Effects of Age and Coion (K+and Na+) on the Toxicity of Thiocyanate to Rainbow Trout (Oncorhynchus mykiss) during Pulse or Continuous Exposure

Thiocyanate (SCN−) is released to the aquatic environment as a result of the treatment of cyanide-bearing wastes from precious-metal mining activity. During continuous exposure alevin rainbow trout (1- and 10-day-old) were approximately 90% more tolerant of SCN−than juveniles (2-month-old). Pulse exposure of alevins for periods greater-or-equal, slanted48 hr were required before postexposure stress reduced tolerance (by not, vert, similar30%) in the 24-hr period following exposure. In contrast, stressing of juveniles after exposures of greater-or-equal, slanted9 hr consistently reduced tolerance by not, vert, similar60%. While coion (K+or Na+for SCN−derived from either KSCN or NaSCN) had no influence on SCN−toxicity for alevins, juveniles exhibited reduced tolerance in the presence on Na+. Although sudden death syndrome was apparent in juveniles, none occurred with alevins. Overall, juveniles were less tolerant of SCN−than alevins, possibly because of the enhanced efficiency of SCN−uptake by gill respiration versus the predominantly vitelline membrane respiration of alevins.