By Suzi Dominy*
Still more to be learned in probiotics application in aquaculture
Probiotics in aquaculture have been around for some thirty years, demonstrating benefits in terms of modulation of the host immune system, as well as enhanced survival, feed utilization and disease resistance. And yet there are many who regard their use with some skepticism. In part this is because the term itself, when applied to aquaculture, can be confusing, since the animals live in a microbial laden environment, which has the potential for manipulation. The rearing water can be used as a vector for providing friendly microbes to the target organism, consequently the term “probiotic” has evolved to overlap with the terms “biocontrol” and “bioremediation agents” rather than simply beneficial bacteria applied in feed.
Speaking at the Biomin World Nutrition Forum 2016 in Vancouver, Dr. Daniel Merrifield, Plymouth University, United Kingdom said the application of probiotics in aquaculture faced unique challenges not faced by applications in humans, other mammals or poultry. Fish are poikilothermic animals and thus their metabolism, and the metabolism of their microbiota (including the embedded probiotic), is heavily dependent on environmental conditions. Although there is sufficient evidence to conclude that most fish species will harbor a core microbiome in their gastrointestinal tracts, evidence also suggests that individual fish of the same species may develop different microbiome phenotypes when reared under different conditions, at different seasons, at different life stages, and/or when fed different diets. The different environmental conditions, as well as the different microbiome phenotypes, are therefore likely to greatly influence the efficacy of probiotic applications in aquaculture operations. This presents quite a challenge when attempting to develop optimal probiotic application strategies.
Dr. Merrifield went on to say that future research efforts must focus on three main themes. “Firstly, gaining a better understanding of the normal microbiomes of fish; for a given fish species to what extent does the microbiome composition, abundance and diversity vary across life history stages? Do different fish genotypes harbor different microbiomes? Do different fish phenotypes (i.e. dominant vs subordinate; fast growers vs slow growers; robust vs disease susceptible) harbor different microbiomes?”
“Secondly, a better understanding of the functional attributes of the microbiome is required. Not just which microbes are present in the gut, but what are they doing? With the ever depreciating costs of sequencing, and with the anticipated improvement of databases to include more strains commonly found in fish, this can be achieved through metagenomics and metatranscriptomics in the coming decade.”
“Lastly, a better understanding of the localized host responses to the microbiome, and how such responses may change when the microbiome is modulated or manipulated. This is beginning to be addressed through the use of transcriptomic appraisal of intestinal samples derived from probiotic fed fish.”
Further research along these lines, as well as proteomic appraisal of intestinal mucus of probiotic fed fish, is warranted. With such information, we can then make more informed decisions as to which probiotics are appropriate for which species, as well as when and how to use them.
A need to re-think the way we approach aquaculture
In addition to the importance of biomics, the threat of mycotoxin contamination and the recognition of aquaculture as an important provider of high quality, nutritious protein, were themes that held the attention of aquaculture delegates at the feed additive company’s biennial conference. However, in spite of its many advantages over other proteins in terms of nutritional benefit, life cycle analyses, input and protein efficiencies, carbon footprint, and nitrogen and phosphorus discharges per unit of protein production, a lot still has to change if we are to feed 9.7 billion people by 2050 and a projected 12.3 billion people by 2100, according to Professor Barry Costa-Pierce from the Department of Marine Sciences, University of New England, USA. The expansion of mariculture will be the most important priority for the world’s protein future, Dr. Costa-Pierce told delegates. However, to realize its potential, management conflicts, due largely to educational deficiencies between fisheries and aquaculture managers, will need to end.
“Aquaculture is routinely managed under agriculture, environment or fisheries agencies that have little knowledge, training or experience in aquaculture with its unique policy needs. Aquaculture and fisheries are so separate structurally and functionally in many countries’ governance systems and academic institutions that institutions and professionals have lost track of their common goal of delivering environmentally friendly, safe, sustainable seafood to the people they serve. Sensible regulatory alignment is needed to deliver products that sustain livelihoods,” Dr. Costa-Pierce said.
More broadly there is a need for institutions to train the next generation of professionals in foods ecosystems. This would create a generation of stewards working in a new paradigm of planning for the supply of ocean and land foods. These professionals would develop and implement more comprehensive “Earth Foods Systems Plans.”
In the ocean professions, especially to fisheries managers, conservationists, and marine science academic institutions in general, aquaculture is a disruptive social ecological set of pioneering technologies. Professional, regulatory, “decision-maker communities” in the aquatic natural resource areas are dominated by fisheries and conservation professionals. More comprehensive training needed for a sustainable food future would result in the development of a cadre of decision-makers who could conduct the integrated planning for agriculture, aquaculture, fisheries, natural ecosystems, and their allied regional social infrastructures. The target areas of the world where this is most needed are where integrated freshwater aquaculture and mariculture can be developed to prevent the untold destruction of terrestrial ecosystems to create more arable lands for terrestrial food production.
Costa-Pierce argued that there is an urgent need to develop cooperative, place-based, global centers of excellence in ocean foods ecosystems. The focus of these centers would be multidisciplinary investigations on experimental, but commercial-sized, mariculture systems located in the EEZ of nations that were representative of their ocean region’s social-ecological-economic conditions. There would also be the innovative opportunities to document the positive roles that restoration aquaculture can have in the Earth’s ocean biogeochemical cycles, habitats, ecosystems, and societies of coastal ocean nations worldwide, as there are numerous examples of aquaculture facilities revitalizing natural aquatic habitats, ecosystems and fisheries, as opposed to degrading the natural environment, as much of terrestrial agriculture is doing. Without such multidisciplinary centers working on real systems, investment plans for the sustainable expansion of mariculture will suffer from a lack of a rational, scientific basis for planning and policy, and continue to be replaced by heresy, junk science, and advocacy, he concluded.
Suzi Dominy is the founding editor and publisher of aquafeed.com. She brings 25 years of experience in professional feed industry journalism and publishing. Before starting this company, she was co-publisher of the agri-food division of a major UK-based company, and editor of their major international feed magazine for 13 years.