444 



HOVEY JORDAN 



~ 



main diagonal current (C). It held this position in the tank indefi- 

 nitely. When left hi the current for two or three hours no change 

 of general position was noted. When the current was shut off, the 

 fish under investigation would swim to the bottom or to one of 

 the corners of the tank, where it would remain relatively quiet. In 

 figure 3, one out of several records is reproduced to show a typical 



reaction. The diagonal line (C) 

 shows the direction of the main 

 current. The elapsed time in min- 

 utes, from the beginning of ob- 

 servations, is given in table 2 for 

 each of twelve successive positions. 

 These positions are indicated in 

 figure 3 by straight lines, the an- 

 terior end of the fish being denoted 

 by a short cross line, and the suc- 

 cessive positions by consecutive 

 numerals placed near the end rep- 

 resenting the tail. 



It should be noted, however, 

 that in this particular experiment, 

 contrary to the most of them, the 

 percentage of posterior and lateral 

 orientations is nearly equal. That 

 posterior orientation is the purpose 

 of shifting the position, is sug- 

 gested by the fact that the fish 



Fig. 3. Twelve successive positions 

 occupied by a normal fish with refer- 

 ence to the main diagonal current, C. 

 To avoid confusion only six positions 

 are indicated on each of the two dia- 

 grams. Position 11 was retained longer 

 than any other; it is therefore re- 

 garded as the most significant orienta- 

 tion. One complete reaction is re- 

 garded as occupying the interval of 

 time between two successive assump- 

 tions of such a position. 



remained 'stationary for a con- 

 siderable time only when it was 

 almost directly tail into the cur- 

 rent, position 11. After this period 

 (about two minutes) it again be- 

 gins a series of changes in position, 

 like those shown in figure 3, which 



lasts for about four minutes, whereupon another period of rest ensues. 

 What I have called one complete reaction, then, requires about seven 

 minutes. It is most important to note that the fish did not at any 

 time head into the current. 



The two different experiments, one with groups and the other with 

 individuals, are consistent in showing that posterior and lateral orien- 

 tation to a current is the normal reaction of Epinephelus striatus. 



