Table 3.-Food of jack mackerel larvae. 



perhaps at the surface, thereby allowing the larva 

 a disproportionate chance of securing individuals 

 of this copepod. 



Jack mackerel larvae may perceive food organ- 

 isms by their color, since M. norvegica, and species 

 belonging to the genera Corycaeus and Oncaea, 

 are among the most brightly colored or least 

 transparent of copepods. Species of the two latter 

 genera also enter into the diet of jack mackerel 

 larvae. Calanoid copepods become more important 

 in the diet of larger larvae, perhaps because of an 

 increased visual acuity, or their larger mouths, or a 

 change in their vertical distribution. Whereas each 

 feeding sardine or anchovy larva normally con- 

 tains only one or two food particles, feeding jack 

 mackerel larvae usually contain more. Some in- 

 testines contained M. norvegica in numbers as 

 high as a dozen with no other observable food 

 items. 



FISHERY BULLETIN: VOL. 74, NO. 3 



Size of Food 



The relatively large mouth of jack mackerel 

 larvae is reflected in the larger food particles 

 ingested (Figure 5). The preponderance in 

 numbers of particles at a size of 120 jum (greatest 

 cross-sectional dimension) is due to the apparent 

 selection of M. norvegica. The gape of the larva 

 apparently increases isometrically with increasing 

 length of the larva. At 3.5 mm long, it can ingest 

 particles up to 225 jum in cross section. Doubling its 

 length to 7.0 mm also doubles its ingesting 

 capacity to particles of about 435 jum in cross 

 section. 



450 



400 



350 



£300 



Q 



8 250 



O 200 

 iij 



M 



7r> 150 



100 

 50 



3 4 5 6 7 8 9 10 II 12 

 LENGTH OF LARVAE (mm) 



Figure 5.- Food size of jack mackerel larvae. 



COMPARISONS 



Type of Food 



The three species may be characterized as 

 primarily crustacean feeders as larvae (Table 4) 

 and the youngest larvae are the most eury- 

 phagous. Crustacean food is predominant in all 

 size groups of the larvae of all three species and, 

 furthermore, becomes increasingly so as the larvae 

 increase in size. Only in the smallest anchovies is 

 noncrustacean food an important part of the diet. 



522 



