The big shrimp farming debate: clear-water v. biofloc
In recent years, the global market for seafood products, including fresh shrimp, has grown, alongside consumer awareness of and demand for sustainably-sourced produce. This has resulted in a shift from traditional pond culture of shrimp, to closed systems that are closer to market, feature enhanced biosecurity, have a minimal environmental impact, and result in improved shrimp production.
A tale of two technologies
Within the shrimp sector, when it comes to building a modern indoor shrimp farm, a choice must be made between the two main categories of closed aquaculture systems: clear-water recirculating aquaculture systems, and biofloc technology systems.
Clear-water systems usually involve an external biofilter for nitrifying bacteria, and filters for removal of solids from the water (some installations use UV systems for water sterilization).
In biofloc technology, the main concept is that the system is designed to benefit bacterial community composition and microbial communities so that they can proliferate in the process of water. A solids filter manages bacterial flocks, which consume nitrogenous wastes and toxic metabolites before being eaten by the cultured species. In short, bacteria both act as a cleaner and make a nutritional contribution.
Luckily, both systems are suitable for growing fresh shrimp; unlike many other species, shrimp can tolerate the high turbidity created by the biofloc system and the constant shifting of the bacterial load in the water.
What you need to know about biofloc
Originally conceived as a natural way to clean water, biofloc systems became popular as a low-cost sustainable aquaculture solution. The clear advantages, compared to traditional pond culture, include greater productivity indicators; the presence of protein-rich flocks – a good source of vitamins and phosphorous for the animals; improved water quality dynamics; and immobilization of toxic nitrogen. In general, the system maintains good mortality and shrimp growth rates, while the overall environmental impact of production is relatively low since the system relies on a limited (or near zero) water exchange.
However, when it comes to achieving industrial-scale, intensive shrimp harvests, production management is challenging, and multiple issues can emerge during the grow-out phase. The system manager needs to be highly trained both as a biologist and as a technician. Indeed, you could say you need to be an artist and a biology expert with many years of experience to make it work – after all, there’s another organism in the tank in addition to the shrimp that needs to be taken care of.
Bacterial populations have a fast metabolism rate that can create rapid shifts in water quality, and some of these changes can have detrimental effects on shrimp health. To avoid this risk, a relatively complicated control system needs to be installed in each individual tank, and technicians must be on duty 24/7 to respond to any deviation in water quality.
Biofloc systems could leave shrimp at risk of disease challenges and welfare issues, as well as expose the shrimp to environmental stress if producers fail to manage the level of suspended solids in the culture water. For this reason, producers usually adopt a compartmental design to better control the water dynamics over the culture period, but a large number of tanks, each with different behavior, makes the process fairly labor-intensive and complicated to control.
In general, the biofloc system requires a start-up period and active management to be successful. Yields aren’t always consistent, partly because it is difficult to understand how individual microbial flocks operate, and how to make them proliferate in a predictable way. Culture water must be constantly mixed, resulting in high energy costs. Also, the nutritional value of the floc as sole nutrient is very poor so supplement feeding is recommended. The system has limited capacity and cannot be scaled while maintaining economic efficiency. Finally, biofloc system performance cannot be improved, and there has been no additional development in yields or other outputs of the system over recent decades.
What you need to know about clear-water systems
Shrimp farms that employ clear-water systems use filtration to remove organic waste and nitrogenous compounds, keeping the water clear and clean at all times. They are therefore much more stable in terms of water quality and can easily be regulated by a simple control system.
The shrimp are artificially fed, and the feed needs to provide all the animals’ nutritional requirements. This enables full control of feed quality and nutritional benefits, which translates into high nutritional benefits in the end product. Feed and water treatment costs are higher than in biofloc systems, but if done properly, the overall economics are much more cost-effective, especially at larger scales.
Getting to the heart of the matter
In a comparison study, conducted at Kentucky State University’s Aquaculture Research Center Pacific White shrimp were grown in both clear water and in biofloc systems for 30 days. Results showed that total shrimp biomass, individual weights and FCR were all significantly better in the clear-water treatment compared to the biofloc treatment. It was not clear exactly what led to these disparities, but the differences in water quality may well have been a factor. The end results indicated that, for indoor marine shrimp production, clear-water recirculating aquaculture systems may be a more productive option than biofloc systems.
Since shrimp hardly swim and require a large surface area, most production systems – whether biofloc or clear water – comprise multiple shallow tanks (commonly referred to as “stacked raceways”). Having come to the conclusion that clear water provides a better production environment than biofloc, the design of the tank still remains a challenge. In Stacked raceways, managing multiple long and shallow tanks is complicated, in terms of feeding, maintaining water quality, heat loss, humidity and other operational factors mainly in cases that the tanks are stacked several meters high. A smart design is required that will not only provide the right balance of water quality and feed, but also maintain these optimal conditions in a relatively contained space.
The most efficient way to manage any shrimp culture is to reduce the number of tanks and enable simple and smart control of the system. This is where ECOshrimp stands out. In an aquaculture breakthrough, our clear-water system uses a limited number of uniquely-designed tanks, while offering all the benefits of a stable, fully-traceable and consistent production routine, without the difficulties and instabilities of biofloc mentioned above.
Compare and contrast
By way of conclusion, the table below shows a general comparison of biofloc, clear-water “stacked raceways” and ECOshrimp’s unique closed aquaculture system for growing shrimp, according to major production criteria. It is clear that ECOshrimp beats the alternatives, across the board.
With thanks to the knowledge-sharing platform, The Fish Site which informed much of this blog.