FISH ACCLIMATION AND THE DEVELOPMENT OF TOLERANCE TO ZINC AS A MODIFYING FACTOR IN TOXICITY (SALMO GAIRDNERI, STEELHEAD)

Acclimation of juvenile steelhead (S. gairdneri gairdneri) and rainbow (Salmo gairdneri) trout to sublethal concentrations of zinc resulted in significant increases in tolerance to zinc. When steelhead were acclimated to 50 (mu)gl('-1) zinc (0.37 of the 96-hr LC50 and 0.80 of the 96-hr LC10), for 1, 2 and 3 weeks, up to 4-fold increase in tolerance was developed. Treatment of rainbow trout in a similar manner at 80 (mu)gl('-1) zinc (0.38 of the 96-hr LC50 and 0.60 of the 96-hr LC10) for 3, 7, 21 and 28 days resulted in approximately 3-fold increase. Acclimation to sequentially increasing non-lethal concentrations of zinc increased the 96-hr LC50 by a factor of 5. Zinc exposure of rainbow trout at 100 (mu)gl('-1) (0.42 of the 96-hr LC50 and 0.86 96-hr LC10) for 17 days developed cross tolerance to cadmium and copper in addition to zinc. Cadmium and copper tolerances increased by factors of approximately 4 and 5, respectively.; Development of tolerance to zinc was dependent on the time and concentrations of metal used during acclimation. The greatest increase in the steelhead acclimation occurred by the 7th day and no further increases occurred as a result of the extension of duration of acclimation. Acclimation of rainbow trout for periods less than 3 days indicated that acclimation had not occurred in the first 3 days, while by the 7th day, increases above 2-fold had occurred. Significantly greater increases in the lethal levels did not occur with further increases in acclimation time to 21 and 28 days. Rainbow trout acclimated to 100 (mu)gl('-1) of zinc for 10 days had increased tolerance to zinc of approximately equal magnitude to those acclimated sequentially to 300 and 500 (mu)gl('-1) of zinc.; Zinc tolerance in rainbow trout was lost soon following cessation of zinc exposure. Deacclimation of the sequentially acclimated rainbow trout resulted in a nearly total loss of acclimation by the 7th day. By the 3rd day of deacclimation tolerance was still retained to the order of 4-fold.; The low molecular weight metal binding soluble hepatoprotein (metallothionein: MT) is known to be involved in metal detoxification. Estimation of MT induction during acclimation of rainbow trout showed a 22 percent increase over the unacclimated fish. A 67 percent average increase occurred in the sequentially acclimated trout. At cessation of acclimation, MT levels gradually decreased and by the 7th day were the same as the controls. Views on the possible involvement of MT in metal cotolerance are expressed, while results strongly suggest the non-metal specificity of MT.