lity rate in the simulated Lake Michigan exposures (Ix) ranged from 2.2 to 

 3.9%, that in the 5x exposures ranged from 3.5 to 5.9%, and that in the 25x 

 exposures ranged from 7.5 to 24.2%. The mortality rate of control fry 

 (7.3%) was higher during this period than that of fry in the Ix or 5x expo- 

 sures. 



During the second 40-day period (days 57-96), which began about 2 weeks 

 after completion of yolk absorption, mortality of fry increased signifi- 

 cantly (P^<0.01) in both the exposed and control groups. This increase was 

 most dramatic, however, among the exposed groups of fry. Mortality rates 

 for all nine exposed groups during this period (19.0 to 35.4%) were signi- 

 ficantly higher (P <0.01) than in the controls (11.2%). By the end of the 

 third 40-day period (days 97-136), the rates of mortality decreased in all 

 treatments when compared with the previous period but mortality rates in all 

 nine exposed groups (4.5 to 13.4%) nevertheless remained significantly 

 higher (P <0.01) than in the controls (1.3%). Mortality rates further 

 leveled off during the fourth 40-day period (days 137-175), but the final 

 cumulative mortality for each of the nine exposed groups was significantly 

 higher (£ <0.01) than that for the controls. The average total cumulative 

 mortality on day 176 in each of the exposed groups ranged from 30.5 to 

 46.5%, whereas that in the control group was only 21.7%. 



Especially noteworthy was the final cumulative mortality of fry in the 

 Ix combination exposure of PCBs and DDE (simulated Lake Michigan exposure) — 

 40.7% or nearly double the final cumulative mortality of the controls (Fi- 

 gure 2). This result suggests that if lake trout in Lake Michigan spawned 

 successfully and their eggs hatched, nearly twice as many of the resulting 

 fry would die within the first 6 months than would have died if these con- 

 taminants had not been present. In nearshore areas, where contaminant 

 levels are generally higher, the potential impact on fry mortality would be 

 expected to increase. At the highest combined level of PCBs and DDE tested 

 (25x), 46.5% of the fry died. 



PHYSIOLOGY OF FRY 



In addition to observations on the mortality of fry during the chronic 

 exposure, observations were made periodically on the growth, swimming per- 

 formance, predator avoidance, temperature preference, and metabolism of the 

 fry. In general, the exposed fry showed no significant physiological 

 effects attributable to the exposure. Although occasional differences were 

 noted in the swimming performance and in certain metabolic measurements such 

 as oxygen consumption rates and whole-body lactate concentrations after 

 swimming, the results were inconclusive because the variability of the data 

 was high. Procedural difficulties prevented the testing of temperature pre- 

 ference at the Ix and 5x exposures; nevertheless, fry exposed to 25x DDE and 

 25x DDE and PCBs in combination for 4 months preferred significantly lower 

 (P^ <0.05) temperatures (9.8 C and 8.7 C, respectively) than did the controls 

 (11.2 C). Because of the inconclusiveness of the observations on the 

 general condition or performance of the fry, together with the inherent dif- 

 ficulty of interpreting the impact of these sublethal effects on the pro- 



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