least by juvenile euphausiids. Euphausiids, like pontellid copepods, were most 

 successful at capturing yolk-sac larvae. Based on laboratory results and known 

 abundances of pontellid copepods, euphausiids, and yolk-sac anchovy larvae in 

 surface waters off the coast of California, it is possible that copepods and 

 euphausiids can have a significant influence on anchovy larvae survival (62, 94). 



Yolk-sac larvae of the Pacific herring Clupea harengus pallasi were offered as 

 prey to the amphipod Hyperoche medusamm in experiments conducted in 500 

 ml beakers (99). The numbers of larvae preyed upon increased as both predator 

 and larval densities increased. But, the number of prey attacked per hour per 

 predator decreased as predator abundance increased. The number of herring 

 larvae attacked per hour increased, but the rate of increased slowed as the 

 concentration of herring larvae was raised. When "flatfish" larvae were 

 provided as alternate prey, the amphipods showed a preference for herring. 

 Amphipods such as Hyperoche medusamm may be an important source of 

 mortality to Pacific herring larvae in the sea, especially when the 

 newly-hatched larvae are concentrated near the spawning areas. 



Kuhlmann (54) investigated the chaetognaths Sagitta setosa and S. elegans 

 and their possible role as predators on several species of fish larvae. Despite the 

 often observed phenomenon in plankton samples of larval fish in chaetognath 

 guts, S. setosa and S. elegans did not prefer the fish larvae in laboratory 

 experiments when copepod prey was present in sufficient quantity. Kuhlmann 

 (54) did not believe that the chaetognaths were important predators on larval 

 fishes. He did find that both 5'. setosa and S. elegans consistently ate fish larvae 

 after starvation periods of 24 to 48 hours if copepods were not offered as 

 alternate prey. 



ROLE OF NATURAL PHYSICAL AND CHEMICAL VARIABLES 



A review of literature dealing with effects of natural environmental factors 

 on development of marine fishes reveals a wealth of information on egg and 

 yolk-sac stages (e.g., 14, 36, 38). However, these factors have not been 

 intensively studied for larval stages from the time of first feeding to transition 

 to the juvenile. 



Light 



Blaxter (16, 18) discussed the preferences of fish for light of specific 

 intensities. This preferendum may vary from day to night and may not be 

 available at the preferred intensity in some shallow water situations where little 

 vertical migration is possible. The evidence reviewed by Blaxter (16) 

 demonstrates that the liglit preferendum is variable among species and also 

 among individuals. 



188 



