FISHERY BULLETIN: VOL. 78, NO. 1 



24 



22 



20 



18 



16 



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t- 



- O 



>- 

 < 

 o 



22.1 



E 

 E 

 If) 



O 



I 



Q. 



cr 

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24 

 22 

 20 



15 16 17 18 19 20 21 

 TEMPERATURE CO 



TEMPERATURE (°C) 



22.1 +.2 

 20. 4 + . 5 

 19.6 +.4 

 19 . 5 + . 8 



19.2 + .1 

 18-9 + .1 

 16.8 +.2 



8 10 12 14 16 18 20 



AGE (DAYS) 



22 



24 26 



Figure 3. — Growth of seven groups of Pacific mackerel larvae reared in the laboratory from hatching (age d) through metamorphosis 

 (15 mm SL). Lines connect means given in Table 1 ; rearing temperatures ( ±2 SE) given on right side of figure and at end of lines. Inset at 

 top: elapsed time (days) from hatching to metamorphosis (15 mm), as a function of rearing temperature. 



on logjj, length were used, it would produce inac- 

 curate estimates. 



Swimming Behavior 



At typical cruising speeds, larval Pacific mack- 

 erel (3-5 mm SL) have a high tail beat frequency of 

 about 30 beats/s and a low tail beat amplitude of 

 0.16 standard length. At slow speeds, tail beat 

 frequency remained relatively constant but the 

 amplitude of the tail beat changed. At higher 

 speeds, both amplitude and frequency changed but 

 the relative increase in amplitude was much 

 greater than that of frequency (Table 2). Thus 

 larval Pacific mackerel, unlike the adults (Hunter 



and Zweifel 1971), predominantly modulate tail 

 beat amplitude to effect changes in speed. 



Cruising speeds of Pacific mackerel increased 

 markedly over the larval period from 0.46 cm/s 

 (1.3 standard body lengths/s) for first-feeding lar- 

 vae (3.6 mm SL) to 5.6 cm/s (3.8 standard body 

 lengths/s) for fish at metamorphosis (Figure 5). 

 This differs from the pattern in adult fishes where 

 speed relative to size decreases with an increase in 

 fish size (Webb 1975). 



Feeding Behavior 



Upon sighting a prey (rotifer or copepod), a Pa- 

 cific mackerel larva advanced toward the prey. 



94 



