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

WATER CHEMISTRY

• Nitrogen cycle – present as atmospheric nitrogen, ammonia, nitrite, or nitrate

• pH• Alkalinity• Hardness• Salinity• Hydrogen sulfide• Supersaturation

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-)

NITROGEN CYCLE

pH scale

ALKALINITY

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

HARDNESS

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

SALINITY

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

HYDROGEN SULFIDE

• Produced by anaerobic breakdown of waste products in water

• Smells like rotten eggs

• Avoid overfeeding

• Aerate to eliminate anaerobic conditions

SUPERSATURATION

• Primary cause is mixing of waters with very different temperatures

• Can be caused by excessive aeration or photosynthesis

• Can cause gas bubble disease

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 82oF.

• Redclaws can get fungal infection below 70oF and die below 50oF

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

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

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

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

AERATION

• Splashing the water

• Pumping air or oxygen into the water

• Spraying the water into the air

• Using chemicals (not a good way)

NITROGEN CONTROL

• Avoid overfeeding – protein breakdown releases ammonia

• Remove excessive feces, uneaten food, dead animals

• Use biofilters (if necessary)

• Water change or replacement

OTHER COMPOUNDS AND SUBSTANCES

• Eutrophication – excessive nutrient enrichment in water

• Heavy metals (lead, mercury, cadmium) – presence of heavy metals can result in contaminated aquacrop

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

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

WEED AND ALGAE CONTROL