Terata-Mortality Relationships
93
1975,1978, 1982, 1992 and 1996 (Lemly 1993,1997). The 1975 survey
was conducted during the period of initial selenium contamination of
the reservoir, before the fishery experienced serious decline. This was
the only survey made when the original assemblage of fish species
was still present in the lake. This data set is quite informative because
it documents levels of teratogenesis in a wide range of species that
represent various feeding modes and trophic positions. Selenium concentrations in whole-body fish samples (juveniles and adults) were
high (40-65 Ilg Se/g dry weight), as was the prevalence of teratogenic
deformities (up to 55 %). Terata were present in all of the 19 species
examined. Surveys conducted in 1978 and 1982 yielded similar results, although only 4 fish species remained in 1978, and 6 in 1982.
Selenium concentrations were very high (up to 130 Ilg Se/g dry weight),
and were closely paralleled by the prevalence of teratogenic deformities, which ranged up to 70% (juvenile and adult fish). The survey in
1992 indicated that gradual recovery was taking place, but there were
still only 9 of the original 20 species present, and numerical abundance was quite low. Concentrations of selenium in fish had fallen to
11 to 20 Ilg Se/g and the incidence of terata did not exceed 11 % (juveniles and adults). Fish were successfully reproducing and it was soon
possible to collect larval fish for examination. Further recovery of
the fishery was evident in 1996. All of the major sport fish had
reestablished and were successfully reproducing. Tissue concentrations of selenium had fallen to 5 to 10 Ilg Se/g, and the frequency
of teratogenic deformities was 6% or lower (larvae, fry, juveniles,
and adults).
Relationships between the amount of selenium in fish tissues, the
prevalence of terata, and associated mortality are shown in Figures
5.1 and 5.2. These figures represent a compilation of all field and laboratory data on teratogenic effects (eg, field studies such as Lemly 1993,
laboratory studies such as Woock et al. 1987). The prevalence of teratogenic deformities is dependent on tissue concentrations of selenium;
more selenium results in more frequent terata. However, the association follows an exponential function rather than a linear relationship.
In natural populations of juvenile and adult centrarchids (ie, not laboratory studies), the inflection point for the function occurs in the range
of 40 to 50 Ilg Se/g dry weight. At these concentrations, about one
fourth of the fish exhibit terata (Fig. 5.1). Beyond the inflection point,
relatively small increases in selenium cause substantial increases in
terata. The maximum observed frequency is 70% for individuals with
body burdens of selenium in the 70 to 90 Ilg Se/g range. The exponential function holds for larval centrarchids as well, but the selenium
concentrations for the inflection point and for the maximum are much
lower. For example, at tissue concentrations of only about 30 to 40 Ilg
Se/g, the frequency of deformities is up to 80%.
93
1975,1978, 1982, 1992 and 1996 (Lemly 1993,1997). The 1975 survey
was conducted during the period of initial selenium contamination of
the reservoir, before the fishery experienced serious decline. This was
the only survey made when the original assemblage of fish species
was still present in the lake. This data set is quite informative because
it documents levels of teratogenesis in a wide range of species that
represent various feeding modes and trophic positions. Selenium concentrations in whole-body fish samples (juveniles and adults) were
high (40-65 Ilg Se/g dry weight), as was the prevalence of teratogenic
deformities (up to 55 %). Terata were present in all of the 19 species
examined. Surveys conducted in 1978 and 1982 yielded similar results, although only 4 fish species remained in 1978, and 6 in 1982.
Selenium concentrations were very high (up to 130 Ilg Se/g dry weight),
and were closely paralleled by the prevalence of teratogenic deformities, which ranged up to 70% (juvenile and adult fish). The survey in
1992 indicated that gradual recovery was taking place, but there were
still only 9 of the original 20 species present, and numerical abundance was quite low. Concentrations of selenium in fish had fallen to
11 to 20 Ilg Se/g and the incidence of terata did not exceed 11 % (juveniles and adults). Fish were successfully reproducing and it was soon
possible to collect larval fish for examination. Further recovery of
the fishery was evident in 1996. All of the major sport fish had
reestablished and were successfully reproducing. Tissue concentrations of selenium had fallen to 5 to 10 Ilg Se/g, and the frequency
of teratogenic deformities was 6% or lower (larvae, fry, juveniles,
and adults).
Relationships between the amount of selenium in fish tissues, the
prevalence of terata, and associated mortality are shown in Figures
5.1 and 5.2. These figures represent a compilation of all field and laboratory data on teratogenic effects (eg, field studies such as Lemly 1993,
laboratory studies such as Woock et al. 1987). The prevalence of teratogenic deformities is dependent on tissue concentrations of selenium;
more selenium results in more frequent terata. However, the association follows an exponential function rather than a linear relationship.
In natural populations of juvenile and adult centrarchids (ie, not laboratory studies), the inflection point for the function occurs in the range
of 40 to 50 Ilg Se/g dry weight. At these concentrations, about one
fourth of the fish exhibit terata (Fig. 5.1). Beyond the inflection point,
relatively small increases in selenium cause substantial increases in
terata. The maximum observed frequency is 70% for individuals with
body burdens of selenium in the 70 to 90 Ilg Se/g range. The exponential function holds for larval centrarchids as well, but the selenium
concentrations for the inflection point and for the maximum are much
lower. For example, at tissue concentrations of only about 30 to 40 Ilg
Se/g, the frequency of deformities is up to 80%.