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 medusanim 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 medusanim 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 S. 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 light preferendum is variable among species and also 
among individuals. 
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