natural food organisms

GUIDE TO THE PRODUCTION OF LIVE FOOD ORGANISMS

SELECTION OF FOOD

Criteria:

1.The food must be perceived by the larvae.

2. The size of food must be such that it can be accommodated by the mouth of the larvae.

3. The feed should have high dietary value especially Highly Unsaturated Fatty Acids (HUFA) essential to the growth and survival of the larvae.

4. The feed can be easily produced in large quantities.

5. The feed can be digested by the larvae.

Types of Natural Food Organisms

1. Phytoplankton

2. Zooplankton

PHYTOPLANKTON CULTURE

In larviculture, the phytoplankton may serve any of the following functions:

(1)provide nutrients via accidental or active ingestion by the larvae;

(2) detoxify the larviculture medium by assimilating or neutralizing inhibitory material; (3) improve the nutritional value of secondary food organisms such as zooplankton;

(4) secrete into the medium metabolic products which facilitate larval growth and/or development

TYPES OF ALGAL CULTURES•Maintenance cultures - natural collections of algae kept in culture vessels in the laboratory; here, succession of the previously less abundant species over the dominant ones may occur.

•Enrichment cultures - refer to crude collections of algae or other algal source materials treated with specially selected culture media which will favour the rapid increase in number of desired algal species.

•Unialgal cultures - refer to populations consisting of a single algal species, although other micro-organisms may be associated.

•Axenic culture - contains a population of a single algal species, all other living organisms being absent.

SAMPLING/ISOLATION TECHNIQUES

•Phytoplankton may be collected by towing through the water special plankton nets made of fine silk bolting cloth (180 meshes/inch2).

•Sampling bottles should be uncovered and illuminated promptly upon reaching the laboratory.

•Competition among species is one of the main difficulties in maintaining a mixed population.

So, there is a need to obtain a unialgal culture

Two conditions must be fulfilled to obtain unialgal or pure cultures: (1)the relevant or desired species must be isolated, and (2) it must be induced to multiply.

Types of Isolation

A. Biological Isolation

Biological isolation of algae can be attained through enrichment culture methods.

B. Mechanical Isolation

Stein (1973) has described a number of isolation methods, the more popular of which include the capillary pipette method, streak-plating, and isolating on agar.

1.Capillary pipette method

This method uses an inverted Petri dish top as an isolation dish.

•place 10–15 drops of the natural collection in the centre of the dish•place 6–8 drops of suitable liquid medium in six positions encircling the natural collection. Each droplet is then assigned a numerical code

•with the use of sterile capillary pipette, transfer the desired algal units from the natural collection to one of the six drops. Desired algal units are located while looking through an inverted microscope or a stereomicroscope

•transfer a single algal unit from the first drop to the second drop

•repeat the process (moving clockwise) until a single algal unit is present in a drop of liquid medium

•transfer the single algal unit to a sterile tube containing liquid culture medium.

GROWTH

•denotes the increase in number beyond that present in the original inoculum •usually refers to changes in the culture of cells rather than to changes in an individual organism.

Growth Phases

1.The lag phase - After the addition of inoculum to a

culture medium the population remains

temporarily unchanged

2. The logarithmic or exponential phase - The cells here begin to divide steadily at constant rate. Given optimal conditions, the growth rate is maximal during this phase.

3. The stationary phase- the logarithmic phase of growth gradually begins to taper off after several hours (or days).

The population remains more or less constant for a time

4. The phase of decline or death - After the stationary phase, the rate at which cells die is faster than the rate of

reproduction of new cells. Here the number of viable cells decreases

geometrically

CONDITIONS AFFECTING GROWTH

1.Illumination2.Temperature3.Culture Medium4.Starter/Inoculum

ZOOPLANKTON CULTURE

Brachionus plicatilis Muller

A. Taxonomic position     Phylum Trochelminthes        Class Rotifera (Notatoria)           Order Monogononta                Suborder Ploima                    Family Brachionidae                      Subfamily Brachioninae                        Genus Brachionus Pallas                             Species plicatilis Muller

B. General Description of Rotifers

Most rotifers are microscopic aquatic animals. The body shape is extremely variable and is divided into three parts: head, trunk, and foot.

C. Potential

The rotifer Brachionus plicatilis is one of the most important zooplankton species presently utilized as live food for various cultivable marine animals.

D. Food and Feeding

Chlorella has probably been the most popularly used algal food for the culture of Brachionus plicatilisOther food may include yeasts (bakers or marine)

E. Culture Techniques

1.Daily Tank Transfer Method2.The “drain–off” system for large tank outdoor culture3.The feedback culture system

The “daily” tank–transfer method

Involves continuous subculture of Brachionus using 0.5 m tanks.

The tanks are initially used for Chlorella cultures.

When Chlorella density reaches about 10–20 × 10 cells/ml inoculation of rotifers is done then are harvested and transferred to another tank. The process of transfer of subculturing continues for an indefinite period. The main disadvantage of this method is that it is too labour–intensive