Development of a new biochemical assay for assessing toxicity in invertebrate and fish sperm

The resazurin assay has been used in a limited manner to evaluate sperm quality in humans and some domestic animals. We have enhanced the sensitivity of the assay by measuring fluorescence instead of absorbance and have adapted it to sperm samples from marine organisms (sea urchins, scallops, fish) to measure tributyltin (TBT) toxicity. Sea urchin, capelin and scallop semen showed measurable levels of activity and an acceptable variation coefficient was obtained while assessing TBT inhibition. As mitochondria seem to be the main target of organotin toxicity, the sensitivity of the resazurin bioassay was compared to TBT effects on sea urchin sperm cell and rat liver mitochondria respiration rates. The resazurin sperm assay was more sensitive to TBT (EC50=0.09 ppm) than respiration rates of sea urchin semen (EC50=9.25 ppm). This information was confirmed by TBT levels showing an uncoupling effect on rat liver mitochondria. Significant differences were observed between monthly sea urchin sperm activities showing that the resazurin test is obviously a parameter varying with seasonal sperm quality.