TUCKER: ANCHOVY AND SEA BASS ENERGETICS 



pies). Total lipid content of five sea bass samples 

 (triplicate subsamples) was estimated by the sulpho- 

 phosphovanillin technique (Barnes and Blackstock 

 1973) using a cholesterol standard. Caloric content 

 of 7-10 h old anchovy eggs and 1-4 h old sea bass 

 eggs (5-12 mg subsamples of five samples for each 

 species— anchovies: 1 or 2 replicates, 8 determina- 

 tions; sea bass: 3 replicates, 15 determinations) was 

 determined by combustion in an oxygen microbomb 

 calorimeter calibrated with benzoic acid. 



Caloric content of larvae was estimated using in- 

 formation on the proportions of protein, lipid, carbo- 

 hydrate, and ash in larvae. Percent protein was 

 calculated as the product of percent nitrogen and 

 6.025 (Brett and Groves 1979). Because of sample 

 shortages, the following assumptions were made: 

 1) Black sea bass carbohydrate content was esti- 

 mated by subtracting % protein, % total lipid, and 

 % ash from 100%. 2) Bay anchovy carbohydrate 

 content was assumed to be the same as that esti- 

 mated for black sea bass 7 h eggs, 28 h eggs, 150 

 h unfed larvae, and 249 h fed larvae. 3) Starving 

 anchovy % ash was assumed to be the same as for 

 fed anchovy larvae. 4) Total lipid content for an- 

 chovies at four stages was estimated by subtract- 

 ing % protein, % carbohydrate, and % ash from 

 100%. The effect of these assumptions on estimated 

 caloric values is minimal because of the small per- 

 centages involved; protein is the predominant con- 

 stituent. The average energy equivalents for heat 

 of combustion were used for conversion of weight 

 to energy: 5,650 cal/g protein, 8,660 cal/g lipid, 

 and 4,100 cal/g carbohydrate (Brett and Groves 

 1979). 



Oxygen uptake was measured with glass capillary 

 differential microrespirometers (Microchemical Spe- 

 cialties Company), calibrated by the potassium ferri- 

 cyanide-hydrazine sulfate method (Umbreit et al. 

 1972). The experimental technique was similar to 

 that described by Grunbaum et al. (1955). The ex- 

 perimental and reference flasks each held 0.65 mL 

 of air, a potassium hydroxide saturated filter paper 

 strip for absorption of carbon dioxide, and 0.35 mL 

 of 0.2 txm filtered seawater. Salinity was 32.0"/ofi 

 for anchovies and 34.3"/o(i for sea bass. Tempera- 

 ture was maintained at 24.0 + 0.05°C for anchovies 

 and 20.0 + 0.05°C for sea bass in a water bath. 

 Fluorescent lighting provided 300 lux. Slight agita- 

 tion was provided by the flow of water in the bath. 

 One to six eggs or larvae (number decreasing with 

 age) were placed in each experimental flask. The fish 

 were allowed to adjust for 10-60 minutes, depend- 

 ing on age; the index droplet was stable after 10 

 minutes, but time was increased to allow for initial- 



ly greater activity of older larvae to subside after 

 confinement. Measurements were made at all times 

 of the day. To ensure that digestion was essentially 

 complete, measurements with fed larvae began 

 more than 2 hours after feeding had ceased. (Diges- 

 tion time for larger bay anchovy larvae was 1.5 

 hours; digestion in sea bream up to 100 pig was 

 almost finished by 2.5 hours; Houde and Schekter 

 1983.) Oxygen consumption was recorded hourly for 

 periods of 3-9 hours (usually 6 hours). The longest 

 that larvae normally would have to go without food 

 is the length of the dark period (10 hours for an- 

 chovies and 12 hours for sea bass). Also, when there 

 is light, larvae expect to eat. Therefore, the mea- 

 surement period for fed larvae was limited to 7 

 hours. Regression equations relating oxygen uptake 

 to age were fitted. Metabolic energy (energy budget 

 term M) was estimated from oxygen uptake with 

 oxycalorific equivalents 0.00425 cal/pL oxygen for 

 anchovies (24°C) and 0.00431 cal/j^L oxygen for sea 

 bass (20 °C). Because movement of larvae in the 

 flasks was restricted and feeding larvae normally 

 were much more active (chasing rotifers) than 

 nonfeeding larvae, the resulting total metabolism 

 values were multiplied by the factor two for lighted 

 periods for fed larvae (14 h/d for anchovies and 12 

 h/d for sea bass). This is the same procedure followed 

 by Houde and Schekter (1983). 



Feeding observations were made in the 10 L rear- 

 ing tanks without handling or otherwise disturbing 

 the larvae. Numbers observed were 160 anchovies, 

 20 for each day of feeding; 128 sea bass, 5 the day 

 before first feeding, and 10-20 for each day of feed- 

 ing. Individual larvae were observed for 10 minutes. 

 The number of prestrike flexes, strikes, and suc- 

 cessful strikes were recorded and the following 

 ratios were calculated: 1) successful strikes/flexes, 

 2) successful strikes/total strikes, and 3) strikes/ 

 flexes. Successful strikes/total strikes is referred to 

 as capture success. Feeding incidence is the per- 

 centage of larvae that captured prey within 10 min- 

 utes. Number of rotifers eaten per day was calcu- 

 lated from the mean of observed 10 min feeding 

 rates for each feeding day. Daily ingestion values 

 (energy budget term I) were calculated with the fac- 

 tor 0.000787 cal/rotifer (Theilacker and McMaster 

 1971). Weight-specific daily ration was calculated 

 using 0.16 )jg/rotifer (best available estimate, from 

 Theilacker and McMaster 1971) and predicted lar- 

 val weights. Energy-specific daily ration was cal- 

 culated from ingestion estimates and estimates of 

 body energy in calorie per individual. Weight of wild 

 zooplankton provided to first feeding bay anchovies 

 by Houde and Schekter (1983) averaged 0.15 ugl 



281 



