Nesting Icefish

Scientists on a German icebreaker called the RV Polarstern were towing an underwater camera across the floor of the Weddell Sea off Antarctica. They were investigating this area because comparatively warm water – 3.6 Celsius, or 38.5 Fahrenheit – was welling up there. They found that someone else was interested in this warm water: about 60 million nesting icefish. 

This species of icefish (Neopagetopsis ionah) lay about a 1,700 eggs in each of these seafloor nests, which the adults then tend. The fish had previously been known to nest in colonies, but the biggest colony seen before had about 40 nests. This one extended across 240 square kilometers of sea floor (93 square miles). It seems that the rising "warm" water is full of zooplankton, on which newly hatched icefish feed, so the adults were all trying to bring forth their babies into this rich environment.

Incidentally the crocodile icefish (including Neopagetopsis ionah) are the only vertebrates that completely lack hemoglobin. They just let oxygen dissolve in their blood plasma and somehow get by with that.