Site Selection-Site selection is the first and generally most critical step for establishing a sustainable aquaculture facility.
-In selecting a site for specific culture system both technical and non technical issues need prime consideration.
-For the long term sustainability of aquaculture enterprise it is good investment sense to select an environmentally sound, low risk site at the outset.-Poor site selection can lead to failure
Site SelectionWater supply reliability and qualitySoil characteristicsTopographyLabor sourceEnvironmental impactSites that have access to an abundant supply of good quality water is a key to successful aquaculture enterprise
Public utilities securityEasy communication systemProtection from natural disastersAccess to the roadEasy access for marketingSeed supplyRoom for expansion
Water QualitySource During cultureDischarge
Water quality issues should be taken into account at every point of the aquaculture cycle. Dr.Claude E. Boyd
SourceHow much?reservoirirrigation canalstreamspringwell
Surface vs Ground water
Ground waterSurface waterLow turbidityHigh turbidityAbsent of or less predators & disease vectorsMore predators & disease vectorsLess exposure to contaminantsGreater exposure to contaminantsHigh mineral contentLow mineral contentLow or no DODO presentHigh iron, Fe contentLow iron contentHigh hardness (more Ca and Mg)Low hardnessHigher extraction costLower extraction cost
Alternative water sourcesRainwater: free, unpredictable, only a supplement, often acidic, poorly buffered.
Municipal water: limited potential due to cost/unit volume, also contains disinfectants (e.g., chlorine).
Recycled water: conserves water, environmentally friendly, biofiltration required, high pumping cost.
Water Quality in AquacultureThe key challenge in aquaculture is to maintain high growth rates under high stocking densities without degrading the water quality.Options for gravity flow on a site should be maximized as it is efficient and cheapPoor water quality = poor harvest
Water QualityDuring cultureTurbid waterClear waterFertile water
What is turbidity?Optical property of water that causes light to be scattered or absorbed rather than transmitted through the water in a straight line.
Caused by suspended materials in the water such as soil particles, plankton and organic detritus. Low turbidityHigh turbidity
Sources of turbiditySoil erosionphytoplanktonanimalsfishaeratorsdeforestation
Advantages of turbidityPrevents growthof rootedaquatic plantsHigh turbidityLow turbidityPond water with no turbidity
Phytoplankton turbidity provides dissolved oxygen and fish food organismsAdvantages of turbidity6CO2 + 6H2O + light energy C6H12O6 + 6O2
Lowers predation of cultured species by birdsAdvantages of turbidity
Disadvantages of turbidityClay and soil turbidity are sometimesdetrimental to fish.
Overabundance of phytoplankton can be dangerous.Disadvantages of turbidityC6H12O6 + 6O2 6CO2 + 6H2O + heat energy
Measuring turbiditySecchi Disk30 cm
Secchi Disc Values for Aquaculture
VisibilityComments< 20 cmDanger of DO problems every night20-30 cmPlankton becoming too abundant30-45 cmIdeal45-60 cmPlankton becoming too scarce> 60 cmWater too clear, inadequate plankton and danger of aquatic weed problem
Water QualityDischargeCatfish pondShrimp pond
Different animal, different optimum water quality conditions
Factors that influence water qualityPhotosynthesis/RespirationWater temperature FertilizationFeedsAerationWater exchange
Photosynthesis/Respiration6CO2 + 6H2O + light energy C6H12O6 + 6O2photosynthesisrespirationC6H12O6 + 6O2 6CO2 + 6H2O + heat energy
TemperatureAll animals have a temperature range, the biokinetic range, within which they can survive.
This range is limited by the upper and lower tolerance limit, and beyond these critical temperatures the animals may live briefly but would eventually die. Species with wide range of tolerance - eurythermalSpecies with a narrow range of tolerance stenothermal
Eurythermal fish Goldfish, Common CarpStenothermal fish Salmonids - < 20-25C
Temperature acts as a controlling factor regulating metabolism and thereby growth important for aquaculturists.
FeedCommon carpMarine shrimpRainbow troutChannel catfish
AerationAspirator Defused airPond aerationpaddlewheelFish mortality dueTo low D. O.
Water exchangeSalmon cagesCarp cagesCatfish racewaysTrout raceways
Testing Water QualityWater quality parametersoften tested are:Dissolved oxygenWater temperaturepHTotal Ammonia NitrogenNitriteAlkalinity/HardnessSalinityWater test kit
How water quality values are expressed as:
ParameterValueDissolved oxygenmg/L or ppmWater temperatureDegrees C or F pHTotal ammonia nitrogenmg/L or ppmNitritemg/L or ppmAlkalinity/Hardnessmg/L or ppm CaC03Salinityg/L or ppt salt
Dissolved oxygen and water temperaturedissolved oxygen and water temperature usually vary over a 24 hour cycle.6 a.m.6 a.m.midnight6 p.m.noon015105Surface dissolved oxygen, mg/L25272931Surface water temperature, CsummerOxygen meter
Stratification can cause dissolved oxygen and temperature to vary at different depths in the same pond.Dissolved oxygen and water temperature
Dissolved OxygenOxygen enters an aquatic system through:
Diffusion (resapan) naturally (wind-aided) or through aerationPhotosynthesisEntry of new water (inflow, runoff)Rain
Atmospheric O2 enters to water through diffusionO2 move from region of high conc. (air) to region of low conc. (water)
Faster through wind (water circulation)
Dissolved Oxygen (DO)Dissolved oxygen (DO) is by far, the most important water quality parameter in aquaculture.
Like humans, fish require oxygen for respiration, survival and growth.
Oxygen consumption and DO requirement by fish increase with temperature and food consumption
Dissolved OxygenBiological processes that influence DO concentration in aquaculture ponds are:
Photosynthesis by green plants
Respiration by all aquatic animals
DO consumption & limitsThe levels of oxygen required to support life, good health and growth of aquaculture organisms vary, depending on factors such as:speciesbody sizewater temperaturefeeding ratesstress level
DO consumption & limitsImplications:
At a given temperature, smaller fish consume more oxygen per unit of body weight than larger fish - for the same total weight of fish in a tank, smaller fish require more oxygen than larger fish.
Actively swimming fish consume more oxygen than resting fish. In raceways, high exchange rates will increase energy expenditures for swimming, and oxygen consumption.
Generally, minimum DO should be greater than 5 mg/L for growth of warmwater fish and 6 mg/L coldwater fishes at their optimum temperature
0 to 2 ppm - small fish may survive a short exposure, but lethal if exposure is prolonged. Lethal to larger fish.2 to 5 ppm most fish survive, but growth is slower if prolonged; may be stressful; aeration devices are often used below 3ppm.> 5 ppm to saturation the desirable range for all.
Dissolved OxygenToo much oxygen hyperoxia - gas bubble disease.
Too little oxygen hypoxia - fish surfacing/suffocating.
Total lack of oxygen anoxia fish dies.
Most fish stops eating and starts dying below 30% DO saturation.
A good rule of thumb Maintain DO levels at saturation or at least 4 ppm at all times.
Dissolved OxygenHow to prevent DO depletion at night?
Run aeration at night
Maintain Secchi disk visibility above 30-50 cm.
Use moderate stocking and feeding rates
Apply fertilizers in moderate amounts and only when needed to promote plankton blooms.
Dissolved OxygenHow to prevent DO depletion at night?
Select and manage good-quality feeds less fines (habuk) and wastage
Dry out bottoms between crops and apply lime to enhance organic matter decomposition.
pH = - log [ H+ ]01234567891011121314acidalkalinepH pH is a measure of acidity (hydrogen ion concentration) in water or soil.
Alkalinity and HardnessThe form alkalinity takes is linked to pH of the system.
Alkalinity and HardnessAlkalinity buffers against diurnal variations in pH.
Total Ammonia Nitrogen
Total ammonia nitrogen ( TAN ) is a measure of the unionized-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.
Ammonia as a % of total ammonia nitrogen
Ammonia, Nitrite, & Nitrate (cont.)Typical pond has bacteria, which in the presence of DO converts (oxidizes) ammonia to the intermediate form of nitrite and then to nitrate. Nitrite is more toxic to fish than ammonia, however, nitrate is relatively nontoxic.
Nitrite + haemoglobin in fish = methaemoglobinHaemoglobin = chemical that carries oxygen throughout fish bodyMethaemoglobin = will not combine with oxygenFish will be asphyxiatedChocolat