We report delayed effects on the growth and marine survival of pink salmon Oncorhynchus gorbuscha, which were exposed to oil as embryos under conditions similar to those observed after the 'Exxon Valdez' oil spill. Pink salmon eggs were incubated in water that became contaminated with polynuclear aromatic hydrocarbons (PAHs) after percolating through gravel coated with weathered oil. Weathering ensured that the PAH composition of the water was dominated by alkyl-substituted naphthalenes and larger compounds. Most survivors of the exposures appeared healthy, and were released to the marine environment with coded-wire tags. Their survival was evaluated when they returned at maturity 2 yr later. Other survivors, also healthy in appearance, were retained in net pens to measure delayed effects on growth during the early juvenile stage. Pink salmon exposed to an initial concentration of total PAH equal to 5.4 ppb experienced a 15% decrease in marine survival compared to unexposed salmon. A delayed effect on growth was measured in juvenile salmon that survived embryonic exposure to doses as low as 18 ppb PAH. Reductions in juvenile growth could account for the reduced marine survival observed in the released fish. The demonstration of delayed effects on growth and survival support claims of delayed effects in pink salmon after the 'Exxon Valdez' oil spill, and indicate the potential for population-level effects resulting from embryonic exposure to oil. KEY WORDS: Exxon Valdez · PAH · Pink salmon · Toxicity testing · Oil pollution · Delayed effectsResale or republication not permitted without written consent of the publisher

Chinook salmon (Oncorhynchus tshawytscha) were reared at densities of 6.6–24.3 kg/ m3 and released as small (9.7–10.3 g) or large (28.2–31.8 g) smolts to determine the effects of fish size at release and rearing density on postrelease growth and adult return rate. Density did not affect survival during rearing, but mean weights for both size‐classes were significantly lower at the highest rearing densities (P < 0.05). Density and size at release affected adult return rates, which were lower for fish reared at high densities for both size‐classes. However, the increased number of smolts produced at higher densities compensated for the reduced return rates by yielding a higher number of returning adults per unit volume of rearing space. The estimated costs for each adult produced were US$11.10–12.00 for small smolts and $13.10–23.80 for large smolts. The lowest costs were projected at the second‐highest density (18.6 kg/m3) for small smolts and at the highest density (20.3 kg/m3) for large smolts.

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