The miscellaneous chemical materials were dissolved or suspended in 

 water before testing, using Tergitol and/or mechanical emulsifier when necessary. 



Tank and pond tests were conducted in a similar manner to that of last 

 year (Tester e_t al. 1954). The only important change involved the pond: the ob- 

 servation tower was moved from the western end to the center of the north side 

 (fig. 1). In brief, testing was conducted as follov/s: the fish were timed and 

 counted in an attraction area during five 3-minute control periods (2-minute 

 periods in the tank); the test material was introduced from the top of the tower 

 into the attraction area through a streeun of water which flowed constantly; and 

 the fish were timed and counted during ten subsequent 3-minute test periods. 

 "Timing" consisted of recording on an electric clock operated by a push switch the 

 number of seconds spent by one or more individuals of the tunny school in the at- 

 traction area. The "attraction area" was a portion of the pond in front of the 

 tower which was marked off by two pieces of string stretching across the pond; it 

 was approximately 39 by 75 feet in area. "Counting" consisted of recording on a 

 hEind counter the number of passes made by each fish in the attraction area while 

 the fish was moving in either a "down" or "up" (easterly or westerly) direction. 

 Materials introduced through the pipe leading from the top of the tower remained 

 in the attraction area for at least 15 minutes and then gradually dispersed. The 

 time and direction of dispersal was governed by the strength and direction of the 

 weak tidal current. Usually a period of at least 30 minutes was allowed to elapse 

 between the end of one experiment and the start (control conditions) of the next 

 to enable introduced materials to disperse or to become diluted to a level well 

 below the threshold of response. 



FUNNEL FOR INTRODUCING MATERIALS 

 VALVE 



3/4" PIPE 



OBSERVATION PLATFORM 



1/2" PIPE 

 ^ TOWER (20 FEET HIGH) 



ELECTRIC PUMP 



OUTLET 

 ( 3 FEET UNDERWATER) 



ATTRACTION AR/EA 



SHALLOWS 



Fig. 1.— Diagram of Pond No. 5 at Coconut Island showing the 

 observation tower, attraction area marked off with 

 string, and the pipes, pump, and funnel used to intro- 

 duce test materials to the pond. 



