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             Egg incubation

1.                                        2.                             3.
  Water is pumped from a 60 metre          Water is pumped to the        The fish tanks are then gravity fed.
  bore hole at a rate of 50m3/hour         header tank where it is

6.                                         The fish use oxygen from      4.
 The water passes through a sediment      the water and excrete their    Water is passed through a filtration
trap before it is piped to the reedbed/    wastes eg. heat, nitrates &   system before being pumped to the
   lake and eventually, the aquifer.        ammonia into the water.        second header tank for re-use.
                     Sparsholt Fish Hatchery
Sparsholt is an ideal place for a cold water fish hatchery. The water, pumped up
from the chalk rocks below, stays at a fairly constant temperature of 11ºC. The
water is well oxygenated throughout the year and is also clear, clean and has a
pH of 7.5. These stable conditions are ideal for breeding trout. Commercial
trials for fish feed are also carried out on trout here. Atlantic salmon are
reared here to restock the River Thames.

The Water System
The hatchery uses borehole water which is pumped up from the chalk aquifer at
a rate of 50 cubic meters (cumecs) an hour. The borehole is 60m deep in order
to keep the flow constant even in drought conditions. The water is 100%
saturated with oxygen at this point. An emergency generator stands by to pump
water from the borehole in the event of a mains power failure as fish would
quickly use the oxygen in their tank and then start dying after 20 minutes in
still water. The water passes through a degassing tower to remove nitrogen
(which would otherwise cause the fish to suffer the “bends” and die) and is then
fed down a system of pipes to the tanks.
The tanks contain various types of fish of different ages/ sizes and at various
stocking densities. The fish breathe oxygen dissolved in the water and eat food.
Their solid, liquid and gaseous waste products (excreta, urine, carbon dioxide
etc) enter the water. The water is continually flowing through the tanks. When
it leaves the tanks it then passes through a drum filter to remove the solids
before being pumped to the second header tank at the top of the site. Then it
flows down through the second set of tanks. The water is filtered again then
passes through two deep sedimentation tanks
In the second sedimentation tank the reduction in flows encourages solids to
settle downwards. (Solids are removed annually.)The clearer water above is
piped off towards the reed bed.
The reed bed receives the water from the hatchery through a perforated pipe.
The half hectare reed bed was planted in Spring 2002 with 14 mainly native
species such as sedges, rushes and yellow iris. Other plants, such as water
cress, are also now growing there. The primary aim of the reed bed is to
increase the wild life conservation value of the area. Its secondary purpose is to
“polish” the water (ie remove nitrates, phosphates and some sediment) from the
hatchery water before it enters the lake.
The lake was constructed early in 2002. Some of the water from the reed bed
passes through the gravel bank into the lake and soaks into the chalk below. The
remaining waste water enters the aquifer through a soakaway in a corner of the
reed bed. All of the water is recycled back into the aquifer.
The Fish
           Rainbow trout, Brown trout and Atlantic salmon are hatched here
from eggs and grown on to ‘fry’ and ‘fingerlings’. Rainbow trout are sold
commercially to fish farms to be grown on for the table. Native Brown trout are
used to restock the River Itchen and the breeding adults are re-released here
after the eggs have been produced.
            Rainbow Trout are a greyish colour with a distinctive pink stripe
along the sides of it’s body. They also have 7-11 oval spots of greyish blue called
‘par’ marks along each side. The Rainbow trout grows well under farm conditions
as it grows quickly and is less ‘stressy’ in the artificial conditions. Brown trout
are overall a more brown colour, they have noticeable red spots on their sides
and spots on their tails.
            In the wild trout are carnivores, feeding on bugs, water insects and
crustaceans when small. Bigger fish will predate on smaller fish and trout are
known to be cannibalistic! At the hatchery trout are fed concentrated dry,
rich, oily food pellets made from fish meal. This provides all they need to grow
and the results are outstanding with 1kg of fish produced from each 0.68kg of
food. However it is expensive. Food partially derived from plants is being
trialled. Due to the good food supply at the hatchery, an adult fish will reach
sexual maturity after 2 years.
            In the wild trout would move up and down the river to search for
food, hiding and waiting in shady spots for their prey. At the hatchery this
habit is not possible although the tanks are covered in black netting to replicate
the shade they prefer.

The Trout Life Cycle
            In November/December wild trout migrate up to the shallow gravel
areas of the river or tributary streams to spawn. Loose gravel is needed for the
fish to dig a shallow hole called a ‘redd’ for the eggs. The ideal temperature for
eggs is between 4-11ºC, hence winter spawning. After the female has laid the
eggs the male fertilises them and covers up the hole. The trout then swim back
down river in a very weakened state. Many die on the return journey.
           Although many eggs get eaten by other fish, those that survive take
approximately 30 days to hatch. Only 2-3% of the fertilised eggs will hatch.
The shell dissolves and leaves the embryonic fish, called an ‘alevin’, which still
has its yolk sac attached to feed from. At about 2-3 months old the fish is
around 26mm in size and called a ‘parr’.
            After another month the fish will acquire a greyish blue colour and
oval markings on each side. These “fry” grow quickly and reach 10cm at about 4
months old and 30cm at about 20 months. Between 1-3 years the fish are known
as “fingerlings”. At about 3-4 years old they begin to breed and return to the
same spawning grounds where they were hatched. A Rainbow trout cannot
breed in the UK in the wild, but if released into a river it may live for only 4-5

Habits of Wild Trout
            Most trout are solitary dwellers, except for the journey up river to
spawn when they may travel as a shoal. Each fish usually keeps to it’s own “lie”,
this is often in a hole under the river bank or large bolder. They chase away
smaller trout or other fish. The largest trout always get the best “lies.” They
will wait and catch food as it passes on the current, such as insect nymphs,
larvae, pupae that rise from the river bed and flies that have hatched on the
surface. A trout can usually find all the food it needs in an area 1m by 3 m. If
food is short the trout will grub in the weeds and gravel for freshwater shrimp
and water hoglice.
           In droughts they will become nocturnal and spend daylight hours
lying motionless in cool pools under overhanging trees. Their eyes cannot adapt
to changes in light as the pupil does not contract in brighter light so they stay
in the shade. There is also less oxygen dissolved in warm water and as trout
require high levels of oxygen they remain inactive until the sunsets.
           The trout can sense other fish and potential food through water
vibrations and acute eyesight. It has a line of nerve endings along it’s lateral line
which detects any water movement.
            The chalk streams and rivers of the South of England are famous
for trout fishing. The River Test in Hampshire is one of the most famous of all.
Trout should continue to thrive in these rivers if they remain free from
pollution and human interference, which will disturb the trout’s natural way of
life. Re-stocking programmes such as that aided by Sparsholt hatchery is
helping to maintain trout populations.

Fish Farming
Fish farming is the intensive production of fish in a managed environment.
About 16,000 tonnes of Rainbow Trout are produced each year in the UK. One
quarter of these fish are used to restock rivers for anglers. The remaining
three quarters are mostly farmed female Rainbow trout which produce food for
people, either as whole fish from 350g to 500g in weight, or fillets. People much
prefer to eat these female fish than male fish.
Reproduction is manipulated and growth is maximised to produce a high yield
from a small area of land. For example a trout farm in the Test Valley produces
about 250 tonnes of fish in water of less than one acre surface area. Rainbow
trout are used for fish farming because:
• they are easier to feed when first hatched
• they grow fast
• they tolerate higher temperatures
• they tolerate lower dissolved oxygen levels
• they are relatively disease resistant

Adult fish spawn in winter. Females that have been “masculinised” (by feeding
tiny amounts of male hormone when first hatched) are used to produce all
female sperm. The eggs are stripped from the females and fertilised with
“female” milt (sperm). The eggs are incubated in cool flowing water in the dark
until the young all female alevin hatch.

Rainbow Trout Production Cycle

HATCHERY (optimum temperature of 8-12 degrees C)
Broodstock and fertilised eggs  4-5 days old     4.5g “fingerlings”

FISH FARM (opt. Temp 15 C)
Fingerlings grow on for 7-9 months from 4.5g to 350g or more to “table” size

The Environmental Impacts of Fish Farming
Trout need flowing cool water with high level of oxygen. Ammonia is the main
waste product from fish, although solid waste is also produced. Waste water
from a fish farm or hatchery will have lower oxygen, a higher BOD (biological
Oxygen Demand) due to the suspended solids and ammonia.
The hatchery at Sparsholt has consent from the Environment Agency for at
least 10 years to discharge water back into the aquifer via the reed bed and
lake. Visiting KS3/4 school pupils have measured water quality at the hatchery
and in the reed bed and fishing lake since 2002. Appropriate equipment and
techniques have been used to measure:
• clarity
• temperature
• nitrates
• oxygen
• pH
The Environmental Impacts of Fish Farming
Results so far have produced some interesting teaching points, especially in
comparison with results from testing the water quality at Ower pond in the
Water emerges from the borehole at ~11 degrees Celcius all year round. It may
change as it passes through the hatchery system, depending on the air
temperature and weather conditions. Temperatures increase on a summer days,
whereas the water may feel quite warm in mid winter! The lake has a large
surface area and is exposed to the wind. Water warms up more slowly than land
and takes longer to cool down.
Clear water is not necessarily clean! The nitrate results must be considered
together with the clarity. Dirty looking water can actually contain very little
nitrate. The reed bed often has a low nitrate level yet has a lot of suspended
solids. Pupils may consider Ower pond water looks “dirty” (ie not at all clear) yet
be surprised that they have not measured any nitrates in it.
In general terms phosphates are the major pollutant in fresh water, usually
derived from detergents used in washing. Phosphate, not nitrate, is the main
limiting factor in plant growth. However it is much easier for pupils to measure
nitrate – with a test strip- and link it with pollution.
Nitrate levels can be related to the excretion of ammonia by fish and the
subsequent breakdown of ammonia to nitrate. (Remind pupils of the nitrate
cycle.) Nitrate found in the lake and reed bed may also be related to fertilisers
and manure applied to the fields around (and in particular field C above) the
lake. Advanced groups of pupils may need to consider:
• if manure or fertiliser was recently applied (manure application on this farm is
limited in quantity and timing in order to prevent water pollution by nitrates)
• if it has rained recently
• if there is any barrier of vegetation preventing run off from the field entering
the lake/ reed bed. (there is a conservation area of trees and wild plants)
The recommended maximum level of nitrate in drinking water is 50mg/litre,
which is the level found in the hatchery water! Therefore, any nitrate removal
by the reed bed is a bonus as it improves water quality. The method of
measuring nitrates used here is not sufficiently sensitive to detect the
additional input of waste from the fish. Levels higher than 50 would indicate
Oxygen is dissolved in water. Oxygen meters are used to measure dissolved
oxygen in the water. The higher the water temperature, the less oxygen will be
dissolved in the water. Cooler water contains more oxygen. Water emerging
from the borehole overflow pipe is often 95-100%.
Animals use oxygen in respiration. Plants produce oxygen as a waste product of
photosynthesis. There are few plants in the hatchery tanks so oxygen levels will
decrease as the fish in the tanks use the oxygen. Levels vary according to how
densely stocked the tank is. Levels around 90%, sometimes lower, are usually
recorded in the fish tanks. The sedimentation tank has, theoretically, no fish
and some plant growth. Oxygen levels here are similar to those in the fish tanks.
Oxygen levels in the reed bed have been recorded, so far, as 75-85%. A wide
variety of invertebrates are breathing oxygen in the water and underwater
plants are producing oxygen by photosynthesis.
Levels in the lake are often recorded at 100%,and water is presumably super
saturated due to diffusion at the water surface, plant photosynthesis and the
mixing effect caused by the wind.
Water at the hatchery is alkaline, usually with a pH of 7.5, as it has emerged
from chalk rocks. However, rainfall is usually slightly acid, as some acids from
the atmosphere have become dissolved in the rain (approx. pH of 6.5).
Therefore, the pH of water indicates the impact of rain and surface run-off on
the system. At the lake and reedbed, where rain has entered the system, the
pH is often 7, ie neutral.
     Fish Farming & Water Quality

     INFLOW                                          FIND OUT…
1.   Where does the hatchery water
     supply come from?                               What the inflow water is like.
                                            •        What effect the fish have on water
     Lake   River      Bore hole   Tap               quality.
                                            •        What is the outflow to the aquifer
2.   The water temperature stays about               like. Is it clean or has it changed?
     the same temperature throughout
     the year. What is its temperature?
            __________ ‘C
                                                                   Site     Site    Site
                                                                    1.       2.      3.
                                                                   Inflow   Fish   Outflow
3.   The water contains _ _ _ _ _ _.                                        tank

     Fish need a constant supply of this    Water
     in order to live. They absorb this     Temperature
     through their gills.                   (‘C)

     If the main water pump fails, an       Water
     emergency g _ n _ _ _ t_ r             Clarity
     switches on .                          (1 clean – 4 dirty)

4.   The fish excrete (get rid of waste)    Dissolved
     into the water. This can lead to       Oxygen
     increases in water …                   (% or mg/l)

     t _ _ _ _ _ _ _ _ _ _, sediments       pH of water
      and n _ t _ _ _ _ pollution           (1 acid – 14 alkali)

     Oxygen levels… increase / decrease
     OUTFLOW                                (mg/l)
                                            note: 50mg/l is
5.   The water is returned to the           maximum level for
     aquifer via a system of _ _ _ _ _.     drinking water.

6.   50 m3 per hour of water is taken
     from the aquifer. The hatchery
     returns …

     the same amount       more      less
                        Fish Farming
                                           * At what time of year do
                                           trout spawn (produce eggs)?
   * What type(s) of fish
   are reared at Sparsholt?                 Jan Feb Mar Apr May June
                                           July Aug Sept Oct Nov Dec

                                            * How many eggs does the
                                            female release when she
* How long do the fertilised                spawns?
eggs take to hatch?
                                               1    20     100      500    1,000
      __________ days

                                          * What % of eggs survive and
                                          develop into fry (small fish) ?
   * What do trout at the                  In the wild …         _______ %
   hatchery eat?                          At the hatchery… _______ %

   * What would wild trout
                                          * What happens to the salmon
                                          fingerlings that are produced?
                                               Sent to fish farms
                                               Kept for fish food trials
                                               Sent to restock the River Thames

The hatchery will grow the fry to
‘fingerlings’ weighing about 4.5g.
                                           * A fish farm on the River
Some will go to fish farms for
                                           Test has 50 x 100 m of
ongrowing to table size (350g).
                                           surface water for farming.
* How long does it take a for a            Approximately how much fish
trout to reach table size?                 does it produce in a year?
3 months   6 months   9 months   1 year        10 tonnes       100 tonnes
                                              250 tonnes     1,000 tonnes
                        Fish Farming

                                         * What happens to the trout
   * What type(s) of fish                fingerlings that are produced?
   are reared at Sparsholt?                     Sent to fish farms
                                                Kept for fish food trials
                                                Sent to restock the River Thames

                                           * At what time of year do
  * What do you need to farm               trout spawn (produce eggs)?
  trout successfully?                      Jan Feb Mar Apr May June
  (food, space, staff etc)                 July Aug Sept Oct Nov Dec

                                       * What jobs have to be done
                                       to keep the fish healthy?

 * Why are fish graded into
 tanks of similar sized fish?

The hatchery will grow the fry to
‘fingerlings’ weighing about 4.5g.        * How much trout is produced
                                          per year in the UK?
Some will go to fish farms for                100 tonnes       1,000 tonnes
ongrowing to table size (350g).            10,000 tonnes      16,000 tonnes
                                          * How much trout does
* How long does it take a for a           Sparsholt’s hatchery produce
trout to reach table size?                per year?
 3 months 6 months   9 months 1 year
                    Fish Farming
                                      * Why do trout need to
                                      live in flowing water?
    •Where do wild trout live?
    •Sea        pond

    •Lakes       rivers

                                       * Why are Rainbow trout
                                       better adapted to fish
                                       farming than wild trout?
  * Why do trout need to live
  in clean water?

    * What do trout at the             Are trout:
    hatchery eat?                      herbivores?       carnivores?

                                       omnivores?        detrivores?
    * What would wild trout

                                  * How long does it take a for a
                                  Rainbow trout to reach table size?
                                  3 months   6 months   9 months   1 year

Draw a Rainbow trout food chain

Draw a wild trout food chain
               Fish Farming

1    Choose a tank of trout.

How many fish in the tank?
(Estimate then check with staff from the hatchery)


What is the average weight of each fish/ fingerling?
(Estimate then check with staff from the hatchery)


Biomass is the amount of living matter in the tank.
no. of fish X weight of fish = biomass in tank

………………… X ………………           = …………………kg

2   Measure the tank.
Width              …………………m

What is the radius?     …………………m

How deep is the water? …………………m

What is the formula for finding the volume of a cylinder?

What volume of water are the fish living in?

                            = ………………………m3

Biomass per cubic meter of water = biomass of fish in kg
                             volume of water in m3

                             = …………………………kg/m3 of water
                          F ish F arm ing
                                           * At what time of year do
                                           trout spawn (produce eggs)?
                                            Jan Feb Mar Apr May June
                                            July Aug Sept Oct Nov Dec
    * What type of fish are
    reared for human food at
         trout           goldfish
                                             * How many eggs does the
                                             female release when she
         salmon          cod                 spawns?
                                               1    20      100       500   1,000
  * Which fish are eaten?
           female                         * What % of eggs survive and
                                          develop into fry (small fish) ?
                                           In the wild …           _______ %
                                          At the hatchery… _______ %
     Male breeding fish are easy
     to spot because they have
     hooked ----
                                             The hatchery will grow the
                                             “fry”. What are “fry”?
                                                How you cook trout!

                                                Fish which have just hatched

                                                Fish that are ready to sell
The hatchery will grow the fry to
‘fingerlings’ . What are fingerlings?
                                          Why do we grow only female
         Fish as big as your finger
                                          fish to eat? Male fish are not
         Young trout                      eaten because:
                                                   they taste nasty
         Food to eat with your fingers!
                                                   they are ugly

                                                   they are tough
                          F ish F arm ing
                                                 What happens to the small
                                                 Rainbow trout that are bred?

   * What type of fish are                              Sent to fish farms
   reared at Sparsholt for                              Kept for fish food trials
   food?                                                Sent to restock rivers in Hants
     Rainbow trout
     Brown trout

                                                   How heavy are rainbow trout
  What happens to the young                        when they are sold for human
  Brown trout (fingerlings) that                   food?
  are produced?                                    10g 100g        350g      500g 1000g

        Sent to fish farms
        Kept for fish food trials
        Sent to restock rivers in Hants

                                          What do rainbow trout at the
                                          hatchery eat?
 * Why are fish graded into               plants              algae
 tanks of similar sized fish?
                                          fish                insects
                                          fish food made from ……………………

                                                   * How much trout is produced
                                                   per year in the UK?
                                                      100 tonnes       1,000 tonnes
Some trout will go to fish farms                   10,000 tonnes      16,000 tonnes
for growing on to table size.
                                                   * How much trout does
* How long does it take a for a
                                                   Sparsholt’s hatchery produce
trout to reach table size?
                                                   per year?
 3 months 6 months    9 months 1 year
Why do we farm fish?
                    Fish Farming

 Where does the water supply           The ideal water temperature for
 for the hatchery come from?           Rainbow Trout eggs to develop is:

       Lake                              2oC            5oC
       River                                   11 o C          15 o C

                                         Does this water cause any
                                         problems for fish?
Rainbow trout grow quicker in
water with a higher/ lower
temperature. The water
temperature at Sparsholt
hatchery is …………… o C all year


                                       Water from chalk rocks is alkaline.
                                       Rain water is slightly acid.
                                       The water here is:
Rainbow Trout are well suited to       Acid       alkaline     neutral
fish farming because:

                                        Cold water contains more/ less
                                        oxygen than warmer water.

                                        The borehole water contains
                                        ………. % oxygen.
                                        The temperature is ………        C.
Moving water contains more/ less
oxygen than still water.
The water in the fish tanks
contains ………% oxygen.
      Fish Farming

          Type of fish ________

age    weight   length