Sometimes, important scientific discoveries remain hidden away in obscure journals for years before the findings receive wider recognition and application.
This year (in February 2023) a scientific paper reviewing the stinging nettle’s potential as a food in aquaculture revealed that the ‘backyard weed’ can boost growth rate, reproduction rate, and immunity levels, as well as reducing stress in fish.
This impressive list of benefits may well see commercial brands incorporating nettles into their fish foods in the future. Ahead of the game, some fish keepers have already begun introducing this wonder plant to their feeding regime. With the right know-how, so can you.
Wild Plants and Me
As a regular writer for Aquariadise, it’s an honor to be invited to write on a topic that I’m especially passionate about. So why not use the opportunity to write about a subject that’s rarely discussed in the aquarium world?
As well as studying fish, I have a keen interest in wild plants, especially those that are useful for humans and animals. Many wild plants have higher nutritional and medicinal properties than domesticated vegetables, so possess enormous potential as health tonics.
Of the many wild plants that can be utilized for fish health and nutrition, the stinging nettle is one of the most promising.
The Remarkable Nettle
The stinging nettle (Urtica dioica) is a ubiquitous plant of the Northern Hemisphere. Often growing near human habitation across Europe, Northern Asia, North Africa, and North America, it is one of the most familiar plants of temperate climates.
Although often considered a backyard weed, nettles are one of the most versatile of our native herbs and can be utilized in a bewildering variety of ways.
While they haven’t been used in aquaculture for long, they have an impressive track record with humans and terrestrial animals which could transfer to fish, too.
|Dried Nettle Nutrient Table per 100g
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Stinging Nettles and Humans
As a proven medicinal and edible plant, nettles have played an important role in human health and nutrition for millennia.
Nettles leaves have among the highest protein content of any temperate plant, and their rich vitamin and mineral content makes them very nourishing when cooked as a vegetable. Nettle soup made from young, tender nettle shoots has become a favorite seasonal treat of mine for many years!
This powerful plant can also be used in teas and tinctures as a medicinal herb. I personally find the tea highly energizing and uplifting, but the remarkable list of medicinal properties includes: Antihistamine diuretic, astringent, antioxidant, antimicrobial, and anti-inflammatory agent.
Nettles are frequently prescribed by herbalists as a remedy for arthritis, anemia, and allergies such as hay fever, as well as issues with the thyroid and adrenal glands.
Stinging Nettles for Animal Food and Medicine
As well as providing a plethora of health benefits for humans, nettles have also proven themselves to be an excellent supplement for farm animals.
Studies of chickens and pigs fed with a small percentage of dried nettles or nettle extracts in their diet showed improved growth rate, immune function, and circulatory system performance.
Because nettles grow so easily and rapidly, they present a promising low-cost, local, nutritional, and medicinal alternative for various types of life stock. Can they do the same for fish?
Scientific Studies of Nettles and Fish
It’s only in the last couple of decades that scientists began experimenting with feeding stinging nettles to fish. Here’s what they found.
Nettle Supplements and Immune Response in Fish
The review of scientific research regarding nettle supplements for fish begins with some impressive findings on improving immune response.
In a 2010 study, researchers fed dried nettle powder to rainbow trout affected with Aeromonas hydrophila bacteria. Of the fish treated with nettles, 96% survived compared to a mere 32% in the control group which was given no treatment. Subsequent studies showed similar findings.
Boasting immune-boosting, antiviral, antibacterial, anti-stress, and antiparasitic qualities, nettles show great potential as an alternative medicine in the treatment and prevention of a multitude of fish diseases.
This is great news for hobbyists like me who are reluctant to treat their fish with strong pharmaceutical medicines such as antibiotics which can compromise other aspects of their health.
Nettles Supplements for Nutrition and Increased Growth Rates in Fish
With a protein content of 27-39%, nettles have one of the highest protein contents of any dried leaf and are therefore among the most promising plants as a high-quality feed supplement for fish.
The same 2023 scientific review referenced above concludes that “both nettle powder (ranging from 0.5% to 12%) and extract with different methods (ranging from 0.01% to 3%) in fish diets demonstrated positive effects on fish growth performance and health status.”
Although most studies on feeding nettles to fish have been conducted on farmed fish such as rainbow trout, one study on the popular aquarium fish the convict cichlid (Amatitlania nigrofasciata) found that 0.01% and 0.05% methanolic extracts of nettle significantly improved weight gain, specific growth rate, and feed conversion ratio compared to those in a control group.
Already renowned as a prolific breeder, studies showed that nettles increased the reproductive rate of convict cichlids, too.
Nettles as a Shrimp Food
While there still aren’t many aquarium hobbyists feeding nettles to their fish, shrimp enthusiasts have known about the benefits of feeding nettle leaves for a long time!
Because shrimp are voracious herbivores with specialized apparatus for feeding on dead leaves and algae, they’ll often chew greedily on dried or boiled nettle leaves once they reach the bottom of the tank.
The practice of feeding nettles to shrimp has become so widespread that there are now companies selling dried leaves, especially as a top-quality shrimp food!
Although some aquarists have reported that smaller shrimp-like cherry shrimp and ghost shrimp aren’t very keen on eating nettles, they seem to be a big hit with larger shrimp like Amano shrimp and vampire shrimp.
Everything in Moderation – The Dangers of Overfeeding Nettles To Fish
Having discovered these impressive findings, you might be already feeling eager to run out to the garden with a pair of scissors to fetch some nettles for your fish tank, but not so fast!
As with any food, nettles need to be fed in moderation, and there are some important reasons for this:
- Firstly, nettles contain phytic acid which, in large enough doses, can inhibit the absorption of important minerals such as iron, manganese, and calcium.
- Secondly, nettles contain oxalate crystals which, when eaten in large quantities, can form insoluble sediments in the kidneys.
- Thirdly, nettles contain saponins, which in large doses can be fatal to fish.
In most scientific studies, dried nettles were fed to fish at 0.5-10% of their total diet with positive short-term health and growth effects. More research needs to be conducted, however, to determine the specific quantities of nettles for optimum effects, as well as the maximum dosage without risking adverse health effects.
How To Grow and Harvest Nettles
Looking through shrimp-keeping forums, you’ll soon come across plenty of hobbyists who grow a patch of nettles in their garden, especially for feeding their shrimp!
Growing your own nettle patch is not only convenient for easy harvesting, but it also means that your crop is less likely to be contaminated by chemicals, pollution, or animal urine which can affect nettles growing by the wayside.
Luckily, nettles are one of the easiest plants to grow! As a professional gardener, I’ve seen nettles growing rampantly in almost every type of soil, in full sun, or even quite deep shade. Their only strict requirement is high soil fertility, so adding some manure will do wonders to help them grow vigorously.
For feeding fish, I’d recommend harvesting nettle leaves while they’re still young and tender. Take a good pair of gloves and a sharp pair of scissors, and simply snip off however many leaves you intend to use. If you live in a city, you may wish to rinse the leaves to remove any pollution residues before processing.
Feeding Blanched Nettles To Fish
Some herbivorous fish and shrimp such as silver dollars, severums, and Amano shrimp may devour entire nettle leaves after blanching them in boiling water.
Simply pour boiling water over your nettle leaves and leave them to blanch for a few minutes to soften the leaves and remove the stings. You can even drink the resulting ‘nettle tea’ as an energizing tonic!
Other types of fish, however, will require you to process nettles more thoroughly before feeding.
Drying and Processing Nettles To Feed Fish
Drying and powdering nettles not only makes them more palatable for many species of fish, but it also allows you to preserve them for several months for year-round feeding!
If your home is relatively warm and dry, you can simply place nettle leaves between two sheets of newspaper and wait for 3-5 days for them to dry. If your living space is more humid, you might need to use an electric food dehydrator to dry them before mold sets in.
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When they are crisp and crumbly to touch you can either rub them between your fingers or place them in a pestle and mortar to grind them into bite-size flakes that can be fed alongside flake foods.
Don’t forget to store your dried nettle flakes in air-tight containers in a cool, dark place to best preserve their precious nutrients!
Nettles show outstanding potential as a herbal food and alternative medicine for fish. Not only are the leaves rich in protein, vitamins, and minerals, but they also possess an impressive array of medicinal compounds that can prevent or even cure certain fish diseases.
While overdosing your fish with nettle leaves could prove dangerous to their health, as an occasional supplement, nettles can boost growth rates and overall health in your fish.
Not bad for a backyard plant that’s often considered a weed!