Tyler K. Linton

The Metabolic Costs and Physiological Consequences to Juvenile Rainbow Trout of a Simulated Winter Warming Scenario in the Presence or Absence of Sublethal Ammonia

Abstract This experiment examined the metabolic costs and physiological consequences of growth and energetics of juvenile rainbow trout Oncorhynchus mykiss in a warmer, more polluted winter environment. Growth under the warm-winter conditions was approximately three times less than equivalent growth of experimental and control groups previously observed under warm-summer conditions. However, during winter exposure, wet weights and total lengths were roughly 30% higher in the “warmed” fish than in the base temperature group due to a combination of greater appetite and higher energy conversion efficiency. Oxygen consumption and nitrogenous (ammonia + urea) waste excretion rates were 30–40% higher for “warmed” fish but were less than one-third of levels recorded in the summer. A corresponding increase in food intake was associated with elevations in whole-body protein and lipid but not carbohydrate. Addition of 70 μmol ammonia/L elevated nitrogenous waste excretion much like in the previous summer exposure, ...

Development of bioassessment‐based benchmarks for iron

Current water-quality criteria for metals typically are derived from toxicity tests with the metal dissolved in clean laboratory water. Estimating the toxicity of iron from such tests, however, is extremely difficult because of the complex solubility and toxicity characteristics of the ferrous and ferric forms of the metal in freshwater. Consequently, a criterion for dissolved iron in freshwater derived from standard laboratory bioassays may not accurately describe the actual bioavailability and toxicity of this metal. A new approach is necessary to adequately protect aquatic life from the direct (toxic) and indirect (physical) negative effects of iron. We present a novel methodology to derive bioassessment-based benchmarks for total iron. This approach involves the use of quantile regression to model the decline in maximum abundance of taxa along a gradient of increasing iron concentrations. The limiting function (e.g., 90th quantile) is used to project the iron concentration associated with a selected reduction in maximum number of organisms (e.g., 20%). The projected declines in abundance of aquatic organisms are interpreted within the larger context of biological responses to increasing levels of stress (i.e., a biological condition gradient). Projections of iron concentration associated with multiple levels of reduction are selected to establish acceptable levels of change in the various tiers of a biological community. The bioassessment-based benchmarks that we establish for total iron (0.21 and 1.74 mg/L) are based on the assumption that if ecological effects-based criteria for total iron are derived and applied, the structure and function of the aquatic community will be protected.

Effects of chronic environmental acidification and a summer global warming scenario: protein synthesis in juvenile rainbow trout (Oncorhynchus mykiss)

Protein synthesis ( Ks), net accretion ( Kg), and degradation ( Kd) in liver, gills, and white muscle were measured using a flooding dose of [ 3H]phenylalanine in juvenile rainbow trout chronically exposed (90 days) to softwater in the presence or absence of sublethal acidity (H 2SO4, pH 5.2) alone or in combination with a 2°C elevation in the normal temperature profile over the months of June–September 1993 (control temperature range 13–24°C). Chronic sublethal exposure to low pH reduced protein synthesis and degradation in both the gill and liver with little apparent impact on white muscle. As a result, protein was increased in the affected tissues. This suggested that both liver and gill have some capacity to compensate for the effects of acid exposure. The 2°C elevation in the normal temperature profile resulted in a slight increase in protein turnover in both gills and liver. However, during the period of peak water temperature, the 2°C elevation in temperature triggered a dramatic reduction in the protein turnover rates in these tissues. The exact mechanism by which these modifications in protein turnover occurred could not be clearly established. Overall, environmental acidification in combination with a summer global warming scenario would decrease fish growth and survival, most notably during periods of

Influence of water hardness and sulfate on the acute toxicity of chloride to sensitive freshwater invertebrates

Total dissolved solids (TDS) represent the sum of all common ions (e.g., Na, K, Ca, Mg, chloride, sulfate, and bicarbonate) in freshwater. Currently, no federal water quality criteria exist for the protection of aquatic life for TDS, but because the constituents that constitute TDS are variable, the development of aquatic life criteria for specific ions is more practical than development of aquatic life criteria for TDS. Chloride is one such ion for which aquatic life criteria exist; however, the current aquatic life criteria dataset for chloride is more than 20 years old. Therefore, additional toxicity tests were conducted in the current study to confirm the acute toxicity of chloride to several potentially sensitive invertebrates: water flea (Ceriodaphnia dubia), fingernail clams (Sphaerium simile and Musculium transversum), snail (Gyraulus parvus), and worm (Tubifex tubifex), and determine the extent to which hardness and sulfate modify chloride toxicity. The results indicated a significant ameliorating effect of water hardness (calcium and magnesium) on chloride toxicity for all species tested except the snail; for example, the 48-h chloride median lethal concentration (LC50) for C. dubia at 50 mg/L hardness (977 mg Cl(-) /L) was half that at 800 mg/L hardness (1,836 mg Cl(-) /L). Conversely, sulfate over the range of 25 to 600 mg/L exerted a negligible effect on chloride toxicity to C. dubia. Rank order of LC50 values for chloride at a given water hardness was in the order (lowest to highest): S. simile < C. dubia < M. transversum < G. parvus < T. tubifex. Results of the current study support the contention that the specific conductivity or TDS concentration of a water body alone is not a sufficient predictor of acute toxicity and that knowledge of the specific ion composition is critical.

Effects of a summer temperature regime representative of a global warming scenario on growth and protein synthesis in hardwater- and softwater-acclimated juvenile rainbow trout (Oncorhynchus mykiss)

Abstract 1. 1. Growth, appetite, gross conversion efficiency and protein turnover rates of liver, gills and white muscle were measured in juvenile rainbow trout chronically exposed (90 days) to soft and hardwater at two temperatures (ambient, ambient temp. +2°C). The temperature regime followed that of inshore Lake Ontario over the months of June–September 1993 as temperature rose from ∼13 to 24°C. 2. 2. Over the initial 60 days of exposure, the addition of 2°C to the ambient temperature increased growth, appetite, gross conversion efficiency and protein turnover by an average of 16%. However, further exposure during the period of peak ambient temperatures, led to an average 20% reduction in growth, appetite, gross conversion efficiency and protein turnover. 3. 3. Increased rates of gill protein turnover and arguably lower rates of growth indicate that the cost of living for a trout acclimated and maintained in synthetic softwater is higher than that of hardwater fish. In addition, lower appetite in softwater fish suggest that life in softwater is itself a mild form of environmental stress.

The effects of elevated summer temperature and sublethal pollutants (ammonia, low pH) on protein turnover in the gill and liver of rainbow trout (Oncorhynchus mykiss) on a limited food ration.

Protein synthesis, degradation and growth of the liver and gills were determined in juvenile rainbow trout (Oncorhynchus mykiss) fed a limited ration and exposed for 90 days to normal or elevated summer temperatures (+2 degrees above ambient) and either low pH (5.2) in softwater or 70 microM total ammonia in hardwater. The limited ration resulted in low rates of growth (< 0.80% per day) and protein synthesis in all fish. In softwater, whole-body growth was significantly inhibited by elevated temperature but stimulated by low pH, although tissue protein metabolism was generally unaffected by these treatments. There was no significant difference in final size between the groups of fish in hardwater, but liver protein synthesis and degradation were significantly lower at +2 degrees C, the reduction in synthesis being due to an inhibition of both the capacity for protein synthesis, Cs and the RNA translational efficiency, kRNA. Gill protein metabolism was unaffected by the experimental treatments in trout in hardwater. The authors conclude that a global warming scenario would be detrimental to protein synthesis and growth in freshwater fish under conditions of food limitation in summer, and when late summer temperatures approached the upper thermal limit of the species, regardless of food availability.

Integrating chemical and biological criteria

We present a system to derive benchmarks for protection of aquatic organisms that, as chemical criteria, promotes regulation of contaminants and, as biological criteria, focuses on an endpoint that adequately represents species abundance. The proposed method utilizes quantile regression to quantify the decline in maximum number of organisms with increasing contaminant concentrations. This limiting function then is applied to project the contaminant concentration associated with a threshold number of organisms. The threshold value is defined according to the studys objective and level of desired protection. Here, we defined it as 0.8 x 90th quantile of the number of organisms in samples from reference sites. We use the proposed system to derive taxon-specific, field-based effect concentrations (FECs) for copper and zinc in Ohio, USA, rivers and streams. Comparisons of results with respective chronic values suggest that only the draft criteria for copper are adequately protective. Projected zinc FECs were far lower than respective estimates of chronic values. The FECs likely are less sensitive to impacts of confounding factors because high numbers of organism in samples are observed when negative effects of other stressors are absent or minimal. We discuss other advantages, limitations, and potential applications of the proposed system.

The effects of elevated winter temperature and sub-lethal pollutants (low pH, elevated ammonia) on protein turnover in the gill and liver of rainbow trout (Oncorhynchus mykiss)

Appetite, growth, and protein turnover (synthesis, growth and degradation) of liver and gills were measured in juvenile rainbow trout (Oncorhynchus mykiss) fed to satiation, and exposed for 90 days to elevated winter temperatures (+2 °C above ambient) and either low pH (5.2) in softwater or 70 μM total ammonia (TAmm) in hardwater. All fish increased in weight during the experiments, but those exposed to +2°C grew significantly more than those at ambient temperature due to a stimulation of appetite. During the relatively constant temperature of the first 75 days, +2 °C caused a significant increase in the rates of protein synthesis and degradation in the liver of hardwater-acclimated fish, as a result of an increase in RNA translational efficiency (KRNA). The elevated temperature also induced an increase in gill protein synthesis in softwater-acclimated fish but in this case the underlying mechanism was an increase in Cs, the capacity for protein synthesis (RNA:protein) rather than in KRNA. The addition of 70 μM TAmm had no effect on protein turnover in either liver or gills of hardwater-acclimated fish. Low pH inhibited protein growth in the liver of softwater-acclimated fish at day 90 under both temperature regimes. This inhibition was effected via a decrease in protein synthesis at control temperature but via an increase in protein degradation when the fish were exposed to both low pH and +2 °C. From these results we conclude that a simulated global warming scenario has potentially beneficial rather than detrimental effects on protein turnover and growth of freshwater fish during winter.

Effects of a Restricted Ration on the Growth and Energetics of Juvenile Rainbow Trout Exposed to a Summer of Simulated Warming and Sublethal Ammonia

Abstract Laboratory tests were conducted to determine the potential effects of a warmer and more polluted environment on the growth and energetics of juvenile rainbow trout Oncorhynchus mykiss fed a fixed restricted ration (1% wet body weight/d) during summer. The fish were exposed either to the naturally fluctuating ambient thermal regime (base, representative of inshore Lake Ontario) or to the ambient regime + 2°C (base + 2°C), both in the presence or absence of 70 μmol total ammonia(T amm)/L (0.013 mg NH3-N/L at 15°C, pH = 7.6). The 90-d exposures lasted from June to September 1994 and were designed to mimic an earlier study in which juvenile rainbow trout were fed to satiation. Relative to the earlier study, the restricted ration markedly increased (4–9-fold) the metabolic costs of nitrogen retention, that is, oxygen consumption per unit protein growth. Rainbow trout from the present study exhibited O2 consumption, and specific growth rates that were 50–75% and 13–20%, respectively, of the O2 and grow...

Long-term exposure to small temperature increase and sublethal ammonia in hardwater acclimated rainbow trout: does acclimation occur?

Abstract Juvenile rainbow trout ( Oncorhynchus mykiss ; initially 2–5 g) were exposed for 90 days to either ambient water temperature (natural thermal regime) or to +2 °C superimposed above the ambient water temperature (simulated global warming scenario), in the presence or absence of a nominal 70 μM total ammonia (1290 μg l −1 ionized (NH 4 + ), 10 μg l −1 unionized (NH 3 ) ammonia). The exposures were conducted in moderately hard de-chlorinated water from Lake Ontario ([ Ca 2+ ] = 0.96 ± 0.02 mM, [ Na + ] = 0.55 ± 0.01 mM, [ Cl − ] = 0.737 ± 0.004 mM) on three occasions: over summer (temperature range, 13.0–21.0 °C; pH = 7.57 ± 0.26) and winter (temperature range, 3.5–7.0 °C; pH = 7.46 ± 0.02) without food limitation (satiation feeding), and during summer (temperature range, 13.0–18.5 °C; pH = 7.38 ± 0.09) with food limitation (1% daily, or restricted ration). Lethal temperature, lethal ammonia (1.8 mM total ammonia; approximately 31 700 μg l −1 NH 1 + , 900 μg l −1 NH 3 ), and lethal temperature plus ammonia challenges were conducted after each 90-day exposure to determine whether or not chronic pre-exposure conferred any increased tolerance to elevated temperature or ammonia. In addition, acute sublethal ammonia challenges (1.0 mM total ammonia; approximately 17 800 μg l −1 NH 4 + , 200 μg l −1 NH 3 ), together with unidirectional Na + flux measurements, were conducted after the two summer exposures to gain further insight into the effects of prior sublethal ammonia exposure on Na + regulation, as influenced by ration. The juvenile trout on unlimited ration and exposed to a warming scenario of +2 °C exhibited a slight, but significant elevation in lethal temperatures in both summer and winter, but the effect was not observed in fish fed a restricted ration. A challenge to lethal temperature and ammonia in combination reduced the lethal temperature anywhere from 3–7 °C for fish from all treatments; pre-exposure to ammonia offered some protective effect. However, prior ammonia exposure did not prolong survival times (LT 50 s) during lethal ammonia challenge, and there was no evidence of acclimation to elevated external ammonia with respect to Na + balance. These results suggest that juvenile trout are likely to adapt to a small temperature increase, such as could be associated with a global warming scenario, but their potential for doing so may be restricted by sublethal ammonia and by nutritional status.