Polar cod embryotoxicity to crude oil water soluble compounds

Experiment Completed: Three days ago, we completed our experiment. It was not without a lot of work and some troubles on the way.

After a mass mortality that seemed pretty much out of control in all our incubators and not at all dose related we were left with too few samples. After barely a week of exposure (start of gastrulation), we decided over a week-end (it always happens then) to start from scratch again!!!

Not without a lot of doubts and questions: Since our rock oiled system had been running for a week already, concentration is the water were already very diluted for this new start. Would we see any effects at all? Were we in such low levels that even sub-lethal effects would be tricky to see?

We needed to through away (well fix…) all the remaining eggs of experiment 1, to prepare the incubators for the new batches. But the fish left in our tanks seemed almost all done with spawning…would we find enough of then for a new start? Were we going to throw all away and not get enough eggs and sperm?

We took our courage “under our arms” and just did it!

New strategy: Obviously the egg quality was very different from female to female…basically spoiling all the incubators if you mixed all the eggs of all available females together. We thus separated the eggs from incubator to incubator, hoping that at least some of the eggs would be of good quality and not just die as soon as the development would reach a little more complicated stage than division…



And it worked, not without the (almost) loss of 2 out of 5 egg batches. But so far the data is really nice…not mortality from the treatment, but clear sub-lethal effects (see fig). The picture shows bachelor student Antoine and colleague Marianne stripping polar cod on sunday evening!

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The Figure shows the larva from one batch of eggs (out of 5) at the end of the experiment (larva left after all previous samplings, etc). The blue bars are the percentage larva free swimming in the incubators, the red are those (still alive) malformed and laying on the bottom of the incubator. The numbers on the bars are the total count of larva per incubator.

Click on this link and you will see the heart beat of our eggs: embryotox



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