Progressive Density and Feed Management (Batch System)
Batch Rotifer Systems start with a fixed inoculum and are allowed to grow in density over a period of 2 to 5 days. Batch systems are not equilibrium systems and values of all parameters from feed requirements and oxygen demand to ammonia increase over time.
Batch rotifer systems start with a small inoculum and are fed a proportionally small amount of feed. As rotifer density increases feed is also increased, as are other inputs such as oxygen. With large doses of a good microalgal feed, rotifer density can increase at a rate in excess of 100% per day. However, a lower growth rate of 50%-80% per day is often considered more practical.
The primary drawback of a batch system is also its primary advantage. A batch system requires more monitoring and more labor to ensure the rotifers are progressing properly and to make adjustments to feed and other inputs. A batch system requires a more hands-on approach and, depending on the hatchery, this may be more or less desirable.
Because Net Biomass Conversion is constant, increasing the feed rate per million rotifers does not waste the feed (within reason). Instead, the culture will grow faster. In the end you will have more rotifers with more feed used; microalgal biomass to rotifer biomass conversion will be constant.
In a batch system the feed rate per million rotifers only determines growth rate and rotifer age. The total feed delivered determines the final biomass of the rotifer harvest.
Quick comparison of Continuous and Batch Protocol Differences
Table D.5: Protocol comparison for determining feed rates
Table D.6: Feed Rate Comparison (Continuous System vs. Batch System) at different harvest/growth rates
(For rotifers with known dry weight biomass per rotifer. The following chart is for the RMI “Mini-L160” with a dry weight of 180ng/rotifer
Note: you cannot estimate feed per million rotifers without knowing the size of your rotifers. Even then it is a poor practice (even if it is established protocol). See the next section.