D. Gordon McDonald

Effects of chronic sublethal exposure to waterborne Cu, Cd or Zn in rainbow trout. 1: Iono-regulatory disturbance and metabolic costs.

The relationships among growth, feeding behaviour, ion regulation, swimming performance and oxygen consumption in rainbow trout (Oncorhynchus mykiss) were compared during chronic exposure (up to 100 days) to sublethal levels of waterborne Cd (3 µg.l(-1)), Cu (75 µg.l(-1)) or Zn (250 µg.l(-1)) in moderately hard water (hardness of 140 mg.l(-1), pH 8). A pattern of disturbance, recovery and stabilization was evident for all three metal exposures, although the degree of disturbance, specific response and time course of events varied. Growth was unaffected by any of the metals under a regime of satiation feeding but appetite was increased and decreased in Cu- and Cd-exposed trout respectively. Critical swimming speed was significantly lowered in fish chronically exposed to Cu, an effect associated with elevated O(2) consumption rate at higher swimming speeds. Branchial Na(+)/K(+) ATPase activity was elevated in Cu-exposed fish but not in Cd-exposed trout. Disruption of carcass Na(+) and Ca(2+) balance was evident within 2 days of exposure to either Cd, Cu or Zn, with subsequent recovery to control levels. The loss of Ca(2+) in trout exposed to waterborne Cd persisted longest, and recovery took approximately a month. The physiological response of trout to chronic Cu exposure involves mechanisms that result in an associated metabolic cost. In comparison, Cd is neither a loading nor a limiting stress and acclimation to chronic Cd-exposure does not appear to involve a long term metabolic cost.

Effects of chronic sublethal exposure to waterborne Cu, Cd or Zn in rainbow trout 2: tissue specific metal accumulation

Tissue specific metal accumulations (gills, liver, kidney and whole body) in rainbow trout (Oncorhynchus mykiss) were compared during chronic exposure (up to 100 days) to sublethal levels of waterborne Cd (3 µg.l(-1)), Cu (75 µg.l(-1)) or Zn (250 µg.l(-1)) in moderately hard water (hardness of 140 mg.l(-1), pH 8.0). A general pattern of tissue metal increase and stabilization was evident for all three metals, although the degree and time course of accumulation varied. The exception to this general pattern was a lack of Zn accumulation in the liver and kidney although small amounts did accumulate in the gills and whole body. Accumulation of Cu occurred primarily in the liver while for Cd the kidney was the major organ of accumulation. Exponential modeling was employed to compare and contrast the saturation concentration and time to half saturation of various tissues. Accumulation of essential metals (Cu and Zn), if it occurred, was rapid and increases were relatively low. For example the time to half saturation during Cu exposures was always less than 2 weeks and the maximum level of accumulation was less than four times background levels. For non-essential Cd, time to half saturation for the liver and kidney was always longer than 5 weeks and modeled saturation concentrations were up to 80-fold higher than background. The response to Cu and Zn suggested an active regulation of tissue burdens while that of Cd appears to be more passive, resulting in continuous metal accumulation over an extended time course. While the initial patterns of accumulation for each metal were generally consistent with the damage, repair and acclimation pattern from concurrent physiological measurements it was clear that tissue metal accumulation was not a good indicator of either exposure of physiological impact.

The role of dissolved organic carbon in moderating the bioavailability and toxicity of Cu to rainbow trout during chronic waterborne exposure

We examined the influence of dissolved organic carbon (DOC) on the bioavailability of waterborne Cu to rainbow trout (Oncorhynchus mykiss) during chronic sublethal exposure. Juvenile rainbow trout were exposed to Cu (as CuSO(4)) and DOC as humic acid (HA, as sodium salt) for one month in synthetic soft water to give treatments with varying combinations of free ionic and HA complexed Cu. The total Cu concentration was 7 microg/l for all treatments (except controls) and HA was added at levels of 0, 2.5 and 7.5 mg/l which corresponded to DOC levels of 1.2, 2.2 and 4.0 mg/l. Fish grew well in all treatments and no mortalities occurred. Cu was highly bioavailable in the treatment with no added HA; gill and liver Cu accumulation occurred as well as a disruption of Na(+) regulation. In Cu treatments with additions of both 2.5 and 7.5 mg/l HA, there was no significant tissue accumulation of Cu. The addition of HA alleviated and delayed the disruption of iono-regulatory mechanisms. A recovery of plasma Na(+) losses was observed and this was associated with an increase in gill Na(+)/K(+) ATPase activity by the end of the exposure. Following the month of chronic exposure the uptake and turnover rates of Cu at the gills and into various tissue compartments were measured through radioisotopic techniques ((64)Cu). While chronic Cu exposure did not result in acclimation (i.e. increased LC50), the uptake rate and extent of Cu uptake into the gills and liver was increased. This study demonstrates that growth and tissue accumulation of Cu are poor predictors of the chronic effects of Cu, and illustrates that HA moderates chronic Cu bioavailability. The lack of a link between Cu bioaccumulation and Cu impact and the role of organic matter in reducing the bioavailability of Cu are important considerations in the context of ecological risk assessment.

Research to Guide Use of Barriers, Traps, and Fishways to Control Sea Lamprey

ABSTRACT This paper provides a rigorous and directed research framework for fostering innovations in the design, implementation, and operation of barriers, traps, and fishways used to control the sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes. It was developed to support the Great Lakes Fishery Commissions milestone pledging to decrease reliance on chemical lampricides and achieve 50% of sea lamprey suppression through alternative control technologies, including barriers and traps. The paper first substantiates the need to develop a long-term research plan for barriers, traps, and fishways by summarizing (i) current management challenges, (ii) the barrier, trap, and fishway options being used to meet these challenges, and (iii) the key uncertainties in our knowledge regarding these options. The paper then proposes a long-term research strategy that envisions a transition from barriers designed to block the upstream spawning migrations of sea lamprey, to barrier and trap combinations that facilitate physical removal of sea lamprey and, in some cases, passage of non-target fishes, to barrier and trap designs that are specific to sea lamprey, transparent to non-target fishes, and safer for operators. Thirteen research needs are identified to support this strategy along with a general work plan on how they can be achieved. The research needs and work plan highlight the exceptional opportunity to develop the Great Lakes basin as a leading, international research center for fish migration and passage, and the development of environmentally friendly barriers.

Interspecific differences in gill morphology of freshwater fish in relation to tolerance of low-pH environments

Five species of fish were chosen to approximate the range of tolerance to low pH seen in freshwater fish. On the basis of published field and laboratory information, which was confirmed by measuring ion losses at low pH (pH 4. 0 and 3.25), the five species ranked in terms of decreasing tolerance to low pH as follows: banded sunfish (Centrarchidae: Enneacanthus obesus), yellow perch (Percidae: Perca flavescens), smallmouth bass (Centrarchidae: Micropterus dolomieu), rainbow trout (Salmonidae: Oncorhynchus mykiss), and common shiner (Cyprinidae: Notropis cornutus). Gills were analyzed for various morphological and morphometric features including lamellar surface area, chloride-cell density and mucous-cell density, sialic acid content, and depth of tight junctions. We conclude from these measurements that acid tolerance is not correlated with either the overt physical dimensions of the gills (surface area, lamellar thickness, diffusion distance) or with the degree of mucification of the surface. It may, however, be correlated with chloride-cell density and branchial ion-transport activity. This relation is interpreted as indicating that sensitivity to low pH is largely a function of the intrinsic ion permeability of the gills. Measurements on trout and perch indicate that one way of reducing ion permeability is via an increase in the depth of tight junctions between adjacent gill-pavement cells.

Gill Design in Freshwater Fishes: Interrelationships among Gas Exchange, Ion Regulation, and Acid-Base Regulation

This study employed three freshwater fish species (rainbow trout, yellow perch, and smallmouth bass) to examine the interrelationships among gas and ion exchange and acid-base regulation by the gills. Interspecific differences in critical swimming speed (U̇crit), electrolyte and nonelectrolyte permeability, O₂ consumption, and rates of net branchial transfer of acid-base equivalents were assessed. The most active species was the rainbow trout, and it ranked highest for all of the above measures. However, the extent of interspecific variation in these parameters was not the same. There were, for example, much larger interspecific differences in U̇crit and electrolyte permeability than in gas-exchange capacity. We conclude that the gills of less active species conserve ions by reducing electrolyte permeability, and that this is achieved with relatively little sacrifice of gas-exchange capacity. However, there is a penalty in diminished capacity for acid-base regulation.

Relative Importance of Water Temperature, Water Level, and Lunar Cycle to Migratory Activity in Spawning-Phase Sea Lampreys in Lake Ontario

Abstract We analyzed historical trapping records from six Lake Ontario tributaries to (1) compare the relative importance of water temperature, water level, and lunar cycle to migratory activity in upstream-migrating sea lampreys Petromyzon marinus and (2) determine whether the relative importance of these variables differs among streams. We found significant stream-dependent differences in the relative importance of the environmental variables. Water temperature was the best predictor of migratory activity in all six streams. The seasonal distribution of migratory activity was related to mean stream temperature, with an estimated peak migration temperature of approximately 15°C. Changes in stream temperature were equally as important. Migratory activity was stimulated when mean stream temperature increased between consecutive days and was suppressed when mean stream temperature decreased between consecutive days. Water level was a reliable predictor of migratory activity only in the two smallest streams....

Research to Guide the Use of Lampricides for Controlling Sea Lamprey

ABSTRACT This paper is one of a series supported by the Great Lakes Fishery Commission that describe research priorities related to each facet of the sea lamprey control program (assessment, pheromones, barriers and trapping, sterile males and lampricides). The specific focus of this paper is research needs related to the use of lampricides. To that end, we first provide a brief history of the lampricide control program and its processes and operations emphasizing the progress that has been made over the last 50 years. We then articulate research priorities for the continued improvement of lampricide use under four major categories; improving the effectiveness of lampricide treatments, improving the understanding of the effects of lampricides on non-target species, gaining a better understanding the mode(s) of toxic action of lampricides, and how they differ between lamprey and non-target species, and finally, initiatives designed to find new and more effective methods of applying existing lampricides and to develop new lampricides, based on new knowledge of chemical vulnerabilities unique to larval sea lamprey. Research priorities are summarized at the end of the paper and sources of additional information concerning lampricide research are provided.

Branchial Acid and Ammonia Fluxes in Response to Alkalosis and Acidosis in Two Marine Teleosts: Coho Salmon (Oncorhynchus kisutch) and Starry Flounder (Platichthys stellatus)

Metabolic acidosis, whether endogenous (exhaustive exercise) or exogenous (ammonium sulfate infusion), had qualitatively similar effects on net ammonia flux (