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Adverse Effect: Reduced Growth Jump down this page to: Steelhead | Chinook Salmon | Delta Smelt | Longfin Smelt | Sacramento Splittail | White Sturgeon | Green Sturgeon | Striped Bass The magnitude of growth effects related to low DO concentrations depends on the severity and duration of exposure to low DO concentrations. Prolonged or repeated exposure to low DO concentrations in laboratory experiments has been shown to reduce growth or developmental rates of fish (Magnusson et al. 1998 in U.S. Environmental Protection Agency 2003). Low DO concentrations can reduce growth by reducing the amount of energy available for growth (i.e., reducing food conversion efficiency) and decreasing food consumption through reductions in activity and loss of appetite (Breitburg 2000; Kramer 1987; Brett 1979; Doudoroff and Shumway 1970). Reduced growth rates of juvenile fishes occur at approximately 2.2 times the DO concentration associated with 50% mortality during 24-hour and 96-hour exposures (Breitburg 2000). Jump to "General Effects" discussion under other adverse effects: Steelhead (Oncorhynchus mykiss) Hypothesis: Juvenile steelhead exposed to DO concentrations lower than the regulatory minimum experience reduced growth rates. 1. What is the mechanism causing this adverse effect? Low DO concentrations can reduce growth rates by limiting rates of aerobic metabolism and the availability of metabolic energy for feeding and growth. 2. Are there critical thresholds associated with this adverse effect?
3. How important is this mechanism? The potential for growth effects increases with severity and duration of exposure to low DO (7 mg/L and below) and the number of fish exposed to such conditions. Significant population effects on steelhead are unlikely because juveniles migrate through the Delta primarily in the winter and spring, before the occurrence of high water temperatures and major hypoxic events in the DWSC. 4. How well is this mechanism understood? The effect of low DO concentrations on the growth of juvenile steelhead has been studied in the laboratory under controlled conditions. Application of these studies to wild fish is limited by our lack of understanding of the physiological and behavioral responses of fish to low DO concentrations and other factors that influence growth (e.g., food supply) of fish in the natural environment. Jump to "Steelhead" discussion under other adverse effects: Chinook Salmon (Oncorhynchus tshawytscha) Hypothesis: Juvenile Chinook salmon exposed to DO concentrations lower than the regulatory minimum experience reduced growth rates. 1. What is the mechanism causing this adverse effect? Reduced DO availability can reduce growth rates in fish by limiting the aerobic processes of metabolism and growth (Cech et al. 1984). 2. Are there critical thresholds associated with this adverse effect?
3. How important is this mechanism? The potential for population-level growth effects increases with the severity and duration of hypoxic conditions and the number of fish exposed to such conditions. Juvenile salmon migrate downstream during high-flow conditions, which correspond to high DO concentrations, so are less likely to experience significant growth effects because of their limited exposure to low DO concentrations in the DWSC. 4. How well is this mechanism understood? The effect of low DO concentrations on the growth of juvenile Chinook salmon has been studied in the laboratory under controlled conditions. Application of these studies to wild fish in their natural environments is limited by our lack of understanding of the physiological and behavioral responses of fish to low DO concentrations and other factors that influence growth (e.g., food supply) in the natural environment. Jump to "Chinook Salmon" discussion under other adverse effects: Delta Smelt (Hypomesus transpacificus) Hypothesis: Delta smelt exposed to DO concentrations below the regulatory minimum experience reduced growth rates. 1. What is the mechanism causing this adverse effect? Many fish experience a decline in growth rate during or after exposure to low DO concentrations (General Effects). No studies on the effect of low DO concentrations on delta smelt growth rates have been published. 2. Are there critical thresholds associated with this adverse effect? The incipient limiting threshold for delta smelt has not been determined. 3. How important is this mechanism? The extent and importance of impaired delta smelt growth rates caused by exposure to low DO concentrations are not known. 4. How well is this mechanism understood? This adverse effect is not well understood because no studies of the effect of low DO concentrations on delta smelt growth have been published. Jump to "Delta Smelt" discussion under other adverse effects: Longfin Smelt (Spirinchus thaleichthys) Hypothesis: Longfin smelt exposed to DO concentrations below the regulatory minimum experience reduced growth rates. 1. What is the mechanism causing this adverse effect? No studies on the effect of low DO concentrations on growth rate of longfin smelt have been published. 2. Are there critical thresholds associated with this adverse effect? The incipient limiting threshold for longfin smelt has not been determined. 3. How important is this mechanism? The extent and importance of impaired longfin smelt growth rates attributable to exposure to low DO concentrations are not known. 4. How well is this mechanism understood? No studies of the effect of low DO concentrations on longfin smelt growth have been published. Jump to "Longfin Smelt" discussion under other adverse effects: Sacramento Splittail (Pogonichthys macrolepidotus) Hypothesis: Sacramento splittail exposed to DO concentrations near the regulatory minimum do not experience reduced growth rates. 1. What is the mechanism causing this adverse effect? No studies on the effect of low DO concentrations on the growth rate of Sacramento splittail have been published. 2. Are there critical thresholds associated with this adverse effect? The incipient limiting threshold for Sacramento splittail has not been determined; however, given that their incipient lethal threshold is so low, it is likely that their incipient limiting threshold is well below the DO regulatory minimum. 3. How important is this mechanism? The extent and importance of impaired Sacramento splittail growth rates as a result of exposure to low DO concentrations are not known. 4. How well is this mechanism understood? No studies on the effect of low DO concentrations on Sacramento splittail growth rates have been published. Jump to "Sacramento Splittail" discussion under other adverse effects: White Sturgeon (Acipenser transmontanus) Hypothesis: White sturgeon exposed to DO concentrations below the regulatory minimum experience reduced growth rates. 1. What is the mechanism causing this adverse effect? Juvenile fish have a particularly high demand for DO as they experience rapid growth and development. Cech et al. (1984) found significantly reduced growth rates among juvenile white sturgeon exposed to hypoxic conditions (58% saturation—4.7–5.7 mg/L) at each of three rearing temperatures they studied (Cech and Crocker 2002). Similarly, Secor and Gunderson (1998) found that hypoxic conditions (3 mg/L) significantly decreased growth in Atlantic sturgeon (A. oxyrinchus). 2. Are there critical thresholds associated with this adverse effect? The incipient limiting threshold for white sturgeon has not been determined, but it is apparently above 58% saturation (4.7–5.7 mg/L), the level at which Cech et al. (1984) found significant growth reductions in white sturgeon. 3. How important is this mechanism? The extent and importance of impaired white sturgeon growth rates attributable to exposure to low DO concentrations are not known. White sturgeon grow very quickly in their early (freshwater) life stages (Moyle 2002) and, presumably, this early rapid growth is important to their survival in later life stages. 4. How well is this mechanism understood? The reduced growth rate of white sturgeon exposed to low DO concentrations is well documented (Cech et al. 1984; Cech and Doroshov 2004). Similar growth effects have been documented for other Acipenser species (Secor and Gunderson 1998; Cech and Doroshov 2004). Jump to "White Sturgeon" discussion under other adverse effects: Green Sturgeon (Acipenser medirostris) Juvenile fish have a particularly high demand for DO as they experience rapid growth and development. Oxygen consumption rates in green sturgeon (A. medirostris) increased 500% between hatching and 31 days post hatch (Gisbert et al. 2001 in Cech and Doroshov 2004). Cech et al. (1984) found significantly reduced growth rates among juvenile white sturgeon exposed to hypoxic conditions (58% saturation—4.7-5.7 mg/L) at each of three rearing temperatures they studied (see also Cech and Crocker 2002). Similarly, Secor and Gunderson (1998) found that hypoxic conditions (3 mg/L) significantly decreased growth in Atlantic sturgeon (A. oxyrinchus). Although little species-specific information is available for green sturgeon, it is likely that information for white sturgeon is generally applicable to green sturgeon. Jump to "Green Sturgeon" discussion under other adverse effects: Striped Bass (Morone saxatilis) Hypothesis: Striped bass exposed to DO concentrations below the regulatory minimum experience reduced growth rates. 1. What is the mechanism causing this adverse effect? Fry (1971) describes oxygen as a “limiting factor” that may influence growth rates. Reduced oxygen availability can reduce growth rates in striped bass by limiting the aerobic processes of metabolism and growth (Cech et al. 1984). 2. Are there critical thresholds associated with this adverse effect? Some studies have found specific conditions that limit striped bass growth.
3. How important is this mechanism?
4. How well is this mechanism understood? The effect of low DO concentrations on reduced growth is fairly well documented. Several studies have investigated the impacts of reduced DO on the growth of striped bass (listed above under 2. Are there critical thresholds associated with this adverse effect?). Jump to "Striped Bass" discussion under other adverse effects: |
The extent and importance of impaired striped bass growth rates caused by exposure to low DO concentrations are unknown. Given the current understanding of DO dynamics in the DWSC (see figure at right) and the fact that most striped bass spawn below the DWSC, this mechanism may have little effect on overall striped bass populations. Until more information is known about spawning habitat use above the DWSC and the timing and abundance of