ABOVE: A diagram showing a General Protocol for Culturing Microalgae.
In most aquaculture operations which involve larval culture it is essential that the laboratory associated with the facility have a good Live Foods room(s).
Live Foods includes unicellular microalgae (many species available of non-motile, diatom, flagellates), rotifers (Branchionus spp) and brine shrimp (Artemia salina).
All commercial bivalve molluscs require microalgae which can be maintained and upscaled from an Algal Room. Throughout the larval life cycle there are changes in microalgae diets for many bivalve molluscs and the hatchery manager must be aware of the needs and requirements of each species of bivalve mollusc being cultured [e.g. scallops, pearl oysters, rock oysters, mussels, clams].
Microencapsulated diets or microalgal paste are alternative ways to satisfy the dietary requirements of most bivalve molluscs, but if possible live microalgae is best to include as a part of the diet. Manufactured diets are not live, so excess can lead to bacterial or fungal growth on uneaten diets.
Aquasearch has feeding schedules for the days of the larval life of blacklip pearl oysters, giant clams, and scallops. These are provided as part of a consultancy to setup a hatchery and in training hatchery technicians.
Aquasearch has its own cheap algal culture media. This has been tested for several years and serves as an example for setting up a good quality but economically affordable Algal Culture Room in third world countries.
One medium is used for the stock microalgae cultures in the Algal area using reduced natural light and another is used for the mass microalgae cultures which can be grown outdoors using natural sunlight. However, when consulting to set up new hatcheries the standard f2 medium and durable culture vessels are used if the client has the appropriate budget.
The marine rotifer Branchionus plicatilis is an important live food, as it is the first food which can be eaten by many marine fish, and some crustaceans such as the mudcrab, Scylla serrata. They generally reproduce asexually (parthenogenesis) but when environmental stress appears they can switch to a sexual mode of reproduction.
The body size of the seawater variety is about 120 microns diameter by 250 microns long. There are two strains that are most used in aquaculture; the large or L strain (0.33 micrograms/rotifer) and the small or S strain (0.22 micrograms /rotifer). They grow best at salinities of 10-20 ppt and the light level should be 2000-5000 lux at a pH of 7.5-8.5. Rotifers can be cultured in continuous, semi-continuous, and batch cultures. Yields can be over 500 rotifers/ml.
The food most often used for the rotifers is Nannochloropsis oculata, but it has been found that higher yields are obtained by using Tetraselmis spp. or combinations of these with diatoms. Yeast can be fed as a supplemental food but it often has to be enhanced with nutrients and vitamins and it can rapidly pollute the culture.
ABOVE: A general morphology of a branchionid rotifer.
Artemia is a crustacean which can be hatched at will from stored dry cysts. The nauplii larvae which are newly hatched have the highest nutritional value for feeding to the target aquacultured larvae. It has been estimated that approximately 85% of cultured marine species will feed on Artemia.
Since commercial dry cysts are relatively expensive, hatcheries on small budgets may consider maintaining breeding adults which happily produce eggs that hatch directly to nauplii rather than producing cysts. Artemia feed on microalgae much as rotifers do, so it is possible to maintain broodstock and routinely collect nauplii larvae for feeding to target aquaculture larvae.
Micoalgae reared with Aquasearch medium
Stock microalgae, Chaetoceros muelleri, reared with Aquasearch medium. This medium is cheap and works as well as the standard f2 algal medium for diatoms, for Chlorella- type microalgae, and for some flagellate microalgae. Dr. Braley has started microalgal labs in hatcheries and laboratories in the Pacific, Australia, S. and SE Asia.
LEFT: Stock microalgae, Chaetoceros muelleri, reared with Aquasearch medium.