Are my plants eating my fish?

Sounds ridiculous, but they could be, says Rupert Collins.

I'm sure that everyone will have heard of carnivorous terrestrial plants such as the Venus flytraps, Sundews and Pitchers, but did you know that there are also aquatic versions?

The Bladderworts (Utricularia spp.) are a varied group of aquatic plants, which possess a highly sophisticated mechanism to catch their food.

They have no roots, and the plants tend to creep or float on the surface.

They have traps comprising small bean shaped bladders, and the plant pumps water out of them until they are flat and curved inward under pressure.

Next to the trapdoor, bristles are present, which act as a trigger. If a hapless prey item (e.g. Daphnia) bumps into them, the trapdoor bends enough to break the seal and the walls spring back to their normal shape creating a vacuum, engulfing the prey within one hundredth of a second. The prey is then chemically dissolved and consumed.

But can they eat fish though? While most Utricularia have very small bladders, there are several species with bladders up to 1.2 cm, and they have been reported to eat fry, tadpoles and mosquito larvae.

So, while adult fish are not really at risk, certainly tiny fry could be eaten.

Utricularia are not sold frequently in the trade, but can be ordered from specialist aquarium plant stores, or can sometimes be found as hitchhikers attached amongst floating plants such as Riccia.

Many have quite beautiful flowers, so might develop a following in the planted tank side of the hobby if there is sufficient demand. Some with interesting foliage have even been incorporated into nature aquariums.

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Why are elephantnoses so hard to keep?

These fascinating oddballs have a reputation for being difficult in the aquarium. So what's the key to success? Rupert Collins explains.

The most common elephantnose in shops is Gnathonemus petersii, but, despite being a fish only for experienced aquarists, it is frequently sold as an oddity for the general beginner’s community tank.

Mormyrid fishes, such as the elephantnose, have specialised adaptations for life in their African river habitats and are one of the few groups able to use and generate electric currents, enabling them to feed, navigate and recognise mates in turbid, murky water. They use more than 2,000 electroreceptor organs (mormyromasts) to build a detailed electrical picture of their surroundings.

In the aquarium they can become stressed under bright lights and when constantly close to other fishes. They need a peaceful and dimly lit tank with plenty of hiding places in which to feel secure.

Gnathonemus uses its fantastically named Schnauzenorgan (trunk) to detect invertebrate foods in the bottom sediment, so in the aquarium require a soft substrate such as a silver sand to prevent damage to this sensitive organ or their scale-less skin.

Mormyrids are also picky feeders, often preferring live or frozen foods to dried offerings. They are also poor competitors, losing out to more outgoing, agile fishes.

As a territorial fish, Gnathonemus is best kept singly, or in groups greater than five, as stronger individuals may bully smaller ones. A large group will require a roomy tank of several hundred litres.

They are also reported to be sensitive to poor water quality, as well as many chemical-based medications.

All considered though, this is a fascinating fish which makes a great aquarium resident, provided the tank is set up for them from the outset.

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Should I worry about the snails in my substrate?

Do you have cone-shaped snails living in your substrate? If so, how much of a pest are they? Matt Ford explains...

It sounds as though you have a colony of thiarid snails, probably Melanoides tuberculata (aka Red-rim melania, Malaysian burrowing/trumpet snail or simply MTS) or possibly Quilted melania, Tarebia granifera.

These are often referred to as aquarium pests since they can reproduce incredibly quickly when there’s a consistent excess of food about.

As you’ve seen, they spend most of their time in the substrate but do emerge occasionally, particularly at night.

They’re often said to be hermaphroditic, so possessing both male and female sexual organs, but in fact reproduce by parthenogenesis whereby females produce embryos which develop unfertilised and give birth to live, fully-formed young.

Males do exist, but in small numbers compared to females.

These snails are beneficial in the majority of aquaria since they eat detritus trapped in the substrate and their movement helps prevent anaerobic spots developing — particularly useful in planted set-ups.

They will not harm live plants, but do consume algae when they emerge at night. If their numbers rapidly increase its usually because of the overfeeding of fishes and/or insufficient cleaning of the substrate.

If you want to remove them don’t use a commercial product as most are harmful to shrimp and some fishes, or add a ‘snail-eating’ fish such as a botiid loach species. Most grow relatively large, exhibit complex social behaviour, meaning a group of eight or more is required and shouldn’t be relied on to eat snails.

Instead, reduce feeding and remove them manually at night or use a ‘snail trap’.

Incidentally, neither species is restricted to Malaysia. M. tuberculata is native to some parts of Africa, the eastern Mediterranean, India, South-East Asia, Malaysia, southern China, as far as the Ryuku Islands (Japan), and the Pacific islands, as far east as northern Australia and the New Hebrides.

T. granifera occurs naturally in India, Sri Lanka, South-East Asia, the Philippines, Taiwan and Japan, and can be told apart from M. tuberculata by the lack of reddish-brown spots on the shell.

Both species of snail are considered highly invasive and have been introduced into many countries where, in many cases, they have had a distinctly negative impact on the native gastropod populations.

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Are there any giant catfish that can really eat humans?

You've probably heard stories that say they can. So we asked Heiko Bleher, who's seen some giant catfish in his time...

No, despite what you may have heard, there aren't. This is a myth, along with age-old claims that giant anacondas or piranhas eat men. People, especially the Caboclos in Amazonia and natives of other parts of South America and in Asia, love to tell these blood-curdling stories!

I have just completed another Amazon expedition where one native of the Makuna tribe told me about a giant catfish (Brachyplatystoma vallentii), which swallows people. Several people had apparently disappeared around the location where the giant fish had been seen and many natives 'confirmed' its existence. Yet when I asked if anyone had actually seen the fish attack anyone there was no answer.

In September 2007 there was a startling 'man-eater' news report with a picture of a 'catfish' nearly 3m/10ft long and head more than 0.9m/3ft wide in the Guangdong reservoir in China. When it was cut open human remains were said to have been found inside. However, it turned out to be a whale shark and the story had been a set-up.

In October 2008 another large catfish was caught in the Great Kali river, between India and Nepal, and it was claimed to have started eating swimmers. This monster was called a Goonch and it was about 1.8m/6ft. This 'monster fish' lived in a stretch often used to dispose of human bodies after Hindu funeral rites.

It was thought this may have led the Goonch to start taking live human victims, but there was never any proof. In fact it eventually turned out to be a Bagarius bagarius catfish which could not even have swallowed a child.

Conclusive proof that giant catfish have eaten humans has yet to be found!

Can I move my Albino corys from a cooler tank to a warmer set-up?

What if you want to transfer your Albino Corydoras to a warmer aquarium? Dr Michael Hardman has some advice.

I would be surprised if yours showed any stress after moving to a warmer aquarium, provided you are careful with their acclimatisation.

Put the Corydoras in a large plastic bag filled with water from the cool aquarium, then place it in the warm aquarium and allow plenty of time for the water inside the bag to slowly warm to the new temperature before releasing the fish.

If you intend to warm a currently cool aquarium, increase temperature by 1°C per day and the fish should be fine.

Corydoras generally prefer cooler temperatures of 23-25°C/73-77°F, so bear this in mind.

This article was first published in the Christmas 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.