|Abstract or Summary
- The effects of sublethal concentrations of kraft mill effluents
(KME) on the growth, food consumption, and swimming ability of
juvenile chinook salmon, Oncorhynchus tschawytscha (Walbaum),
were studied from February 1966 to May, 1967.
The KME used in these studies was obtained from two pulp and
paper mills producing paper from unbleached pulp. Samples were
collected weekly during the experimental periods from settling
lagoons of mill A, and waste outfalls of mill B. Acute toxicity bioassays
of these wastes were performed periodically, and 96-hour
median tolerance limits (TL[subscript m]) were estimated for the salmon and for guppies (Poecilia reticulata Peters). Water and wastes were
introduced into 16 experimental chambers by a system of head boxes
and siphons. In each experiment, growth rates of salmon continuously
exposed to three waste concentrations and of controls were evaluated at four different feeding levels. The waste concentrations
were adjusted so as to provide for nearly constant increments of
biochemical oxygen demand (BOD). Tubificid worms were the food
organism in all experiments. The feeding levels employed ranged
from an unrestricted ration, through several restricted rations, to
The growth rates of salmon were found to be reduced at all
concentrations of KME from mill A (0.5 to 4.0 mg/liter BOD) when
the ration was unrestricted, and were reduced at all concentrations
with BOD increments greater than 0.5 mg/liter when the next lower
ration was fed. Some death occurred within 16 days at all feeding
levels at concentrations having a BOD increment of 4.0 mg/liter.
At low feeding levels, no consistent differences in growth attributable
to KME were observed. Dilutions of waste from mill B had
only small effects on the growth of chinook salmon.
Salmon held in clean water and fed worms which had been exposed
to KME from mill A showed only slight decreases in growth
rate, except when they were fed worms exposed to 100-percent effluent
which reduced the efficiency of food utilization considerably.
When salmon were exposed to two concentrations of KME from mill
A and then tested for swimming ability, no differences of maximum
sustained swimming speeds attributable to the wastes were found.
Except at the 4.0 mg/liter BOD level of waste from mill A, no reduction in the appetite of salmon exposed to KME was found in
the growth experiments. Any reductions in the growth rates observed
can be attributed to KME-caused decreases of the efficiency
of food utilization for growth. The higher metabolic rates of the fish
kept on the high ration presumably were responsible for the increased
effects of the KME on these fish.