By Ph.D. Stephen Newman
Aquaculture is the fastest growing global agribusiness. While this growth has been and will continue to be subject to volatility, the overall trend over the last three or more decades has been a consistent increase in farm reared seafood. The nature of the aquatic environment offers many unique challenges to sustainable production, and truly sustainable shrimp farming paradigms remain elusive.
Aquaculture is the fastest growing global agribusiness. While this growth has been and will continue to be subject to volatility, the overall trend over the last three or more decades has been a consistent increase in farm reared seafood. In 2022, FAO reported for the first time that the total biomass from aquaculture surpassed that of the fishery. The number of species being farmed is increasing and the overall tonnage from the top three (aside from bivalves), shrimp, tilapia and salmonids —continues to increase.
The nature of the aquatic environment offers many unique challenges to sustainable production.
Unfortunately, the term sustainable has become a buzzword much as eco, green, etc. have. It has become a target for puffery-based marketing and is being bandied about by many in an effort to set their products/production apart from the mainstream.
The Oxford dictionary defines sustainability as:
1. The avoidance of the depletion of natural resources to maintain an ecological balance and
2. The ability for a practice to be maintained at a certain growth rate or level (indefinitely).
Considering how this applies to aquaculture with an open and honest assessment strongly suggests that, in general, we are still a long way away from this. True sustainability requires the development of production paradigms that allow future generations to meet their needs.
There are many challenges to this. Perhaps the greatest is that there is no one universal approach that everybody agrees is sustainable. Impediments to sustainability, while not always obvious, include, but are not limited to:
1. Damage to the environment. This comes in many forms ranging from discharge of untreated waste streams to the indiscriminate use of antibiotics, chemicals, and drugs to address challenges that can potentially be prevented by taking a proactive approach.
2. Reactive approaches to mitigate the impact of disease. Diseases are a major impediment to sustainability. Yet preventing the problems, i.e. being proactive is not the norm. Some NGOs that audit production fail to address this while claiming that their specific methodology is the path to sustainability.
3. Short term gains (i.e. profits) become more important instead of consistent long-term gains that are a result of enlightened and reproducible management strategies.
Shrimp farming has historically relied heavily on the use of disinfectants in an attempt to start with “sterile” environments. They are often used under conditions that do not ensure that this is the case and the damage that wide spread application of disinfectants can do to benign microbiomes can lead to changes in the microbiome that ensure that animals will be impacted by the bacteria that survive.
Vibrios are often the focus of this even though they are largely harmless and an important element of healthy microbiomes. There is mounting evidence that the use of disinfectants can make things worse. Strains of Vibrio parahaemolyticus, a species that contains pathogens of humans as well as shrimp, have short generation times and the ability to become metabolically inactive (Viable but Non Culturable-VBNC) and by virtue of the biofilms that they create can be refractory to a variety of modalities intended to rid them from an ecosystem.
While there are opportunistic strains, there are also several strains that cause massive disease problems by virtue of specific toxins. These are the etiologic agents of Early Mortality Syndrome (EMS) and/or Acute Hepatopancreatic Necrosis Syndrome or Disease (AHPNS or AHPND) as well as those responsible for transparent post-larvae disease (TPD).
There is solid evidence to support that the use of disinfectants can actually decrease productivity and is not a sustainable practice. Basically, one is creating an environment that is consistent with the proliferation of these obligate pathogens at the expense of the myriads of harmless bacteria.
“One major challenge (among others) that many aquaculturists face is the lethora of products in the marketplace that claim to be able to reactively solve problems. Some, such as antibiotics, when used correctly are valuable tools that unfortunately are all too often abused.”
Correct usage entails targeting bacterial (or fungal) diseases. When this is done correctly it requires isolating the pathogen, establishing that is indeed a pathogen and not the result of poor-quality rearing conditions that weaken the animals, determining appropriate levels of application and ensuring that they are used correctly adhering to withdrawal times and proper dosage rates.
While aquaculture is only one industry where this can be an issue, the reality is that the unrestricted use on humans is a far greater threat to the continued utility of the current set of antibiotics. This notwithstanding the consistent abuse of antibiotics in some instances in shrimp farming, whether it be prophylactic treatments of broodstock or a shot gun attempt to deal with mortalities of unknown origin can result in increases in resistance to these valuable tools and is not a sustainable practice.
With the genetic revolution in full swing, microbiome manipulation has become a favored marketing tool. This is in spite of the fact that the vast majority of bacteria, viruses, fungi, protozoa, etc. cannot be cultured. Powerful statistical tools are used to characterize organisms that cannot as of yet (or perhaps never) be grown under controlled conditions.
“I am struck by how easily shrimp farmers appear to be all too regularly duped into believing that there are magic bullets. The universal thought process seems to be that some very fundamental aspects of the production process are not critical for success and that if we can avoid ensuring things like biosecurity, reduction of pathogen loads, reduction in stress, i.e. proactive management of animal health challenges, some solutions will come along that validate this.”
There are I believe, among others, a number of reasons for this. One is that most of the worlds shrimp farmers are not biologists with educational backgrounds in the sciences and a focus on aquaculture. Poverty driven production paradigms are common.
As efficiencies increase and profit margins become slimmer, there is a tendency towards consolidation which leaves most of the poverty driven paradigms out of the picture. Another is the tendency to repeat things that might have worked well at one time even in the face of change that ensures that what was once readily reproducible is no longer.
Another issue is the widespread availability of a myriad of materials that have been “proven” to be effective in reactively dealing with diseases. There are many publications on a wide range of compounds, including a variety of chemicals and biochemicals, plants and plant extracts as well as bacteria both dead and alive and their extracts, that have been shown to positively impact survivals or growth, etc.
“Most of these use models to prove the thesis. Typically, these are microcosms of some kind that by their very nature do not accurately reflect several aspects of real-world production paradigms. Notably many are closed to some degree and typically small scale. Often, aquaria are used to validate claims of efficacy.”
These materials are usually fed. Although bathing animals in them is what may actually be occurring in addition to whatever may be ingested. In a closed system like an aquarium, water is not flowing through at a rate similar to the movement and dilution impact seen in real world conditions.
As the animal shreds the pelleted feed to ingest it, the materials that end up being tested are at concentrations much higher compared to typical real world production conditions. This ensures that the animal is not just ingesting it on or in feed but also absorbing it potentially through ingestion in the water but as well via uptake by phagocytic cells in the gills.
Aquaria studies may be flawed by the very nature of their inherent limitations. Arguably, if a material has no effect in an aquarium, it has little prospect of functioning in the field. On the other hand, seeing a benefit in an aquarium does not mean that the benefit will be seen in the field.
All too often marketing data from field observations is cherry picked. There are more than a few instances where it seems apparent that whoever designed the experimental protocols had a poor understanding of the scientific method. Selling the product is the goal, not actually ensuring that the product functions in the claimed manner under what are usually highly variable field conditions.
Anybody who has extensive experience in shrimp farming will tell you that it is prone to a great deal of variability. Typically, there are many possible reasons although more often than not farmers have a poor understand of why. Correlative statistics are used to make it appear that we might have some idea although rarely with plausible underlying mechanisms to explain why something is apparently working.
“Cause and effect often remain elusive. This is not to say that there are not materials that can indeed be consistently beneficial, although once shrimp are in most pond environments, the only practical mechanism of delivery is via the feed (with a few exceptions). It would be very costly to bathe shrimp, even in smaller commercial ponds in a material that has been established to be largely or solely effective via this route.”
At Aquaintech Inc. in the late 1990s we developed a parabiotic that was extensively tested in the field. Many billions of Pls were bathed in the material prior to being stocked in ponds. The results were not consistent in terms of a case-by-case cost benefit but overall, strongly suggested that there was a benefit that could be justified (it added pennies to the cost of a 1000 pls).
Since that time, many workers have published observations that seem to support the potential of this approach although almost all have been done in aquaria. This supports observations that some things that work in aquaria can work in the field. It is important to make the distinction that this was via water borne delivery. When the product is fed under field conditions impacts largely disappear.
So, in conclusion, truly sustainable shrimp farming paradigms remain elusive. Using RAS systems with highly controlled environments does offer some potential. Production in ponds outdoors has a long way to go and, in most instances, may never be. There are some who are looking at indoor production in ponds although these are not typically biosecure and a failure to proactively manage the presence of obligate pathogens ensures that these systems will continue to be plagued with largely preventable challenges.
As I have written many times, caveat emptor. Many of the solutions being touted are not solutions in reality and any that advocate that one can ignore the fundamental and common-sense aspects of animal husbandry should be taken with a huge grain of salt.
Stephen G. Newman has a bachelor’s degree from the University of Maryland in Conservation and Resource Management (ecology) and a Ph.D. from the University of Miami, in Marine Microbiology.
He has over 40 years of experience working within a range of topics and approaches on aquaculture such as water quality, animal health, biosecurity with special focus on shrimp and salmonids.
He founded Aquaintech in 1996 and continues to be CEO of this company to the present day.
It is heavily focused on providing consulting services around the world on microbial technologies and biosecurity issues.
sgnewm@aqua-in-tech.com
www.aqua-in-tech.com
www.bioremediationaquaculture.com
www.sustainablegreenaquaculture.com
