1000.0 



1.0 



NTENSr 



B= BELOW SURFACE 

 A= ABOVE SURFACE 



25 50 75 100 125 150 



CENTIMETERS FROM SOURCE 



Figure 1. — Light gradients at the three light intensities 

 used in the experiments. 



The fish were taken at random from a storage 

 tank and transferred to the experimental tank, 

 where they were allowed to accommodate for 

 periods of 30 minutes to 15 hours before each 

 trial. Except where light or dark adaptation was 

 at issue in the experiment, the period preceding- 

 each trial was at room illumination. I found no 

 significant difference in the responses of indi- 

 vidual herring allowed a half-hour or full-hour 

 period of accommodation to the tank. Once the 

 fish recover from tlie initial disturbance after 

 transfer, it is not likely that any further time for 

 accommodation is necessary. This factor should 

 not affect the results of the experiments, because 

 for any given experiment the accommodation 

 periods of all fish were the same. Accommodation 

 periods were progressively reduced throughout 

 the series to save time. 



No attempt was made to acclimatize the fish 

 to arbitrarily selected temperatures because facili- 



ties for this purpose were not available. The fish 

 were transferred from water at seasonal temper- 

 atures to the experimental tank. Because temper- 

 ature acclimatization exerts a definite influence on 

 the subsequent reactions of fish to temperature, it 

 could conceivably affect their response to light at 

 different temperatures. For that reason I have 

 specified the acclimatization (= seasonal) temper- 

 ature for the fish used in each experiment 

 (table 1). It will be noticed, however, that several 

 combinations of acclimatization and experimental 

 temperatures produced no qualitative difference 

 in the results of experiments where the effect of 

 temperature was being tested. 



An experiment consisted of several trials in 

 which the variables of interest were given pre- 

 determined values; each trial could be given a 

 different set of conditions or could replicate 

 another trial. For experimental variables that 

 could be changed quickly (e.g. light location or 

 intensity), several trials were completed in a 

 single day. For conditions that required a longer 

 time to establish (e.g. temperature or gas content) , 

 only one trial could be completed in a day, and 

 an experiment might last several weeks. In pro- 

 tracted experiments of this sort, when only two 

 treatments were involved, the trials were alter- 

 nated; when several were involved in the same 

 experiment, the trials were ordered randomly. 



Two routine procedures were used. When fish 

 were tested singly (experiments 1 to 4), the 

 attracting light w^as turned on at the right end of 

 the tank for 5 minutes, and the amount of time 

 spent by the fish in the illuminated half of the 



FACTORS INFLUENCING ATTRACTTION OF ATLANTIC HERRING TO ARTIFICIAL LIGHTS 



75 



