UK rockpool fish suckles young

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The unborn embryos of the European eelpout, (Zoarces viviparous) have been discovered 'suckling' while still inside their mother's body, explaining the mystery of how they gestate for six months, one of the longest periods of any fish.

Details of the discovery are published in the Journal of Experimental Marine Biology and Ecology. Scientists in Denmark made the discovery while researching other aspects of the fishes physiology. 

The eelpout is a viviparous species, (giving birth to live young), but it has long been speculated upon how it managed to give birth to such large fry after such a protracted pregnancy when egg yolk alone would not sustain the young.

Professor Peter Skov of the University of Copenhagen explained how he came across embryos attached to the female fish's ovarian follicles while dissecting a recently dead specimen.

Further study discovered that a canal at the tip of each follicle supplied the developing embryo with a fluid containing proteins, fatty acids and glucose as well as rich in oxygen allowing the embryos to remain inside their mother long after they have used up their yolk sack.

The European eelpout, also sometimes known as the Viviparous blenny is found around the coast of the UK as well as much of Northern Europe. Growing to around 50cm/20" it is usually found in coastal waters, particularly rocky shores and can often be found completely out of the water at low tide under seaweed as it can breathe air. Females give birth to up to 400 fully-formed young.