Trout FishingEngland

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The life cycle of trout

     The life cycle of trout has not changed that much in millions of years before the first trout angler arrived on our planet. All trout species are born in fresh water including the sea going forms. Female trout lay their eggs in a redd ( i.e. a shallow hole that acts as a egg nest) which it makes using its tail fin. The female trout lays its eggs in the redd in quick  flowing river or stream water.Lake trout lay their eggs close to the  river or stream that feeds the lake or  in certain circumstances where  possible  may go upstream to spawn before returning to the lake. The reason for this is that trout eggs have a relatively thick membrane which require oxygen-rich water to keep them alive. Slow moving streams and lakes make poor spawning grounds for trout. Spawning trout seek out a silt free gravel bed to make a redd. When this is dug out the female is joined by the male in the redd and the female lays up to 4,000 eggs which are simultaneously fertilized by the males milt. Many eggs are lost during this mating process carried away by the current and many are devoured by fish. The time that  spawning occurs is related to latitude (i.e. the length of the day).In England and Wales this usually occurs in November to December for native brown trout. It is estimated that only 1% of all eggs laid will  make it to their first year. Trout do not guard their eggs although the female will often cover the eggs with gravel using her tail fin to protect them after laying. The fertilized eggs are about 4 mm in diameter and dependent upon the trout species will hatch in between 3 to 5 months. The period of incubation also depends upon the temperature of the water. As a general rule the warmer the water the quicker the eggs will hatch. By spawning in November to December native brown trout in England and Wales give their young the best possible chance of survival because as the water warms slightly in the spring the types of food the young need to grow when they hatch also starts to proliferate. However, if the water gets too warm at above 10 to 15 degrees centigrade the water then looses too much dissolved oxygen which can be fatal to the eggs, with the advent of global warming it remains to be seen what effect this will have on future trout populations. The long period of incubation also leaves the eggs somewhat susceptible to predators and disease at this stage in the life cycle of trout.There are very few places in the UK where the rainbow trout which was introduced from North America breeds.Almost all rainbow trout in the UK are artificially propagated and are sterile.

   After about twenty weeks at 10 centigrade the trout egg embryos have developed enough for two black eye spots to be visible through the egg membrane . This is known as the eyed egg stage of development. Providing the water temperature has been affable when its time for hatching an enzyme is released in the eggs which causes the eggs membrane to soften thereby allowing the newly formed alevins or sac-fry to escape. This is known as the hatching stage. Alevins are about 16 mm  long and still have their their yolk sacs attached to them. This is known as the swim-up stage. Alevins are light sensitive and normally remain hidden from the light and predators in the gravel bed feeding off the rich nutrients in their yolk sacs. In around ten to twenty days their yolk sacs have been absorbed into their bodies and they have reached about 26 mm in size. After this they emerge as fry feeding on plankton and pieces of floating organic matter. Another month and the fry have start  to take on the distinctive markings of their species and have reached the juvenile stage of development. Upon reaching 10 to 15 centimeters young trout fry are referred to as fingerlings.

The life of young trout is very dangerous, predators such as kingfishers, herons, otters, and vermin such as mink and cormorants along with other fish including its own species are always a threat to its survival. Responsible trout anglers always release young native trout thereby encouraging the life cycle of trout .Sea trout (or sewin in Cymru) differ in their spawning habits only in the fact that sea trout return from the sea to fresh water to spawn. This also goes for other species of sea trout such as the American steelhead trout much favored by our friends the yanks and the ocean trout beloved of many Aussie trout anglers. Have a nice day and g’d day t ya all.