FISHERY BULLETIN: VOL. 85, NO. 2 



copepod diets with those in a study by Hunter (1976) 

 where northern anchovy were fed Brachionus, 

 50-100/mL, and copepods, Tisbe 0.01/mL, at 17°C 

 and Gymnodinium was fed as the first food. The 

 curves show that among experiments there appear 

 to be diet-induced differences in weight at length 

 (Fig. 3). 



Metabolism 



The caloric equivalent of metabolism for northern 

 anchovy larvae ranging in age from first feeding to 

 25 days was determined using the relation between 

 the metabolic rate and fresh dry weight (Model 2, 

 Table 5) and by converting the oxygen uptake to 

 calories using an oxycalorific equivalent of 0.00463 

 cal/f.<L O9 (Brett and Groves 1979). I assume the 

 metabolic rate approximates "routine" metabolism. 



200 



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 > 



o 



O 80 



z 

 < 



60 - 



40 



4 5 6 7 8 9 



STANDARD LENGTH (mm) 



Figure 3.— Relation between dry weight and standard length for 

 northern anchovy fed several diets where Gymnodinium was the 

 first food. 



I also determined the caloric equivalent of metab- 

 olism for first-feeding northern anchovy by starving 

 them, determining the weight loss, and converting 

 the loss to calories. Starving larvae lost an average 

 of 10% of their body weight per day for 3 days, after 

 which larvae must have continued to lose weight, 

 but no decrease could be measured (Fig. 4). The time 

 to maximum weight loss was 3-4 days, the time of 

 irreversible starvation for northern anchovy from 

 the onset of feeding (Lasker et al. 1970; Theilacker 

 and Dorsey 1980). Larvae that weighed an average 

 of 0.0211 mg at 3 days of age weighed an average 

 of 0.0148 mg on day 6. The weight loss (0.0063 mg) 

 X 5.4 cal/mg, which is the assumed caloric equiv- 

 alent for northern anchovy tissue, equals 0.0339 

 calories, or a metabolic demand of 0.011 cal/day. 

 This value, determined at a slightly lower temper- 

 ature, corresponds well with the value obtained for 

 first-feeding northern anchovy weighing 0.0211 mg 

 using respiration measurements (0.013 cal/day). 



Evacuation Rates 



Gut clearance times for northern anchovy larvae 

 appeared to be independent of larval age; however, 

 the weight of food evacuated per hour increased 

 with age because the stomach contents increased. 

 Because the larvae fed at a constant rate after the 

 gut was filled and defecated continuously, the gut 

 clearance rate for actively feeding northern anchovy 

 larvae was constant. The average gut clearance time 

 for anchovy feeding on 25 rotifers/mL was 1.15 

 hours (SE = 0.13; range 0.7-1.5 hours; n = 6 tests). 

 Reducing the prey density to 2/mL increased the 

 average gut clearance time to 1.5 hours (range 1.2- 

 1.8 hours; n = 2 tests) for the rotifer diet and 2.73 

 hours (SE = 0.26; range 2.0-3.3 hours; n = 4 tests) 

 for the copepod diet. 



Nonfeeding northern anchovy cleared their guts 

 in 2.8-5.8 hours, depending on their size and stomach 

 capacity (2.8 h/4.8 mm; 4 h/6.3 mm; 5 h/7.9 mm; 5.8 

 h/8.5 mm). 



Daily Consumption of Rotifers 

 and Growth Efficiency 



Daily consumption was less on the low-density diet 

 and, as a percent of body weight eaten per day, con- 

 sumption ranged between 31 and 86%, depending 

 on prey concentration and fish size (Tables 10, 11). 

 For both rotifer diets, weight-specific consump- 

 tion decreased with increasing body weight (Fig. 

 5). 



Gross growth efficiencies were higher for north- 



220 



