Last month on June 8th we noted World Oceans Day 2023 with much mention of our precious seas and oceans in terms of environmental protection, climate change and pollution. The latter is of course deeply concerning with the large tonnage of plastics entering the marine environment either directly, or by way of our rivers and waterways to the seas. It has recently been calculated that there is now 5.25 trillion macro and micro pieces of plastic in our ocean with an estimated 46,000 pieces in every square mile of ocean, weighing up to 269,000 tonnes. Every day around 8 million items of plastic route their way into our oceans. It is a very frightening statistic to appreciate and grasp. This major problem is now attracting global attention as it is a matter of grave concern to our shared biosphere and its diversity of organisms from the microbial, planktonic, invertebrate, vertebrate classes of all orders and species.
Plastics breakdown to the micro level and potentially to even nano dimensions. They were first identified in small marine annelid worms but are now present even in the tissues of higher animals. Microplastics, which are tiny plastic particles measuring less than 5 millimetres in size, have become widespread in marine environments due to pollution and improper waste disposal. The potential disruption of the complex food chain is undoubtable and will ultimately affect humans and may already have taken some effect.
As aquaculture expands at increasing rates, we have been dependent to a great extent on marine sourced ingredients although these are being used more strategically in the last few decades. Fortunately, we are less dependent due to the surge in alternative raw materials from terrestrial sources such as oilseed grain proteins, insect meal and cultured algae for oil for compounded diets. However, we should be concerned in the aquafeed sector until this problem relating to aquatic and marine ingredients can be resolved to some degree of certainty. As a nutrition scientist with a focus on fish nutrition and aquafeeds, the safety and efficacy of our food chain is of paramount importance.
There have been recent discussions regarding whether fishmeal could be a vector to deliver microplastics into farmed fish and entering into the edible components like muscle and end products. We know that nano-scale particles can accumulate in human and animal models with speculation that they can even bridge the blood brain barrier. There is much evidence that their absorption from the gastrointestinal tract is feasible, and particles can translocate into the gut, lungs, liver, heart, nerves, and brain.
The interaction between marine microplastics and the gut microbiota of farmed fish is an area of growing concern and research. When fish consume water or food contaminated with microplastics, these particles can accumulate in their digestive systems. This ingestion can have various implications for the gut microbiota, which refers to the diverse community of microorganisms residing in the fish’s gastrointestinal tract. Studies have shown that microplastics can physically damage the intestinal tissues of fish, leading to inflammation and changes in gut morphology. These alterations can disrupt the balance of the gut microbiota, potentially affecting its composition and function.
The gut microbiota plays a crucial role in nutrient metabolism, immune response, and overall health of the host organism. Research has demonstrated that exposure to microplastics can lead to shifts in the diversity and abundance of gut microbial communities in fish. These alterations may impact the fish’s ability to digest and absorb nutrients, impair their immune system, and increase their susceptibility to diseases. Furthermore, microplastics can act as carriers or adsorbents for various chemical contaminants, such as persistent organic pollutants and heavy metals. When fish consume microplastics laden with these contaminants, they can be absorbed by the gut and transferred into the bloodstream. This can result in toxic effects not only on the fish but also on the gut microbiota, as some microorganisms may be sensitive to these pollutants. Investigations are being conducted at a fundamental level on the zebrafish as a model to study potential invasive routes into the body. Various exposure levels in controlled aquarium facilities in several universities are exploring the effects of microplastics on physiology, metabolism, bioenergetics, and immunology. Plastic particles can disrupt the balance of the gut microbiota, potentially affecting its composition and function. The gut microbiota plays a crucial role in nutrient metabolism, immune response, and overall health of the host organism. Research has demonstrated that exposure to microplastics can lead to shifts in the diversity and abundance of gut microbial communities in fish. These alterations may impact the fish’s ability to digest and absorb nutrients, impair their immune system, and increase their susceptibility to diseases. Farmed fish are a major source of seafood globally, and any disruptions to their gut microbiota can have cascading effects on their growth, reproduction, and susceptibility to diseases. Additionally, if these contaminants are passed along the food chain, they may pose risks to human health when consuming fish products.
Addressing this issue requires a multifaceted approach. Efforts should focus on reducing the input of microplastics into marine environments through better waste management and stricter regulations. Additionally, sustainable aquaculture practices that minimise the exposure of farmed fish to microplastics and other pollutants should be implemented. Further research is needed to better understand the mechanisms underlying the interaction between microplastics and gut microbiota and to develop strategies to mitigate the potential impacts on fish and human health.
Scanning the news in the aquaculture domain, I was interested to learn that investment is being sought to construct a large-scale 10,000 tonne integrated African catfish farm in Croatia. I have always been a fan of this relatively hardy species (Clarias gariepinus) that is well known and favoured in Nigeria and South Africa. We actually have a mini city operation in Plymouth under the management of my former Nigerian student, Dr Ayodeji Adeoye. Indeed, I have supervised several doctoral students working on their nutrition during my time at the University of Plymouth resulting in many scientific papers to test novel ingredients for this versatile species. I hope the new development in Europe succeeds as it is a fine, nutritious, and good quality fish to eat.
I was intrigued by a recent report on a media platform concerning the use of PAPS Processed Animal Proteins with emphasis on PBM, Poultry Byproduct Meal in studies with rainbow trout. The authors found very positive results when inclusion levels in diets were up to 36%. This is hardly surprising as I have been involved with earlier work reporting similar data in several peer-reviewed publication. However, the report is wrong regarding legislation stating that approval has not been granted to date by the EU for PBM use in aquafeeds. It has been approved by the EU Commission since 2013 (COMMISSION REGULATION (EU) No 56/2013) of 16 January 2013, but it is the confidence of retailers and the fish feed industry sector that is at issue here due to remaining public concerns in Europe on the safety of the food chain involving animal derived proteins since the BSE outbreaks in the late 1990s.
My colleague Dr Stephen Woodgate led our comprehensive review paper (Reviews in Aquaculture, 2022) on this topic recently which discuses PBM and other PAPs for aquaculture, legislation, and the future of these products from the rendering industries.
Our July issue contains many articles and features, including our usual feed and nutrition related reports. There are many news updates so please enjoy our mid-year 2023 edition. There will be of course many meetings and workshops in the autumn in different parts of the world and the EAS event in Vienna, Austria in September where the latest developments in aquaculture nutrition and feed technology will be showcased. We may cross paths.
