HUNTER: BEHAVIOR OF LARVAL ANCHOVY 



1 to 2 sec (Table 1). During a burst the tail 

 and body beat continuously from side to side 

 without interruption, and the larva accelerated 

 and decelerated rapidly. Bursts of continuous 

 swimming usually occurred in the absence of any 

 observed stimulus although some bursts were 

 stimulated by accidental contact with other lar- 

 vae or the walls of the tank. 



During the third day of larval life (age 2 

 days) a new swimming pattern appeared which 

 was to become the dominant mode of locomotion 

 throughout the rest of larval existence. The new 

 mode of swimming was intermittent swimming, 

 consisting of alternate periods of swimming and 

 gliding; typically the larva executed one full 

 tail beat, paused, and glided forward without 

 beating the tail and then repeated the sequence 

 of beating and gliding. The mean proportion 

 of time devoted to intermittent swimming in- 

 creased during the third and fourth days of 

 larval life, more or less in proportion to the de- 

 crease in the time spent in rest (Figure 2). By 

 the fifth day of larval life about 85% of the ob- 

 servation period was composed of intermittent 

 swimming whereas the proportion of time de- 

 voted to rest during the day was nearly zero. 



With the appearance of intermittent swim- 

 ming the frequency and duration of continuous 

 swimming decreased. Bursts of continuous 

 swimming occurred once or twice per minute 

 during the first 2 days of larval life whereas by 

 the tenth day they occurred only once in 5 min, 

 and the duration of the bursts also declined over 

 the same period (Table 1). Bursts of contin- 



Table 1. — Proportion of observation time spent in con^ 

 tinuous swimming and the mean duration, and mean fre- 

 quency, of bursts of continuous swimming during the 

 first 10 days of anchovy larval life. 



LU 

 O 



_l 



a. 

 < 



Q 

 UJ 

 LxJ 

 Q. 

 (/) 



FREQUENCY 



Figure 2. — Relationship between speed, tail beat fre- 

 quency, and tail beat amplitude for anchovy larvae for 

 all types of swimming. Equation for line is V/A ^= 

 — 1.11 -)- 1.59 F where V/A is speed (cm/sec) divided 

 by tail beat amplitude (cm), and F is tail beat frequency 

 (beats/sec). 



uous swimming occurred at a low frequency 

 throughout the rest of larval life. 



The appearance of intermittent swimming co- 

 incided with the appearance of feeding behavior. 

 Feeding behavior was closely associated with in- 

 termittent swimming; food was sighted during 

 intermittent swimming and the larvae advanced 

 on the prey using this mode of lomocotion. 



POSSIBLE SIGNIFICANCE OE 



SPONTANEOUS BURSTS OF SWIMMING 



IN YOLK-SAC LARVAE 



The regularity of the bursts of continuous 

 swimming of yolk-sac larvae (age 0-1 day) sug- 

 gests that the bursts may have a respiratory 

 function. Yolk-sac larvae have no functional gill 

 filaments, and oxygen must be obtained through 

 the integument. Thus the regular bursts of con- 

 tinuous swimming could be necessary for gas ex- 

 change. I conducted a short experiment to test 

 this hypothesis. 



I measured the duration and frequency of 

 bursts of swimming of age day and 1 day lar- 

 vae in open 10-liter containers containing water 



823 



