5
Teratogenic Deformity
Index for Fish
Introduction
Excessive selenium can cause a wide variety of toxic effects in fish
(see Chapter 3). The most prominent outwardly visible symptom of
selenium poisoning is teratogenic deformities. When observed in the
field concurrently with elevated tissue selenium residues, terata can
be used as an easily recognized, reliable indicator of selenium toxicity.
Because of this characteristic, they are a useful tool for evaluating
selenium hazards in aquatic ecosystems. However, a simple notation
of the presence of deformities is not an assessment of mortality and
potential long-term impacts on fish populations. Such an assessment is
needed to fully understand the level of ecological damage that has
taken place. To make such an assessment, it is necessary to link the
prevalence of terata with corresponding degrees of mortality. This linkage can be derived by examining laboratory and field studies that document teratogenic mortality in response to selenium exposure. I have
reviewed that information and used it to develop the Teratogenic Deformity Index (TDI) presented in this chapter. The TDI provides field
verification of reproductive failure and assesses the magnitude of toxic
impacts to current and future generations of fish. The examples presented illustrate how TDI is applied to fish population sampling data.
Occurrence and Persistence
of Teratogenic Effects
Teratogenic deformities are a permanent pathological marker of selenium poisoning. They are congenital malformations that occur due to
excessive selenium in eggs. The process begins with the diet of the
parent fish. Excess dietary selenium (>3 Ilg Se/g) causes elevated concentrations of selenium to be deposited in developing eggs, particu89
Teratogenic Deformity
Index for Fish
Introduction
Excessive selenium can cause a wide variety of toxic effects in fish
(see Chapter 3). The most prominent outwardly visible symptom of
selenium poisoning is teratogenic deformities. When observed in the
field concurrently with elevated tissue selenium residues, terata can
be used as an easily recognized, reliable indicator of selenium toxicity.
Because of this characteristic, they are a useful tool for evaluating
selenium hazards in aquatic ecosystems. However, a simple notation
of the presence of deformities is not an assessment of mortality and
potential long-term impacts on fish populations. Such an assessment is
needed to fully understand the level of ecological damage that has
taken place. To make such an assessment, it is necessary to link the
prevalence of terata with corresponding degrees of mortality. This linkage can be derived by examining laboratory and field studies that document teratogenic mortality in response to selenium exposure. I have
reviewed that information and used it to develop the Teratogenic Deformity Index (TDI) presented in this chapter. The TDI provides field
verification of reproductive failure and assesses the magnitude of toxic
impacts to current and future generations of fish. The examples presented illustrate how TDI is applied to fish population sampling data.
Occurrence and Persistence
of Teratogenic Effects
Teratogenic deformities are a permanent pathological marker of selenium poisoning. They are congenital malformations that occur due to
excessive selenium in eggs. The process begins with the diet of the
parent fish. Excess dietary selenium (>3 Ilg Se/g) causes elevated concentrations of selenium to be deposited in developing eggs, particu89