4. Cages vs Pens
Fish pens:
Larger, more open structures, used in open water bodies like lakes, lagoons, and bays
Typically made of nets or ropes and anchored to the bottom
Used to rear larger, predatory fish
Allow for more water flow
Fish cages:
Smaller, enclosed structures, used in lakes, reservoirs, and coastal waters
Made of a mesh or netting material and suspended from a floating platform
Used to rear smaller, herbivorous or omnivorous fish
Provide a more controlled environment for the fish
5. Pen culture
A fixed enclosure in which the bottom is the bed of the water body.
The pen or enclosure may be (a) completely enclosed on all four sides in the middle of a bay,
with no foreshore
6. Construction of pen culture
Shape, size and design of the pens:
On the basis of the pen culture it may be circular, square, and rectangular in shape depending
upon the harvesting.
The size of pens depends upon a number of physical factors such as location, water depth and
biotic parameters. Large cages of 200m3 or above may constructed for pen culture.
The height of the pens depends upon the water level during entire culture period. The height
also depends upon the jumping behaviour of cultured species. The height of pen may be at least
50cm. But about 30cm of the cages are fixed into the bottom to keep the pen wall secured.
7. Materials Used for Pens:
Screen
Small meshed to prevent the escape of fry and fingerlings
Resistant to long exposure in sun and water
Steady enough to resist current, wind action and wave action
Resists the attack of crabs and other animals
Cheap and easily available, easy to handle
Supporting Structures :
Matured and well seasoned bamboo are generally used as supporting materials, relatively in
shallow waters.
Other supporting materials like floats and heavy sinkers like stones are used as supporting
materials
8. Types of pen
Bamboo Screen Pens - This is the simplest type of pen made with fixed bamboo poles in the
bottom soil of water bodies, surrounded with fine meshed netting materials. Bamboo screen
fencing is suitable in narrow and shallow rivers, flooded fields and other very shallow water
bodies.
Monofilament Cloth Fencing Pens - These types of pens are surrounded by monofilament
netting material with required size. The screen wall is arranged just like a fry net.
9. Cage construction
Cage size
Normal size 20-60 m cube
Range from one to several
hundred cubic meters
It depends on size of water
body, the availability of
aeration, and the method of
harvesting
10. Components of cage
1. Frame: it is made up of wood, plastic, steel
mechanically strong, resistant against corrosion, and easily repairable or
replaceable
11. Coating
Frames of wood, iron, and
steel should be coated with a
water-resistant substance
like epoxy, or an asphalt
based or swimming pool
paint.
12. Design of frame
• rectangular, square or
cylindrical shapes
• Do not affect
production
14. Floats/Floatation devices
The frame is provided with floats to keep the upper part of the cage at or above
the water surface.
Flotation can be provided by metal or plastic drums, sealed PVC pipe, or
styrofoam.
15. Mesh or netting
Functions: keep the fish stock
together; protect the stocks
against harmful external
influences; allow free water
exchange between the inside
and outside water.
16. Lid characteristic:
• The manager of the cage needs to
be able to observe feeding
behavior
• He must have easy access to the
cage to remove uneaten feed and
any dead fish.
17. Feeding rings
Retain floating feed and prevent wastage.
The rings consist of small-mesh (2 mm or
less) screens suspended to a depth.
Feeding rings should enclose only a portion
of the cage.
rings surrounding the entire cage perimeter
may reduce water movement through the
cage.
18. Feeding tray
If sinking feed (pressed sinking pellet)
is used, small cages require a feed tray to
minimize loss of feed.
These rectangular trays can be made of
galvanized sheet metal or mesh (2 mm;
galvanized or plastic)
They are suspended from the cover to a
depth.
20. Types of cages
Fixed cages:
Installed in shallow water body
with depth 1 -3 m
A fixed cage is essentially a net
bag supported by posts which are
anchored to the bottom or lake
they are inexpensive
pilings are used, they also provide
horizontal support
21. Floating cages
They are supported by floating
frame where in net bags are kept
hanging in water without
touching water
Water bodies with depth more
than 5m
22. Components of floating cage
HDPE Pipes(- Flexible - Easy to Install – Light)
Filling Material for Pipes(EPS (Expanded Polystyrene) - Light )
Brackets Stoppers
24. Submersible cages
Airlift ballast assembly is added to the system to
allow the cage to quickly surface and submerge.
This airlift device controls submergence through
buoyancy adjustments.
When the cage is operated at the surface, the bag is
inflated, offsetting the weight of the ballast.
To submerge the cage, the bag is deflated (via hose
at the surface) reducing the system’s reserve
buoyancy. The cage stops its descent when the
ballast weight reaches the seafloor
25. Mechanical aerators
Aeration is most commonly needed at night
or during still, overcast days.
Mechanical aerators like paddlewheels or
vertical pumps can be placed near cages
where they create currents through the
cages
