Effects of an acute silver challenge on survival, silver distribution and ionoregulation within developing rainbow trout eggs (Oncorhynchus mykiss)

Rainbow trout eggs were acutely challenged with silver (as AgNO3) at differ ent stages of development from fertilization through to hatch in moderately hard water (120 mg CaCO3 1(-1), 0.70 mM (25 mg 1(-1)) Cl-, 1.3 mg 1(-1) DO C, 12.3 +/- 0.1 degreesC) at measured total silver concentrations of 0.11 /- 0.004, 1.55 +/- 0.15, and 14.15 +/- 1.52 mug 1(-1). Four separate acute challenges were conducted, each consisting of 5 days exposure to the respec tive silver concentration, followed by 4 days recovery after transfer to si lver-free water (series 1, 1-10 days post-fertilization; series 2, 8-17 day s post-fertilization; series 3, 16-25 days post-fertilization; series 4, 23 -32 days post-fertilization). Mortality was not significantly different fro m control during exposure to 0.11, 1.55, and 14.15 mug 1(-1) total silver i n series 2, 3 and 4 (mortality for series 1 data could not be calculated fo r technical reasons). In the four days of recovery following silver exposur e, however, there was significant mortality at 14.15 mug 1(-1) total silver reaching 100, 31 and 72% in series 2, 3 and 4, respectively, indicating eg gs are more sensitive in the period of 8-17 and 23-32 days post-fertilizati on at this temperature. Mortality following silver exposure was associated with ionoregulatory impairment in series 3 and 4, where up to 60% of whole egg [Na+] and [Cl-] was lost relative to controls at 14.15 mug 1(-1) total silver. Significant but smaller reductions in egg [Na+] and/or [Cl-] were a lso observed at 0.11 and 1.55 mug 1(-1) total silver. The greatest accumula tion of silver in whole eggs and chorions occurred in series 4, reaching co ncentrations of 0.53 mug g(-1) (eggs) and 15.5 mug g(-1) (chorions) in the 14.15 mug 1(-1) treatment. The accumulation of silver in the whole eggs and chorions of the 0.11 mug 1(-1) treatment was not different from controls t hroughout embryonic development. Of the total silver content, only a small proportion of silver was found in the embryos (1-17%), indicating that the chorion is a protective barrier during acute silver exposure. (C) 2000 Else vier Science B.V. All rights reserved.