Life Cycle of the Sea Trout

LIFE CYCLE OF THE SEA TROUT

fish	age	length	wt	name	habitat	life style
embryonic stage	0	4mm dia	.01g	egg	redd	In November, at the redd, the cock 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, 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	Yolk has been absorbed and it is fending for itself.
juvenile	further 1 month	-	-	fry	river	Gradually acquire characteristic body markings of bluish or purple colour on the back and 9 - 10 oval spots of the same colour (parr marks) along the middle of each side. 95% mortality in first three months as a fry in the wild.
sea trout indigenous to UK	3-4 months	>10cm	-	fingerlings	river	Territorial behaviour and migrate downstream 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 deeper pools and the metabolic rate slows down. During the following spring, as the water temperature rises, feeding is resumed and a gradual movement downstream occurs.
	22 months	13cm			river	A gradual change of appearance occurs. A deposit of guanine in the scales gives a silvery tint and they become distinguishable from the brown trout with whom they share the habitat. In a further month the parr marks have almost disappeared and they collect in shoals in the lower reaches of the river.
	25 -28months	20cm		smolt	sea	The shoals drop downstream during the night. A 'spate' will mitigate the change from fresh to salt water and particularly at these times the fish migrate to sea. Those fish not migrating return upstream for one more summer's growth.
	28- months	20cm			sea	The abundant food supply in the sea allows them to grow rapidly. Sea trout remain within the continental shelf, some even within the estuary.
	2+ years	25cm		whitling finnock herling peal	sea to river	After only a few months at sea most return to the river to spawn. After spawning they return to sea.
	2+ years	25-45cm		mature	sea to river	Sea trout return annually to the river to spawn. As they do not venture as far afield as the salmon the homing instinct is less developed and there is a tendency to 'stray' into other nearby rivers. This is a useful 'fault' as it means that there is a natural repopulation of denuded rivers.
	5-6 years	45cm	3Kg	normal lifespan
				record

ALTERNATIVE NAMES

Latin name	Wales	USA	Cornwall	Lake District	W. Ireland	UK
Salmo Trutta	sewin	steelhead	peal	herling	white trout	sea trout salmon trout finnock

Life Cycle of the Sea Trout