# Histotrophy

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{{Short description|Form of aplacental viviparity}}
'''Histotrophy''' is a form of [matrotrophy](/source/matrotrophy) exhibited by some live-bearing [shark](/source/shark)s and [rays](/source/Batoidea), in which the developing [embryo](/source/embryo) receives additional nutrition from its mother in the form of uterine secretions, known as [histotroph](/source/histotroph) (or "uterine milk"). It is one of the three major modes of [elasmobranch](/source/elasmobranch) reproduction encompassed by "[aplacental viviparity](/source/aplacental_viviparity)", and can be contrasted with yolk-sac viviparity (in which the embryo is solely sustained by [yolk](/source/yolk)) and [oophagy](/source/oophagy) (in which the embryo feeds on [ova](/source/ovum)).

There are two categories of histotrophy:

*In '''mucoid''' or '''limited histotrophy''', the developing embryo ingests uterine [mucus](/source/mucus) or histotroph as a supplement to the energy supplies provided by its [yolk sac](/source/yolk_sac). This form of histotrophy is known to occur in the [dogfish shark](/source/Squaliformes)s (Squaliformes) and the [electric ray](/source/electric_ray)s (Torpediniformes), and may be more widespread.
*In '''lipid histotrophy''', the developing embryo is supplied with [protein](/source/protein) and [lipid](/source/lipid)-enriched histotroph through specialized finger-like structures known as '''trophonemata'''. The additional nutrition provided by the enriched histotroph allows the embryo to increase in mass from the egg by several [orders of magnitude](/source/orders_of_magnitude) by the time it is born, much greater than is possible in mucoid histotrophy. This form of histotrophy is found in [stingrays and their relatives](/source/Myliobatiformes) (Myliobatiformes).

==References==
* {{cite book |title=Reproduction and Sexuality in Marine Fishes: Patterns and Processes |author=Cole, K.S. |publisher=University of California Press |year=2010 |isbn=978-0-520-26433-5 |pages=8–9}}
* {{cite book |title=Reproductive Biology and Phylogeny of Chondrichthyes: Sharks, Batoids and Chimaeras |editor=Hamlett, W.C. |publisher=Science Publishers |year=2005<!--|isbn=1-57808-271-4-->|isbn=1-57808-314-1 |pages=46–47}}

Category:Embryology
Category:Ichthyology
Category:Live-bearing fish

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Adapted from the Wikipedia article [Histotrophy](https://en.wikipedia.org/wiki/Histotrophy) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Histotrophy?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.