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Saturday, June 6, 2015

Killifish, which does not follow fish rules and survives without water !!!

In mid 1970s – Kairavini Pushkarini ran dry – for sometime, there were small patches of water – containing so many fish – the guppies ! – it further shrank to become a cricket field and exploits of some were so much hailed.....  the one Q that always ran in mind was – when it gets filled with water again – wherefrom those marine life appear ?   In Sept. 2009, when SYMA was involved in cleaning the tank by taking the water out, cleaning the bed and refilling again – fish were bought elsewhere were reintroduced !

Elsewhere, a team  from Indiana University and Dartmouth College has identified genes and regulatory patterns that allow some organisms to alter their body form in response to environmental change. Understanding how an organism adopts a new function to thrive in changing environments has implications for molecular evolution and many areas of science from climate change to medicine, especially in regeneration and wound healing.  The researchers examined how the Atlantic killifish modifies its gills to live in freshwater or seawater.

The name killifish is often used to describe small fish of the Fundulus genus. In Rhode Island, at least two species of Fundulus are present: the common mummichog and the striped killifish. The body shape of these fish is standard for both species. Both have a rounded back and belly, a soft dorsal fin situated far back on the body, a thick and rounded tail, a flattened head, a blunt snout, and a small mouth. A killifish is any of various oviparous (egg-laying) cyprinodontiform fish.  Because of living in ephemeral waters, the eggs of most killifish can survive periods of partial dehydration.

Here is something very interesting read in BBC today -  :  When we think of fish, there are certain assumptions we make. There are male fish, and female fish, and these fish mate to create little fish, which inherit traits from both parents. Over a few years, the little fish grow and grow, until they become old fish. Fish  live in water only. We take that one for granted – hence the phrase "a fish out of water", meaning something weird or odd, something that shouldn't be.  They swim, ideally in huge expanses of water, such as rivers, lakes, seas and oceans.

However, there is one group of fish that does not follow any of these rules. Kriptolebias marmoratus can create clones of itself - Known as killifish, these small innocuous-looking creatures measure just a few inches long. Many species are flamboyant and kept as pets in aquaria. But others look ordinary, and in their own way are among the oddest fish on the planet, a few can claim to be the world's most extreme. That's because some killifish don't reproduce like other fish. In fact, one species doesn't reproduce in the same way as any other vertebrate.

Killifish don't like to grow old – well, not old in the conventional sense. They don't mature like other fish, and many killifish species will live and die with a year. One species survives for less than three months, making it among the shortest-lived of all known vertebrates. They have other ways of breathing, apart from using their gills.

And swimming isn't really their thing. They prefer to live puddles and pools, and have evolved their whole life strategy to cope without water, rather than with it. Some species can survive out of water for more than two months. They will leave it to go for a walk and they even hunt on land. There are a number of killifish species living across Africa and South America. Most are adapted to living in places where water is scarce, or where water levels change drastically from season to season.

Some do live in larger bodies of water, but many survive in isolated pools, created as lakes and rivers periodically dry. At that point all the fish perish !!!  that creates a fundamental challenge – how do the fish survive and reproduce when the water eventually runs out? A new review of how killifish do thishas just been published in the journal Biological Reviewsby Andrew Furness at the University of California, Riverside in the US.  One major adaption, which different killifish species have independently evolved, is to live their whole lives within a single year, using a number of unique tricks. During the wet season, when pools are full, the fish hatch. They quickly grow to maturity and start spawning, which they keep doing until the pools start to dry. At that point all the fish perish. This cycle of life can be so quick that one species, the turquoise killifish (Nothobranchius furzeri) of equatorial Africa, lives for an average of just 10 weeks. The mangrove killifish is the only known vertebrate hermaphrodite that can fertilise itself....... but,  they leave behind eggs in the soil, and these eggs represent the entire surviving populations of killifish.

These eggs survive the dry season in a dormant state, or diapause, buried in the soil until the following rainy season. The return of the rains causes eggs to hatch and the cycle begins anew, says Furness. To do this, different killifish are able to stopping growing as embryos, and then start again when conditions are right. And they can stop at different times during their development, delaying the growth of major organs, such their skulls, hearts and circulatory systems. They can then delay hatching for days, weeks or months.

Most fish breathe with their gills, passing water over them to extract oxygen. The mangrove killifish however, can also breathe through its skin. That’s critical for the fish's survival as mangrove killifish live in the most extreme habitat, within the mangrove forests of the west Atlantic, a tangle of thick tree roots and deep mud.Other fish species frequent mangroves, but they usually move in and out as water conditions vary. Mangrove killifish spend their whole lives here. This water then disappears during the dry season, leaving the fish high and dry. Some survive in diminishing pools, while others are left clinging to the mud or tree branches. Essentially, the fish have moved onto land as the water recedes, and survive by breathing air through their skin. They even excrete waste through their skin and tests have shown that mangrove killifish can survive out of water for up to 66 days.

Extreme, very interesting and some which we would have deemed as not facts, indeed.
With regards – S. Sampathkumar

22nd May 2015.
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