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Fish From “Twilight Zone”

17.11.2014
Fish From “Twilight Zone”

Three deep-diving explorers from San Francisco have brought back a batch of living fishes they discovered on a Philippine coral reef at depths where only a few divers dare venture. The team of divers from California Academy of Sciences' Steinhart Aquarium were on an expedition from the National Science Foundation. In cooperation with the Philippine government they explored deep-sea life in Verde Island Passage as a part of a Coral Triangle study. The coral triangle is considered to have the most biodiversity in the world. The Philippines sits at the northern edge of the triangle.

The Verde Island Passage Corridor occupies more than 1.14 million hectares between the provinces of Batangas, Oriental and Occidental Mindoro, Marinduque and Romblon in the Philippines. A 2005 study has dubbed the Verde Passage as the world's "center of the center of marine shorefish biodiversity," hosting the greatest number of shorefish species. A coral survey conducted in Anilao, Balayan Bay, recorded an impressive 319 species and 74 genera of hard corals. More than half the Philippines' documented fish species as well as many globally threatened species can be found here.

Fish From Twilight ZoneThis study was conducted at a depth of between 300 and 500 feet, an area often referred to as the twilight zone. Catching fish at this depth is the easy part of getting them to the surface. Divers at this depth can only stay about 30 minutes before starting an up to five hour journey back to the surface decompressing along the way. Fish caught at this depth seldom make it to the surface alive. Air pockets with the fish, such as the swim bladder, can expand with the decrease pressure and may even explode. One, not perfect method, is for the diver to use a needle inserted into the bladder to allow expanding gases to escape. It does not always work. This team used a device that would be sealed when the fish was caught. The fish would initially be held at the same pressure as it was caught. As the divers ascended they would slowly release some of the pressure in the tank allowing the fish to adjust gradually.


The fish and corals that the divers brought back to the academy in Golden Gate Park are now acclimated to surface waters and will eventually be exhibited there. They include varied species of cardinalfish (Ostorhinchus), wrasses (Oxycheilinus), fairy basslets (Pseudanthias), sand perches (Parapercis) and hogfish (Bodianus).

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