Donald G. Stevens

Avoidance of Copper and Nickel by Rainbow Trout as Monitored by a Computer-Based Data Acquisition System

Abstract The avoidance response of rainbow trout Salmo gairdneri to copper and nickel solutions under several exposure regimes was evaluated with a computer-based data acquisition system interfaced with a linear, plexiglass chamber with countercurrent water flow. The best estimates of the avoidance thresholds for these metals were 6.4 μg/liter total copper and 23.9 μg/liter total nickel (95% confidence limits were 2.6–15.5 and 10.2–54.3 μg/liter, respectively). For each metal, avoidance threshold concentrations were not different whether fish were exposed in shallow or steep concentration gradients. Also, no significant differences (P > 0.05) were found when fish received multiple, increasing exposures or a single exposure in steep-gradient conditions. Rainbow trout initially avoided low copper concentrations, but were attracted to higher ones (330–390 μg/liter) during shallow-gradient tests. Under similar test conditions, fish were attracted to low nickel concentrations (about 6 μg/liter), but avoided hi...

Acutely Lethal Levels of Cadmium, Copper, and Zinc to Adult Male Coho Salmon and Steelhead

Abstract Flow-through acute toxicity tests of cadmium, copper, and zinc were conducted with adult male coho salmon (Oncorhynchus kisutch) and adult male steelhead (Salmo gairdneri). The 96-h LC50 values for copper were 46 and 57 μg/liter, and for zinc were 905 and 1,755 μg/liter, for coho salmon and steelhead, respectively. Mortality induced by cadmium was slow in onset, but 50% mortality occurred after more than a week at 3.7 μg/liter for coho salmon and 5.2 μg/liter for steelhead. Hardness and alkalinity of the water supply were higher during the toxicity tests with steelhead, complicating direct comparisons between the two species.

Avoidance Responses of Salmon and Trout to Air-Supersaturated Water

Abstract Coho (Oncorhynchus kisutch), sockeye (O. nerka), and chinook (O. tschawytscha) salmon smolts, and rainbow trout (Salmo gairdneri) avoided air-supersaturated water when tested in a shallow round tank. Steelheads (S. gairdneri) did not consistently avoid the supersaturated water and died from gas bubble disease. The salmon and rainbow trout generally avoided 145 and 125% saturation but did not always avoid 115%. Territorial activity reduced avoidance by steelheads and rainbow trout.

Carbon Dioxide and Oxygen-Nitrogen Ratios as Factors Affecting Salmon Survival in Air-Supersaturated Water

Abstract Juvenile sockeye salmon (Oncorhynchus nerka) were exposed to lethal levels of air-supersaturated water (120 percent, 125 percent, 130 percent total gas saturation) containing different oxygen-nitrogen ratios and different carbon dioxide concentrations. Fish mortality was not significantly different at different carbon dioxide levels (1.7 to 22.0 mg/liter CO2) when tested at the same total gas saturation concentrations. Total gas saturation levels are much more important than the O2/N2 ratios, as fish mortality will not occur unless total gas saturation exceeds 100 percent, regardless of the O2/N2 ratios. There was a significant decrease in mortality when the ratio of oxygen to nitrogen was increased while holding the total percent saturation constant. Much more extensive and severe signs of gas bubble disease developed at high O2/N2 ratios than at low O2/N2 ratios, indicating that oxygen plays a significant part in forming external emphysema and lesions.

Relationships between Temperature Units and Sensitivity to Handling for Coho Salmon and Rainbow Trout Embryos

Abstract The relationship between embryo development, expressed as cumulative temperature units (TU; the number of TU is the difference between the daily mean temperature and 0°C), and the timing of the period during which embryos are sensitive to handling was determined for coho salmon (Oncorhynchus kisutch) and rainbow trout (O. mykiss, formerly Salmo gairdneri). Each day after fertilization, a different group of embryos was subjected to standardized handling stress; subsequent survival in the group was compared to that of unhandled controls. Both species were incubated at three temperatures. The sensitive developmental stages (when handling significantly lowered survival; P ≤ 0.05) for coho salmon embryos was 90–139 TU at a mean incubation temperature of 8.9°C, 95–145 TU at 10.5°C, and 84–124 TU at 12.7°C. Minimum survival (about 20%) occurred at 111, 115, and 98 TU for temperatures of 8.9, 10.5, and 12.7°C, respectively. Rainbow trout embryos survived significantly less well when handled at 99 and 98 ...

Effect of low dissolved oxygen on aquatic life stages of the caddisfly Clistoronia magnifica (Limnephilidae)

Embryos, larval stages (instars I–V), pupal stages, and pharate adults of the caddisfly Clistoronia magnifica (Limnephilidae) were exposed to a range of dissolved oxygen (DO) concentrations (0.9–8.3 mg/L) for 4–88 days in the laboratory. Some embryos suspended growth at low DO, resuming growth and hatch when DO was increased. Embryos and larvae all had 96-h EC50 values (50% mortality at 96 h) of about 2.0 mg/L DO. The statistical Effect and No-Effect Thresholds for larvae exposed through two molts from instars I–III were 1.6 and 2.4 mg/L, respectively. At DO concentrations below 4.6 mg/L, egg hatch, larval development, molting success, time of molting, pupation, and adult emergence were delayed.

Observations on Gas Bubble Disease among Wild Adult Columbia River Fishes

Abstract A high incidence of gas bubble disease was found among sahnonids and shad sampled from the air-supersaturated Columbia River. Post-capture eye damage to sockeye salmon also may be related to supersaturation of the river.

Survival of Salmon Smolts in Sea Water after Exposure to Air-Supersaturated Water

Abstract Smolts of sockeye salmon (Oncorhynchus nerka) were held at 117, 115, 113, 110, 108, and 100% saturation in air-supersaturated fresh water at 12.5°C for 3 weeks. At 117% saturation 70% of the fish died, and at 115%, 5% died. Survivors were severely stressed and exhibited many signs of gas bubble disease. When the smolts were transferred to sea water and held for 10 days, no deaths occurred and they recovered rapidly.