Calculating Feed Dose
Feed rate is determined by Wet Weight Biomass produced (or more accurately by Dry Weight Biomass produced), the feed conversion ratio of the microalgal concentrate used and the efficiency of your grow-out protocols.
Rotifer Count is a useful proxy for rotifer mass once rotifer mass per million rotifers has been determined. Rotifers vary considerably by strain and growing conditions.
Rotifer mass (g/million rotifers) can change significantly over time in response to feed, growing conditions, and season. This can significantly affect production results when feeding according to rotifer count without taking these changes into account.
Continuous Systems Dose for Biomass Harvested Each Day
Table E.3: Microalgae Concentrate Feed per hour per 100g of rotifer harvest (wet weight). Also shown is the corresponding number of rotifers harvested at different rotifer sizes
Feed rate is determined by the Wet Weight Biomass of rotifers you need to harvest each day. For a stable system, do not adjust the feed rate every time rotifer density changes, the system will find its own equilibrium.
- The Wet Weight Harvest number should be used as an estimate of harvest per feed. Each hatchery is different and the feed conversion rate will vary from time to time and hatchery to hatchery. Let your system find it’s own equilibrium.
- It is possible to feed according to the number of rotifer to be harvested after adjusting for the size of the rotifer.
- It is also possible to feed according to the number of rotifers in the tank prior to harvest, after adjusting for rotifer size and desired harvest rate (growth rate). In a harvest range of 25% to 50%
- FeedBatch = FeedCont x Harvest (%), where:
- FeedBatch = Feed rate: ml per hour per 100 grams Wet Weight rotifers in the culture
- FeedCont = Feed rate: ml per hour per 100 grams Wet Weight rotifers harvested (from chart 6.1 above)
- Harvest (%) = percent of rotifers harvested per day (25-50%)
* However, it is easiest to simply feed according to the Wet Weight Biomass you wish to harvest. Please see “Equilibrium Management” in section D.6.2. | Rotifer Production: methods.
Wet weight is easily obtained by screening the whole or a small percentage of your harvest and blotting the bottom of the screen with a paper towel to remove excess moisture. If you know the number of rotifers you need to harvest and their size, but not their Wet Weight Biomass, use the Lorica Length to Biomass Calculator (Table 6.2) below the feed table.
Table E.4: Rotifer length to mass conversion
a. These numbers are mathematical approximations using the RMI “Mini-L 160” as the base data point. Actual numbers will vary depending on rotifer shape (thin vs. plump) and composition (density).
b. Rotifer length is measured as the distance between the anterior tip if the lorica with the corona retracted and the base of the foot. Rotifers retract their corona when fixed with formalin.
c. Better data can be obtained by screening a liter of rotifer culture and dividing the weight by the number of rotifers in the liter of culture.
1.Harvest rate (% of culture harvested per day) does not affect harvested biomass at equilibrium. It affects the median age of rotifers in the rotifer culture by affecting feed per rotifer and the rate at which rotifers grow. Please see “Population Dynamics” inset Box and Table D.4 in D.6.1 | Rotifer Production, Continuous vs. Batch
2. Feed rate (Table 6.1 above) is determined by: (1) The biomass of rotifers needed for harvest together with (2) feed density and (3) the Net Biomass Conversion rate of the feed.