Batch vs Continuous Production

Aquaculture is all about producing aquatic animals or plants in captivity, the essence of which is to generate a financial profit from our investment of time and capital.  Irrespective of the species being produced, the farm can stock and harvest simultaneously or in batches, with very different outcomes as the strategy utilised directly impacts farm profitability.
 
Batch stocking involves introducing fingerlings (or nauplii or spat or seedlings, etc) to the whole farm or recirculating system (RAS) simultaneously.  The entire farm then grows to market size concurrently and harvesting is done over a relatively short period of time as the fish attain market size.  Batch stocking is most commonly implemented in a highly seasonal climate with outdoor infrastructure or where each production unit needs to be sterilised between consecutive batches.  Further advantages relate to simplicity where all the fish, or whatever are farmed, are the same age and therefore have the same requirements, simplifying feed utilisation and management.
 
Disadvantages associated with batch stocking start with the market.  Delivering the annual crop to the market over a short period of time can result in a temporary glut in the market.  This results in the farmer being a price taker, not a price setter.  Also, the production infrastructure is designed to comfortably accommodate the highest biomes that it needs to carry over the lifespan of the stock, and batch stocking means that when the fry and fingerlings are in the system, they have generous amounts of space around them, but when the fish get to market size the infrastructure is optimally utilised.  Consequently, the infrastructure is significantly underutilised for much of the growth period.
 
The alternative method is called continuous stocking, whereby each growth entity or infrastructure system contains fish of different ages.  As the larger fish are harvested, small fish are stocked into the system. This results in a farming system where fish are harvested and the equivalent numbers restocked on an ongoing basis, allowing the biomass in each system to remain relatively constant.  In this instance the infrastructure is better utilised because the standing stock is constantly close to the optimal according to the design for that infrastructure, which is especially good for the healthy operation of a biofilter.  A further massive advantage is that the market can be supplied on a continual basis with smaller quantities of fish, thereby enabling niche markets to be sought and better prices to be obtained due to the trickle of fish into the market rather than a once off annual glut of fish.  Handling and processing smaller quantities is also far simpler than the logistics associated with larger, infrequent harvests.
 
In the batch stocking example the farmer is able to empty and sterilise the infrastructure between crops where is in continuous stocking this is not possible. As a consequence, continuous stocking requires a high degree of attention to detail when it comes to biosecurity and pathogen exclusion.  If parasites or pathogens due find their way into the RAS, they need to be dealt with appropriately and urgently within this system.
 
Research conducted on our fish farm in South Africa showed that the batch stocking of tanks within a RAS produced half the tonnage of fish that could be grown in the same tanks when continuous production was utilised.  Continuous production is therefore the preferred method wherever possible.  This often means that recirculating systems are used in temperate climates to avoid the seasonality associated with farming under ambient conditions and to facilitate year-round production and harvests.  Ultimately, continuous stocking results in more efficient utilisation of infrastructure which in turn leads to better farming profits.