VLYMEN; SWIMMING ENERGETICS OF THE LARVAL ANCHOVY 



however, depends on incorporating what actually 

 occurs into an easily manipulated theoretical 

 energy construct. 



Although the point of this study is to evaluate 

 the swimming energetics in an indirect but non- 

 manometric manner, it is nevertheless interest- 

 ing to compare the calculated energy using the 

 theoretical model wdth values obtained using O2 

 consumption measurements obtained with an- 

 chovy larvae. Such experiments in limited num- 

 bers have been performed by Lasker (pers. com- 

 mun.) using more than one larva per experiment 

 and with the animals confined to small volume 

 containers. No knowledge of activity levels was 

 possible during these experiments and the values 

 obtained reflect total O2 uptake per experimental 

 period averaged for the number of larvae per con- 

 tainer. Lasker believes, however, that activity 

 levels during such experiments are below natural 

 levels because of the inhibiting effects of the con- 

 tainer surfaces and crowding. The value obtained 

 from such experiments was 4.36 ± 1.05 A/lOa/mg 

 dry wt/h. Assuming an RQ of 0.70 we get 1 ^il O2 

 = 0.005 cal ± 0.00035 (Lasker, 1962). Thus, the 

 caloric equivalent of the anchovy larval respira- 

 tory rate is between 0.0153 cal/mg dry wt/h and 

 0.0289 cal/mg dry wt/h with a mean value of 

 0.0218 cal/mg/h {n = 23). A comparison between 

 the theoretically determined energy value and the 

 mean O2 uptake value given above requires a 

 simultaneous knowledge of swimming activity 

 expressed as an excursion frequency. Such infor- 

 mation is not available and it is precisely our 

 inability to make simultaneous observations of O2 

 consumption and activity offish larvae that neces- 

 sitates the type of study undertaken in this paper. 

 Excursion rates observed during 5-min feeding- 

 searching periods have been measured (Hunter, 

 1972) using large containers. For the periods ob- 

 served the excursion rate appropriate to a 1.4-cm 

 larvae was found to be 1.57 ± 0.03 excursions/s 

 with the mean time devoted to intermittent 

 swimming being 82.6% ± 1.2% . This value is prob- 

 ably a maximum for activity since satiation would 

 probably lead to a decrease in excursions as would 

 the lack of observable food particles. Since avail- 

 able O2 measurements were not collected during 

 feeding, some modification of the above activity 

 value has to be made to compensate for the inhibi- 

 tion of the container and the absence of food before 

 these values can be used for comparison. 



The O2 consumption measurements of anchovy 

 larvae were performed in small 70-ml containers 



in light and darkness. The only relative activity 

 measurements that have been performed for simi- 

 lar situations were on 28-day-old herring larvae 

 ca. 1 cm in length in a variety of light conditions by 

 Blaxter (1973). Although herring are continuous 

 swimmers, unlike anchovy larvae, the use of rela- 

 tive activities was deemed an appropriate way of 

 estimating the activity variation of a similar sized 

 nonfeeding organism in the following manner. For 

 herring larvae at 10 different light levels the 

 mean percent difference between maximum and 

 mimimum activity levels was found by Blaxter 

 (1973) to be 78.6%, maximum activity being 

 defined as mean activity plus two standard errors 

 and minimum activity as mean activity minus two 

 standard errors. Although this change is large, it 

 probably reflects behavioral modulation more 

 than effects of the container since in Blaxter's 

 experiment the container (a long tube) contained 

 approximately 1,500 ml of seawater. Thus, re- 

 garding the O2 consumption experiments on the 

 anchovy as repiesenting the minimum activity 

 levels of that organism in the same relationship of 

 active to inactive as found from Blaxter ( 1973), we 

 can, using known maximum excursion rates dur- 

 ing feeding from Hunter (1972), calculate the 

 minimum excursion rate or activity correspond- 

 ing to our O2 measurements and hence the energy 

 consumption for swimming based on that excur- 

 sion rate. This analysis assumes the geometric 

 swimming behavior during feeding and nonfeed- 

 ing is the same, an assumption confirmed by ob- 

 servation. 



Using the mean O2 consumption value 0.0218 

 cal/mg dry wt/h and the dry weight of a 1.4-cm 

 larva from Lasker et al. (1970) we get an expendi- 

 ture of 22.6 X 10' cal/h. Taking 1.57 excursions/s 

 as the mean maximum activity value, decreased 

 by 78.6% to convert to minimum activity levels, 

 and multiplied by the theoretically determined 

 energy per excursion of the 1.4-cm larva of 144.8 

 ergs/excursion, we get 4.91 x 10 cal/h. This value 

 yields an estimate of metabolic swimming 

 efficiency of 24.6% for the 1.4-cm larval anchovy 

 assuming a poikilothermic basal metabolic rate of 

 0.05 iu\ Og/mg wet wt/h. This efficiency is quite 

 high when compared to valiles obtained for larger 

 fish where efficiencies in the range of 8 to 15% 

 (Webb, 1971) are observed. However, such exper- 

 iments are usually done on large fish constrained 

 by relatively small tanks, swimming continu- 

 ously, and using a caudal propeller mode of pro- 

 pulsion. Thus any comparison of the above results 



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