Growth & Contraction models

The effect of a toxicant in the development of the nematode can be evaluated by measuring the body length of synchronous worms before and after exposure, then comparing them to a vehicle-control. The bodies of the worms are observed employing a light microscope with 10X magnification and with image analysis software.

Some authors have reported the warming of the worms to 50 °C in order to make them straight and ease the process of measuring their length. The immobilization of the worms can also be achieved by using sodium azide. However, growth can also be evaluated by registering the length of a curve, drawn from the tip of the head to the tip of the tail along the dorsal-ventral half of the animal intestine, using the reference line. Width measurements are taken in the vulva, drawing a line on the ventral side of the animal between the front edge and the posterior periphery of the vulva.

Other authors have proposed measuring the surface area for the flat worm . Currently, some laboratories have hightech equipment, such as COPAS Biosort, which measures the optical density of the worm as an endpoint of growth. The advantage is that the COPAS Biosort can analyze hundreds of nematodes per minute, and it can also evaluate mortality and fluorescence statistics.

For growth assays, some authors perform 24 h exposure periods with E. coli OP50 as food, whereas in other studies, E. coli uvrA, previously killed by UVA radiation is used; in this case, the exposure is carried out for 72 h and feeding is re-dosed every 24 h.