This is a video about sea trout (Salmo trutta) hatching.
From British daily The Guardian:
* Lizzy Davies in Paris
For the first time since records began a healthy-looking sea trout has been discovered in the Seine, prompting Paris authorities to claim a resounding success in their bid to clean up the river after years of pollution and neglect. …
It is an amazing turnaround for a river which, in the 1960s, was so full of human, agricultural and industrial waste that it was declared a biological wasteland. The Seine used to be so dirty that Parisians joked that swimming in it would be more effective suicide method than jumping off one of its bridges.
But over the past three decades scientists and urban planners – at regional and central government levels – have managed to dramatically reduce industrial discharges and levels of heavy metals such as mercury, lead and copper.