Life Cycle of the Brown Trout

LIFE CYCLE OF THE BROWN TROUT

These timings are approximate. In colder northern climates, or where there is less food available, development can be delayed. Before the days of air transport, the successful introduction of brown trout into distant countries was made possible by reducing the temperature of the fertilised ova and thus artificially prolonging its development. As part of "ecological imperialism", brown trout were introduced to India (1863), Tasmania (1864), Australia & New Zealand (1867), and South Africa (1876). Brown trout from Germany were introduced to the U.S. in 1882, and all these introductions established self-sustaining populations.

fish	age	length	wt	name	habitat	life style
embryonic stage	0	4mm dia	.01g	egg	redd	In November, at the redd, the cock (who often develops a typical 'kyped' jaw in the mating season) rubs his body against the hen to excite her. The hen lays on her side and by moving her tail fin up and down rapidly, she excavates a trench in the gravel. She then releases the demersal eggs (5-10,000) into the trench and the cock releases milt upstream to fertilise the eggs. The eggs have an adhesive outer layer which enables them to stick together.
	1-2 sec	4mm dia	.01g	green egg	redd	The head of the sperm makes its entry through the micropyle (a minute aperture in the ovum membrane) the tail which has propelled it, being left outside. The nuclei of egg and sperm fuse and this single cell immediately divides into two. The egg starts to absorb water as soon as it is released, causing it to swell, harden and close the micropyle, so fertilisation has to be almost immediate.
	14 days	4mm dia	.01g	eyed egg	redd	The embryo has developed sufficiently for the eyes to be seen as two black dots. Fungus is the biggest cause of mortality to incubating eggs.
hatching stage	30-100 days	4mm dia	.01g	hatching egg	redd	The time of hatching depends on the water temperature. An enzyme is secreted which softens the eggshell and allows the alevin to break through. The hatch coincides with the warming spring weather which is also affecting the development of the micro-organisms which are their food supply.
larval stage	30-100 days	16mm	-	alevin	redd	When hatched the alevin retains its yolk sac .
	further 1 month	26mm	-	alevin	river/lake	Yolk has been absorbed and it is fending for itself.
juvenile	further 1 month	-	-	fry	river/lake	Gradually acquire characteristic body shape and colouration which is very dependant on the location. 95% mortality in first three months as a fry in the wild.
brown trout indigenous to UK	3-4 months	>10cm	-	fingerlings	river/lake	Territorial behaviour is exhibited and move to deeper, more secure runs where the food supply is more plentiful. In first summer they grow to about 7.5cm, with the rate of growth dependent on the food supply. During the winter months they move to warmer, deeper locations and the metabolic rate slows down. During the following spring, as the water temperature rises, feeding is resumed.
	22 months	13cm			river/lake	A gradual change of appearance occurs, acquiring the characteristic red blotches. The overall colour can vary significantly, to match the general habitat.
	2+ years	25-45cm		mature	river/lake	Brown trout return annually to the redd to spawn. This may involve travelling from the freshwater lake up the incoming stream, or there may be suitable locations near the lake shore. A gravel substrate is required for a suitable redd.
	5-6 years	45cm	3Kg	normal lifespan		Brown trout are generally regarded as more terratorial, but slower growing than rainbow trout. They feed hardest in the Spring, May and June being regarded as optimal months. Fishing for brown trout on the Irish loughs is often targeted at the annual hatch of Mayfly (usually mid-May).
			32lb	record	Loch Awe	Brown trout can live up to 20 years.

Life Cycle of the Brown Trout