The diagram below summarises the main trout lifecycle stages. For an ext detail on every stage, see the pertinent section in the text and also photographs below.

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Sea trout (also called sewin or peel) and brown trout room the same types (Salmo trutta) yet sea trout adults go to sea to feed and also return to freshwater to spawn. The sea trout lifecycle is slightly different – inspect the sea trout page fordetails.

Trout lay your eggs in nests in the flow gravels, recognized as redds. The female (hen) builds the nest, usually between November and also January when the water is cold and also carrying lots of oxygen, due to the fact that that is what the eggs require tohatch.

She looks for gravel with agood circulation of water pass through, therefore the gravels need to be loosened and largely cost-free from silt and also between 5and 50mm indiameter.

The hen fish will start by testing the gravels with her anal fin. If the gravels room good, she will certainly dig ahole, transforming on her side and also flexing herbody.


Once ahen fish starts to dig in the gravel, she will attract the attentionof males that will follow each other and also attempt be in place simply when she lays she eggs. The procedure of digging and also chasing deserve to last for aquite little bit (hours or even days) and also at this time the is regularly easy to see trout.Below is avideo the sea trout on aredd in the Dorset Frome, courtesy of john Aplin, showing usual pre-spawning behaviour.

The video below provides an underwater view of ahen sea trout cutting aredd.Video courtesy of chris Conway and the Ness FisheriesBoard.

Eventually the hen fish will certainly release some of her eggs right into the redd. The male (cock) fish will release his sperm or milt end the eggs to fertilise them. The hen then moves forward and digs again to throw up gravel to cover the fertilised eggs.Sometimes the eggs space fertilised by asmall young maletrout referred to as a ​‘precocious parr’. In the video clip below, ayoung trout sneaks in at roughly 32seconds.Video courtesy of chris Conway and the Ness FisheriesBoard.

On some riverswith clean water,atrout redd have the right to be very obvious – it looks choose apatch of very clean gravel, heaped into amound frequently with ahollow downstream the the mound. Redds can vary big in size, indigenous 50cm2to end 150cm2.Small trout generally develop smaller redds in finer gravel, and huge sea trout can create redds the dimension of akitchen table height with lot bigger stones. How countless eggs space laid likewise depends top top the dimension of the hen trout – a500g trout will frequently deposit roughly 800eggs.

For more information on trout spawning and also identifying redds, download this PDF document.

As the egg develop, you have the right to see trout ova develop within them. This is referred to as the ​‘eyed ova’ stage. How easily the eggs will hatch counts on water temperature – cooler water way slower advancement in theegg.

At 7.80C the eggs will certainly hatch in 60days yet at 4.70C they will take 97days to hatch. Generally, that is presume that many eggs hatch in February and the age of atrout is measured from this ​‘birthday’. How many eggs flower varies enormously depending upon quality that the water and also gravel – it have the right to be as low as 4%, or exceed 80% where conditions are reallygood.

The freshly hatched trout are dubbed alevins, and also they live in the gravel, feeding turn off the remaining yolk the is fastened to their body for 14 – 30days, again temperature influencing their rate of development.


Once the yolk has actually been eaten, the alevin come to be fry, arise from the gravel, relocate towards the light and also start to feed on tiny insects in thewater.

Mortality rates at this highly breakable stage are very high. The fry are just afew centimetres long and consume alot the energy, therefore they require to discover food quickly, and also plenty that it. They also become territorial – they want to be out of sight of other fry, so require habitat that has plenty of stones and also plants to allow them come hide from the neighbours. And also they space still very tiny, so they require shallow water (1 – 40cm) that isn’t as well fastflowing.

The transition from living off theyolk to independent feeding is acritical life stage,and the one in ~ which the bulk of mortality takesplace.


A trout of less than one year old is called aparr.They are recognisably trout now, yet have distinctive fingerprints or parr marks along the side which they shed as lock getolder.

Parr have similar habitat needs to fry: lot of of cover to hide from each other and also from predators, specifically fish eat birds. They have the right to cope with deeper and also faster water together they grow. In stimulate to discover their own territory, castle will progressively drop downstream through the circulation rather 보다 fight their method up against theflow.


It is quite an overwhelming to tell whether aparr is salmon or trout. One clue is the habitat — salmon parr tend to prefer quicker riffles 보다 trout together they space stronger swimmers. The diagram listed below from the Atlantic Salmon Trust, identify the main differences.

Salmon parr (I) can generally be identified from young brown/​sea trout (II) by the more streamlined shape, deeply forked tail, much longer pectoral fin, lack of orange top top adipose fin, smaller sized mouth, cheater snout, just 1 – 4 spots on gill sheathe (often one big spot), well characterized parrmarks.

Adult brown trout that remain in the flow retain your territorial behaviour, and will safeguard their areas or ​‘lies’. Most trout will have actually afeeding lie, commonly in an area wherein the river existing acts together aconveyor belt for food for this reason they have the right to simply confront upstream and catch invertebrates as they drift past, expending as little energy as possible. Castle will also have one or more resting lies, wherein they are much safer from predators. Generally this will certainly be under an undercut bank, tree root, absent or log.Larger trout will frequently occupy pools in the river specifically when resting and also in warmer weather. Deep pools space cooler 보다 the shallow riffles in summer, and also the depth provides them feeling secure frompredation.

As trout become older, lock can adjust from eat invertebrates to eating small fish (they become​‘piscivorous’) and also their fishy diet can include young trout and also salmon.A piscivorous trout is no the very same as aferox trout, which are uncovered in some deep glacial lakes and also eat fish, however which are genetically quitedistinct.

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Based on range readings, the basic view isthat trout will generally live for roughly 6or 7years, but this number is very variable. Over there is anecdotal and also photographic proof that some trout can live agreat transaction longer.For example,ferox trout life in cold, nutrient-poor lochs have the right to be very slow cultivation andlong-lived. A23-year-old fish from Loch Killin, Inverness is theoldest ferox onrecord.