522 
Fishery Bulletin 95(3), 1997 
(Taubert and Coble, 1977; Tanaka et al., 1981; 
Campana and Neilson, 1982; Neilson and Geen, 1982, 
1985; Neilson et al., 1985; Maillet and Checkley, 1991; 
Moksness, 1992). 
Growth histories of fish are determined primarily 
through back calculation by using either a direct 
proportion or some nonlinear relation between otolith 
size and fish age (Maciena et al., 1987; Thorrold and 
Williams, 1989). Recent studies have used the rela- 
tion between increment width (IW) and growth rate 
to show growth histories (Maillet and Checkley, 1990; 
Molony and Choat, 1990; Wright et al., 1990). Key 
assumptions for this use are that distance between 
increments is proportional to growth rate and that 
the increments are produced daily (Beamish and 
McFarland, 1983). 
The objectives of this study were to validate the 
daily periodicity of otolith increments in juvenile 
weakflsh, Cy noscion regalis, and to describe the re- 
lation between otolith IW and changes in feeding 
rate, specific growth rate, and condition factor. 
Materials and methods 
Experiment 1 (daily otolith increment 
validation) 
Juvenile weakflsh were captured in Delaware Bay 
in August, 1987, maintained in the laboratory in a 
recirculating seawater system under a photoperiod 
of 14 h light/10 h dark at 22°C (0.20 SE), 20 %c, and 
fed ad libitum on squid. Fifty-eight fish were injected 
with a 200-mg oxytetracycline hydrochloride/0. 1 mL 
saline solution and held in recirculating seawater for 
26 days. Throughout the 26-d period, between 1 and 
5 fish were removed and measured (SL), and their 
otoliths were removed for analysis. Fish sizes ranged 
from 68 to 150 mm SL. 
Experiment 2 (effect of ration level on 
increment width and specific growth rate) 
Weakflsh were reared from eggs fertilized in the labo- 
ratory and raised to the juvenile stage in recirculat- 
ing seawater (photoperiod=14L/10d at 22°C, 20 %c). 
Individual fish were held in 20-L circular containers 
and fed ad libitum for two days to determine maxi- 
mum ration (pretreatment period). Each day, fish 
were fed a known weight of live mysid shrimp 
( Neomysis americana) in excess of what they could 
consume. Fish were allowed to feed for 24 hours 
whereupon uneaten mysids were collected and 
weighed. Maximum ration was determined to be ap- 
proximately 20% body weight/d. 
Experimental treatment rations were randomly 
assigned on the third day of the experiment. Fish 
were weighed to the nearest 0. 1 g and randomly as- 
signed one of six daily rations: 100% maximum ra- 
tion (MR, n- 5), 90% MR (n= 4), 80% MR (n= 4), 60% 
MR (n= 4), 40% MR (n= 4), 20% MR (n= 4, Table 1). 
Feeding levels were also calculated as percentages 
of body weight for individual fishes. For 14 days, fish 
were fed daily at these assigned levels; that is to say, 
they were allowed to feed for 24 h whereupon un- 
eaten mysids were removed and collectively weighed. 
Fish were re weighed on day 7, and final weights and 
lengths were measured on day 14. The absolute 
weight of the daily feeding level offered (as a per- 
centage body weight) was adjusted on day 7 to ac- 
count for growth and maintain ration levels as a func- 
tion of fish weight. Specific growth rate (SGR) was 
calculated for each fish as 
SGR = [(In Wj 4 - In W 0 )/ 14] x 100, 
where W 14 = the wet weight (g) on day 14; 
W 0 = the initial wet weight (g); and 
14 = the duration of the treatment period in 
days. 
Mean specific growth rates were calculated for each 
treatment. Fulton’s condition factor (K) at the end of 
the experiment was calculated for each fish as 
K = W / L 3 x 10,000, 
where W = the wet weight (g); and 
L = the standard length (mm). 
Daily ration (percentage body weight/d) was cal- 
culated for each fish for each day on the basis of the 
Table 1 
Summary of ration levels. Actual treatment feeding levels 
and daily ration calculated based on calculated daily fish 
weights. 
Feeding levels 
(% of maximum ration) 
Daily ration 
(% body weight/day) 
Estimated 
feeding level 
Actual 
feeding level 
Mean 
Week 1 
Week 2 
100 
100 
23.8 
26.4 
21.3 
90 
66 
15.6 
16.1 
15.0 
80 
58 
13.9 
14.6 
13.3 
60 
46 
11.0 
11.1 
10.9 
40 
32 
7.6 
7.7 
7.5 
20 
17 
4.1 
4.1 
4.1 
