July 28, 2022
Trials at University of Arizona determine if bioavailable catechins from plants can protect shrimps from diseases
Recent challenge trials in the University of Arizona's (US) Aquaculture Research Facility, led by Dr. Arun K Dhar and Paul Schofield, investigated whether bioavailable catechins recovered from Camellia sinensis plants delivered prophylactic effects that protect commercially farmed shrimp against bacterial and viral diseases.
The trials were on the request of Dr. Roger Duffield, director of Theales Corporation Limited, who has spent more than 10 years investigating the prophylactic effects of these compounds in humans and animals.
During the trials, the polymer-coated catechins were mixed into commercial shrimp feeds before the shrimp were challenged with one of the two pathogens.
In the two AHPND challenge trials, an average of 60% of those shrimp fed 0.28g of prophylactic per 1kg feed survived, compared to 5% of the control shrimp, which were fed conventional commercial shrimp feeds.
In the first challenge, 30% of the shrimp survived with two lost to cannibalism, while in the second AHPND trial 90% of the shrimp survived.
Meanwhile, in the WSSV challenge trial, although all the infected shrimp died, those fed the control diet were all dead by the end of day 1, while those fed diets containing the polymer-coated catechins lived for up to eight days after the introduction of the virus.
According to Dr. Duffield, these impressive results are likely to improve after some fine tuning – not least by reducing the size of the polymer particles, in order to make them easier for the shrimp to ingest.
"The 250 micron particle size used in these trials was too large, so we need to reduce them to 200 microns or less," he explained. He will also increase the concentration of the prophylactic actives.
"In the further study, the dosage will be 0.40 grams of active per kilogramme of shrimp feed [i.e. an inclusion rate of 0.2%]. We expect to achieve higher prevention results with AHPND and at least 50% prevention with WSSV through smaller particle sizes and newly polymer coated catechins," said Dr. Duffield.
He added: "Based on the scientific evidence, we expect to achieve commercial acceptance against these diseases in the repeat study through improved particle size of the prophylactic that will deliver improved overall consumption by the shrimp."
Thanks to the innovative polymer coating techniques, which have been supported by scientific validation, the shelf life of catechins can be extended for several years and also with improved prophylactic effect on a range of species, including humans, once ingested.
"Green tea catechins are free radical scavengers The challenge is to get them into the blood without metabolism or degradation," Dr. Duffield said. "In clinical studies with both human and animals, the prophylactic catechins were active for more than 48 hours."
Dr. Duffield pointed to a 2016 study from Thailand that established the value of catechins in the prevention of disease in shrimp challenged with WSSV – research that he noted appears to been overlooked since.
"Our objectives is to now repeat our previous study with shrimp including challenges with additional Gram positive and Gram negative bacteria," Dr. Duffield said.
After the next challenge trial, the completion of the scientific platform will involve a commercial tank investigation as part of the commercialisation process.
In the meantime, researchers at the National Metrology Institute of South Africa (NMISA) - which is part of the Department of Trade and Industry South Africa - will work on producing a prophylactic particle size of 20 microns in order to efficiently feed juvenile shrimp at the start of the commercial shrimp farming cycle.
According to Dr Duffield, "the potential to increase production of the prophylactic is considerable, thanks in part through our relationship with the Tea Board of India which is the largest producer of Camellia sinensis tea bush leaf in the world".
"Based on current understandings, we expect to commercially produce and price the prophylactic in the region of 3-4% of the retail cost per kilogramme shrimp feed," he added.
- The Fish Site