FISHERY BULLETIN: VOL. 69. NO. 3 



SWIMMING AND FEEDING BEHAVIOR 

 OF Labidocera 



REACTION TO THE LARVAL TAIL BEAT; 

 BITING AND INGESTION OF LARVAE 



We noted that individual Labidocera ignored 

 motionless fish larvae or floating eggs. How- 

 ever, when a larva beat its tail in the close vi- 

 cinity of a swimming labidoceran, the copepod 

 swam immediately toward the beating tail and 

 grasped the larva. The tail beat of the larva 

 was often stimulated by the chance touch of a 

 copepod's antenna. Figures 2a and 2b show a 

 L. jollae female which caught a 3-day-old ancho- 

 vy by the tail and partially ingested it. Figure 3 

 shows another larva caught behind the head 



Figure 2. — (a) Labidocera jollae female, 3 mm long, 

 and a 3-day-old anchovy larva 6 mm long which was 

 captured by the tail and half ingested, (b) Enlarge- 

 ment of the head and setae of the copepod shown in 2a. 



Figure 3. — The head of a Labidocera jollae female show- 

 ing a newly captured 3-day-old anchovy larva caught 

 behind the head. 



by another female. Response to the larval tail 

 beat is typical of all the copepods we have ob- 

 served which attack fish larvae. 



Often a copepod would capture, then drop a 

 larva, inflicting a wound by biting the thin epi- 

 thelium. The anchovy larval skin is only about 

 2 to 3 /i thick in the finfold and tail regions and 

 appears to be easily injured. In every instance, 

 a bite which damaged the larval skin resulted in 

 the death of the larva. Therefore, in our experi- 

 ments mortality due to a copepod was the result 

 of either actual capture and ingestion of a larva 

 or biting that resulted in damage fatal to the 

 larva. Hence, the number of larvae reported as 

 "killed" in an experiment is the sum of fatalities 

 due to biting and the number of larvae actually 

 ingested. For both sexes of each Labidocera 

 species the time of ingestion of anchovy larvae 

 varied between 6 and 25 min. In one instance 

 an L. trispinosa male caught and completely con- 

 sumed two larvae in 1 hr. If we increased the 

 number of larvae to six or more in a 200-ml 

 Petri dish containing two copepods, mortality 

 through biting alone increased and the time dur- 

 ing which a larva was held by a copepod varied 

 from a few seconds to minutes. For example, an 

 L. jollae female attacked six larvae in 50 min. 

 The individual larvae were held only 10 to 60 sec 

 and not ingested. All six larvae died subsequent 

 to the attack. 



658 



