TCDD [2,3,7,8-tetrachlorodibenzo-p-dioxin, a toxic contaminant found in 2,4,5-T herbicide preparations] exposure for 96 h at 0.54 ng/g (amount of TCDD in test container/g wet body wt) had no effect on food consumption, wt gain or survival of young coho salmon (Oncorhynchus kisutch) during a 60-day postexposure period in a static-water toxicity test. Growth and survival 114 days after exposure to 5.4 ng/g TCDD were reduced, and the reductions were greater after 24 h than after 12 h exposure to TCCD. These effects were first observed 56 days after exposure. The body burden of TCDD in young coho salmon 114 days after exposure increased with the level and duration of exposure. The half-life of the whole-body TCDD residues was at least 109 days after fish were placed in clean water. Guppies (Poecilia reticulata) exposed to 0.8 ng TCDD/g developed fin disease 42 days after exposure. There was a significant decrease in the diseased fin condition 42-69 days after exposure. Guppies had no increase in fin disease after exposure to 0.08 ng/g TCDD.