Winter Stress Syndrome and Selenium Toxicity
53
Winter Stress Syndrome
and Selenium Toxicity
Characteristics and Symptoms
Winter Stress Syndrome (WSS) is a term I coined to describe a condition of metabolic distress in warm-water fish (Lemly 1993b). The syndrome develops when external stressors that cause increased metabolic
demands are present when water temperature decreases in the autumn. Cold weather, and the associated short photoperiod of winter,
environmentally "programs" these fish for reduced physical activity
and food intake, and they do not respond to the stressors with increased
feeding. If the elevated metabolic demands persist, stored body lipid
necessary for overwintering is depleted, body condition drops, and the
fish may die. The key element in WSS is the influence of environment
on behavior, that is, reduced feeding as a result of cold water temperature and short photoperiod.
Many species of fish in temperate regions of North America undergo a
normal seasonal period of reduced feeding, decreased body condition,
and lowered nutritional status during winter (Oliver et al. 1979; Toneys
et al. 1980; Thompson et al. 1991). This, in turn, results in an annual
cycle of ability to resist metabolic stressors. WSS is a serious threat to
these fish because it occurs when their capability to compensate is at its
lowest point. Stressors that are normally tolerated during warm weather
and active feeding can become lethal as water temperatures and food
intake drop in late autumn (Lemly and Esch 1984; Lemly 1993b).
Three conditions must be met concurrently in order for WSS to develop: (1) a significant metabolic stressor must be present; (2) cold
water temperature must be present « 1O°C); and (3) fish must respond
to cold water temperature by reducing activity and feeding. The stressor alone is usually not sufficient to cause problems, but when combined with reduced feeding as water temperatures drop, it can cause
the syndrome to develop within 60 days (Lemly 1993b). Fish in the
later stages of WSS are somewhat thin and appear to be undernourished. The stressor increases the nutritional requirements of fish by
increasing metabolism and oxygen consumption. If food intake is
adequate to offset these demands, that is, if water temperature
remains warm enough to promote active feeding, no change in condition or apparent health occurs. However, cold water temperature
causes reduced feeding, and a nutritional deficit can soon develop
(Lemly 1993b).
Several physiological factors contribute to the nutritional deficit
and metabolic distress. Pathological conditions may develop in direct
53
Winter Stress Syndrome
and Selenium Toxicity
Characteristics and Symptoms
Winter Stress Syndrome (WSS) is a term I coined to describe a condition of metabolic distress in warm-water fish (Lemly 1993b). The syndrome develops when external stressors that cause increased metabolic
demands are present when water temperature decreases in the autumn. Cold weather, and the associated short photoperiod of winter,
environmentally "programs" these fish for reduced physical activity
and food intake, and they do not respond to the stressors with increased
feeding. If the elevated metabolic demands persist, stored body lipid
necessary for overwintering is depleted, body condition drops, and the
fish may die. The key element in WSS is the influence of environment
on behavior, that is, reduced feeding as a result of cold water temperature and short photoperiod.
Many species of fish in temperate regions of North America undergo a
normal seasonal period of reduced feeding, decreased body condition,
and lowered nutritional status during winter (Oliver et al. 1979; Toneys
et al. 1980; Thompson et al. 1991). This, in turn, results in an annual
cycle of ability to resist metabolic stressors. WSS is a serious threat to
these fish because it occurs when their capability to compensate is at its
lowest point. Stressors that are normally tolerated during warm weather
and active feeding can become lethal as water temperatures and food
intake drop in late autumn (Lemly and Esch 1984; Lemly 1993b).
Three conditions must be met concurrently in order for WSS to develop: (1) a significant metabolic stressor must be present; (2) cold
water temperature must be present « 1O°C); and (3) fish must respond
to cold water temperature by reducing activity and feeding. The stressor alone is usually not sufficient to cause problems, but when combined with reduced feeding as water temperatures drop, it can cause
the syndrome to develop within 60 days (Lemly 1993b). Fish in the
later stages of WSS are somewhat thin and appear to be undernourished. The stressor increases the nutritional requirements of fish by
increasing metabolism and oxygen consumption. If food intake is
adequate to offset these demands, that is, if water temperature
remains warm enough to promote active feeding, no change in condition or apparent health occurs. However, cold water temperature
causes reduced feeding, and a nutritional deficit can soon develop
(Lemly 1993b).
Several physiological factors contribute to the nutritional deficit
and metabolic distress. Pathological conditions may develop in direct