Aquaculture Systems

1. Aquaculture Systems Operation & Maintenance David Crisostomo DC Aquatic Systems Cooperative Extension Service University of Guam

2. OperationUnderstanding Water Quality • Water quality is critical for successful culture of aquatic organisms • All parameters interact with each other very quickly. • Some can be controlled, others are subject to the outside environment….such as temperature and rainfall.

3. Water Quality Parameters • Dissolved Oxygen - Enters water from 3 main sources… • Diffuse through the surface of the water-natural • From agitation or aeration-mechanical • From submerged aquatic plants….not floating plants-biological

4. Dissolved Oxygen Cycle • Level of DO is function of light, water quality and nutrient level. • Natural diurnal fluctuation

5. Process of O2 transfer • Oxygen molecules are diffused into the water at the air/water interface. This interface occurs around an air bubble and/or around a droplet of water. • More O2 is transferred with smaller bubbles or water droplets per unit of energy. • More transfer happens if partial pressure differentials are high.

6. Dissolved Oxygen • Several factors affect the solubility of oxygen in water…elevation, temperature and barometric pressure. Higher temp and higher elevation decrease oxygen solubility (amount of O2 the water can hold). You can predict the solubility with the D.O. calculator at this site http://antoine.frostburg.edu/chem/senese/101/solutions/faq/predicting-DO.shtml

7. Water Quality Parameters • Temperature - acts to regulate metabolism. Fish are cold blooded, meaning their metabolism is determined by external temperatures. • Influences the holding capacity of gases in the water (including oxygen). The greater the temperature, the less oxygen can be carried in the water. • Influences the form of nitrogen present in the water. Higher temperatures shifts nitrogen compounds to the more toxic unionized form..ammonia (NH3)

8. Nitrogen Cycle • Nitrogen is present in 3 major forms in water. • Ammonia is present primarily as a result of excretion of the fish. This is the most toxic form. • Ammonia shifts between the un-ionized form (NH3) and ionized form (ammonium - NH4-) • Important because NH3 is more toxic to fish and plants.

9. Nitrogen toxicity • Ammonia is broken down in 2 steps by aerobic bacteria..the first step is to a less toxic form called nitrite (NO2). Still toxic and can cause brown blood disease • NO2 attaches to hemoglobin, preventing O2 from being carried by the hemoglobin. Blood turn brown and eventually fish can die. • The process is carried out by a group of bacteria known as Nitrosomonas. They are aerobic…requiring oxygen to survive.

10. Nitrogen Cycle • Nitrite (NO2) is utilized by another group of bacteria…called Nitrobacter. These aerobic bacteria use nitrite and convert it to a form called nitrate (NO3). • Nitrate is relatively non-toxic. It is also the most preferred form of nitrogen for plants. • Temperature and pH influence the survival and productivity of these bacteria (pH 7.2-8.5)

11. pH • pH is a measure of the acidity of the water. • It is given as a number from 1-14. • A reading less than 7 is called acidic. • A reading over 7 is alkaline or basic • A reading of 7 is neutral. • Most food fish prefer water between 6.5 and 8.5 • Many ornamental fish prefer pH levels from 5.5-7.5

12. pH • Why does pH shift? • Natural processes like photosynthesis and respiration remove and add carbon from the system. During photosynthesis, carbon is removed. Adding carbonates (CO3) provides a supply of carbon to keep the pH from shifting drastically. • 6CO2 + 6H2O + Energy  C6H12O6 + 6O2

13. pH • A natural daily event is to see pH rise during daylight hours and drop during night. This fluctuation should be minimized for health of the fish

14. Hardness • A measure of the amount of Calcium and Magnesium in water. It influences the pH by providing a buffer, so there are no sudden shifts in pH. It is measured in ppm CaCO3. The calcium is also used by fish and crustaceans for shell, scale, teeth and bone formation. The pH must be acidic to break the Ca-CO3 bond • Free calcium in the water helps with osmoregulation

15. Alkalinity • Alkalinity is a measure of the amount of CO3 and HCO3- (carbonates and bicarbonates). These have a quicker reaction and stabilizing effect on pH. Gypsum and commercial lime are sources of carbonates.

16. Alkalinity • The most important components of alkalinity are carbonates and bicarbonates.  The total alkalinity concentration should be no lower than 20 mg/L CaCO3 in production ponds.  Pond pH can swing widely during the day, measuring from 6 to 10, when alkalinity concentrations are below this level. Preferred range is 50-150mg/l

17. Salinity • A fish must maintain osmotic levels in its body • They must keep water in or out of the body, depending on salinity of the environment. • They do this by Osmoregulation • Osmoregulation is controlling internal solutes • Involves energetic cost of active transport • In bony fishes this can be 5% of metabolic rate

18. Solute regulation • Transport solutes across the body surface

19. Saving energy • Salinity is increased in aquacultutre of freshwater fish to help reduce stress and can improve growth by reducing the energy needed for osmoregulation. • This savings in energy can be redirected towards other functions, such as growth or reproduction.

20. Aeration • The process of increasing dissolved oxygen to water. • Aerators designed for efficient O2 transfer. • Types of commercial aerators • Blowers • Diaphragm pumps • Aspirating aerators • Paddlewheels

21. Types of aerators • Blowers - high volume, low pressure. Long lasting, durable. • Cost - higher than diaphragm pump of same operating power, but with more air.

22. Diaphragm pump • Higher pressure, but lower volume than blower. Durable and can change diaphragm when necessary.

23. Aspirating aerator • Most efficient aerator. Propeller spins rapidly, drawing air down the shaft. • Blower assisted aspirator increases the volume of air injected into the water.

24. Paddlewheels • Agitate water and move water around pond. Efficient and durable. Electric or PTO driven

25. Testing for D.O. • Secchi Disc - most valuable when used to compare week-week or month-month. A reading of 12” -18” is best for aquaculture

26. Waste Management • Removal of solid waste is crucial. • Prevents less ammonia from being released. • Improves clarity for light penetration..good for algae production. • Keep fish in good health.

27. Environmental factors • Attention to the affect of aquaculture to the environment can reduce problems, improve profitability, and maintain social responsibility. • Aquaculture can be bad for the environment if not planned properly. • Recycling opportunities are available in all aspects of aquaculture.

28. Growth Factors  Feed – nutrients, digestibility, cost, availability  Temperature  Dissolved oxygen and stress  Water quality  Crowding  Males vs females  Disease

29. Integration with plants & Animals • Use of freshwater effluent to irrigate plants is a god way to recycle waste products. • Irrigation to garden plot • Aquaponics (Aquaculture / Hydroponics) system

30. 2 Crops per Drop • Each drop of water used can go towards growing fish and a plant crop in standard garden plot

31. Aquaponics • Fish and plants share the same water in the system as it recirculates through each component.