Picture a coastal Andhra Pradesh shrimp producer staring at their fish tank which has become muddy and everything in it dying due to the feed they have been provided. They are dying not because of any disease or predators but due to the undigested feed and dropping waste with all the organic matter decomposing at the bottom of the tank and therefore releasing ammonia and nitrites back into the water. This buildup of nutrients in the fish tank is a slow build-up over time and poses a major threat to all types of global aquaculture.
The Hidden Cost of Feeding Fish:
The rise of aquaculture has made it possible for us to consume over half of all global seafood production. However, there’s a hidden challenge that comes with this rapid growth. When you think about how efficiently fish or shrimp convert feed to body weight, it’s pretty low. Research done by ACS Omega reported that 20-30% of nitrogen found in the feed actually gets taken up by the fish/shrimp. The remaining 70-80% ends up as waste (like ammonia, uneaten pellets, and excrement) and works its way into the water column.
This accumulation of waste creates a risk of creating toxic environments as well. Added levels of ammonia can attack gill tissue within fish. Nitrite can prevent oxygen from being transported in the bloodstream. While nitrate was once assumed to be fairly benign in freshwater systems, when it builds up to certain levels in marine systems, it can have negative effects on reproduction and development in those species, resulting in delayed hatching times, reduced growth, and increased mortality rates (per research conducted through Aquaculture Systems Technologies). Additionally, if this effluent gets dumped into open bodies of water, it can stimulate algal bloom formation, create dead zones in the ocean, and ultimately lead to ecosystem collapse.
Current solutions to managing this wasted material in aquaculture (water exchange, chemical treatment, and mechanical filtration) cost a lot of money, consume a lot of energy, and continue to have some ecological footprint. So, aquaculture farmers remain stuck in a never-ending cycle where the more production they do, the more waste they produce, and vice versa.
Now Let’s Enter Biopolymers Which Is “Nature’s Own Fix”
Science is finally catching up with this issue in a truly revolutionary manner. A group of naturally occurring biodegradable polymers known as Polyhydroxyalkanoates (PHAs), formed by microbes (when under stress) are being viewed as a means to manage waste in aquaculture systems and also provide fuel for the denitrification process (the biological conversion of toxic nitrate into non-toxic nitrogen gas).
PHAs are not synthetic compounds made in a lab; rather, they are created by bacteria within their bodies to store energy. It’s been discovered by researchers that PHAs can also provide carbon for the denitrification process when PHAs are added to aquaculture systems.
One study documented by the Global Seafood Alliance on recirculating aquaculture systems indicated that HAs-based bioreactors removed Nitrate from these systems at rates greater than 2.5kg of Nitrates converted to N2 gas per cubic meter per day using only naturally occurring biocatalysts and without the need for additional and expensive chemical additives as well as complicated computerized control systems. Unlike traditional sources of carbon (i.e., methanol and ethanol), PHAs are a self-contained means of adding carbon into the system. PHAs will only release carbon at the same rate that the bacteria can consume it, thus eliminating the potential for overdosing and creating sulfide toxicity.
Beyond Waste: A Full-Circle Benefit
The continuation of this trend gets more exciting with the publication of research in the Journal of Agricultural and Food Chemistry (2024) which shows that providing farmed species with PHA-rich microbial matter has quantifiable positive effects on immune stimulation and improved gut health, as well as the suppression of common pathogens. From a farm perspective, the implementation of PHA-based biofloc technology results in more than just environmental benefits (cleaning water and air); it produces a supplemental feed source for farmed species that reduces the need for antibiotics and increases survival rates.
An additional study also published in Frontiers in Physiology has validated that the addition of PHB (a type of PHA) to aquaculture suspended solids has resulted in double the production yield and a more effective removal of ammonia from tank water, effectively transforming a waste management problem into a productive biological cycle.
Research published in AIMS Microbiology (2024) also demonstrates that beneficial bacteria, encased in alginate-based biopolymer capsules, have been shown to survive transit through the gut with greater than 90% viability and to give farmers the tools necessary to modify the microbial environment in their tanks and with their fish.
A Glimpse of the Road Ahead:
There are difficulties with biopolymers as well including production price and the transition from research lab to commercial pond is presently in process. There is now a trend toward aquaculture business with countries such as Indonesia, Brazil and Egypt implementing biofloc technology into their everyday operations. Research backing up biofloc technology also continues to expand as the years go by.
As we try to meet the global demand of 8 billion+ people and continue to meet seafood needs with restrict supply, the aquaculture industry cannot afford to ignore treating waste. Biopolymers have an extraordinary benefit to our planet as they are ecological, economic and biological solutions changing the largest cost for the farmer into a large asset.
The shrimp farmer’s murky pond doesn’t have to stay that way.
