Effects of pulsed- and spiked-exposure to methoxychlor on early life stages of rainbow trout

In pulsed experiments, rainbow trout Salmo gairdneri eggs (1 week pre-hatch) and 3 day old alevins were exposed to methoxychlor (0, 46, 120, 270, 580 ug per litre) for 2 h, then transferred back to clean water. In spiked experiments, 1.5 day old eggs and resultant alevins were maintained for 68 days in tanks which initially contained nominal methoxychlor concentrations of 0, 3 or 30 ug per litre. Measured concentrations in samples collected 1 h after spiking were 0, 1.0 and 9.2 ug per litre. Toxicant concentrations were allowed to decay naturally (half life approximately 1.7 days according to previous data). In general, methoxychlor had no effect on the 10 survival, growth and development parameters examined. Eggs exposed to the high methoxychlor concentration in spiked experiments hatched earlier than controls but, as fish size, composition and developmental stage at hatch were unaffected, this was probably of questionable biological significance. However, until more was known about methoxychlor exposure regimes in natural environments, the possibility of long term effects on fish reproduction could not be ruled out.