TUCKER: ANCHO\T AND SEA BASS ENERGETICS 



0.066 fiL/h/yolk-sac larva, at 26°C, two degrees 

 higher. 



Sea bass were more active, were more efficient 

 feeders, and spent more time feeding than anchovies 

 (Fig. 5). Sea bass also were more capable predators 

 from first feeding through the eighth feeding day. 

 At first feeding, sea bass were 2.5 days older and 

 were better developed than anchovies. Bay anchov- 

 ies in this study had about the same capture success 

 (Table 8) as bay anchovies and sea bream studied 

 by Houde and Schekter (1980). Black sea bass cap- 

 ture success was similar to that of lined sole. North- 

 ern anchovy larvae feeding on 10-60 BrachionusI 

 mL at 17°-18°C (Hunter 1972) were less successful 

 than bay anchovies in the present study, but they 

 struck more often and therefore consumed more 

 rotifers per hour. Northern anchovy capture success 

 was relatively low, ranging from 11% at first feed- 

 ing to 60% on feeding day 8. For 20 ng larvae, a 

 rate of about 50 strikes/h (Hunter and Thomas 1974) 

 multiplied by 39% capture success gives a feeding 

 rate of 20 rotifers/h vs. 13/h for bay anchovies and 

 16/h for black sea bass. 



Daily rations for bay anchovies and black sea bass 

 were intermediate among published estimates from 

 rearing studies using high larval and food densities 

 (Table 8). Theilacker and Dorsey (1980), in a review 

 article, reported weight-specific daily rations of 70- 

 300% for larvae fed one or more prey mer mL. 

 Houde and Schekter (1983) reported high weight or 

 calorie-specific daily rations of 202-379% for 10-100 

 ^ig bay anchovies fed 1 copepod nauplius/mL at 

 26°C. 



During the first 3 days of starvation, weight and 

 calorie loss were similar for both species; however, 

 sea bass conserved weight and calories better dur- 

 ing the late stages of starvation (Tables 5, 6, 7). Sea 

 bass also gained weight and calories faster when fed 

 (Table 7). Conservation probably resulted partly 

 from a rearing temperature four degrees lower and 

 partly from physiological differences. Better growth 

 probably resulted from a combination of more effi- 

 cient feeding, higher ingestion rate, lower temper- 

 ature, and different physiology. During the first 24 

 hours after EP, fed anchovies lost more weight and 

 calories than unfed anchovies (-0.015 vs. -0.008 

 cal). During the first 24 hours after EP, fed sea bass 

 lost about the same weight and calories as unfed sea 

 bass (-0.011 vs. - 0.010 cal). This impHes that an- 

 chovies at first lost more energy to feeding activity 

 than they gained from their food, while sea bass 

 broke even. 



Overall gross growth efficiencies (G/I) of 9% for 

 anchovies and 14% for sea bass were at the lower 



end of the known range for early larvae. Published 

 G/I values for larvae fed one or more prey per mL 

 are 11-46% (Theilacker and Dorsey 1980; Houde 

 and Schekter 1983; Theilacker 1987). The decrease 

 in sea bass gross growth efficiency after 4 days of 

 feeding (229 hours, Table 6) may be related to de- 

 creasing suitability of rotifers as food for sea bass 

 (Tucker 1984). After the first few days of feeding, 

 larval growth of both species probably would have 

 been enhanced by the addition of larger prey 

 (Hunter 1980). The effect of small prey on growth 

 may have been greater for sea bass, which have 

 larger mouths and probably can handle larger prey. 

 As a larva grows, the benefit:cost ratio for feeding 

 on constant energy food particles tends to decrease 

 (Theilacker and Dorsey 1980). This principle appears 

 to apply to sea bass, as suggested by reduced feed- 

 ing after the first two days and decreasing growth 

 efficiency after the fourth day. If, in nature, bene- 

 fit:cost (food energy:expended energy) drops close 

 to one, the rule of fast early growth is violated and 

 the larva is vulnerable to a given type of predator 

 for a longer time. 



Overall M/I values of 24% for anchovies and 28% 

 for sea bass were lower than Brett and Groves' 



(1979) average of 44% for typical, young, well-fed, 

 fast-growing carnivorous fish; however, M/I is likely 

 to be lower in larvae. One explanation for Houde 

 and Schekter's (1983) lower M/I for anchovies (Table 

 8) is the high ingestion rate. Hunter and Kimbrell 



(1980) estimated that 3-5 d old Pacific mackerel, 

 Scomber japonicus, use about 18% of ingested 

 calories for metabolism at 19°C. 



Overall coefficient of utilization (CU), which is 

 metabolizable energy expressed as a fraction of in- 

 gested energy, (G -i- M)/I, was slightly lower in an- 

 chovies (33%) than in sea bass (42%). The coefficient 

 of utilization for young fish has been estimated at 

 73% (G = 29%, M = 44%) by Brett and Groves 

 (1979) and 65-75% by Ware (1975). Ingested energy 

 unaccounted for by growth and metabolism, 67% for 

 anchovies and 58% for sea bass, was assumed to 

 have been egested or excreted, F&U/I. These values 

 are higher than Brett and Groves' (1979) mean of 

 27% for young fish, but similar to values for other 

 larvae. Larvae are not as efficient at using their food 

 energy as larger fish but do not need as much of it 

 for activity and maintenance. 



The energetics approach can be used to compare 

 adaptations to feeding environments. Although roti- 

 fers are not normally eaten in large quantities by 

 anchovies or sea bass in nature, the results of this 

 study are probably indicative of normal feeding ecol- 

 ogy, especially if larvae encounter patches of food 



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