Fish of the reservoirs and burns


There is very little survey data regarding the fish populations of the country park reservoirs. What information that does exist relates to when stranded fish were relocated when the reservoirs were drained in 1995. This provided a good record of fish species in the reservoirs at the time. Four species were found: pike; brown trout; roach and perch. All these species, apart from brown trout, were introduced to the reservoirs, most likely for fishing. It is illegal to introduce fish to water bodies as this disrupts their natural ecology and can lead to negative effects on fish stocks and other wildlife.

Pike (Esox lucius)

Pike is easy to identify with its green and cream mottled markings, long body and a mouth full of sharp teeth! Pike adapt to suit their conditions. They live in a range of water temperatures and clarities, feeding upon numerous prey species and living in various sized groups. The pike is very flexible and can adapt to changing environments, altering food sources, tactics and behaviour. Spawning takes place between March and May and this process can last several weeks. During spawning the much larger female may be joined by up to three males. Larger females can lay up to half a million eggs, these sticky eggs are attached to underwater plants until hatching. Once making it past the early stages of life Pike grow rapidly.

Brown trout (Salmo trutta)

The brown trout is one of Scotland’s few native fish. It belongs to the Salmonidae family, which includes Atlantic salmon and rainbow trout. It is most closely related to the Atlantic salmon and in some cases is still able to cross breed. It can live in still or flowing water with water quality being the major confining factor. There is a vast variation in strains of brown trout, from silvery with bright red spots to brown yellow. The trout is a predator and has a wide diet of both aquatic and terrestrial insects, including blood worm, mayflies and grasshoppers. Spawning takes place on a gravel bed in approximately November to December. Egg development is dependent on water temperatures but typically takes three to four months.

Perch (Perca fluviatilis)

Perch can easily be identified by their greeny-brown colouration, distinctive stripes and dorsal fin containing 13-15 long spines. The dorsal fin also has an intense dark spot at the base. The tail and under fins are orangey in colour. The perch lives in slow-moving rivers, deep inland water and ponds. Like most fish they prefer to be near the cover of vegetation, under water crevasses or structures. Spawning takes place in April when the females produce sticky bands of eggs which they wrap around vegetation awaiting fertilisation. After approximately three weeks the eggs hatch, initially feeding from the yolk sack and moving onto floating fragments. Young perch shoal, staying close to banks, but as they reach maturity they become a lot more solitary and begin to feed on insects and small fish, including perch.

Roach (Rutilus rutilus)

The roach has a scale-less head and large scales across their relatively wide bodies. They have bright silvery sides and a dark brown/green back. The pelvic and rear fins range in colour from orange to bright red. The iris of the eye is also red. Roach like slow moving rivers or inland water bodies, especially where there is substantial weed growth. Roach feed upon insect larvae, snails, insects and plant matter. Spawning takes place between April and June, eggs – as many as 100,000 – are yellowish and attached to algae, vegetation and under water tree roots. Eggs will hatch between 9-12 days later.


The Brock Burn springs south west of Newton Mearns in East Renfrewshire and travels north across the entire country park. It links into the Barrhead dams at Balgray Reservoir and then heads through Darnley Mill towards Priesthill. It meets with the Levern Water in the Pollok area of Glasgow. The Aurs Burn from Barrhead and the Walton Burn are the Brock Burn’s two main tributaries.

Studies of the fish populations in the Brock Burn system were carried out by the Clyde River Foundation (CRF) in 2005 and 2006. Their studies were partly funded by the country park project. The CRF used 'electrofishing' to carry out the studies. This method generates an electric field in the river that temporarily stuns the fish. This is the most effective method when studying the ecology of a river catchment wide area.

Five fish species were found in the two sampling sites within the country park: brown trout; three-spined sticklebacks; stone loach; minnow and eel.

Brown trout (Salmo trutta)

Brown Trout are widespread and common in the Clyde and its tributaries. They prefer clean water systems and their abundance in the Brock Burn is a good sign of this. In the Brock Burn it has been noted that the Brown Trout are somewhat unique in the Clyde system as they have a red colouration to the leading edge of the dorsal fin.

Three-spined stickleback (Gasterosteus aculeatus L.)

The three-spined stickleback is a small fish usually 4-6cm in length. Its colour varies between a brown to green/brown with a lighter under belly. This fish has three spines before the dorsal fin – this is thought to make it awkward for predating fish to swallow them. They feed upon small water invertebrates, fish eggs and young fish. Spawning is an interesting process - males build an underwater nest of vegetation, females come and look at the nest and if they like it lay their eggs, this can be done by several females. Once the eggs are fertilised the male guards the nest wafting water over them as the oxygen in it helps development. Once hatched the male stays with the young for about one week until they can lead independent lives feeding on small worms and water fleas. It is extremely unusual for fish to show any parental care which makes this species really special!

Stone loach (Barbatula barbatula L.)

The Stone Loach grows to approximately 14cm and is easily identified by six barbells around the mouth which are used to locate invertebrate prey when feeding at night. Its colouration varies from brown, green and yellow with darker blotches on the side and a lighter underbelly. As its name suggests stone loach can usually be found under rocks, gravel and in crevices waiting to catch small creatures that pass by. It prefers fast moving, clean rivers with a gravel or sand bottom. Breeding takes place from April to June when eggs are laid amongst gravel or water plants.

Minnow (Phoxinus phoxinus L.)

The minnow is the smallest member of the carp family and rarely grows larger than 10cm. Minnows have a rounded body with very small scales, the sides and upper body are an olive green colour with a creamy underbelly. They have a series of darker blotches along their sides. A breeding male can be spotted by its red belly. These fish are mainly found in rivers and streams that are clean and have well oxygenated water. They eat small insects, algae and water plants. They breed between April and June with the female laying eggs in gravel at a slow moving point in the river.

European silver eel (Anguilla anguilla L.)

Eels are common across the UK. Adults are easily identified by their long narrow body, protruding lower jaw and slimy skin. They are usually brown on the back and a dull yellow on the sides. As they reach maturity the back grows darker and the belly becomes silvery. They are bottom feeders, eating insect larvae, worms, molluscs, crustaceans and dead fish in half light.

The eel has an amazing life cycle; breeding takes place in winter in the Sargasso Sea (western Atlantic Ocean) - where it is thought all European eels breed – then young eels migrate to fresh water where they grow, before returning to sea to spawn. The eel larvae drift in plankton for up to three years before they reach the coast of Europe travelling on the Gulf Stream. They then transform into ‘glass eels’ named as such due to their transparency. As they travel up river inlets into fresh water they become darker and are known as elvers. Here they grow and take the dull yellow colour of adults. Eels stay in fresh water until they reach sexual maturity (when they turn to a silvery colour) which is between 6-12 years for females and 9-20 years for males.

At this time they return to the sea on a dark, stormy or moonless night. Throughout their life they live in mud, under stones and crevices. This species has a very long life span – eels can reach a maximum age of 85!