size

is


0.5


inch;


for


larger

fish,


the


mesh


size


can

increase.
Cage

design
Cages

are


designed

with


a

float,


which

is


commonly

made


of


4-

inch


PVC

pipe.


The


PVC

pipe


will


float


if

it

is
properly
sealed,


but


if

a

leak


occurs,


the


entire


cage

could


sink.

Provide


back

up

flotation


by

filling


the


PVC
pipe

with


foam

available


in


a

spray


cans

or


a

foam

material

such

as

swimming


pool


noodle


floats.


Cages


are
also

equipped

with


a

feeding


ring

of


smaller


mesh


material

(1/8


to


3/16


inch)


that


surrounds


the


top


12

inches
of

the


cage

and

is


used

to


prevent


feed


from

being


splashed


through


the


outer


mesh


of


the


cage

where


fish
cannot

consume

it.


All


cages

should


have

lids


to


prevent


the


fish

from

escaping


and

to


protect

them

from
predation.

Cages


are


usually

positioned

at


a

dock

for


ease

of


feeding


and

harvesting

and

to


enable


easy
assessment

of


fish

health.


If

the


cage

is


not


located


at


a

dock,


access

will


be

limited


to


a

boat.


Fouling


of


the
cage
material

can

limit


the


exchange


of


water;


periodic


cleaning


with


a

broom


or


brush


will


help


prevent


this.
Stocking
densities
Stocking

densities


of


5–7.8


fingerlings

per


cubic


foot


(177–276


per


cubic


meter)


are


commonly

used.


Some
producers

stock


a

smaller


2-


to


3-

inch


(5.08–7.62


cm)


fish

and

grow

them

in


0.25

-

inch


mesh


cages

until


they
are

6–8

inches


(15.24–20.32


cm)


long.


Other


producers


stock


6-


to


8-

inch


fish

and

grow

them

in


0.5

-

inch
mesh.

If

6-


to


8-

inch


fish

are


stocked,


market

size


of


1.5


pounds


can

be

attained

in


4–6

months.

If

2-


to


3-

inch
fish
are


stocked,


culture


time


can

take


12–14


months


and

usually

involves

harvest


and

restocking

at


a

reduced
density
at


6

months.

Production


of


5.78


pounds


per


cubic


foot


(93.5


kg/m3)

is


commonly

achieved.
Harvesting
from

cages
Harvesting

fish

from

cages

is


accomplished

by

partially


lifting


the
cage
out


of


the


water


to


concentrate


fish,


which

are


then


removed


by
nets,

weighed,


and

loaded


into

live


hauling


trucks

or


transported

for
packaging
whole

on

ice.

The


use

of


an

anesthetic

other


than


carbon
dioxide
to


sedate


the


fish

before


harvesting

and

handling


is


not
allowed

for


food


fish

without


subsequent


periods


of


withdrawal


before
they

enter


food


markets.


Some

cage

culture


occurs


in


water
exceeding
10

feet


in


depth.


Stratification


of


these


deep


water


bodies
commonly
occurs.


Typically


cages

are


positioned

on

the


surface


and

don't


penetrate


more


than


4

ft.


deep.
This

positions


the


fish

in


the


warmest


water


and

subjects

them

to


the


potential


of


large


diurnal


fluctuations

in
dissolved
oxygen


(DO)


concentrations.
Therefore,

the


use

of


aeration

is


necessary.


Deep


water


bodies


stratify


according


to


temperature


and

can
divide
into

more


than


two

layers.


During


at


least


one

time


each

year,


this

can

cause

problems,


particularly


if
the

water


body

is


divided

into

three


strata.
The

deeper

strata


of


water


are


typically

much


lower


in


DO

than


the


surface


strata.


In


the


fall,

as

warm


surface
water

temperatures


cool


rapidly


following


rain

or


a

rapid


change


in


atmospheric


temperature,


the


water


in


this
layer

becomes

denser

and

sinks,

causing


lower


layers

to


exchange


with


the


top


layer,


bringing

deeper

water
with

low


DO

to


the


surface


(termed


a

turnover).


The


problem

with


this

is


the


rapid


rate


of


DO

change.