HUNTER: BEHAVIOR OF LARVAL ANCHOVY 



100- 



a> 

 u 



« 



o. 



80 



60 



V) 

 UJ 



o 

 o 



(O 40 



o 



z 



o 



UJ 

 UJ 



u. 



20 







/' 



I I I I I I I J 1 1 1 1 1 ll 



5 

 LARVAL 



10 

 AGE (days) 



20 



30 



Figure 9. — Feeding success (percent of prey captured) 

 of anchovy larvae of various ages fed Brachionus. 

 Larval age is plotted on log scale, equation for line is 

 percent success = 93.2 (log age) — 33.30. Two open 

 circles, larvae fed Gymnodinium. 



100 



c 

 u 



k. 



a> 



Ck. 



CO 

 CO 



o 



O 50 



CO 



o 



UJ 

 UJ 



u. 



1 



12 3 4 5 6 



FED ARTEMIA (days) 



Figure 10. — Feeding success of anchovy larvae fed 

 Artemia for the first time at age 17 days (0 days on 

 abscissa) and for 5 additional days. The line connects 

 mean values. 



the level of success had reached the same level 



as it had after 2 weeks of feeding on Brachioniis. 



One interpretation of these results is that a 



considerable proportion of feeding experience on 



one type of prey is transferable vi^hen larvae feed 

 on a new prey. On the other hand, the surpri- 

 singly long period (about 2 weeks) required to 

 achieve a high level of feeding success on Brach- 

 ionus suggests that maturation of sensory and 

 locomotor systems may also play a role in an- 

 chovy larval feeding behavior during the first 2 

 weeks of larval life. 



ESTIMATION OF VOLUME SEARCHED 



In this section I combine the estimates made 

 in the previous section to estimate the volume of 

 water searched by larvae per hour and will use 

 this estimate and others in a subsequent section 

 to calculate the density of food required by lar- 

 vae to meet metabolic requirements. 



The volume of water searched per hour by 

 larvae was calculated by multiplying the cross- 

 sectional area of the reactive perceptive field by 

 the distance traveled per hour by larvae. I made 

 separate calculations for the photographic and 

 the visual speed estimates given in Table 3. In 

 both calculations the speed estimates were ad- 

 justed for the proportion of time spent swim- 

 ming, 82.6%, and they were extended from 

 distance/sec to distance/hr. In this and all sub- 

 sequent calculations I have made larval age and 

 length interchangeable by using the growth 

 equation It — 3.246° °^"' given by Kramer and 

 Zweifel (1970) who reared anchovy larvae at 

 17 °C under conditions similar to those used in 

 this study. 



The estimate of the volume of water searched 

 per hour increased exponentially with size (Fig- 

 ure 11). The two volume estimates were close 

 for larvae less than 10 mm long but they diverged 

 for larger ones. There was no reason to select 

 one estimate over the other and, consequently, 

 I chose to use the average of the two for future 

 calculations. When the two estimates are aver- 

 aged the outcome is nearly the same as the re- 

 lationship, volume searched/hr = 1,000L^ 

 where L is larval length in cm and volume is in 

 cm^ or simply, liters searched/hr = U. Exam- 

 ination of Figure 11 shows the line for U falls 

 almost midway between the two estimates. I 

 shall use the average estimate in the rest of the 

 calculations, but U could be used with only a 

 negligible difference. In the larger larvae L^ 



833 



