Fly Fishing - The Lifecyle of a Brown Trout
Posted on September 28, 2008 - Filed Under Arts and Entertainment
A detailed overview of the lifecyle of wild brown trout and sea trout. Describes how brown trout mate, spawn, hatch and grow to adulthood.
Spawning
Before hatching, the brown trout ova will have lain for between
four and twelve weeks, depending on temperature, within the covered hollow of a
clean gravel bed known as a redd. The
water will be well oxygenated and quite cool (usually less than 16° C) and most
likely upstream from the trout’s usual haunts. The parent hen trout creates the hollow during
mating by quickly sweeping her tail from side to side across the gravel creating
a nest (the design of the nests provide a percolating effect to the ova and
keep them well oxygenated and free from fungal growths). Into it, she will then lay several hundred of
the 4000 or so ova she will lay in total, before moving slightly further
upstream to repeat the process, simultaneously covering the previous hollow
with the gravel excavated by her tail.
The ova are fertilized by the male trout which, positioned beside and
slightly upstream of her, will secrete milt into the current, some of which
will make contact with the ova.
During this process some of the brown trout ova will be lost
to the current. More will be eaten by
other fish and others will be lost to environmental factors such as poorly
oxygenated (particularly polluted) water.
The oxygen content of water above 24° C will be deadly to the ova and
indeed trout in general. It has been
estimated that only 1% of the ova laid by the female will survive for more than
a year. The mating process also weakens
the trout and it can take as much as three months for them to regain
fitness. Closed seasons for brown trout
fishing were introduced in the UK to accommodate this period of recuperation.
The beginning of the mating period starts in winter and is
governed by day length. The actual calendar
month therefore will be reliant on latitude.
In the UK the period is generally between November and late February.
Hatching
The ova can take from four to twelve weeks to hatch. The length of this period being dictated by
the water temperature, warmer water generally producing quicker incubation
times. The ova develop into the ?eyed
egg’ stage, so called because two black spots are visible through the ova
membrane. Following this, the ova hatch
into yolk-sac fry or alevins. The
yolk-sac is the alevin’s food supply as their digestive system is
developing. The strange looking creature
becomes more recognisable as fry as the yolk-sac, which hangs from the alevins
throat, is consumed. At this stage, a
period of between 12 and 20 days, they emerge from the darkened safety of the gravel
bed to spread downstream and start feeding.
Brown Trout Fry
The fry will tend to shoal where the water flows less
quickly, normally near to the river bank, where they feed on tiny invertebrates
and plankton. By now they are beginning
to develop the marking of their species and become identifiable as brown trout
fry. This is a dangerous stage for the
young trout and they will be fed upon by all manner of creatures including
other fish, mink and birds. Once they have
reached roughly three to four months in age (10 ? 15cm) they are known as
fingerlings. A 95% mortality rate has
been estimated for fish reaching this period.
The Adult Brown Trout
A brown trout is mature between one and two years of age and
theoretically can live for up to twelve years, spending most of their time
avoiding predation and saving as much energy as possible. They tend to be territorially individualistic
and will seek out lies, the bigger fish usually securing the best, which offer
them an energy efficient source of oxygen and a good supply of food. They also require a nearby bolt hole for protection
from the many predators found in rivers and lakes. They will eat almost any creature of the
right size (typically insects, small fish, frogs and even crabs) and will not
move far, maybe as much a metre only , from their lie to find it.
Sea Trout
Sea Trout and Brown Trout are the same species (Salmon trutta). The parent fish mate in the same manner as
the brown trout but they have migrated from salt water to the river rather than
simply moving upstream. They are
generally indistinguishable from brown trout in looks and behaviour although
once they move from the fry stage they are known as a parr rather than a
fingerling.
At about three years old they start to become visibly more
silvery than a brown trout. Now known as
a smolt their gills begin to develop in a manner that will enable them to
process salt water. Once they reach
about a pound in weight they will migrate to the sea where they will feed with
gusto and acquire more weight. Their
return journey back to fresh water to spawn can happen as early as that same
year or in some circumstances they may wait for up to four years.
Vist the Fly Fishing Journal online to search through hundreds of locations to catch brown trout.
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