all about trout


rainbow trout

Trout is the name for a number of species of freshwater fish belonging to the genera Oncorhynchus, Salmo and Salvelinus, all of the subfamily Salmoninae of the family Salmonidae. The word trout is also used as part of the name of some non-salmonid fish such as Cynoscion nebulosus, the spotted seatrout or speckled trout.

Trout are closely related to salmon and char (or charr): species termed salmon and char occur in the same genera as do trout (Oncorhynchus – Pacific salmon and trout, Salmo – Atlantic salmon and various trout, Salvelinus – char and trout).

Most trout, such as lake trout, live in cold, freshwater lakes and/or rivers exclusively, while there are others such as the Rainbow trout (Onchorynchus mykiss), which may either live out their lives in fresh water, or spend two or three years at sea before returning to fresh water to spawn; a habit more typical of salmon. A Rainbow trout that spends time in the ocean is called a Steelhead.

Trout that live in different environments can have dramatically different colourations and patterns. Mostly, these colours and patterns form as camouflage, based on the surroundings, and will change as the fish moves to different habitats. Trout in, or newly returned from the sea, can look very silvery, while the same fish living in a small stream or in an alpine lake, could have pronounced markings and more vivid colouration.  It is also possible that in some species this signifies that they are ready to mate. In general, trout that are about to breed have extremely intense colouration. They can look like an entirely different fish outside of spawning season. It is virtually impossible to define a particular colour pattern as belonging to a specific breed; however, in general, wild fish are claimed to have more vivid colours and patterns.

As a group, trout are somewhat bony, but the flesh is generally considered to be tasty. The flavour of the flesh is heavily influenced by the diet of the fish. For example, trout that have been feeding on crustaceans tend to be more flavourful than those feeding primarily on insect life.  According to the British Nutrition Foundation, trout contain one of the lowest amounts of dioxins (a type of environmental contaminant) of all oily fishes.

Trout can live for approximately seven years.  Most trout are born, mature, lay eggs and die in lakes or streams. Some trout, however, become very large migratory fish and can travel more in their seven years than some people do in a lifetime!  In this way, they are similar to their salmon relatives. In fact, they may migrate from their lake or stream to the ocean and back three or four times.

At two years old, trout are ready to reproduce. Their colours change by getting brighter, and they find mates. Some species mate in the autumn, others in the spring. A female trout lays her eggs which are then fertilized by a male in a redd (nest), built in the gravels of a freshwater lake or stream. Baby trout (alevins) hatch before they are ready to swim, so live on the yolk from their egg sacs.

Young trout (troutlet, troutling, fingerling or fry) use up the food in their egg sacs and swim around in the lake or stream where they were born. They now have to find their own food, mostly tiny organisms called zooplankton. Over the next few years, fry grow by eating mostly insects and worms; where they develop their spots, stripes and brilliant colours of an adult trout.

Many trout live in just a short stretch of stream and need just a few basics to survive: cold/clean water, food, places to hide from predators and clean gravel to lay their eggs in.  All the land around a stream that drains into it, is known as the stream’s watershed. Trout are affected by what happens in their whole watershed; therefore something that happens on the land can change, have an impact or compromise their stream habitat.

Fish can see, hear, smell and feel but none of their senses are quite as a humans.  A trout has a well-developed sense of smell by using special holes known as ‘nares’ to sniff out tiny bits of chemicals in the water.  As they don’t breathe air, they can’t smell anything outside of their watery habitat.  Fish can use their sense of smell to find their way back home to where they were born, because they remember exactly what their home streams smell like!

Trout have broad angle vision, so they can see very well when they look up, but vision is blurred if looking from side to side.  This explains why they are so good at dodging predators, such as birds, that come from above!  However, a trout can look and focus out of both corners of each eye simultaneously meaning that it can see in almost every direction at once.

Trout have inner ears, allowing them to hear just as a human would.  Trout also have two lateral lines, one on either side of the body; special sense organs used to ‘feel’ sounds.  Lateral lines allow trout to hear sounds too low for human ears.  They also use lateral lines to find food, escape predators and keep away from obstacles.



Trout farming was introduced to the UK in the 1950’s by a Danish entrepreneur. Since that time the industry has grown to its current size of almost 360 trout farms.

Rainbow trout, although native to North West America, has been introduced to regions throughout the world. Having been introduced in the 19th Century, it is the most popular trout to farm in the UK, as it copes best with the climate and farming system.

Around 16,000 tonnes of Rainbow trout are produced in Britain each year, with around 75% of this farmed by table producers.

Fish farms usually concentrate on different aspects of the life cycle. Hatcheries produce ova from brood stock and sell on to fingerling producers who grow fingerlings and fry from the eggs. Fingerling producers supply Re-stockers and Table producers. Table producers in turn provide fish to Processors, while Re-stockers will supply Fisheries. Some farms may undertake several of these business activities and in addition may have a shop, a smokery/processing unit, or a Fishery (where anglers can fish in artificially stocked lakes) that is often open to the public.

Trout is farmed widely in the UK, but particularly in central and southern Scotland, south England and North Yorkshire.

Although trout can be bred to different sizes, they generally reach their harvesting size at 300-400g in approximately seven and a half months, building muscle by swimming against the current of the water as it passes through the farm.

Once harvested, the trout will be processed for use. Larger farms often have processing facilities on site, which contain machinery designed to gut, fillet, smoke and pack the fish, depending on what is required. The trout may then be sold direct to customers at farm shops, or sent to wholesale markets, caterers or retailers.


• Trout have teeth on the roof of the mouth, called vomerine teeth, and this helps to distinguish trout from salmon. In trout the teeth are a strong double row; in adult salmon in freshwater, they are small and a single row or absent.

• Trout scales have growth rings, as new hard tissue is added around the edges as they grow. They can be read just like growth rings in a tree.  However, trout don’t have scales for the first month of their life.

•  The majority of trout die before their first birthday. Mortality rates in their first year of life are typically 95% or greater, falling to around 40 – 60% in subsequent years.

• Trout can rapidly change colour, getting darker when being aggressive, lighter
when being submissive or in response to changing background colour.

• Trout, like most other fish, cannot regulate their body temperature – they tick over at the same temperature as the water in which they swim. The temperature tolerance levels of trout range between a couple of degrees up to around 25°C. However, trout will be uncomfortable in water above about 20°C.

• The earliest account of flyfishing (AD 200) is by the Roman scholar Aelian who recorded Macedonians ‘cast with rods to speckled fish’.

• Tickling trout is an old poaching method of feeling for trout underneath undercut river banks and hoisting them out by hand.  Trout don’t laugh when they are being tickled!

• Trout have a brain about the size of a pea, but are very capable of (apparently) outwitting fishermen most of the time!

• The calm before a storm may be one of the best times to catch fish, including trout. Studies have shown that trout respond to sudden changes to their environment like a rain storm by feeding heavily.

• After the last Ice Age, the rivers of Britain were populated by wandering sea trout who found empty habitat niches in the newly ice-free rivers.

• There is only one true native trout species in the British Isles: Salmo trutta.

• Trout and salmon are especially vulnerable to climate change and global warming because they are dependent on an abundance of clear, cold water. As coldwater habitats warm, rising temperatures will have negative impacts on a variety of life history phases—from eggs to juveniles to adults (Trout Unlimited, 2012).


rainbowtrout browntrout seatrout
Rainbow Trout Brown Trout Sea Trout

Trout Unlimited Stream Explorers
British Trout Association 

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