water quality - what you should know to keep your fish alive

8/9/2019 Water Quality - What You Should Know to Keep Your Fish Alive

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Subhendu Datta

WATER QUALITY

What You Should Know

To Keep Your Fish Alive

Dr. Subhendu Datta

Sr. Scientist

Kolkata, India

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To a great extent, thesuccess or failure of

fish culture isdetermined by water

quality



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Water Quality – Why Is It Important?

• Your fish live in it

• Are supported by it

• Receive their oxygen from it

• And excrete in it

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• Water quality factors influence and interact

with each other

• What may cause problems in one situationmay be harmless in another

• Influences effectiveness/toxicity oftreatments



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• Most disease problems can be avoidedwith proper management of waterquality

• This includes maintaining water quality at alevel that provides an environmentconducive to fish health and growth

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Water Quality Variables

• Temperature

• Dissolved oxygen

• Total ammonia-nitrogen, NH3, NO-2

• Alkalinity

• Hardness

• pH

• Carbon dioxide



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• For each 10°C (18°F) rise in

temperature the metabolic rate doubles

• Controls the reaction rate of chemicals

• Influences solubility of gases in water

• Influences toxicity of ammonia and therapeutants

• Optimum temperature for tilapia growth is 85-88 °F

Water Quality VariablesTemperature

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Water Quality VariablesDissolved Oxygen

• First limiting factor for growth and fish health

• Solubility decreases with increasing

temperature and elevation

• Respiratory rate increases with increasing

temperature, activity and feeding

• In general the minimum DO should be ≥ 60%

of saturation or ≥ 5 ppm (mg/L)

• > 2 ppm in biofilter effluent



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Total Ammonia-Nitrogen

• Usually the second limiting factor – nitrogenous

waste: feces & feed

•TAN includes ammonium ion (NH4+)

and ammonia (NH3)

• The proportion of NH3 increases with increasing

temperature and pH

• < 0.05 mg/L NH3

• < 0.5 mg/L nitrite-N (NO-2) ,

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Percent of Total Ammoniain the Un-Ionized Form at

Various Temperatures and pH

percent Ammonia

Temperature (ºF) (pH) 7.0 8.0 9.0

___________________________________________

50º 0.19 1.83 15.7

68º 0.40 3.82 28.4

86º 0.80 7.46 44.6



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Water plants Food

Excessfood

Fishes

PeptidesAmino acids

Urine

Urea

Ammonia(NH )

Algae

Nitrate (NO )

Nitrite (NO )

Feces

2

3

3

The Nitrogen Cycle

0.8

0.6

0.4

0.2

0.02 6 10 14 18 22

8

6

4

2

0

Ammonia(mg/l)

Nitrites &Nitrates(mg/l)

NHNO

NO

23

3

Time in Days

Time Requiredfor Bio-Filter to Mature



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Water Quality Variables - Alkalinity

• Is the buffering capacity of water –

absorbs acids and/or bases

• High alkalinity prevents wide pH fluctuations

• Maintain levels between 75-120 mg/L as CaCO3

• 7 grams of alkalinity consumed by 1 gram of NH3

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100

50

04 5 6 7 8 9 10 11 12

Free CO HCO CO

Percent of Total CO 2

3- =

2 3

pH

Effects of pH on Various Buffers



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• Hardness 50 – 100 mg/L as CaCO3

• pH 7 – 8

• Carbon dioxide < 20 mg/L

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Total Dissolved Gases

Supersaturation caused by:

• leaking water lines

•air leak on low pressure side of pump

• source of water

• mixing cold and hot water

Recommended total dissolved gas pressure <104%



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Water Balance in Freshwater Fish

Salts

Large quantitiesof dilute urine

Ammonia

Water

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Stressors

• Poor water quality

• Environmental conditions

•

Improper handling



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Most Fish Diseases

Are Stressed Mediated

Stress is a physiologic state caused by a procedure,

environmental condition or other factor which interferes withthe fish’s ability to maintain a “normal” state. It extends theadaptive responses of an animal beyond the normal range orwhich disturbs the normal functioning.

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Low Level Mortality

100%

M

O

R

T

A

L

I

T

Y

0%

Peracute

Acute

Chronic

Time

Usually the first sign of waterquality/environmentalproblems



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Loading Effects

Number of fish which cansuccessfully live and growin a given amount of waterdepends on:

• DO level

• Metabolic rate of thefish

• Amount being fed

• Pathogen load

• Water exchange rate

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Management Recommendations

• Maintain water quality within suggested guidelines

• Maintain fish loadings at optimum levels of 1/4 to1/3 lb./gallon (1/2 lb./gallon maximum)

• Monitor water quality on a regular basis/keep goodrecords



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Management Recommendations

• Low DO: increase aeration; stop feeding

• High CO2: increase aeration; add air strippingcolumn

• Low pH: add sodium bicarbonate; reduce feedingrate; check ammonia & nitrite

• High NH3: exchange system water; reduce feedingrate; check biofilter, pH, alkalinity & DOin biofilter

• High nitrite: exchange water; reduce feed; add 6ppm chloride per 1 ppm nitrite; checkbiofilter, pH, alkalinity & DO in biofilter

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Good Stuff To Know• ~ 300 square feet biofilter material per 100 lbs. fish

• Add 0.125 to 0.167 lbs. baking soda/ 100 gallons tomaintain alkalinity

• Add 0.275 to 0.413 lbs salt/100 gallons to maintain

chloride levels of 200 – 300 ppm

• Do not make any rapid changes to any WQparameter, except to increase DO


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Resources

• SRAC Publications:http://www.msstate.edu/dept/srac/publicat.htm

• Hach WQ test kits: http://www.hach.com/

• LaMotte WQ test kits: http://www.lamotte.com/

• Equipment Suppliers:

• http://aquaticeco.com/

• http://www.tecinfo.com/~aqcenter/

• Eagar, Inc. 1-800-423-6249

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