3. 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
4. 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
5. 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
9. Figure 2.2. Some types of marine algae used
as
food in aquaculture (a) Tetraselmis spp. (b)
Dunaliella spp. (c) Chaetoceros spp. (Laing,
1991)
10. 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
11. Temperature controlled room for maintenance of algal
stock cultures in a bivalve hatchery: stock cultures in
test tubes (left)
and inoculation hood (right).
13. 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
14. 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
16. Growth dynamics
Growth of an axenic culture of micro-algae
characterized by five phases
1. Lag or indution phase
2. Exponential phase
3. Phase of declining growth rate
4. Stationary phase
5. Death or "crash" phase
17.
18. 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
19. 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
20. 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)
21. Phase of declining
growth rate
Cell division slows down
when
nutrients
light
pH
carbon dioxide
other physical and
chemical factors
begin to limit growth.
22. Stationary phase
the limiting factor and the
growth rate balanced,
results in a relatively
constant cell density
23. Death or "crash" phase
water quality deteriorates
nutrients are depleted to a
level
incapable of sustaining
growth.
Cell density decreases
rapidly
Culture eventually
collapses.
25. 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
26. Algal culture techniques
Open Closed.
uncovered ponds and tanks
(indoors or outdoors)
are more readily
contaminated
closed culture vessels such
as tubes, flasks, carboys,
bags, etc
27. 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
28. Advantages and disadvantages of
various algal culture
techniquesCulture 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
29. Advantages and disadvantages of
various algal culture
techniquesCulture type Advantages Disadvantages
Axenic Predictable, less prone to
crashes
Expensive, difficult
Non-axenic Cheaper, less difficult More prone to crashes
30. Advantages and disadvantages of
various algal culture
techniquesCulture type Advantages Disadvantages
Continuous Efficient, provides a
consistent
supply of high-quality
cells,
automation, highest rate
of
production over
extended
periods
Difficult, usually only
possible to
culture small quantities,
complex,
equipment expenses may
be high
Semicontinuous Easier, somewhat
efficient
Sporadic quality, less
reliable
Batch Easiest, most reliable Least efficient, quality
may be
inconsistent
32. 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
33. 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
34. 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)
36. 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
37. 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
40. 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
41. 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.
42. Continuous culture
Algae Culture density for
highest 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 galbana
Monochrysis lutheri
Pseudoisochrysis
paradoxa
20 000 2-3
Continuous culture methods for various types of algae in 40 l
internally-illuminated vessels (suitable for flagellates only) (modified
from
Laing, 1991),
45. DISADVANTAGE
OF
Continuous 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.
46. 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
47. 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
48. 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
49. Nutritional value of
micro-algae
Depends 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
51. 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
52. use of micro-algae in
Aquaculture
Pinhead shrimp
Added during the non-feeding nauplius stage
algae available immediately upon molting
into the protozoea stage.
53. Penaeid shrimp
Requirements for cultured algae in hatchery
and
nursery culture of bivalve molluscs (Utting
and Spencer, 1991
54. 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 chanos
Halibut Hippoglossus hippoglossus
55. 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
56. 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
57. 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