Do hormones restrict the growth of fish?
Neale Monks advises a PFK reader on the causes of "stunting" in the aquarium.
Q. I am aware that some species of fish produce a growth inhibiting hormone that can have marked effects in a densely stocked aquarium.
Is this hormone removed from the water by filtering it through carbon?
Peter Russell, email
A. You are correct that there is some evidence that chemicals produced by fish as they grow can suppress the growth of other fish of the same species in their immediate environment. This is primarily an issue for fish farmers, and I believe most of the evidence for this phenomenon comes from studies of cyprinids (such as carp) and salmonids (such as trout).
It's important to note that some fish clearly don't work this way, for example Tilapia (cichlids farmed as food) can grow to large sizes seemingly regardless of stocking density provided water quality is adequate. Aquarists will also be aware that catfish like plecs, Channel catfish and Iridescent catfish also seem to reach large sizes, even in overstocked tanks.
In any case, while chemicals produced by growing fish may be responsible for "stunting" under some circumstances, other factors may be at play as well. An overcrowded tank is an unhealthy environment, and unhealthy fish won't grow as well as healthy fish.
High nitrate levels for example are often characteristic of overstocked tanks, and even if not immediately toxic, nitrate does have an appreciable effect on the health of your fish. Fish grow continually through their lives, but they grow more quickly when young, so if kept in an aquarium that's too small for the first year or two, a fish may never reach its largest size no matter how well it's kept thereafter.
You can often see this with Clown loaches, a species that rarely reaches its full size in captivity because so few people keep them in adequately large aquaria as youngsters, let alone as adults.
So while (fresh) carbon should remove hormones from the water, aquarium size and water changes are factors that affect nitrate level. If you want a fish to reach its full potential, the key thing is to keep it in a clean, spacious tank, and not to rely on chemical media to remove dissolved metabolites or hormones.
Neale Monks
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Are my guppies fighting?
Neale Monks has some advice for a reader who's concerned about possible tension between his male guppies.
Q. I have a 65 l./14 gal fully cycled aquarium, containing four male Blue guppies. I recently added another four male guppies, this time Red snakeskin, and they seem to be pestering each other a lot and I can't tell if they are fighting.
I've read that male guppies will generally refrain from pestering each other. Why is this not the case where my guppies are concerned? Is this behaviour likely to calm down once the guppies get used to each other? And if not, are they likely to cause each other any serious harm?
Sharn Cooper, email
A. I suspect people have different experiences with guppies, and a good deal depends on the numbers kept. In very large groups (like you see in pet shops) the males seem to do little harm to each other, perhaps because no one individual can bully, or be bullied, all the time. But in smaller groups, especially twos and threes, you find one male becomes the aquarium 'boss' and spends a lot of his time harassing any other males kept with him.
An interesting observation has been made with another livebearing species, Ameca splendens, which is practically extinct in the wild but has been kept by aquarists for decades.
Observations of wild specimens and those descended from recently caught specimens indicates males spend most of the time feeding on algae and relatively little time fighting. But the farmed specimens in the hobby are descended from specimens collected in the 60s and 70s, and after generations of maintenance in aquaria, the males we keep as pets spend most of the time fighting and very little time feeding.
Why? One hypothesis is that because we feed them good quality food for just a few minutes per day, these fish have more time to spend on other things, like fighting and breeding. Males that spent time fighting were favoured because the alternative, spending their time feeding, wasn't helpful.
Indeed, the pushier the male, the more likely he got to breed, and the more likely his aggressive genes got passed on into the next generation of Ameca splendens.
But the wild specimens don't have this luxury as the food they eat, algae, is not nutrient rich and they need to graze for hours to take in the calories they require. Wild males will be very careful about wasting energy on chasing away another male unless it's absolutely necessary. If you're an aggressive male you could well end up starving to death long before you had a chance to mate, whereas a more cautious male who built up his energy reserves carefully would be in a good position to impress a passing female and father her offspring.
It's very probable that something similar has happened with guppies, and given how we've bred guppies into countless varieties, their behavioural genes are likely very mixed up too. Some batches may well be more aggressive than others, even within the same basic variety.
Add to this things like the size of the tank, the number of male guppies, the availability of females, and the presence or otherwise of bigger, potentially threatening tankmates, and you can easily see how the behaviour of male guppies could be a very difficult thing to predict.
Anyway, to cut a long story short, yes, male guppies fight, and yes, if their fins are repeatedly damaged then problems like finrot can occur. They may calm down once a pecking order is established, but don't bank on it.
Adding more males can reduce tension, as will providing suitable hiding places at the top of the tank where the guppies live, particularly floating plants (Amazon Frogbit and Indian Fern are the two easiest options here).
Neale Monks
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How do I keep a Fire eel in the aquarium?
What's the best tank set up for keeping a Fire eel (Mastacembelus erythrotaenia)? Dr Heok Hee Ng advises on how to provide the right conditions for these giant fish.
The Fire eel (Mastacembelus erythrotaenia) is one of the largest spiny eels to be encountered in the aquarium trade, reaching a maximum size of 80cm/32”. Sizes of 1m/40” or more have been reported in the aquarium literature, although these remain unverified.
Captive fish are unlikely to grow this big and usually reach about two-thirds this size in the aquarium. But even a Fire eel at 50cm/20” is a bruiser of a fish, so a minimum tank size of 400 l/88 gal (approximately 120 x 60 x 60cm/48 x 24 x 24”) is highly recommended for one.
Spiny eels typically enjoy hiding during the day, so the tank should be dimly lit and offer plenty of hiding spaces in the form of large chunks of driftwood or PVC pipes.
Many spiny eels show a tendency to burrow and Fire eels are no exception. For this reason, it is best to keep rooted aquatic plants in the tank to a minimum, or to dispense with them altogether.
As with other spiny eels, Fire eels are great escape artists, so a tight-fitting tank cover is a necessity.
Because Fire eels are typically found in large lowland rivers, they are less demanding with regards to water chemistry compared to some of the more habitat-specific species, such as Macrognathus circumcinctus.
A temperature of about 24-28°C/75-82°F, and a pH of about 6.0-7.5 is just about right. The water should be slightly hard at 6-12 GH.
Fire eels are generally peaceful towards tank mates, although they may be aggressive towards conspecifics.
Conventional wisdom dictates that one fish per tank works best, and that peaceful tank mates that are too large to be eaten, like medium to large barbs, are ideal.
Fire eels are ominivorous, although they most readily take meaty foods in the aquarium.
Younger fish can be fed both live and frozen bloodworms, brineshrimp and other invertebrates. Older fish can learn to take larger food items, such as earthworms, chopped or live shrimp and pieces of fish and mussels.
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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.
Frequently asked questions on salt and transporting fish
Matt Clarke answers some of the most common questions on how and why salt is used when fish are being transported, and explains what should be done when they arrive.
Why is salt added when fish are being shipped?
Freshwater fish are saltier than the water they live in and their skin is semi-permeable.
The concentration gradient between the freshwater and the fishes' saline innards mean that they leak salts into the water and need to pump them back in to their bodies (via special cells in the gills) to keep their bodies salty. This is called osmoregulation.
When freshwater fish get stressed, as they can do when they're being flown across the world in a bag, they leak bodily minerals into their water.
Research has shown that adding salt to their transport water can minimise the amount of salts they lose, which in turn reduces stress.
This can dramatically reduce the number of fish that die on the journey and should mean that the fish are less likely to develop diseases when they're being quarantined.
Does salt reduce stress?
Yes. Several studies have shown that many fish, even those that never live in salty water, have lower stress levels and higher survival rates during and after transport when salt is present in their water. For these reasons, salt is widely used during transit for fish, both in aquatics and in aquaculture.
In 2001, two Brazilian scientists, Caneiro and Urbinati, studied the stress levels of a big, predatory characin called Brycon cephalus during transport.
The fish were shipped in water containing different concentrations of salt and their blood was sampled during the journey to see how much stress they were under.
By analysing the blood of the fish and monitoring the levels of chemicals and hormones which are produced under stress, the scientists were able to determine what effect the salt was having on their health.
When the fish were packed in unsalted water, or in water containing just 0.1g per litre of salt, analysis showed that the stress hormone plasma cortisol had built up, indicating that the fish had been stressed by the journey.
However, when the fish were packed in water containing 3ppt salt, this hormone wasn't produced.
At a dose of 6ppt, the blood glucose levels of the fish stayed the same, so Caneiro and Urbinati reckon that 6ppt is the best dose for shipping this species.
Brycon cephalus comes from the very soft, acidic waters of the Amazon basin. Most people wouldn't normally consider fish from this sort of environment as being particular tolerant of salt!
Another scientist suggested 2ppt as a guideline, but most Singapore suppliers are said to dose their fish with salt in transport at a rate of 0.5-3ppt.
Some studies have found that very high levels can have remarkable effects, with some species reportedly shipping well in water containing doses as high as 9ppt. This is close to isotonic.
What does 'isotonic' mean?
Older PFK readers may remember an early 1990s' TV advert for Lucozade Sport drink featuring Liverpool footballer John Barnes. His end quote was: "It's in balance with your body fluids." And that's what isotonic means, in a nutshell.
Freshwater fish usually have an internal salt level of about 10ppt, so if the water in your tank is also 10ppt, it's said to be isotonic. At isotonic levels, the water is about as salty as the fishes' innards, so it won't lose much salt at all.
However, isotonic levels in transport may well be a bit over the top for many fish, and they're not really designed to live in water of this salinity for long, so such levels aren't advisable.
Surely Discus, Cardinals and other wild-caught fish aren't salted?
Actually, many are. In 2001, Waichman, Pinheiro and Marcon studied the techniques used by fish suppliers operating on Brazil's Rio Negro, where many Discus, Cardinals and Hatchets and other species are imported from.
Their study showed that salt was used when the fish came from the first holding station upriver and at the exporter's facility in Manaus.
However, here the authors guessed that it may, in fact, cause more harm than good as these fish come from such incredibly mineral deficient water.
Should newly imported fish be kept in salted water?
In some cases, yes, and this is more important than many people realise. If the fish have been imported in salted water, research has shown that losses are lower if they are added to salted tanks and then gradually acclimatised back to freshwater over a period of days.
For example, Lim et al (2002) shipped guppies from Singapore in water with 1, 3 and 9ppt of salt, and then placed the fish in either freshwater or water containing the same level of salt to their transport water.
When the fish were added to freshwater, the level of losses in all batches were about the same.
However, when they were placed in tanks containing the same salt level to their transport water, and then acclimatised back to freshwater via a 30% daily water change, losses were greatly reduced!
Lim reckons that the addition of salt, even only 1ppt, is critical to the recovery of guppies after transport.
Therefore it's important that your dealer, or his wholesaler, puts newly imported fish into salted tanks (if they arrived in salted shipping water) to start off the quarantine process.
Lim calls this 'recovery water'. The fish then need to be gradually acclimatised to freshwater through daily 30% water changes to dilute the salt.
There is no need for the shop, or you, to keep guppies or other non-brackish species in salted water permanently. Indeed, none of the experts we spoke to advocated long term salt use.
Besides, guppies are freshwater fish, anyway.
My dealer says he tested the water in the fish bags and has matched his chemistry to that. Good idea?
Possibly not, as he may be measuring the salt in the transport water. Similarly, it's not wise to match the pH.
Carbon dioxide builds up in the bag on the journey which causes the pH to plummet.
If the pH shows a very low level, this might not, in fact, be the pH of the water prior to the journey. Speaking to the supplier is best, but that's rarely possible.
How should I acclimatise the fish when I get them home?
Since the fish will be physiologically adapted to life in water that may be different to yours, you'll need to acclimatise them slowly and carefully to minimise any shock.
It's often recommended that new fishkeepers simply float bags of new fish on the surface of the tank for half an hour and then gently release them.
In my opinion, this isn't the best way to do things. If you float a bag of water that's 23C in an aquarium of 25C, it will take less than a couple of minutes for the bag water to equilibrate. Try it if you don't believe me.
Since fish can't get used to any changes in chemistry through a plastic bag, the other 28 minutes of floating serve no purpose whatsoever. Tip the fish straight into the tank and the rapid change in chemical concentrations will shock them.
Instead, I believe it's important to slowly add aquarium water to the water in the bag from the shop over a fairly long period of time.
If you put a small cupful of water into the bag every five minutes for 45 minutes, the fish will gradually be introduced to the type of water in your tank.
It is true that fish do not become fully adjusted to changes in the water for some time, but in practice, this definitely works. No dealer would dream of introducing new fish without getting them used to the water beforehand.
If your dealer sells his fish from salted tanks, take care when acclimatising them. We wouldn't advise you to try and maintain a low level of salt in your tank, unless the fish are brackish. Slowly get them into freshwater instead.
This is an item from the Practical Fishkeeping archives.
Are there several types of Labidochromis caeruleus?
Labidochromis caeruleus is one of the most popular African cichlids in the hobby, but is there more than one form? Professor George Turner explains.
There are several colour forms of Labidochromis caeruleus. All seem to be geographic races, so only one colour form is found at any stretch of shoreline.
In most places they are white. Sometimes, they have a dark band in the dorsal fin. The lovely bright yellow form usually seen in the trade has a restricted distribution in the wild. There is also a strange-looking form that is white with yellow on the back.
All these forms will probably interbreed, but I have no idea what the offspring would look like!
In the fourth edition of Malawi Cichlids in their Natural Habitat, Ad Konings also includes in this species some ‘BB’ forms with blue males with black bars and brownish females.
I am a bit sceptical as they look more like a form of Labidochromis chisumulae to me, but I have an open mind!
This article was first published in the December 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.
What fish can I add to control filamentous algae?
What natural controls can you add to your aquarium to deal with growths of filamentous algae in your community tank? Dr Heok Hee Ng has some suggestions.
Filamentous algae is perhaps one of the easier types of algae to control.
Several fish species can be considered, depending on the composition of your community tank. One prime candidate among the lage eaters is the American flagfish (Jordanella floridae) which grows to about 6cm/2.4”. Mollies (Poecilia sphenops/P. latipinna/P. velifera) are similarly suitable, if slightly larger, candidates.
Also consider algae-eating cyprinids. These include Siamese algae eaters (Crossocheilus spp.), which usually reach 15cm/6” in size, or members of the genus Garra (such as the Panda garra, G. flavatra), many of which reach the same size as Siamese algae eaters, although a few reach 25cm/10”.
Algae-eating cyprinids generally require fairly well-oxygenated water and are sensitive to high temperatures, so try to keep water below 26°C/79°F.
Avoid getting standard algae-eating plecs such as Bristlenoses (Ancistrus spp.) or Otocinclus spp., as these eat very little if any filamentous algae.
This article was first published in the December 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.
Are Black widows a good first tetra to breed?
Looking for a new breeding project? Dr Heok Hee Ng advises on breeding the Black widow tetra.
Black widow tetras (Gymnocorymbus ternetzi) are good if breeding tetras for the first time. They are relatively hardy and can tolerate a wide range of conditions, especially since those in the trade are commercially bred.
Black widows are not too difficult to sex either, as the males are smaller and more slender than females, are darker and have a wider anal fin and a narrower dorsal fin.
A suitable breeding set-up should consist of several males and females, although it is possible to use only a pair. The breeding tank should be bare, with two or more spawning mops and a sponge filter.
Water conditions for breeding should be on the soft, acidic side (pH about 6.0, GH not more than 8) and temperatures around 24-26°C/75-79°F.
Lighting should be subdued, and covering the sides and back of the tank helps. Prior to any spawning attempt, the fish should be conditioned with ample feeds of live and frozen food. Keep up with water changes to maintain quality.
The fish should be monitored closely after being introduced to the breeding tank, as tetras are notorious egg eaters and parents must be removed as soon as spawning is complete, typically in the morning. Remove the spawning mops, shaking them to remove all eggs to the tank floor.
Tetra eggs are sensitive to light and the tank should be shielded for five to six days. The eggs typically hatch in about 24 hours, with the fry becoming free swimming after five or six days. Then they can be fed infusoria or similar fry food, graduating to brineshrimp nauplii after another 48 hours.
During this time, make frequent small water changes to maintain quality without creating drastic changes in conditions.
This article was first published in the December 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.
What is an OB morph?
Some African cichlids are available as OB morphs. Professor George Turner explains what they are.
OB morphs are naturally occurring colour forms of certain African cichlids. They are found in several lakes, including Victoria, Kivu and occasionally Tanganyika.
However most OB fish in the trade are from Lake Malawi where they occur in the Pseudotropheus zebra group (sometimes called Maylandia or Metriaclima), Tropheops, Labeotropheus and the fin biter Genyochromis.
In the wild, 99% of OBs are females.
This is an example of a natural colour polymorphism, where the OB and the ‘normal’ — sometimes called the BB form — are found together in the same population of fish.
This is almost certainly something to do with appearance, because OB forms are always found in shallow clearwater habitats. Mate choice, competition and predation are all possible factors.
The blotchy pattern seems to be a disruption to the process of distributing the dark melanin pigment.
Instead of being evenly spread over the body, the melanin cells are concentrated in dense dark blotches, leaving the underlying yellow or orange colour to show through in gaps between.
Fish with very few blotches are sometimes called O-morphs.
OB fish are perfectly natural and healthy and will readily interbreed with each other and with the normal form of the same species.
This article was first published in the December 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.
What conditions do halfbeaks need?
How do you keep halfbeaks in the aquarium? Dr Heok Hee Ng has the information you need.
These depend on the halfbeaks you keep, as members of the Hemiramphidae family live in habitats ranging from very acidic peat swamps to open ocean. I’ll deal with the freshwater species here as they are more commonly encountered in the trade.
Halfbeaks generally require plenty of swimming space and a steady but not too strong current. They should be kept moderately warm at 23-27°C/73-81°F, although excessive temperatures should be avoided as they are sensitive to dissolved oxygen levels.
They are also good jumpers, which they frequently do when alarmed, so a tight-fitting lid is necessary. They can be fed a variety of live and frozen foods, including but not limited to bloodworm, Daphnia, brineshrimp and small insects such as fruit flies.
Members of the genus Hemirhamphodon (including H. pogonognathus, H. tengah and H. chrysopunctatus) typically require very soft (2 GH or less) acidic to very acidic water (pH 3.0-6.0), while those of the genus Nomorhamphus require less acidic (pH 6.5-7.5), soft to moderately hard (6-12 GH) water.
Although Nomorhamphus can be maintained in marginally brackish water (to 1.003 sg), they, or at least N. liemi — the most common species available — are best maintained in freshwater.
Members of the genus Dermogenys (including D. colletti, D. pusilla, D. siamensis and D. sumatrana) are hardier and tolerate a wider variety of water conditions.
Halfbeaks thrive in slightly acidic (pH 6.0-7.5), soft to moderately hard (6-12 GH) water and most do well enough in slightly brackish (sg to 1.005) conditions. They are sensitive to condition changes, particularly soon after purchase, so carefully acclimatise them.
This item was first published in the December 2009 issue of Practical Fishkeeping. It may not be reproduced without written permission.
How do I keep Pseudomugil signifer?
The Pacific blue-eye is one of the smaller species of rainbowfish. Heiko Bleher offers some advice on its care.
There are quite a few different variants of this fish. They are found along almost the entire Pacific river drainage of Queensland, Australia, from the extreme northern part to the extreme southern state border into New South Wales.
Pseudomugil signifer are freshwater fish, but I found some populations in brackish habitats and tidal mangrove creeks. Yet I am sure those in the hobby are all freshwater populations and offspring of the latter.
The aquarium set-up should be of sandy ground with not too large gravel and driftwood. Aquatic vegetation could consist of Cyperus (maybe C. difformis or C. helferi), Eleocharis (maybe acuta, dulcis or spacelata), Hydrilla verticillata, Hydrocotyle ranuncloides, Potamogeton species (crispus, geayi or pectinatus), Lagarosiphon major and Myriophyllum rubra.
If you have problems finding any of those you can also use Vallisneria gigantea.
As mates I suggest Ornate rainbowfishes (Rhadinocentrus ornatus), one of the Melanotaenia trifasciata populations or Melanotaenia splendida splendida, some gobies like the Empire gudgeon (Hypseleotris compressa) or a Mogurnda species (such as M. adspersa, clivicola, larapinatae or the type species M. mogurnda).
Water parameters depend on population. Some come from very alkaline habitats, but they should be pH 5.8-7.0; conductivity 50-200 µS/cm. Temperature in nature ranges from 15-29°C/59-84°F.
This item was first published in the December 2009 issue of Practical Fishkeeping. It may not be reproduced without written permission.
Is my Bronze Corydoras full of eggs?
Your Corydoras is looking huge and has visible small red lines on her body. Is she ripe with eggs? Dr Michael Hardman advises.
It sounds like your Bronze cory is indeed mature and ripe with eggs. The small red lines are probably blood vessels that serve the ripened ovaries. The vessels become visible as the ovaries swell and press against the body wall — so there’s nothing to worry about there.
In most tropical fishes, an increase in temperature causes the ovaries to develop and the eggs to ripen. Usually, a second cue is needed to release the eggs (ovulation). The classical cue is a 30-50% freshwater change using dechlorinated water a few degrees cooler than the aquarium.
Provided you have two or three mature males per female, a day or two following the water change you should eventually see some eggs.
If your corys spawn and you want to raise the babies, get a breeding net. Once spawning is complete, carefully roll the eggs off the glass or plants and into the net and add an anti-fungal agent.
Depending on temperature, the eggs will hatch in three to five days and then the fry will feed on their yolk sacs for four to five after that. Start adding finely powdered flake or tablet food, better still newly-hatched Artemia or microworm, from day three, a couple of times a day until they are large enough to be released into the aquarium.
This item was first published in the December 2009 issue of Practical Fishkeeping. It may not be reproduced without written permission.
Does the Glassfish, Parambassis ranga, need salt?
Is Parambassis ranga a freshwater or brackish species, and how do you keep it? Heiko Bleher advises.
Parambassis ranga was originally described in 1822 by Hamilton as Chanda ranga, saying: “This is a beautiful little fish, about an inch and a half long, and it is found in the fresh waters of all parts of the Gangetic provinces.”
This indicates clearly that it is a freshwater fish and I’ve never found it in any brackish habitat. In February 2009 I collected it again near the Brahmaputra river in Assam near Tezpur, India, in a freshwater lake. Water parameters were pH 7.5, conductivity 96 µS/cm and temperature 28.9°C/84°F.
It is very easy to keep this fish, providing it comes from a good source, is healthy and well acclimatised. It can be sensitive when first introduced to the aquarium, so quarantine for 14-21 days. Keep it in a group of three to five, preferably more.
Give them a planted aquarium with Colisa lalia, nemacheiline loaches, some Botia, (B. dario, Yasuhikotakia almorhae), Badis or Dario species, Danio (formerly Brachydanio) and Devario species, Hara or Erethistes catfishes and similar smaller fishes from India, Myanmar or Thailand. Try to buy all from one single supplier/source.
This item was first published in the December 2009 issue of Practical Fishkeeping. It may not be reproduced without written permission.
What are the easiest tropical fish for beginners?
I'm new to tropical fishkeeping. What fish would you recommend for a newcomer?
If going for a bog-standard community tank of smaller tropical freshwater fishes, then simple fish such as danios and livebearers are your best bet for easy first timers.
We’d recommend Zebra danios initially, and these should be kept in groups of six or so in tanks of 45cm/18” or more. If you don’t fancy them, there’s also a spotted variety called the Leopard danio, a blue one called the Pearl danio and various newer varieties such as the Glowlight, Danio choprai, which is a sort of orangey-pink colour.
Ideal livebearers for the newcomer include platies and Endler’s livebearers or guppies. Platies become the largest, at around 5cm/2” long, with guppies next biggest, and Endler’s livebearers the smallest.
All breed prolifically, so be prepared for babies. If you don’t want to get over-run, go for groups of just males.
This item was first published in the November 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.
Do Tiger barbs really nip fins?
Tiger barbs are famous for being nippy, but is there anything the fishkeeper can do to minimise problems?
Tiger barbs, Puntius tetrazona, can nip the fins of long-finned fishes, such as guppies, Siamese fighters, gouramis and angels. However, if you keep them in a larger group, say six to 12, the chances of this happening are much less than when you only have a couple.
When kept in a larger group, the barbs will be more preoccupied with chasing each other and displaying to the opposite sex, so generally won’t nip fins as much.
Of course, it’s safer to keep them apart and they are rarely, if ever, a problem with fast-moving fish or those species without long, trailing pelvic fins or long tails.
This item was first published in the November 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.
How do I keep Saccodon dariensis?
The rarely seen Saccodon dariensis has recently turned up in imports from Colombia. What's the best way to keep this unusual parodontid fish.
I did not know this rarely imported Panamanian and northern Colombian characoid species was available in the hobby. In the late 1970s and early 1980s, when I started to research and collect throughout Panama, I brought them back several times.
At that time the species was still placed in the genus Parodon and I found its type locality in the Río Cupe at Cituro and elsewhere in panama south of the Charges River. It is a great bottom-dwelling characoid and to me is the most beautiful of the parodontids.
Its habitat is sandy ground, some rocks and driftwood, and rarely submersed plants. In some places large Echinodorus species were growing along the shore, along with high grass and bog-plants. However, in the region of Yaviza it was found over a faster flowing rocky area.
My suggestion is to have a good flow, a beige sandy bottom with some gravel and round smaller and larger rocks, driftwood and some large Echinodorus, which can grow out of the water.
Also consider adding other tough plants, such as Spatiphyllum and Eleocharis species, as well as some floating plants like water hyacinth, Eichhornia crassipes. Water parameters should comprise pH 6.0-7.0, conductivity 100-300 uS/cm, and the temperature in nature ranges from 24°-29°C/75-84°F.
As for tank mates I would add some Blue acaras, Aequidens pulcher or A. coeruleopunctatus, Geophagus crassilabris or G. pellegrini, Cryptoheros nanoluteus or C. septemfasciatus, Gasteropelecus maculatus (or another species), Sturisoma panamense, Ancistrus spinosus or A. chargesi. Why not some poeciliids like the very nice Brachyrhaphis episcopi, or B. roseni, or just wild guppies (Poecilia reticulata)?
This item was first published in the November 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.