FISHERY BULLETIN: VOL. 78, NO. 3 



100 



I 



o 

 E 



E 

 o 



20 



40 60 



Time — h 



100 



Figure 6. — Percentage cumulative mortality of northern an- 

 chovy larvae continuously exposed to copper during test II: num- 

 bers next to curves are the exposure concentrations in /ng Cu/1. 



of larval exposure. During exposures >200 fxg 

 Cu/1, synergism between copper toxicity and star- 

 vation may have played a role in the mortality and 

 the shape of the 277 and 289 /xg Cu/1 mortality 

 curves (Figures 5, 6) may show this effect. 



No obvious abnormalities were noted in the dead 

 larvae. Before death, larvae tended to sink to the 

 bottom of the exposure chambers and often exhib- 

 ited head shaking movements and whip 

 movements in which head and tail met. 



Examples of the cumulative mortality data used 

 to calculate LCg^ values and to generate the toxic- 



ity curves (Figure 7) are given in Tables 1 and 3. 

 Chi-square values for embryo cumulative mortal- 

 ity curves at every observation time were signifi- 

 cant. This variation from the logit model may pos- 

 sibly be due to changes in copper sensitivity as the 

 embryos developed. Chi-square values for larval 

 cumulative mortality curves at different observa- 

 tion times indicate a better fit to the logit model. 

 The embryonic and larval toxicity curves reflect 

 several developmental changes in sensitivity 

 (Figure 7). A slight increase in copper sensitivity 

 can be seen in the embryos during hatching. When 

 we estimated the embryo ILC^q, we considered 

 only mortalities before hatching. For embryos, the 

 estimated ILC50 was found to be 190 /xg Cu/1, and 

 was reached approximately 24 h after the start, of 

 copper exposure. The sudden increase in mortality 

 of the larvae at about 40 h probably was the result 

 of starvation. Only mortalities before this time 

 were considered in the larval estimated I LC^^ . The 

 ILC50 for the northern anchovy larvae was found 

 to be higher than for embryos: 370 /xg Cu/1 copper, 

 and was reached about 32 h after the start of 

 copper exposure. The estimated 24-h LC50 was 398 

 /xgCu/1. 



DISCUSSION 



We found the embryonic stage of the northern 

 anchovy to be more sensitive to copper than the 

 larval stage. This is in keeping with the majority 



200 



J J Period of 

 J_ f yolk sac 

 absorption 



1 

 100 



Figure 7.— Toxicity curves fornothem 

 anchovy embryos and larvae con- 

 tinuously exposed to copper. 



200 



500 



800 



jug Cu/C 



680 



