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One of most interesting demersal species is eelpout or viviparous blenny.

It is the only viviparous species in the Baltic, so-called arctic relict. The word “vivipary” means that the embryo develops inside the body of the mother.

In opposite to most of the fish species, which lay thousands, tens of thousands or even hundreds of thousands of eggs, thus periodically filling the sea with myriads of fish larvae, the reproduction of the viviparous blenny is rather similar to mammals. So, the males fertilize females and some three months later female fish gives birth to typically some tens of young fishes which are already quite similar to the adults.

However, fish don’t have “placental viviparity” which for example humans have. So, while women have uterus in which growing child is connected to mother via umbilical cord, the larvae hatched from the eggs inside the ovary of the female viviparous blenny “swim” freely in the nutritious ovarian fluid which they also “eat and drink”. But no umbilical cord means no navel. Check this out next time when you see this fish.
Viviparous Blenny (Zoarces viviparus)
Viviparous Blenny (Drawing: Nordisk familjebok, band 33, sida 1008)