Standard 96-hour bioassays with “total” oil solutions in fresh water and seawater determined differences in sensitivity of the developing life stages of pink salmon (Oncorhynchus gorbuscha). Eggs were the most resistant and emergent fry (yolk sac absorbed) the most sensitive to acute 4-day exposures. In fresh water, the 96-hour median tolerance limit (TLm) of fry was 0.4 ml oil/liter mixed mechanically (12 ppm as measured in subsurface water by infrared spectrophotometry). In seawater, it was 0.04 ml oil/liter mixed mechanically (6 ppm as measured in subsurface water by infrared spectrophotometry).
Three life stages of alevins were exposed to 10-day sublethal exposures of the water-soluble fraction to determine what doses might affect growth. Growth was affected most severely in alevins exposed during later developmental stages. Decreased growth was observed in fry after 10-day exposures at the lowest dose tested–0.015 ml oil/liter mixed by water agitation (0.73 ppm in subsurface water by infrared spectrophotometry–less than 10% of the 96-hour TLm limit for that life stage).
In fresh water, susceptibility of early life history stages of pink salmon to oil pollution is great at the time of emergence (completion of yolk absorption). Susceptibility is even greater in seawater after fry migration.