Reproduction & Fertility models

Brood size is the end point used to evaluate whether a toxic environment affects reproduction of the nematodes, placing exposed adult or L4 worms onto fresh plates.
The number of offspring at all stages is counted and compared with a control group. Counting is facilitated by heating the worms to 50 °C and staining them with Bengal red. In several studies the fertility rate is calculated by counting the total number of larvae at the end of the test and dividing by the total progeny recovered to the total parents. This assay may also be carried out using the COPAS Biosort by measuring optical density. Moreover, the gonad size, obtained by image analysis under a microscope, has been utilized to evaluate the effects on reproductive organs. Toxic effects may also be seen as changes in the egg-laying pattern and the number of eggs or larvae at different time intervals. Finally, the rate of egg laying can be estimated by placing adult worms exposed to fresh plates and counting the number of eggs laid in 1 h.

Reproductive toxicity can also be assessed by calculating the percentage of L4 larvae that develop fertilized eggs after exposure. Gravid hermaphrodites are considered to have at least one egg inside their bodies. To count the number of eggs in the uterus, nematodes can be transferred to a bleach solution, which dissolves the body of the worm, directly exposing the eggs and allowing them to be counted under a light microscope.