WATER QUALITY IN AQUACULTURE

Introduction Part 1

Aquaculture and Seafood

Aquaculture is growing as a source of the world’s seafood supply.

Capture from the oceans is maximized.

Benefits of AquacultureAbility to bring

fresh, or even live, seafood to market at a specific time and quantity.

US seafood market

Asian fresh seafood market

Aquaculture is based on water

The key to the successful culture of aquatic organisms is maintenance of water quality.

Poor water quality = poor harvest.

Fish ponds in China

Water Quality

• Source • During culture• Discharge

“Water quality issues should be taken into account at every point of the aquaculture cycle.”

Dr.Claude E. Boyd

SourceFrom where?

underground

surface

Source

How much?

reservoir

irrigation canal

stream

spring

well

Sourcequality

populated

Red tide

underground

unpopulated

forested

pasture

Water QualityDuring culture

Turbid water

Clear water

Fertile water

Water QualityDischarge Catfish pond

Shrimp pond

Factors that influence water quality

Photosynthesis/RespirationWater temperature FertilizationFeedsAerationWater exchange

Photosynthesis/Respiration

6CO2 + 6H2O + light energy C6H12O6 + 6O2

photosynthesis

respiration

C6H12O6 + 6O2 6CO2 + 6H2O + heat energy

Water temperature

=

=

active

inactive

zz z

zzz

Fertilization

organic inorganic

FeedCommon carp

Marine shrimp

Rainbow trout

Channel catfish

AerationAspirator Defused air

Pond aeration paddlewheel

Water exchange

Salmon cages

Carp cages

Catfish raceways

Trout raceways

Testing Water QualityWater quality parametersoften tested are:

Dissolved oxygenWater temperaturepHTotal Ammonia NitrogenNitrite/NitrateAlkalinity/HardnessSalinity

Water test kit

How water quality values are expressed

Parameter Value

Dissolved oxygen mg/L O2

Water temperature C (Celsius) pH

Total ammonia nitrogen mg/L N

Nitrite mg/L NO2-

Nitrate mg/L NO3-

Alkalinity/Hardness mg/L CaCO3

Salinity g/L salt

Dissolved oxygen and water temperature

dissolved oxygen and water temperature usually vary over a 24 hour cycle.

6 a.m. 6 a.m.midnight6 p.m.noon

0

15

10

5

Surface dissolved oxygen, mg/L

25

27

29

31

Surface water temperature, C

summer

Oxygen meter

Stratification can cause dissolved oxygen and temperature to vary at different depths in the same system.

Dissolved oxygen and water temperature

Epilimnion

Thermocline

Hypolimnion

High temperatureHigh dissolved oxygen

Low dissolved oxygenLow temperature

pH = - log [ H+ ]

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

acid alkaline

pH pH is a measure of acidity (hydrogen

ion concentration) in water or soil.

neutral

Total Ammonia Nitrogen Total ammonia nitrogen ( TAN ) is a measure of the ammonia (NH3) and ammonium levels (NH4

+) in the water The ratio of ammonia and ammonium varies in an

equilibrium determined by pH and water temperature.

0%10%20%

30%40%50%60%

70%80%90%

7 7.4

7.8

8.2

8.6 9 9.4

9.8

pH of water

NH 3

as %

of T

AN

at 20Cat30C

Ammonia as a % of total ammonia nitrogen

Nitrite/Nitrate

NH4+ +1.5 O2 + Nitrosomonas NO2

- + 0.5 O2 + Nitrobacter NO3

-

feces

Bacterialdecomposition

Alkalinity and Hardness

alkalinity hardnessTotal titratable bases Total divalent salts

HCO3-

bicarbonateCO2

3-

carbonate calcium magnesiumMg2+Ca2+

Calcium bicarbonate

Ca( HCO3 )2

Calcium carbonateCaCO3

Magnesiumbicarbonate

Mg( HCO3 )2

Magnesium carbonateMg CO3

.

4 5 6 7 8 9 10 11pH

0.00

0.25

0.50

0.75

1.00

mol

e fra

ctio

n

H2CO3 andfree CO2

HCO3 - CO32-

bicarbonate carbonateCa(HCO3) 2 CaCO3

Alkalinity and HardnessThe form alkalinity takes is linked to pH of the system.

Alkalinity and HardnessAlkalinity buffers against diurnal variations in pH.

Salinity

Freshwater is less than 2 g/L

Brackish water is 2 g/L to 34 g/L

Sea water is more than 34 g/L

NaCl

End of IntroductionPart 1

Good Water Quality = Good Harvest

WATER QUALITY IN AQUACULTURE

Introduction Part 2: Applications

Classification of aquaculture systems

• Salinity of culture water.• Producer/consumer

relationship. • Type of culture unit.• Species• Management intensity

Salinity• Freshwater has a low ionic

concentration (i.e. streams, rivers, ponds and lakes).

• Saltwater has a high ionic concentration (ocean waters).

• Brackishwater has an ionic concentration between freshwater and saltwater ( mangroves ).

Producer/consumer relationship

• Commercial aquaculture

• Subsistence aquaculture

Type of culture unit

• Many different culture units are used to grow aquatic organisms.

• The culture unit selected is based on economic, space and water concerns.

• The type and size of the culture unit will determine water quality management.

Type of culture unit:Earthen Pond

Levee ponds

Reservoir Pond

Type of culture unit: Cage/PenCages in lake

Cages in ocean

Pen

Type of culture unit: Tank

Circular tank

Rectangular tank

Raceway culture

Trout farms using raceways

Species• The species cultured will determine

stocking density, water quality levels desired and the most appropriate system to use.

Management intensity

Levels of aquaculture management are closely tied to water quality.

Extensive management – no control of water quality

Semi-intensive management – some control of water quality

Intensive management – control of water quality

Extensive management

Marine shrimp

Semi-intensive managementChemical fertilizer

Supplemental feeds

Animal manures

Intensive managementAeration in ponds

Water exchange in tanks

Nutritionally completepelleted feeds

Water quality concerns:• Water pollution• Salinization• Sedimentation• Spread of disease

Other concerns:• Wetland destruction• Wasteful of resources• Biodiversity• Land conversion• Social impacts

Public perceptions of aquaculture

Water quality concerns

Shrimp pond effluent in ThailandCages in Indonesia

Other concerns

Preservation of freshwater wetlands

Preservation of saltwater mangrove

End