122 
Fishery Bulletin 113(2) 
Jones et al., 2012). A recent taxonomic review of speci- 
mens considered to be Sebastes inermis has provided 
evidence that they are a species group of 3 congeners: 
S. inermis, S. ventricosus, and S. cheni on the basis of 
morphological and genetic analyses (Kai and Nakabo, 
2008). Sebastes cheni dominates the fish community of 
the vegetated habitats (seagrass and macroalgal beds) 
in coastal waters of the Seto Inland Sea, off south- 
western Japan (Kamimura and Shoji 2009; Kamimura 
et al., 2011). Juveniles settle in vegetated habitats at 
~20 mm in total length (TL) and grow to 60 mm TL in 
their first summer. Juveniles of several Sebastes spe- 
cies have been shown to exhibit a strong association 
with seagrass and macroalgae during the postsettle- 
ment period, inhabiting substrates, such as kelp and 
rocky reef, until they reach a body size of >60 mm TL 
(Love et al., 1991, 2002; Plaza et al., 2002; Dauble et 
al., 2012). Recent surveys have indicated that survival 
during the substrate-associated period has the poten- 
tial to determine the abundance of regional Sebastes 
stocks in the eastern and western North Pacific (Ad- 
ams and Howard, 1996; Laidig et al., 2007; Kamimura 
and Shoji, 2013). 
Predation is considered one of the most impor- 
tant sources of mortality during the early life stages 
of fishes (Houde, 1987). The instantaneous predation 
rate of juvenile white rockfish during night in sea- 
grass beds in the Seto Inland Sea was -5.1% in a 
study conducted in 2009-2011 (Kinoshita et al., 2012). 
Furthermore, size-selective predation, by which white 
rockfish juveniles <30 mm TL were eaten more fre- 
quently than those >30 mm TL, was observed during 
night in the macroalgal bed (Kinoshita et al., 2014). 
Generally, ontogenetic improvement in swimming and 
schooling behaviors during the early life of fishes is 
believed to enhance fish survival by the development 
of antipredator behavior (Masuda and Tsukamoto, 
1998). Information on how the interactions between 
juvenile white rockfish at various sizes and diurnal 
changes in their behavior affect predation probability 
is indispensable for the formation of a comprehen- 
sive understanding of survival mechanism in juvenile 
habitats. 
In our study, effects of body size and light inten- 
sity on swimming and schooling behaviors of juvenile 
white rockfish were examined under laboratory condi- 
tions. We hypothesized that swimming and schooling 
behaviors develop during the juvenile period and that 
the effect of light condition on these behaviors begins 
to operate during this period. In addition, antipredator 
behaviors among species were compared by using data 
reported for other species in previous studies. 
Materials and methods 
Experimental fish 
White rockfish larvae and juveniles reared at the Hi- 
roshima Prefectural Farming Fisheries Center were 
60 
40 
20 
• *t 
Dry pellets 
Frozen copepods 
Artemia nauplii 
Rotifers 
• • 
40 
80 
Age (d) 
120 
160 
Figure 1 
Growth of larval and juvenile white rockfish (Sebastes 
cheni) in the laboratory experiments conducted in 2012 
to determine the development of swimming speed and 
schooling behavior of white rockfish in relation to light 
intensity. Error bars indicate standard deviation, and 
arrows indicate day of experiment. Shaded bars indi- 
cate feeding schedule, during which rotifers (Brachio- 
nus sp.) were supplied from day 0 to day 55, brine 
shrimp (Artemia sp.) nauplii from day 13 to day 80, 
frozen copepods from day 25 to day 80, and dry pellets 
from day 50 to day 151. 
used for our experiments. Larvae were extruded from 
adult white rockfish (4-6 years old) on 5-9 January 
2012. Mean larval TL at extrusion was 6.4 mm. Roti- 
fers (Brachionus sp.) were given to fish as feed from 
day 0 to 55, and the food supply for fish included 
brine shrimp ( Artemia sp.) nauplii from day 13 to 
80, frozen copepods from day 25 to day 80, and dry 
pellet from day 50 to day 151 (Fig. 1). Water tem- 
perature of the rearing tanks increased from 11°C 
to 17°C during the experiments. To investigate the 
ontogenetic changes in swimming and schooling be- 
haviors, experiments were conducted with fish in 5 
length classes, covering the postsettlement stage (20- 
60 mm TL): 1) 23.4 mm TL (standard deviation [SD] 
1.4) by day 61; 2) 30.3 mm TL (SD 3.1) by day 78; 3) 
41.1 mm TL (SD 2.4) by day 112; 4) 49.4 mm TL (SD 
2.8) by day 140; and 5) 58.6 mm TL (SD 2.9) by day 
151 (Fig. 1). 
Lux (lx) was used as the light intensity unit for 
comparison of behaviors of other fish species in pre- 
vious studies. Six levels of light intensity (0.1, 1, 
10, 100, 1000, and 10,000 lx) were set by using 1-5 
incandescent bulbs (40 or 500 W) and translucent 
black vinyl sheets, which allowed some light to pass 
through them, in an experimental room (1.8x0. 9x1. 8 
m). Light intensity was measured with a digital light 
