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April 26, 2005

Tiny Reef Fish Has Shortest Life Span

SYDNEY (AFP) -- A tiny reef fish which survives for up to 59 days has the shortest lifespan of any vertebrate animal, according to researchers in Australia.

The discovery of the pygmy goby's lifespan has helped broaden understanding of the evolutionary limits of animal biology, according to a statement from James Cook University in the northeastern city of Townsville.

Postgraduate student Martial Depczynski and Professor David Bellwood studied the life cycle of the pygmy goby (Eviota sigillata) on the Great Barrier Reef.

The fish, which grows to between 11 and 20 millimetres (0.4 to 0.8 of an inch), lays down a series of daily rings in its otoliths or ear stones, helping researchers record lifespan.

"We believe the extraordinary life cycle of pygmy gobies has probably evolved in response to the high mortality rates seen in small coral fish," Depczynski said in the statement.

In such cases, he said, evolution often favoured a 'Live fast, die young strategy in which rapid growth and maturation compensates for reduced life expectancy.

This theory was supported by the Turquoise killifish, which was previously thought to have the shortest lifespan among vertebrates (animals with a spinal cord). These live in rain pools in Africa and must finish their reproductive cycle before the pools dry up.

Even though pygmy gobies survive less than two months, they lead a hectic life.

"They hatch from minute eggs which are vigorously defended by the father," said Depczynski.

"They then develop as ocean larvae for three weeks, nearly half of their lifetime, before settling on a coral reef where they grow to sexual maturity.

"With a reproductive life span of just 25 days, the female pygmy goby lays only three clutches of around 136 eggs in a lifetime."