1. Algae Production, Biology and Species
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Biology
Microalgae: microscopic single-celled eukaryotic planktonic algae
To be magnified 100 – 400X in order to recognize family
Reproduction by cell division
Some species have own movements by flagella, other drift passively
Divided in 9 divisions according to pigment types etc.
Photoautotrophic (also heterotrophic) organisms
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Photosynthesis
As with all plants, algae photosynthesise, i.e. they convert carbon into organic matter. Light is the source of energy, which drives this reaction with wavelength and photoperiod the main factors.
Photosynthesis: 6CO2 + 6H2O = C6H12O6 + 6O2
In the dark, algae shifts from photosynthesis to respiration, and the equation is reversed and glucose is needed for energy
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Growth dynamics
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Growth dynamics
1. Lag or induction phase
This phase during which little increase in cell density occurs is relatively long when an algal culture is transferred from a plate to liquid culture.
2. Log or exponential phase: the cell density increases as a function of time according to a logarithmic function.
3. Phase of declining growth rate; cell division slows down when nutrients, light, pH, carbon dioxide or other physical and chemical factors begin to limit growth.
4. Stationary plateau phase: the limiting factors and the growth rate are balanced, which results in a relatively constant cell density.
5. Death or "crash" phase: water quality deteriorates and nutrients are depleted to a level incapable of sustaining growth. Cell density decreases rapidly and the culture eventually collapses.
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Light
Energy source
Intensity; not to low, not to high (photo-inhibition)
Fluorescent tubes emitting either in the blue or the red light spectrum are preferred, as these are the most active wavelengths for photosynthesis.
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Nutrients
As the concentrations of cells in phytoplankton cultures are generally higher than those found in nature, algal cultures must therefore be enriched with additional nutrients and mineral to make up for the deficiencies in the seawater.
Nutrients as nitrate and phosphate are important for synthesis of DNA
Minerals, trace elements and vitamins are important for synthesis of pigments, enzymes etc.
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Criteria for choosing the right species
Sufficient nutritional requirements for both the fish larvae and rotifers
Not poisonous for the predators
Sufficient cell size and digestibility in order to be filtered and digested by the rotifers
High reproduction rate, reliable and sustainable in standardized commercial growing systems
Kriterier for valg av art
Høy næringsverdi for både fiskelarver og hjuldyr. Her er det viktig å merke seg at hjuldyr er en varmtvannsart, men torsk er en kaldtvannsart. Det vil dermed ha ulike preferanser ovenfor f.eks flerumettede fettsyrer. Derfor bør en velge art som har en næringsverdi som er tilpasset både hjuldyret og fiskelarvens behov.
Ved valg av ny art som ikke er brukt i marin yngeproduksjon må en være sikker på at de generellt ikke er giftige eller produserer forbindelser under sub-optimale forhold som fiskelarver og hjuldyr kan være sensitiv ovenfor.
En må videre ta hensyn til cellestørrelse og fordøybarhet til at de aksepteres av hjuldyrene men at de også har en struktur som ikke skader larvene
Videre må algearten ha kapasitet og være robust nok til i settes inn i intensive storskala produksjonssystemer.
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9. Information about species
Different algal species are grown for different species of fish or shrimp depending on the culture technique. The typical species cultured are as follows;
Shrimp culture
Fish culture
Tetraselmis chuii
Tetraselmis suesica
Nannochloropsis sp.
Isochrysis galbana
Chlamydamonas sp.
Chaetoceros gracilis
Monochrysis lutheri
Nannochloris atomus
Skeletonema sp
Chrorella sp.
Nannochloropsis oculata
Spirulina platensis
Pavlova lutheri
Dunaliella sp.
Pseudochrysis galbana
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10. Information about some microalgae species
Prasinophyceae – greenish coloured algae
Tetraselmis chuii
Large green flagellate, often used in larval rearing of shrimp, fish and shellfish
Optimal salinity /00
Optimal temperature C
Typical densities in mass culture celles/ml
Very high lipid content
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11. Prynesiophyceae – golden brown flagellate
Isochrysis sp.
Used especially as a primary algae
in shellfish hatcheries
Size: 3-5 um
Spherical to pear shaped
Isochrysis galbana tahition
Size: 5-6 um
Prefer temperatures up to 30 C and high light intensities
High DHA level and is therefore
used for growing rotifers
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12. Eustigatophyceae – greenish yellow algae
Nannochloropsis
Small green flagellate
Size: 2-4 um
Used in rotifer production
Popular as greenwater
Keeps suspended in the water column
High total lipid content and EPA level.
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13. Bacillariophyceae - Diatoms
Chaetoceros sp.
non-chainforming marine diatoms
golden brown, rectangular in shape
Size:4-6 um
Optimal temperature: 25 and 30 C
Optimal salinity: 17 and 25 ppt
Light intensity: 500 to 10,000 lux
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14. Nutritional value in some species
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Summary algae species
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