RICE and HARRISON: COPPER SENSITIVITY OF PACIFIC HERRING 



was greater than that of the tubing to reduce the 

 flow velocity at the mouth of the siphon. The 

 mouth of the siphon was covered with nylon net- 

 ting (505-)U,m pore size) to prevent the loss of or- 

 ganisms from the chamber. A gentle stream of 

 bubbles delivered to the bottom of the chamber 

 provided aeration and mixing. All exposure 

 chambers were immersed in a water bath whose 

 temperature was monitored. Illumination was 

 provided by the fluorescent lighting in the 

 laboratory and followed the regular ambient 

 photoperiod. 



The exposure period, the nominal copper con- 

 centration, and the total number of embryos or 

 larvae exposed during a typical experiment are 

 given in Table 1 . Each experiment was repeated at 

 least once. All exposures were initiated by the 

 addition of appropriate amounts of copper chloride 

 to the chambers. The continuous exposure of the 

 test organisms continued until all animals died or, 

 in the case of embryos, until hatching occurred or, 

 in the case of the larvae, until yolk sac absorption 

 occurred. The pulsed exposures were terminated 

 by transferring exposed embryos to an exposure 

 chamber containing control seawater. 



The following measurements were taken as in- 

 dices of the toxic effect of copper: cumulative mor- 

 tality with time, percent hatching, and larval 

 length at hatching. The embryos or larvae were 

 examined within the exposure chambers at each 

 observation period with a 7 x beam dissection mi- 

 croscope with a 21-cm depth of field. The criterion 

 for embryo death was the lack of heart beat or body 

 movement. Since the embryos were attached in 

 clusters, dead embryos were not removed until the 

 termination of a test. Larvae that hatched from 

 pulse exposed embryos were collected, anes- 

 thesized with a 1% quinaldine solution, and pre- 

 served in 5% Formalin^ in seawater. Measure- 

 ments of the hatched larvae were made with an 

 ocular micrometer and all obvious deformities 

 noted. The criterion for larval death was a failure 

 to respond to a gentle prod with a polished glass 

 rod. Dead larvae were removed during each obser- 

 vation period and preserved in 5% Formalin in 

 seawater. 



Total copper concentrations were measured two 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Table l. — Experimental conditions and median lethal times for bioassays determining the sensitivity of Pacific herring embryos 



and larvae to copper. 



'50% mortality not achieved at this concentration. 



2Slope significantly different from control slope (P<0.01) (Snedecor and Cochran 1967). 

 ^Slope significantly different from control slope (P<0.05) (Snedecor and Cochran 1967). 

 •"Determined according to the method of Litchfield and Wilcoxon (1949). 



349 



