Blue crab embryos develop in egg sacs (nine stages) for 14 to 20 days after which they 'hatch' from the egg sacs into a swimming zoea stage (stage 10). Until they emerge from the egg sacs, embryos depend on lipids and lipovitellin stored within the eggs. A number of organic and inorganic toxicants were found to inhibit hatching. For example, at a fenvalerate concentration of 3.2 μg l-1 only 50% of embryos hatched while 90 to 95% of the controls hatched. Pesticides, including chlorphyrifos, cypermethrin, fenvalerate and diflubenzuron, inhibited hatching at concentrations ranging front 1.8 to 5.9 μg l-1 (EC50s). The most toxic of the metals tested was mercuric chloride and the most toxic of all compounds tested was methyl mercury. The addition of mercuric chloride at concentrations above 4.0 μg l-1 to stage three embryos resulted in stage 7 embryos with no heart beat. Abnormal eye spots were produced by exposure to high concentrations of metals. Time lapse video with a high definition digital camera was used to follow and document both normal and abnormal developments of the eyes, hearts and hatching process. In addition, the time lapse video was used to determine the time of the first appearance of a pulsating heart and eye spots. The advantages of crab embryos as a test for development toxicants include: (1) availability of embryos for most of the year: (2) sensitivity of embryos to toxicants; (3) nutrients for developing embryo are obtained from yolk so no external feeding is necessary; (4) good reproducibility of the assay; (5) use of culture plates allows the testing of many toxicants and concentrations in a small space and at low cost; (6) tests take from 2 to 6 days depending on stage used at the beginning of the assay; (7) obvious end point of the assay, i.e. emergence of zoea from egg sac.
All Science Journal Classification (ASJC) codes
- Aquatic Science