View
37
Download
0
Category
Tags:
Preview:
Citation preview
The base of the food chain in the marine environment comprises Phytoplankton
Phytoplankton is the main producer in marine enviornment
Most frequently used in commercial culture operations
What is micro-algae???
commonly known as seaweed
• Also referred to as phytoplankton, microphytes, or planktonic algae
Produce mass quantities of zooplankton (rotifers, copepods, brine shrimp)
This zooplankton serves as food source for larval and early-juvenile stages of crustaceans and fish
Major classes of cultured algal species
More than 40 different species isolated and cultured as pure strains in intensive systems
currently used 8 major classes and 32 genera
Class
Cyanophyceae Bacillariophyceae Haptophyceae Chrysophyceae Prasinophyceae Cryptophyceae Xanthophyceae Chlorophyceae
Figure 2.2. Some types of marine algae used asfood in aquaculture (a) Tetraselmis spp. (b)Dunaliella spp. (c) Chaetoceros spp. (Laing,1991)
A generalized set of conditions for culturing micro-algae Parameters Range Optima
Temperature (°C) 16-27 18-24
Salinity (g.l-1) 12-40 20-24
Light intensity (lux) 1,000-10,000 (depends on volume and density
2,500-5,000
Photoperiod (light: dark, hours)
16:8 (minimum)
24:0 (maximum)
pH 7-9 8.2-8.7
Temperature controlled room for maintenance of algalstock cultures in a bivalve hatchery: stock cultures in test tubes (left)and inoculation hood (right).
Why mixing is necessary??? To ensure all cells of the population
equally exposed to the light and nutrients
To prevent sedimentation of the algae
To avoid thermal stratification
To improve gas exchange between the culture medium and the air
Mixing achieved by
stirring daily by hand (test tubes, erlenmeyers), aerating (bags, tanks)
using paddle wheels
jetpumps (ponds)
NB: not all algal species can mixing tolerate vigorous
Growth dynamics
Growth of an axenic culture of micro-algae characterized by five phases
1. Lag or indution phase 2. Exponential phase3. Phase of declining growth rate4. Stationary phase5. Death or "crash" phase
Lag or induction phase
little increase in cell density occurs
relatively long when an algal culture is transferred from a plate to liquid culture
attributed to the physiological adaptation of the cell metabolism to growth
Lag phase(Cont.)
the increase of the levels of enzymes and metabolites involved in cell division and carbon fixation
exponentially growing algae have short lag phases, which can seriously reduce the time required for upscaling
Exponential phase
key to the success of algal production
the cell density increases as a function of time t according to a logarithmic function
Ct = C0.emt Ct and C0 being the cell
concentrations at time t and 0
m =specific growth rate (dependent on algal species,light intensity and temperature)
Phase of declining growth rate
Cell division slows down when
nutrients light pH carbon dioxide other physical and
chemical factors
begin to limit growth.
Stationary phase
the limiting factor and the growth rate balanced,
results in a relatively constant cell density
Death or "crash" phase
water quality deteriorates
nutrients are depleted to a level
incapable of sustaining growth.
Cell density decreases rapidly
Culture eventually collapses.
Algal culture techniques Indoor Outdoor
allows control over illumination, temperature, nutrient level, contamination with predators and competing algae
make it very difficult to grow specific algal cultures for extended periods
Algal culture techniquesOpen Closed.
uncovered ponds and tanks (indoors or outdoors)
are more readily contaminated
closed culture vessels such as tubes, flasks, carboys, bags, etc
Algal culture techniques
Axenic =sterile Xenic.
free of any foreign organisms such as
bacteria and require a strict sterilization of all glassware, culture media and vessels to
avoid contamination.
impractical for commercial operations
Advantages and disadvantages of various algal culture techniques
Culture type Advantages Disadvantage
Indoors A high degree of control(predictable)
Expensive
Outdoors Cheaper Little control (less predictable
Closed Contamination less likely
Expensive
Open Cheaper Contamination more likely
Advantages and disadvantages of various algal culture techniques
Culture type Advantages Disadvantages
Axenic Predictable, less prone tocrashes
Expensive, difficult
Non-axenic Cheaper, less difficult
More prone to crashes
Advantages and disadvantages of various algal culture techniques
Culture type Advantages Disadvantages
Continuous Efficient, provides a consistentsupply of high-quality cells,automation, highest rate ofproduction over extendedperiods
Difficult, usually only possible toculture small quantities, complex,equipment expenses may be high
Semicontinuous Easier, somewhat efficient
Sporadic quality, less reliable
Batch Easiest, most reliable
Least efficient, quality may beinconsistent
Batch culture method
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
In practice, algae are transferred to larger culture volumes prior to reaching the stationary phase
Batch culture method
larger culture volumes are brought to a maximum density and harvested
The following consecutive stages might be utilized: test tubes,
2 l flasks, 5 and 20 l carboys, 160 l cylinders, 500 l indoor tanks, 5,000 l to 25,000 l outdoor tank
Batch culture method
According to the algal concentration, the volume of the inoculum amounts to 2- 10% of the final culture volume
Where small amounts of algae required indoor culture employs 10 to 20 l glass or plastic carboys (may be kept on shelves backlit with fluorescent tubes)
Batch culture method ADVANTAGE
Batch culture systems widely applied because of
Simplicity and flexibility
Allowing to change species
To remedy defects in the system rapidly
Batch culture method DISADVANTAGE
Batch culture not necessarily the most efficient method
harvested just prior to the initiation of the stationary phase
must thus always be maintained for a substantial period of time past the maximum specific growth rate.
the quality of the harvested cells may be less predictable than that in continuous systems
need to prevent contamination during the initial inoculation and early growth period
require a lot of labour to harvest, clean, sterilize, refill, and inoculate the containers
Continuous culture
Culture in which a supply of fertilized seawater continuously pumped into a growth chamber
The excess culture simultaneously washed out, permits the maintenance of cultures very close to the maximum chamber
Two categorie
Turbidostat culture chemostat culture
Continuous culture
turbidostat culture chemostat culture
the algal concentration is kept at a preset level
by diluting the culture with fresh medium
by means of an automatic system.
a flow of fresh medium is introduced into the culture at a steady, predetermined rate.
The latter adds a limiting vital nutrient (e.g.nitrate) at a fixed rate
in this way the growth rate and not the cell density is kept constant.
Continuous culture
Algae Culture density forhighest yield (cells per μl
Usual life of culture(weeks)
Tetraselmis suecica 2 000 3-6
Chroomonas salina 3 000 2-3
Dunaliella tertiolecta 4 000 3-4
Isochrysis galbanaMonochrysis lutheriPseudoisochrysis paradoxa
20 000 2-3
Continuous culture methods for various types of algae in 40 linternally-illuminated vessels (suitable for flagellates only) (modified fromLaing, 1991),
Continuous culture
Diagram of a continuous culture apparatus (not drawn to scale):
(1) enriched seawater medium reservoir (200 l); (2) peristaltic pump; (3)resistance sensing relay
(50- 5000 ohm) (4) lightdependent resistor (ORP 12); (5) cartridge filter (0.45 μm); (6) culture vessel (40 l); (7) six 80 W fluorescent
tubes (Laing, 1991).
ADVANTAGE OFContinuous culture
Producing algae of more predictable quality
Amenable to technological control and automation
DISADVANTAGE OFContinuous culture
Relatively high cost and complexity Requirements for constant illumination
and temperature mostly restrict continuous systems to indoors
This only feasible for relatively small
production scales.
Harvesting and preserving micro-algae
High-density algal cultures concentrated by either chemical flocculation or centrifugation
Products such as aluminum sulphate and ferric
chloride cause cells to coagulate and precipitate to the bottom or float to the surface
Recovery of the algal biomass is then accomplished by
1.siphoning off the supernatant 2.skimming cells off the surface
Harvesting and preserving micro-algae
Coagulated algae no longer suitable as food for filter-feeders
Centrifugation of large volumes of algal culture
usually performed using a cream separator
Cells deposited on the walls of the
Centrifuge head as a thick algal paste
The resulting slurry stored for 1-2 weeks in the refrigerator or frozen
Harvesting and preserving micro-algae
Cryoprotective agents (glucose, dimethylsulfoxide) added to maintain cell integrity during freezing
Cultures stored in hermetically sealed vials lose their viability more rapidly than those kept in cotton-plugged vials
Concentrated cultures of Tetraselmis suecica kept in darkness at 4°C maintain their viability
Nutritional value of micro-algaeDepends on
1. cell size 2.digestibility 3. production of toxic compounds 4.biochemical composition
There marked differences in the compositions of the micro-algal classes and species
Nutritional value
Protein 12-35%
Lipid 7.2-23%
Carbohydrate 4.6-23%
Micro-algae can also be considered as
a rich source of ascorbic acid (0.11-
1.62% of dryweight,
a mixture of
algal species supplies the animals
with an adequate amount of both
nutrients
Use of micro-algae in Aquaculture
Bivalve molluscs
Intensive rearing of bivalves relied on the production of live algae
Comprises on average 30% of the operating costs in a bivalve hatchery
use of micro-algae in Aquaculture
Pinhead shrimp
Added during the non-feeding nauplius stage
algae available immediately upon
molting into the protozoea stage.
Penaeid shrimp
Requirements for cultured algae in hatchery andnursery culture of bivalve molluscs (Utting and Spencer, 1991
Use of micro-algae in Aquaculture
Marine fish "green water technique" part of the
commonly applied techniques for rearing larvae of
Gilthead seabream Sparus aurata Milkfish Chanos chanosHalibut Hippoglossus hippoglossus
Effects of the presence of micro-algae in the larval rearing tank
stabilizing the water quality in static rearing systems(remove metabolic by-products, produce oxygen);
a direct food source through active uptake by the larvae with the polysaccharides present in the algal cell walls possibly stimulating the non-specific immune system in the larvae
Effects of the presence of micro-algae in the larval rearing tank
an indirect source of nutrients for fish larvae through the live feed (i.e. by maintaining the nutritional value of the live prey organisms in the tank)
increasing feeding incidence by enhancing visual contrast and light dispersion
microbial control by algal exudates in tank water and/or larval gut
Effects of the presence of micro-algae in the larval rearing tank
an indirect source of nutrients for fish larvae through the live feed (i.e. by maintaining the nutritional value of the live prey organisms in the tank)
increasing feeding incidence by enhancing visual contrast and light dispersion
microbial control by algal exudates in tank water and/or larval gut
Recommended