RICE and HARRISON: COPPER SENSITIVITY OF PACIFIC HERRING 



The toxicity curve for herring embryos is pre- 

 sented for the purpose of discussion only, since the 

 90 h delay until the onset of mortality, regardless 

 of concentration, biases the toxicity curve for com- 

 parison with other organisms without a reaction 

 period. Sprague (1969) recommended that a con- 

 centration that killed SO^r of the population dur- 

 ing an exposure sufficiently long that acute lethal 

 action has ceased (incipient LC50) be used as the 

 single most useful criterion for toxicity. The inci- 

 pient LC50 is not influenced by the bias introduced 

 by the reaction period. The estimated incipient 

 lethal level for herring embryos was found to be 33 

 /xg/1 copper. 



Only larval deaths earlier than 100 h after 

 hatching were considered in the construction of 

 the larval toxicity curve since larvae surviving 

 beyond approximately 200 h after hatching have 

 begun yolk sac absorption, and the apparently 

 synergistic effects of copper stress and starvation 

 can be observed in the larval time vs. percent 

 mortality curves (Figure 4). The estimated incip- 

 ient lethal level for herring larvae was found to 

 be 900 /xg/1 copper. 



Thirty-six Hour Pulsed Embryo Exposures 



Pulses of copper exposure for 36 h showed that 

 the sensitivity of herring embryos to copper 



100 



changed as the embryos developed (Figure 6, 

 Table 1). A 36-h pulse of 100 /xg/l copper delivered 

 during the reaction period (Pulse I) had the 

 greatest effect upon hatching and the length of 

 larvae at hatching (Table 3). A 36-h pulse of 100 

 fxg/\ copper delivered just before hatching (Pulse 

 III) had a signficant effect on larval length at 

 hatching, but the percentage of embryos hatching 

 was actually greater than controls. 



Table 3. — Percent Pacific herring embryos hatching and mean 

 larval length at hatching for three groups of Pacific herring 

 embryos exposed to 36-h pulses of 100 /ng/1 copper. Each group 

 received a pulse at a different time during development. 



•Significantly different from controls (P<0.01) (Snedecor and Cochran 

 1967). 



DISCUSSION 



Several features of the toxic response of herring 

 at various stages of their early life history are of 

 interest. Previous tests examining the sensitivity 

 of other fish embryos and larvae to copper have 

 found that the larval stage is the more sensitive 

 stage (Hazel and Meith 1970; McKim and Benoit 

 1971, O'Rear 1972; Gardner and La Roche 1973; 



c 

 a; 

 o 



0) 

 Q. 



80 - 



> 60 - 



(0 

 •M 



L. 



o 



E 



> 



JO 



Z3 



E 



D 



o 



40 



20 - 







40 



80 120 160 



Hours from fertilization 



200 



Figure 6. — Percent cumulative mor- 

 tality of three groups of Pacific herring 

 embryos exposed to 36-h pulses of 100 

 /j.g/1 copper. Each group received a pulse 

 at a different time during development. 

 The cumulative mortality observed for 

 Pacific herring embryos continuously 

 exposed to 100 /xg/l copper (See Figure 

 3) is shown for comparison. 



Pulse 

 I 



Pulse 



Pulse 



353 



