Plants and algae prove their usefulness in boosting fish immunity

Water scarcity, fish health, and antimicrobial resistance have all grown in importance in African aquaculture in recent years, with policymakers racking their brains over the costs and environmental effects of conventional measures to control. prevention and management. Fortunately, alternative treatments based on plants and algae offer interesting solutions.

While the larger farms have agreements with international companies that provide vaccines and other tailor-made medicines, the majority of fish farmers cannot afford such agreements. However, natural herbs have been used for decades in managing fish health in Africa and are now gaining popularity.

The ISKN outbreak on Lake Volta in 2018-2019 resulted in an estimated 80% tilapia mortality, and farmers also suffered from unsold stocks as customers did not want to buy diseased fish, despite the fact that ‘it was safe for consumption. The government launched a three-year tilapia vaccination program to address the challenge, but larger farms have deployed other strategies. Besides purchasing vaccines from international pharmaceutical companies, most of them are currently using heat treatment to provide the fry with some immunity. In addition, several farms on the lake have experimented with a garlic, ginger and turmeric cocktail, with varying degrees of success.

Enoch Tetteh, a fish farmer operating in Akuse, also works as a private extension worker, helping smallholder farmers to maximize their production. Since the ISKN outbreak, he has used neem tree extract to help improve tilapia survival and fitness.

“I boil and mix the leaves of the neem tree, and mix them with the food. I impose a two-day fast on the fish and introduce food. In most of the farms where I did this treatment, improvements were seen after five days. Mortalities were drastically reduced and over 80 percent of surviving fry were introduced into farmers’ ponds. I think that herbal plants have a major role to play in African fish farming, and I am working with a few others to find solutions, ”he explains.

At a recent forum organized by the West Africa section of the World Aquaculture Society, Professor Rina Chakrabarti from the Aquatic Research Laboratory of the Delhi University suggested that the thorny straw flower (Achyranthes aspera), a traditional method used to induce fish growth and immune stimulation, is a viable candidate for solving similar problems encountered around the world. Herbal compounds, she said, are a better therapeutic agent than antibiotics. Other benefits of natural immunostimulants, she said, include biocompatibility, biodegradability, cost-effectiveness and environmental friendliness.

A recently published study Food additives for medicinal plants Improved survival capacity and growth performance of Clarias gariepinus (African catfish) against bacterial infections (2021), reported that garlic (Allium sativum), Siam grass (Chromolaena odorata) and Ceylon spinach (Triangular talinum) improve the growth and survival of farmed African catfish. They noted the problem of antibiotic residues and the development of antibiotic resistant microbial strains, and the fact that “the implication of the costs of using chemicals and antibiotics in fish farming reduces profitability and not all of them. are not effective “.

In Diagnosis and control of fish and shellfish diseases, (Chapter 9, Use of Medicinal Plants in Aquaculture), Miriam Reverter and others stated that: “The plant species that have shown the highest potential for use in aquaculture are garlic (Allium sativum), Grenada (Punica granatum), Bermuda grass (Cynodon dactylon), Indian ginseng (Whitania somnifera) and ginger (Zingiber officinale) “.

They also stated that “algae are considered to be a rich source of original bioactive molecules which exhibit multiple bioactivities. In aquaculture, several recent studies have shown the potential of algae for the treatment of pathogens or for improving the fitness of fish ”.

Interesting findings are also reported in the deployment of algae in bioremediation. In Application of photosynthetic microalgae as effective biostabilizers and pH biopurifiers in sustainable aquaculture of Clarias gariepinus fry (African catfish) (2018), Ahamefule and others have reported finding Chlorella lewinii and Dimorphus music scene be “very effective in maintaining the quality of aquaculture water, and thus extend the life of the water before changing”. The objective of the study was to “develop a method to prolong water retention, and thus reduce the frequency of water changes in fish ponds by regulating and / or stabilizing the pH of the water, and by maintaining low concentrations of toxic nitrogenous wastes ”.

This will certainly find an echo in Africa, where fish farmers face problems with water supply. In Cameroon, a dispute between fishermen, herders and farmers over dwindling water resources led to violent clashes on December 5, killing 22 people and displacing 30,000 people, many of whom fled to struggling Chad. And in Tanzania, which experienced record high temperatures and little rainfall instead of the usual rains in mid-October, the Dar Es Salaam Water and Sewerage Authority (Dawasa) implemented a water rationing program until in November, due to the reduction in water production from 520 million liters to 460 million per day. A fish farmer from Dar Es Salaam explained that “luckily I have a borehole, but my thoughts are with my colleagues who do not”.

Although there is no apparent water crisis in Ghana, boreholes have become the usual source of water for fish farming. Nowadays, very few people would set up a fish farm without building a borehole, and some existing fish farmers are now building them to ensure regular access to water.

In an interesting development, Fredrick Kpamber, research director for the Bio Green Agro project, focusing on sustainable aquatic derivatives in Ghana, says he is convinced that a diet with adequate algae in a chemical-free colloidal suspension reliably prevents infections of fish, especially ISKNV and streptococcus. affect their land use along the Volta, which is their source of direct untreated water; although other nearby fish farms upstream and downstream of their location have been struggling, with diseases causing huge losses and even farm closures.

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