Page 863 - The Toxicology of Fishes

Reproductive Impairment of Great Lakes Lake Trout by Dioxin-Like Chemicals 843

Species sensitivity of embryo-larval stages
2500
toward 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-TCDD LD50 (pg/g-egg) 1500
2000

1000

500

0
Fathead minnow
White sucker
Lake herring
Rainbow trout
Lake trout Brook trout Fundulus heteroclitus Channel catfish Medaka Northern pike Zebrafish

FIGURE 21.7 Species sensitivity towards 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Embryos were exposed as freshly
fertilized eggs by waterbath during water hardening or egg injection prior to epiboli. (Data are from Elonen et al., 1998;
Guiney et al., 1996, 1997; Helder, 1981; Henry et al., 1997; Toomey et al., 2001; Walker and Peterson, 1994b; Walker et
al., 1991; Wright, 2006.)

vascular endothelium by TCDD may trigger edema and vascular dysfunction between hatching and
swim-up; that is, a cascade of events initiated by AhR binding of TCDD may increase the permeability
of vascular endothelial cells culminating in edema. In support of this interpretation, Guiney et al. (1998)
showed that yolk sac edema fluid in TCDD-exposed lake trout is an ultrafiltrate of blood. What is not
known is whether induction of CYP1A catalytic activity or some other event subsequent to AhR activation
by TCDD in the vascular endothelium of lake trout sac fry is causally related to TCDD-induced
cardiovascular dysfunction. Evidence from zebrafish indicates that induction of CYP1A in the endothelial
cells or other locations of the developing fish embryo is not required for developmental effects of AhR-
related toxicity (Carney et al., 2004); however, these same finding have not been demonstrated in trout,
particularly lake trout. Although it is highly likely that the mechanistic findings related to the toxicity
of AhR ligands observed in zebrafish are applicable to salmonine species, some verification of this model
is needed.

Species Differences in TCDD Toxic Potency
The susceptibility of freshwater fish species to early-life-stage mortality caused by exposure of fertilized
eggs to TCDD varies widely. The rank order sensitivity for 11 fish species shows that lake trout is the
most sensitive, followed by brook trout and rainbow trout (Figure 21.7). The eight non-salmonine species
are less sensitive. The rank order, beginning with the most sensitive fish species (based on egg TCDD
LD ), is lake trout (40 to 85 pg/g), brook trout (138 to 200 pg/g), rainbow trout (230 to 488 pg/g),
50
Atlantic killifish (Fundulus heteroclitus) (250 pg/g), fathead minnow (539 pg/g), channel catfish (644
pg/g), lake herring (902 pg/g), medaka (1110 pg/g), white sucker (1890 pg/g), northern pike (2460 pg/g),
and zebrafish (2610 pg/g) (Elonen et al., 1998; Guiney et al., 1996, 1997; Helder, 1981; Henry et al.,