Adaptations of river creatures
Questions and facts for teachers to lead class discussions
focusing on the adaptations of freshwater creatures found in the Itchen.
Otter
Freshwater Fish
Dragonfly
Otter
Otters are semi-aquatic. They spend a lot of time in water, swimming and hunting. How are otters
adapted to river life?
What helps them swim?
 Webbed feet
 Muscular, tapered tail
 The ability to close their ears and nose when under water
 Water repellent fur
Otters can swim comfortably at about one metre per second for up to eight hours.
What keeps them warm?
 Very dense, short fur which traps a layer of air to insulate the animal
How do they find food?
Common otters feed mainly on fish and the occasional water bird, frog or small mammal may be
taken.
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Many sensitive hairs on the snout help the otter locate its prey.
Eyesight - otters can see as well under water as above it, which makes it easy for them to
hunt for fish.
How do they communicate with other otters?
Otters are usually solitary and are very territorial. They leave droppings (called spraint) to mark
their territory. Otters can fight over territory and produce cat-like noises when fighting.
Otter cubs stay with their mother until they’re a year old. Mothers communicate with her cubs
vocally with a high-pitched whistle.
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Freshwater Fish
Perch
Bullhead
How do fish like this perch and bullhead breathe underwater?
They have gills where oxygen passes into the fish’s bloodstream. Gills have a large surface area
and are structured very similarly to lungs, however, they are much more efficient. A typical human
lung may extract up to 25% of the oxygen from the air however a fish will extract 80% of the
oxygen from water.
What makes fish good swimmers?
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Fish are generally streamlined to assist movement through water. They have a pointed
front, bulky middle and tapered tail.
Fins help fish move and keep their position in the water. The fins have spines in them to
stiffen them and make them even better for swimming.
Fish have strong tails to propel them in the water.
Fish have an internal gas-filled organ called a swim bladder, which helps them control their
buoyancy. This allows them to stay at the same depth underwater without exerting energy
by swimming.
How do they find food?
Most fish are carnivorous. The size and position of the mouth indicates food size and mode of
feeding. Bottom feeders usually have down positioned mouths, surface feeders have upward
positioned and open water feeders have symmetrical mouths.
Fish have:
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a lateral line (usually visible as faint lines running lengthwise down each side from the gill
covers to the base of the tail) for detecting vibrations
nostrils for chemo sensing
taste organs in the mouth for sensing odours
eyes for visual sensing
Fish are camouflaged from their prey e.g. perch have striped bodies so they can hide in weeds to
stalk their prey and bullhead are mottled in colour so they can sit on the river bed and ambush their
prey.
Fish are cold blooded, which means the food they eat isn’t used for warming their body like in
warm blooded animals, but converted into body mass.
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How do fish escape from predators (humans and other fish)?
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The tail fin allows fish to move forward rapidly to escape predators.
Fish are often camouflaged to blend in with the river weeds or river bed – see above.
Scales over the body and spines in the fins offer fish protection.
Swim bladders also act as a resonating chamber to receive sound.
Fish in shoals (or schools) are better at detecting predators and evading capture.
Often have a dark top (less visible from predators above) and light coloured belly (less
visible from predators below).
Dragonfly
Dragonflies have existed on Earth for millions of years. How are they adapted to life in and near
water? Dragonfly nymphs live in the river and adult dragonflies live near the river.
How do dragonfly nymphs feed, move and breathe in
water?
Nymphs have big eyes so they can see their food in the water
and a bottom lip called a mask to catch their food with.
Nymphs breathe by extracting oxygen from the water using
breathing tubes behind the gut. Water is drawn in through the
anus. The water can be shot out rapidly to propel the nymph
through water to evade predators or pounce on prey.
How do adult dragonflies move?
Dragonflies are cold blooded. They bask in the sun to warm
up their flight muscles.
They are very good flyers:
 They are bullet shaped
 They can fly forward and backward and change
direction quickly
 Can reach speeds of over 20mph
 Dragonflies are relatively light for their size.
Around two thirds of a dragonflies weight is
muscle.
How do they feed?
Dragonflies are predators, feeding on smaller insects.
They have very good vision – their eyes are made up of thousands of
tiny lenses that they use to see.
They have very strong jaws to bite into insects.
They are stealth hunters flying quietly and quickly to catch their prey.
How do they reproduce?
They lay their eggs in a sticky substance which holds the eggs to an
anchor e.g. a plant in the river.
They lay lots of eggs, to increase chances of some of their young
surviving to adulthood.
How do they escape predators (e.g. birds)
Their eyes are sensitive to movement and detecting predators.
Their agile and fast flight helps them to escape predators.
www.itchennavigation.org.uk/education
nymph
adult