YAMASHITA and BAILEY: BIOENERGETICS OF LARVAL WALLEYE POLLOCK 



of dyed rotifers in the gut to larval dry weight at 

 times and t (in hours). R is the calculated in- 

 stantaneous rate of gastric evacuation. 



Ingestion Rate 



About 10 larvae from both high and low prey- 

 ration tanks were sampled 5 times each day at 

 1.5-3 h intervals during the light period. Prey 

 were removed from larval guts, counted, their 

 widths measured, and the degree of larval diges- 

 tion determined. Total gut content in dry weight 

 per larva was determined by summing the prod- 

 uct of the width-specific dry weights of rotifers 

 and digestion factors. 



Asymptotic curves of the form 



S ~ ^ma.\ -^ (1 



,-F( 



), 



were used to describe ingestion rates, where S is 

 the ratio of gut content to larval dry weight ( x 

 100%) at time t (in hours) after initiation of hght 

 period, Smax is the asymptotic gut content (%) 

 and F is the instantaneous rate of gut fiUing. 



Weight-specific daily ration (/) as a percent of 

 body weight was estimated for larvae using the 

 Elliot and Persson (1978) model: 



m 



I = 2 (5, - S,-i e-«'0 RUKl - e-«'0 



In this model, t, is the duration of each time in- 

 terval (0 in hours; S, is the mean gut content at 

 the end of interval (0 as a percent of larval dry 

 body weight; and m is the total number of in- 

 tervals during a light cycle. So was assumed to 

 be 0; and S„,, the gut contents at the end of 

 the light period, was approximated as (S,„_i + 

 S,„-2V2. 



Metabolic Rates 



Oxygen consumption rates were measured 

 using the micro-Winkler technique (Carrit and 

 Carpenter 1966; Strickland and Parsons 1972). 

 We assumed that there are four metabohc activ- 

 ity levels: 1) resting or basal (Mre)', 2) routine 

 (Af,-o), which includes M^p plus a cost for an 

 lights-on generated activity; 3) feeding iMf,X 

 which includes Mre and an additional cost for 

 specific dynamic action (SDA); and 4) active 

 (M„), which includes M^e plus increments due to 

 lights-on activity and SDA, and an additional 

 cost of pursuing and capturing prey. 



Oxygen consumption rates for the different 



levels were measured as follows: 



1. Mre- larvae were allowed to void their guts 

 for 24 hours and were then incubated in dis- 

 solved oxygen (DO) bottles for 24 hours in com- 

 plete darkness. 



2. Mrn- larvae were allowed to void their guts 

 for 24 hours and were incubated for 12 hours in 

 the hght during daytime. 



3. Mfy,: larvae with full guts after a 12 h feed- 

 ing period were incubated for 12 hours in the 

 dark during nighttime. 



4. Ma', larvae with a few rotifers in their guts 

 were incubated for 12 hours in the light during 

 daytime vrith rotifers at a density of 5 individ- 

 uals/mL. 



Sixty milhhter DO bottles were used for condi- 

 tions 1-3 and 300 mL DO bottles for condition 4. 

 The bottles were set in a black container filled 

 with seawater. Each bottle contained 5-30 lar- 

 vae depending on larval and bottle size. Three to 

 five replicates with control blanks (containing 

 rotifers in condition 4) were carried out for each 

 age and condition at 6.2 ± 0.1(SD)°C. Light 

 intensity at the top of bottles was 6-9 jj-E/s/m^ 

 during the light period. 



The value for M^e used here may be larger 

 than that of other studies that use anesthetized 

 larvae (HoUiday et al. 1964; de Silva and Tytler 

 1973; Davenport and Lonning 1980; de Silva et 

 al. 1986), as larvae normally move at night, even 

 though at a much reduced level (Batty 1987). 

 However, our method ehminates possible biases 

 involved with the use of anesthetics. The active 

 metabolism (Af„) was probably underestimated 

 owing to restricted activity and feeding in 300 

 mL bottles, and to effects of handling. Re- 

 stricted feeding in DO bottles was evidenced by 

 the lower number of ingested rotifers in guts at 

 the end of experiments compared with the num- 

 ber of ingested rotifers in the guts of larvae in 

 the 120 L tank. 



Energy Budget 



Energy budgets (in calories per day) were de- 

 termined for feeding larvae from 7 to 21 days 

 fi'om posthatching using the equation: 



I = G + M + E 



where / = ingestion, G = growth, M = metabo- 

 hsm, E = nitrogenous and fecal excretions. Ex- 

 cretion was not measured, but the total loss of 



527 



