WEIHS: RESPIRATION AND DEPTH CONTROL W ENGRAUUS MORDAX 



This prediction has now to be compared with the 

 requirements of the organisms to determine if ad- 

 ditional oxygen is needed. Data for oxygen con- 

 sumption at 17° C of late-stage anchovy eggs and 

 larvae of differing ages as a function of time since 

 spawning has been obtained by Theilacker,^ by 

 measurement in a respirometer. These data were 

 adjusted to 20° C, the temperature at which most 

 of my experiments were conducted (Figure 5), by 

 means of a temperature-growth correlation for 

 larval northern anchovy (Zweifel and Hunter^). 

 This adjustment was made by calculating the size 

 of the larvae at 17° C at the ages recorded by 

 Theilacker, then translating these into age for the 

 same size at the new temperature, which gave a 

 smaller size because growth rates increase with 

 temperature. Thus, an estimate for the oxygen 

 requirements at 20° C of size-defined larvae was 

 obtained as a function of their age ( the 20° C line in 

 Figure 5). 



The value of the ratio of oxygen consumption 1 d 

 after hatching to that at hatching was about 1.6 

 (Figure 5). Returning now to Figure 3 we see that 

 the ratio for the average percent of time spent 

 swimming of the two age-groups is approximately 

 1.66. I conclude, therefore, that the distance be- 

 tween the day and day 1 curves in Figure 3 is an 

 indication of the increased general activity of the 

 larvae as they grow. This correlation indicated in 

 Figures 3 and 5 serves as an additional verifica- 

 tion of both Theilacker's respirometer data and 

 the present swimming data. 



To compare experimental values of oxygen con- 

 sumption to the prediction of the model we plot the 

 data as Figure 6, where the horizontal lines show 

 the range of oxygen requirements (from Theilack- 

 er's data) at hatching and 24 h later. The steady- 

 state oxygen available by steady-state diffusion 

 only (after the initial transient) obtained from the 

 time-dependent first term in Equation ( 12) is now 

 superimposed. Figure 6 indicates that pure diffu- 

 sion supplies all the oxygen required for the day 

 larvae only when <42±47f of the O2 saturation 

 concentration is available. This changes to 63 ± 4% 

 of saturation for the day 1 larvae. The sharp dis- 

 continuity in the swimming data, occurring be- 



0.61- 



^G. Theilacker, Fishery Biologist, Southwest Fisheries Center 

 La Jolla Laboratory, National Marine Fisheries Service, NOAA, 

 La Jolla, CA 92030, pers. commun. November 1978. 



"Zweifel, J. R., and J. R. Hunter. 1978. Temperature 

 specific equations for grovrth and development of anchovy (En- 

 graulis mordax) during embryonic and larval stages. Unpubl. 

 manuscr. , 37 p. Southwest Fisheries Center La Jolla Laboratory, 

 National Marine Fisheries Service, NOAA, La Jolla, CA 92038. 



0.5 



0.4 



0.3 



0.2 



0.1 



/ 



/ / 



20»C / / 



/ / 



// 



/ / 17 'C 



/ 



/ 

 / 



/ 



/ /X"" Hatching 



).ol \ L 



2 4 6 8 10 12 



DAYS 



14 



Figure 5. — Oxygen consumption by northern anchovy eggs and 

 larvae versus time elapsed since spawning. Open circles indicate 

 experimental data for 17° C. The line for 20" C is extrapolated 

 from the 17^ C data with the aid of the Zweifel and Himter model 



(see text). 



s[o,] 



Figure 6. — Estimated oxygen requirements (J^) of northern 

 anchovy larvae at day (hatching) and day 1, and steady-state 

 oxygen supply by diffusion versus oxygen in percentage of sat- 

 uration concentration (S[02]). The triangle and circle denote 

 concentrations at which observed swimming behavior changes 

 at day and day 1, respectively (see Figure 3). 



115 



