Shellfish Breeding and Hatchery Management (2+1)

27.2.2 Algal culture techniques

Algal culture techniques are classified as below:

1. Indoor and Outdoor culture method

2. Open and Closed culture method

3. Batch culture

4. Continuous culture method

5. Semicontinuous culture method

1. Indoor and Outdoor:

Indoor culture allows control over illumination, temperature, nutrient level, contamination with predators & competing algae, where as outdoor algal culture systems make it very difficult to grow specific algae culture for extended periods.

2. Open/Closed:

Open culture such as uncovered ponds & tanks (indoor or outdoors) are mostly readily contaminated than closed culture vessels such as tubes, flakes, Carboys, bags etc.

3. Axenic (=sterile)/xenic:

Axenic cultures are free of any foreign organisms such as bacteria & require strict sterilization of all glass ware, culture media & vessels to avoid contamination. The latter makes it impractical for commercial operation.

4. Batch continuous & Semi continuous

Batch culture technique:

The batch culture consists of a single inoculation of cells into a container of fertilized seawater followed by a growing period of several days & Finally harvesting when the algal population reaches its maximum or near maximum density.

Inoculation 2-10%

Continuous culture:

Two categories

1. Turbidostat culture

2. Chemostat culture

Turbidostat culture:

In which the algal concentrationis kept at a preset level by diluting the culture with fresh medium by means of an automatic system.

Chemostat culture:

In which a flow of fresh medium is introduced into culture at a steady, predetermined rate. The latter adds a limiting vital nutrient (eg nitrate) at a fixed rate and in this way the growth rate & not the cell density is kept constant.

Semi-continuous culture:

The semi-continuous techniques prolongs the use of large tank culture by partial periodic harvesting followed immediately by topping upto the original volume & supplementing with nutrients to achieve the original level of enrichment.