Fish can survive without the Sun

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Understanding how some fish can obtain their energy from a non-photosynthetic source makes it plausible that life may exist on planets less hospitable than the Earth.

A study authored by Katherine Roach, Michael Tobler and Kirk Winemiller and published in the current issue of the journal Ecology provides evidence that a vertebrate is capable of deriving most of its organic carbon and nitrogen without the involvement of energy from the Sun.  

The research focused on populations of the Atlantic molly (Poecilia mexicana) found living in a stream system associated with the Cueva del Azufre (sulphur Cave) in Tabasco state, Mexico.

This stream system consists of four habitat types with different combinations of exposure to light and toxic hydrogen sulphide: a sulphidic cave stream within the Cueva del Azufre, the sulphidic surface stream El Azufre (which flows out of the sulphur cave and is fed by additional sulphide springs at the surface), a non-sulphidic cave stream within the Cueva Luna Azufre, and various non-sulphidic surface streams and rivers.

The authors analysed gut contents and stable isotope signatures (of carbon and nitrogen) of primary producer and consumer tissues to estimate the production sources assimilated by the mollies.  

Based on their results, the authors concluded that while the mollies from the non-sulphidic cave and surface streams and those from the sulphidic surface streams utilised energy primarily derived from the Sun (i.e. directly or indirectly from photosynthetic organisms), those from the sulphidic cave streams obtained their energy mostly from sulphur-oxidising bacteria (which do not utilise energy from the Sun, but obtain it from the toxic hydrogen sulphide in a process known as chemoautotrophy instead).  

This unique food chain consisting of hydrogen sulphide to bacteria to fish contributes further evidence of alternative energy production sources supporting animals in extreme environments.

According to senior author Katie Roach: " ecosystem in the cave is basically self-sustaining without much input from plants at the surface. As a result, our research has implications for discovering life outside the earth. If these complex vertebrates can thrive on sulphur bacteria, why couldn’t similar, more evolutionary derived organisms be supported by chemoautotrophic bacteria on other moons or planets such as Europa, one of Jupiter’s moons? It may not be altogether impossible."

For more information, see the paper: Roach, KA, M Tobler and KO Winemiller (2011) Hydrogen sulphide, bacteria, and fish: a unique, subterranean food chain. Ecology 92, pp. 2056–2062.

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