Aquaculture
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     Microphytes

 
     
 
Name : microalgae, microphytes or phytoplankton.
Scientific name :  

Species

Classe

fig.1 T. Iso
fig.2 fig2: Chaetoceros calcitrans
fig.3 fig3: Skeletonema costatum
Isochrysis aff. galbana
(T. Iso) ( fig.1 )

Haptophycae

Isochrysis galbana

Haptophycae

Pavlova lutheri

Haptophycée

Chaetoceros calcitrans
forma pumilum

Bacillariophycae

Chaetoceros calcitrans ( fig.2 )

Bacillariophycae

Chaetoceros gracilis

Bacillariophycae

Thalassiosira pseudonana (clone 3H)

Bacillariophycae

Skeletonema costatum ( fig. 3 )

Bacillariophycae

Rhodomonas salina

Cryptophycae

Tetraselmis suecica

Prasinophycae

Tetraselmis chui

Prasinophycae

Tetraselmis striata

Prasinophycae

Size :

 

Microalgae are unicellular species which live either isolated or in chains. Depending on the species, their sizes range from a few micrometers (µm) to a few hundreds of micrometers.

Microalgae constitute the basic foodstuff for numerous aquaculture species, especially filtering bivalves. They provide them with vitamins and polyunsaturated fatty acids, necessary for the growth of the bivalves which do not know how to synthesize it themselves.

 

Culture techniques and production cycle

Algae are grown in hatcheries, inside 300 liter flasks. The maximum concentration is reached in a few days.
The production of cells still follows relatively empirical ways; it consists essentially of discontinuous cultivation, either outdoor in tanks or ponds, or indoor in large plastic flasks. The erratic cultivation conditions generally induce major variations in the quantity of algae, which in turns leads to fluctuations in the growth of the animals which feed on them.

Cultivation periods last three to seven days, at the end of which the total production volume is fed to animals. In order to meet the nutritional needs of the animals, at least two different species of microalgae must be fed to them. In some hatcheries, the volumes concerned can reach up to hundred cubic meters per day.

Evolution of the production

Bio-reactor for continuous algae
distribution to molluscs larvae in hatchery
Tests are in progress to produce algae within closed, continuous systems, in order to meet the nutritional quality requirements requested by the hatcheries. Finely tuned control of the cultivation parameters enables some of the cellular compounds (aminoacids, polyunsaturated fatty acid concentrations) to be stabilized or even set to precise levels. Compared with discontinuous cultivation – in which final concentrations rarely exceed one tenth of a gram per liter of sea water – continuous systems make it possible to obtain concentrations that are ten to twenty times higher.

 

Product value enhancement

Algae freshly fed to farmed animals - using pumps or gravity flow systems - are clearly the best source of food for molluscs farms. The use of frozen lumps did not give convincing results for the growth of bivalves, but gave better results as food for zooplankton, which in turn will be consumed by crustaceans or fish.

In fish farms, the continuous presence of microalgae has a beneficial effect on the growth and health of animals (green water phenomenon).

Phytoplankton figures

6 number of phytoplankton hatcheries producing for bivalve spats necessary for cultivation; Grainocean (17), Satmar (50), Ferranges (85), Sodabo (85), Kerner hatchery (56) Tinduff hatchery (29).
2 minimum number of phytoplankton species to be fed to bivalves to meet their nutritional needs.
10 à 20 times higher : the concentration of microalgae in the continuous production systems with respect to that achieved in discontinuous systems.

Strengths / Weaknesses

Strengths Weaknesses
Situation at the basis of whole French aquaculture production
Image of “health” food (functional food)
Possibility of “off-soil” cultivation, a guarantee of quality and control
Highly dependent on water quality (problems of pollution)
Major difficulties to shift to high production volumes
Numerous problems of contamination with outdoor crops

To know more

The research programs on seaweed culture
The teaching week
 

Mis à jour le Update 13/02/06
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