Water quality is essential for fish health and growth. Key water quality parameters include dissolved oxygen, nitrogen compounds, pH, alkalinity, hardness, salinity, and toxins. Maintaining optimal water quality prevents disease, stress, and losses. Proper aeration, waste removal, biofiltration, stocking density, and water changes are important management practices for controlling water quality.

1. WATER QUALITY AND
MANAGEMENT
(ch 8) [objectives]
• Describe water quality
• Describe important water management practices
• Calculate water volume
• Explain how weeds and algae are controlled
• Describe how to prevent aquaculture water
pollution
• Describe how to dispose of used water

2. Water Resources
• Water quality
• Water quantity
• Water sources
Inadequate water quality causes more losses than anyInadequate water quality causes more losses than any
other problem!other problem!

3. To a great extent, the
success or failure of
fish culture is
determined by water
quality

4. Water Quality – Why Is It Important?
• Your fish live in it
• Are supported by it
• Receive their oxygen from it
• And excrete in it

5. Water Quality – Why Is It Important?
• Water quality factors influence and interact
with each other
• What may cause problems in one situation
may be harmless in another
• Influences effectiveness/toxicity of
treatments

6. Water Quality – Why Is It Important?
• Most disease problems can be avoided
with proper management of water quality
• This includes maintaining water quality at a
level that provides an environment
conducive to fish health and growth

7. Water Balance in Freshwater
Fish
Salts
Large quantities
of dilute urine
Ammonia
Water

8. Water Balance in Saltwater Fish
Small quantities of
concentrated urine
Ammonia
Water
Drinks
sea water

9. WATER CHEMISTRY
• Nitrogen cycle – present as atmospheric
nitrogen, ammonia, nitrite, or nitrate
• pH
• Alkalinity
• Hardness
• Salinity
• Hydrogen sulfide
• Supersaturation

10. Nitrogen
• Atmospheric nitrogen (N2) makes up 80%
of the air we breathe
• Ammonia – produced by breakdown of
proteins; present as ionized (NH4+) or
unionized (NH3); unionized is 10X as toxic
• Nitrite (NO2-)
• Nitrate (NO3-)

11. NITROGEN CYCLE

12. Water plants Food
Excess
food
Fishes
Peptides
Amino acids
Urine
Urea
Ammonia
(NH )
Algae
Nitrate (NO )
Nitrite (NO )
Feces
2
3
3
The Nitrogen Cycle

13. pH scale

14. 100
50
0
4 5 6 7 8 9 10 11 12
Free CO HCO CO
Percent of Total CO2
3
- =
2 3
pH
Effects of pH on Various Buffers

15. ALKALINITY
• Measure of the pH buffering capacity of
water (prevents major pH shifts)

16. HARDNESS
• Measure of calcium and magnesium in
water (crawfish need calcium for their
shells)

17. SALINITY
• Measure of the amount of sea salts in
water (measured in parts per thousand –
ppt)

18. HYDROGEN SULFIDE
• Produced by anaerobic breakdown of
waste products in water
• Smells like rotten eggs
• Avoid overfeeding
• Aerate to eliminate anaerobic conditions

19. SUPERSATURATION
• Primary cause is mixing of waters with
very different temperatures
• Can be caused by excessive aeration or
photosynthesis
• Can cause gas bubble disease

20. TEMPERATURE
• The temperature of the culture water must
match the tolerance levels of the aquacrop
• Improper temperature can cause poor
growth or death
• Tropical species such as the redclaw
crawfish grow best at 82o
F.
• Redclaws can get fungal infection below
70o
F and die below 50o
F

21. WATER QUALITY MANAGEMENT
CONCERNS
• Oxygen depletion
• Buildup of nitrogen compounds
• Presence or excess of other compounds
and substances
• Turbidity and color
• Excessive growth of weeds and algae
• Plankton bloom

22. SIGNS OF OXYGEN DEPLETION
• Fish gasp at surface
• Fish group around incoming water
• Fish go off feed
• Nonfish animals leave water
• Slow growth
• Repeated health problems
• Change in water color
• Fish-eating birds present

23. Decomposing
materials
Low dissolved
oxygen (cool)
High dissolved
oxygen (warm)

24. CAUSES OF OXYGEN
DEPLETION
• Overstocking – aquacrop uses up all the oxygen
• Weather – limited photosynthesis on cloudy
days
• Time of day – lowest oxygen levels in hot
weather just before sunrise
• Decay of feed – uneaten food will consume
oxygen
• Feeding activity – aquacrop uses more oxygen
• Competition – trash fish and pests use oxygen

25. CAUSES OF OXYGEN
DEPLETION (continued)
• Decay of vegetation – dead weeds,
leaves, grass uses up oxygen
• Water temperature – the colder the water,
the more oxygen it can hold
• Salinity – the saltier the water, the less
oxygen it can hold
• Equipment failure – when aeration devices
fail

26. AERATION
• Splashing the water
• Pumping air or oxygen into the water
• Spraying the water into the air
• Using chemicals (not a good way)

27. NITROGEN CONTROL
• Avoid overfeeding – protein breakdown
releases ammonia
• Remove excessive feces, uneaten food,
dead animals
• Use biofilters (if necessary)
• Water change or replacement

28. OTHER COMPOUNDS AND
SUBSTANCES
• Eutrophication – excessive nutrient
enrichment in water
• Heavy metals (lead, mercury, cadmium) –
presence of heavy metals can result in
contaminated aquacrop

29. TURBIDITY AND COLOR
• Turbidity – presence of suspended
particles of soil or plankton in water
• Color – plankton blooms and release of
tannic acid from decaying vegetation

30. WEEDS AND ALGAE
• Can cause harvesting problems
• Can create off-flavor in some organisms
• Chemical control – uses herbicide
• Biological control – uses plant-eating
organisms
• Mechanical control – physical removal
• Environmental control – draining or
lowering water level during cold weather

31. WEED AND ALGAE CONTROL

32. Stressors
• Poor water quality
• Environmental conditions
• Improper handling

33. Most Fish Diseases
Are Stressed Mediated
Stress is a physiologic state caused by a procedure, environmental condition or
other factor which interferes with the fish’s ability to maintain a “normal” state. It
extends the adaptive responses of an animal beyond the normal range or which
disturbs the normal functioning.

34. Low Level Mortality
100%
M
O
R
T
A
L
I
T
Y
0%
Peracute
Acute
Chronic
Time
Usually the first sign of water
quality/environmental problems

35. Loading Effects
Number of fish which can
successfully live and grow in a
given amount of water depends on:
• DO level
• Metabolic rate of the
fish
• Amount being fed
• Pathogen load
• Water exchange rate

36. Management Recommendations
• Maintain water quality within suggested guidelines
• Maintain fish loadings at optimum levels of 0.0275 to 0.035 kg/ liter
1/3 lb./gallon (1/2 lb./gallon maximum)
• Monitor water quality on a regular basis/keep good records

37. Management Recommendations
• Low DO: increase aeration; stop feeding
• High CO2: increase aeration; add air stripping column
• Low pH: add sodium bicarbonate; reduce feeding rate; check
ammonia & nitrite
• High NH3: exchange system water; reduce feeding rate; check
biofilter, pH, alkalinity & DO in biofilter
• High nitrite: exchange water; reduce feed; add 6 ppm chloride per 1
ppm nitrite; check biofilter, pH, alkalinity & DO in biofilter

38. 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