Effect of methallibure on gestation in the guppy, Poecilia reticulata

Methallibure treatment (1 mg fed on alternate days to a female and a male kept in 1 liter of 25% seawater) started from 1 or 7 days postpartum (early gestation) inhibited gestation in the wild guppy, Poecilia reticulata. A few of the fish treated from 7 days postpartum (2/9) did give birth, but the young either were dead at birth or did not survive long after birth. When treatment was started 2 weeks postpartum (midgestation), gestation was not inhibited, but 25% of the young were born dead while the rest showed retardation of postnatal growth. Several possible interpretations of the results are discussed.