Life Cycle of the Rainbow Trout

LIFE CYCLE OF THE RAINBOW TROUT

The rainbow trout was introduced into the UK from North America. There are exceptional places in the UK where wild rainbow trout breed naturally, the overwhelming majority of rainbow trout in the UK are bred artificially in hatcheries for supermarkets or put-and-take fisheries. The sea-going version in the USA is called a 'steelhead'.

ALTERNATIVES

Brook trout, Tiger and Golden trout have also been brought from USA.

fish	age	length	wt	name	habitat	life style
embryonic stage	0	4mm dia	.01g	egg	hatchery	Eggs and ovarian fluid from 3 females are stripped into a bowl (containing no water, so that the micropyles remain open for longer). Milt from a male fish is stripped into the bowl and thoroughly mixed with the eggs.
	1-2 sec	4mm dia	.01g	green egg	hatchery	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.
	14 days	4mm dia	.01g	eyed egg	hatchery	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. This can be treated with Malacite Green fungicide.
hatching stage	30-100 days	5mm dia	.01g	hatching egg	hatchery	The time of hatching depends on the water temperature. An enzyme is secreted which softens the eggshell and allows the alevin to break through.
larval stage	30-100 days	16mm	-	alevin	hatchery	When hatched the alevin retains its yolk sac and this may be referred to as the SWIM-UP stage.
	further 1 month	26mm	-	alevin	hatchery	Yolk has been absorbed and the alevin is fed on a high protein diet.
juvenile	further 1 month	-	-	fry	hatchery	Gradually acquire characteristic body markings of bluish or purple colour on the back and 7-11 oval spots of the same colour (parr marks) along the middle of each side.
rainbow trout	3-4 months	>10cm	-	fingerlings	hatchery	May - September are active feeding months. The fish are fed on high protein pellets.
	20 months	30cm	250g	'portion size'	hatchery	Supermarket fish
	24 months	25-45cm	1Kg	mature male	freshwater	Put-and-take fishery trout are usually infertile.
	36 months	25-45cm	1Kg	mature female
	5-6 years	45cm	3Kg	normal lifespan	freshwater	Mature trout released into the reservoirs at the 36 month stage will grow on to about 8lb.
				record	freshwater	The record-size trout are specially bred for the purpose.

Life Cycle of the Rainbow Trout