Effect of cadmium on early developmental stages of the sheepshead minnow (Cyprinodon variegatus )

Cadmium uptake by the early developmental stages of the sheepshead minnow, Cyprinodon variegatus , was studied over a 7.5‐d post‐hatch period. After chorionic hardening (about 4 h after fertilization), eggs were placed in filtered water from the Patuxent River, Maryland (diluted to 5%90 salinity), and dosed with cadmium concentrations of between 0.39 and 1,020 μg L −1 . At the highest cadmium concentrations studied, hatching was delayed up to 3 d and larvae had spinal deformities. Growth inhibition was not clearly dose‐related, although larvae from all cadmium treatments were significantly shorter than controls. The lowest dry weights were recorded from the 5.8 and 1,020 μg Cd L −1 treatment groups. Cadmium uptake peaked at 12 h after fertilization. Calcium levels in eggs and yolk‐sac larvae reared in 446 μg Cd L −1 were greater than in controls after the first 2 d of development but fell behind thereafter, reaching only 50% of the control calcium level after 7.5 d. Inhibition of calcium uptake persisted even after cadmium levels had peaked and fallen to the control level. Phosphorus and sodium concentrations in eggs and larvae were not affected by cadmium exposure. Ninety‐three percent of the cadmium accumulated by the egg was associated with the chorion, and 68% of this could be removed by a glycine buffer.