 

 the bureau's scientific staff, Dr. Charles J. Fish and IVIarie Poland Fish, 

 were detailed to join the Arcturus oceanographic expedition, the former 

 to supervise the oceanographic work and the latter to investigate the 

 distribution and early development of ocean fishes. The cruise lasted 

 six months, February 14 to July 30, 1925, during which time the Gulf 

 Stream, Sargasso Sea, North Equatorial Current, Antilles Current, 

 Mexican Current, and the Galapagos and Cocos Island regions were 

 investigated. In all 1 13 stations were made and numerous collections 

 of plankton and many physical and chemical data were secured. Any 

 conclusions drawn at this time must necessarily be of a very general 

 nature and subject to modification or change when the data have 

 been studied more carefully. 



The Arctur us entered the Pacific during a recurrance of the dreaded 

 El Nino, a warm, counter water mass from the north, which about 

 once in 20 years penetrates along the South American coast as far as 

 Peru, carrying tropical fishes and other marine forms far beyond their 

 usual range in this area and causing enormous destruction to the life 

 of the cold Humboldt Current as well as to the guano birds, which 

 rely upon pelagic marine organisms for food. The loss to Peru in 

 guano alone at such times is tremendous and forms a problem of 

 national importance. Temperature sections taken by the Arcturus 

 in this region indicate that El Nino does not in reality divert the 

 Humboldt Current from its course, as is popularly believed, but flows 

 over it as a comparatively thin film. Everywhere in the Galapagos 

 region Humboldt temperatures were encountered below 100 meters. 

 It is therefore highly improbable that a warm and consequently 

 lighter current of temporary nature pushed aside the permanent cold 

 and heavier Humboldt Current by wedging between it and the coast, 

 particularly as previous records show the latter body of water to be 

 of a slightly higher salinity. 



The vertical distribution of life in the ocean formed one of Doctor 

 Fish's most important problems. Everywhere the same zones could 



