Effects of Low pH on Eyed Embryos and Alevins of Pacific Salmon

Abstract

Ten-day bioassays were conducted to assess the sensitivity of eyed embryos, newly hatched alevins, and buttoned-up alevins of coho (Oncorhynchus kisutch), chinook (O. tshawytscha), sockeye (O. nerka), pink (O. gorbuscha), and chum (O. keta) salmon to low pH. Acid sensitivity varied significantly both with stage of development and with species. The various stages and species were ranked in order of decreasing sensitivity to low pH on the basis of significant differences (P < 0.05) in 10-d LC50 values. Stage sensitivities (10-d LC50 pH range) were ranked buttoned-up alevins (4.4–5.2) > newly hatched alevins (4.4–4.9) > eyed embryos (3.6–4.0) for all species except coho. Coho were more sensitive as newly hatched alevins than near button-up. Species sensitivities were ranked (chum, pink) > sockeye > chinook > coho for eyed embryos, coho > (chinook, sockeye) > (pink, chum) for newly hatched alevins, and (chum, pink, sockeye) > chinook > coho for buttoned-up alevins. Ten-day LC10s for eyed embryos ranged from pH 3.82 for chinook to pH 4.18 for chum. LC10s for the most sensitive alevin stage of each species ranged from pH 5.01 for coho to pH 5.74 for chum. Incipient lethal levels could not be estimated for any stage or species because no toxicity curves approached a pH threshold during the test period. Aberrant behavior was noted in buttoned-up alevins of pink and chum exposed to pH 6.0–6.1 but not in other species at levels above those causing acute mortality.