5. General Culture Procedures
5.6 Mass Culture on Formulated Diets
A frequently used formulated diet in rotifer culture is Culture Selco® (INVE NV, Belgium) available under a dry form. It has been formulated as a complete substitute for live microalgae and at the same time guarantees the incorporation of high levels of EFA and vitamins in the rotifers. The biochemical composition of the artificial diet Culture Selco® (CS) consists of 45% proteins, 30% carbohydrates, 15% lipids of which 33% are (n-3) HUFA, and 7% ash. Its physical characteristics are optimal for uptake by rotifers: the particle has a size of 7 mm, remains maximally in the water column when a relatively strong aeration is applied, and does not leach. The diet needs to be suspended in water and mixed with a blender (this is a Quick time movie).. mixed with a blender (this is a Real Player movie)..prior to feeding, which facilitates on one hand the possibilities for automatic feeding but on the other hand requires the use of aeration and cold storage. The following standard culture procedure has been developed and tested on several rotifer strains in 100 l tanks.
Cilindro-conical tanks of 100 l with dark smooth walls (polyethylene) are set up in shaded conditions. The culture medium consists of diluted seawater of 25 ppt kept at 25°C. No water renewal during the 4-d culture period. Air stones are installed a few cm above the cone bottom of the tank to allow sedimentation and possible flushing of waste particles. Food floccules are trapped in pieces of cloth which are suspended in the water column, or in an air-water-lift trap filled with sponges (Fig. 3.6.).
Furthermore, all efforts are made to maintain a good water quality with minimal accumulations of wasted food by assuring short retention times of the food particles. This is achieved by using high starting densities of 200 rot.ml-1 and the distribution of small amounts of feed at hourly intervals. This latter can easily be automated by pumping the feed suspension from a gently aerated stock kept in a refrigerator at 4°C for up to 30 h (Fig. 3.7.). Applying this feeding strategy, an optimized feeding regime is developed in function of rotifer density and thus culture performance. It should be indicated that this protocol is developed for the L-strain and should be slightly adapted (less feed) when a S-strain is used.
Applying this standard culture strategy a doubling of the population is achieved every two days, reaching a harvest density of 600 rotifers.ml-1 after four days only, which is better than for the traditional technique using live algae (and baker's yeast). It should be emphasized that hygienic precautions should be taken to avoid contacts among different rearing units. All material used during the production (glass ware) can be disinfected in water baths with NaOCl, HCl or other disinfectants. After each production cycle (4 days) the tanks, airstones and tubing need to be disinfected thoroughly. In order to avoid crashes it is recommended that after approximately one month of culture the complete system is disinfected and the cultures are started again using rotifers from starter cultures.
Figure 3.7. Refrigerated feed suspension distributed to the individual rotifer tanks by means of a peristaltic pump. (click to see video)
In commercial hatcheries, peristaltic pumps(this is a Quick time movie).. peristaltic pumps(this is a Real Player movie)..are not always available. Also in this case the artificial diet can be fed on a daily basis at a concentration of 400-600 mg per million rotifers, administered in 4 to 6 rations with a minimum quantity of 50 - 100 mg.l-1 culture medium. Analogous production outputs are achieved under upscaling conditions in commercial hatcheries.
1.
Introduction
2. Morphology
3. Biology and Life History
4. Strain Differences
5. General Culture Procedures
