Many of the tropical fish seen in pet stores are not fully grown.  The final size of the fish varies dramatically between species.  This is a list of the sizes that individual species are likely to grow to.  Only some species are listed here, and adult fish of the same species vary somewhat in size.  This is meant as a general guide to help you avoid buying fishes that will outgrow your tank.
Oscars: Astronotus ocellatus
Tinfoil Barb: Puntius schwananfeldi
Bala Shark: Balantiocheilus melanopterus
Apollo Shark: Luciosoma spilopleura
Six-barred Distichodus: Distichodus sexfasciatus (may grow larger in wild)
Banded Leporinus: Leporinus fasciatus
Red Piranha: Natterer’s Piranha: Rooseveltiella nattereri
Clown Loach: Botia macracantha (may grow larger in nature)
Green Snakehead: Channa gachua, Ophiocephalus kelaartii (often only 8 in)
Four-eyed Fish: Anableps anableps
Cuckoo catfish (female): Synodontis multipunctatus
Royal Panaque, Royal plecostomus: Panaque nigrolineatus (16 in)
Gold Nugget Plecostamus: Scobinancistrus sp.
Giant Whiptail, Golden Whiptail: Sturisoma aureum

Sources:

Butler, Rhett A. 1999-2008. Mongabay.com - San Francisco, CA

Practical fish keeping http://www.practicalfishkeeping.co.uk/pfk/pages/home.php

Mills, D. 1987 Illustrated Guide to Aquarium Fishes. Galaxy Press, England

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Corydoras are among the best tropical fish for the home aquarium. They are small, they aren’t aggressive toward smaller fish, they are hard for bigger fishes to eat, and they help keep the tank clean by scavenging food off the bottom.  Despite rumors to the contrary, they do not eat fish poop and they do require feeding.  They prefer to eat food off the bottom so they need to be fed food that sinks.

They will happily eat sinking tablet foods. There are several different types of these which can be found at most pet stores. They also enjoy frozen foods, especially frozen blood worms. Live worm-type foods are eagerly accepted so long as they are small enough for the fish to eat.

Types of Corydoras

There is an astonishing number of Corydoras species. The number of named Corydoras species was 156 in 2006 (Fuller, 2006), with new species being discovered faster than they could be named. These fish originally come from South America, mainly from the great river basins of the Amazon, the Orinoco and the Rio Negro.

The most common Corydoras species in the tropical fish hobby is the Bronze Corydoras, Corydoras aeneus, followed by the Peppered Corydoras, Corydoras paleatus, but there are many are other species available. They range in size from scarcely over an inch in the case of Corydoras hastatus, pygmaeus, and habrosus to approximately 3 inches for Corydoras aeneus and others. Fish that look like Corydoras but are larger are probably in one of the genera Brochis or Schleromystax, both of which are closely related to the genus Corydoras. The common Corydoras are usually between two and three inches in size with Corydoras aeneus being approximately three inches when adult.

With so many species, there are many different color patterns available. Most Corydoras patterns contain contrast in dark and light coloring, or large amounts of gray. Different color patterns will appeal to different people, but the intricate pattern of spots on Corydoras trilineatus makes it one of the most beautiful species.

Corydoras Behaviour

Corydoras school. Almost all species are bottom dwellers and enjoy digging in the gravel. The schools often sit on the bottom or hover and swim just above it. The exceptions are the dwarf species which will often be found schooling in mid-water as well as near the bottom. These smallest corydoras have a slightly different and more streamlined shape when compared to the Bronze Corydoras. The shape of these small Corydoras is probably due to their preference for mid-water swimming where a more streamlined shape is useful.

Corydoras can absorb oxygen from air taken into the gut and for this reason will sometimes dart to the surface for a breath of air and then back down to the bottom. This is normal behavior, but if all your Corydoras are doing this constantly then there may be inadequate dissolved oxygen in your tank.

I have kept Corydoras for many years and I have never seen recognisable aggressive behavior by Corydoras against members of their own species or any other, including towards much smaller individuals that have beaten them to the food, and partially grown fry of other fish species.

Corydoras are egg-depositors and will lay eggs on any available flat surface including the walls of the tank, the tank heater, and tank decorations. Reports on whether they eat their eggs are mixed so you may wish to separate the eggs from the adults.

With their even temperament, myriad species, and comical appearance, Corydoras are much more than just tank scavengers. When given what they need to flourish they are a fascinating and beautiful addition to the tank.

References:

Fuller, I. 2006 Starting with Corydoras. http://www.scotcat.com/articles/article33.htm

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Many of the tropical fish seen in pet stores are not fully grown. The final size of the fish varies dramatically between species. This is a list of the sizes that individual species are likely to grow to. Only some species are listed here, and adult fish of the same species vary somewhat in size. This is meant as a general guide to avoid buying fishes that will outgrow your tank.

Some of these species are sometimes illegally wild-caught and exported from their countries of origin; just because it is on this list is not a recommendation for keeping it.

Enormous Tropical Aquarium Fishes (Over 16 in.)

Red Tail Catfish: Phractocephalus hemioliopterus
Arapaima, Pirarucu: Arapaima gigas (potentially to 16 ft. usually less)
Arowana: Osteoglossum bicirrosum, Osteoglossum vandelli
Black Arowana: Osteoglossum ferreirai
Asian Arowana/Green Arowana: Scleropages formosus
Australian Arowana: Scleropages jardini
African Arowana: Heterotis niloticus
Tiger Shovelnose Catfish: Pseudoplatystoma fasciatum
Shovelnose Catfish: Sorubim lima
Reticulated Pimelodid: Perrunichthys perruno
Plecostamus, Pleco, Suckermouth Catfish: Hypostomus plecostomus
Snow King Plecostomus: Liposarcus anisitsi
Blue-eyed Panaque, Blue-eyed Plecostamus: Panaque suttoni
Sailfin Plecostamus: Pterygoplichthys gibbiceps
Walking Catfish, Albino clarias: Clarias batrachus
Fire Eel: Mastacembelus erythrotaenia
Ornate bichir: Polypterus ornatipinnis
Knife Fish; Featherback: Notopterus chitala
Mozambique Mouthbrooder: Oreochromis mossambicus
Gourami: Osphronemus goramy
Black Shark: Labeo chrysophekadion

Sources:

Butler, Rhett A. 1999-2008. Mongabay.com - San Francisco, CA

Practical fish keeping http://www.practicalfishkeeping.co.uk/pfk/pages/home.php

Mills, D. 1987 Illustrated Guide to Aquarium Fishes. Galaxy Press, England

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Many popular aquarium fishes come from the Amazon Basin. These fish include tetras, corydoras catfishes, suckermouth catfishes, dwarf cichlids, discus, piranhas and many others. Some of these species arrive in our fish tanks after being captive bred in many places around the world, but many others are wild caught and some are new imports that have only just been discovered. There are almost certainly more species that have not been discovered yet. What are the effects of climate change and deforestation in the Amazon on wild fish?

Effects on the Amazon

The combined effects of deforestation and climate change are likely to result in significant drying of the Amazon Basin as well as disappearance of half or more of the forest, possibly within the next 20 years (Nepstad et al, 2008). The reasons for the drying are twofold: cutting the forest reduces the ability of the forest to create its own climate, and the warming climate means increased evaporation and more fires. The increased rate of fire reduces the area of forest further, making the situation worse. Loss of the Amazon rainforest would also accelerate climate change by removing one of the world’s most important carbon sinks.

Potentially, deforesting a large part of the Amazon, when combined with climate change is likely to result in a Savannah type ecosystem with much less water over most of the area now covered by the Amazon rain forest. Some models predict the loss of the Amazon from climate change even without deforestation (Harris et al, 2008). These changes are likely to be very difficult to reverse, and drying of the forest has already been observed (Li et al., 2008).

Effects on Fish

Put together, this means fewer streams in which fish can live and breed. Smaller streams will likely disappear entirely while water levels are lowered in larger streams and lakes. A possible preview of some of the effects might be the 2005 Amazonian drought. This drought was primarily caused by unusually warm sea surface temperatures in the tropical north Atlantic. In 2005, streams disappeared and lower water levels in larger streams and lakes caused fish kills as well as increased fire (Marengo et al, 2008).

If these changes occur as predicted by current models, the area of habitat available to the fish species that depend on the forest will be vastly reduced, and many species will probably go extinct. Those that don’t will be scarcer they are now and will need to be bred in captivity if they are to continue appearing in hobbyist’s fish tanks. Considering how many aquarium fish species come from the Amazon, this is likely to have a major impact on the hobby.

What Can We Do?

This is not a scenario likely to be attractive to most fish keepers, but there are things that can be done to make the situation less devastating. The two key variables are climate change and deforestation in the Amazon basin. Therefore, all the usual methods of reducing climate change apply. Information on how to reduce climate change, and links to other informative sites, can be found here, and at many, many other sites on the Internet.

Reducing deforestation in the Amazon is a little more tricky for those of us who do not live in South America. More about the problems plaguing the Amazon, as well as possible solutions to these problems, can be found here.

References:

Harris, P. Huntingford, C., Cox, P. (2008) Amazon Basin Climate under global warming: the role of the sea surface temperature. Philosophical Transactions of the Royal Society 363: 1753-1759

Li, W., Fu, R., Robinson, I., Juarez R., Fernandez, K. (2008) Observed Change of the standardized precipitation index, its potential cause and implications to future climate change in the Amazon region. Philosophical Transactions of the Royal Society 363, 1767-1772.

Marengo, J., Nobre, C., Tomasella, J., Cardoso, M., and Oyama, M. (2008) Hydro-climatic and ecological behavior of the drought of Amazonia in 2005 Philosophical Transactions of the Royal Society 363,1773-1778

Nepstad, D., Stickler, C., Soeres-Filko, B., Merry, F. (2008) Interactions among Amazon land use, forests and climate: prospects for a near term forest tipping point. Philosophical Transactions of the Royal Society 363, 1737-1746

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Lighting for plant growth is rather a specialized topic. Most plants need quite bright light to grow properly. Because water absorbs light much more quickly than air does, a deep tank needs a lot of lighting if you want to grow plants.

Types of Plant Lights

The most common aquarium lighting is the normal output, or standard, fluorescent. Standard fluorescents come in many different spectra. Some are optimized for plant growth, and are sold as plant lights in pet stores and garden shops. These produce less intense light than metal halide, Very High Output (VHO), or T5 fluorescents, but the color spectrum produced is still designed to encourage healthy plant growth. People often use one, two, three, or four of these tubes together to light a tank brilliantly enough to suit the plants they wish to keep.

VHO fluorescents and T5 fluorescents are much brighter than standard fluorescents. They are most commonly used in reef tanks and planted freshwater aquaria.

Metal halide lighting can be used in planted freshwater aquaria, but its main use is lighting reef tanks. It is expensive and the extremely high light levels it produces are not necessary for the vast majority of freshwater planted aquaria.  It may well be useful in very deep tanks in which live plants grow.

LED lights intended for use as plant lights can be found on the Internet here. Given the efficiency of LEDs, this form of lighting will likely become much more common in the future. As with any new technology, the early versions sometimes have problems.

Low Light Plants and Standard White Fluorescent Lighting

There are certain plants that will do well even in the absence of special plant lights and high light levels. These include Java Fern, Microsorium pteropus, Java moss, Vesicularia dubyana, and Crystalwort, Riccia fluitans, among others. Many plants will grow under standard white fluorescent lighting so long as there is enough light, but you will get better growth under plant lights.

Sunlight

Contrary to popular wisdom, a small amount of sunlight over a short period of time may do no harm and significantly improve plant growth. The reason sunlight has a bad reputation is because too much sun will cause a tank to overheat. This can kill both fish and plants.

The best plant growth I ever had occurred when I sat my 7 gallon tank near a north-facing window where it got a small amount of sun during the early morning. For artificial lighting the tank had one compact fluorescent light bulb. My main plant problems with that tank was too much green algae, and a water lily that would not grow because I kept digging up the bulb when I cleaned the tank.

In conclusion, when picking lighting for your planted tank, you need to consider the types of plants you wish to keep and the depth of the tank.  Deep aquariums need stronger lighting than shallow ones, and light requirements vary among plant species.  At least there are many options for you to choose from.

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The cherry barb, Puntius titteya, is a common aquarium fish that is an easily spawned egg layer. The fry are somewhat hard to rear as they require extremely small food and protection from their parents, but when these needs are met they do very well. This is a description of my experiences in spawning and rearing cherry barbs.

My first male and female began courting the evening I took them home from the pet shop. They began spawning the following morning, and did so frequently after this. The male was extremely assiduous in courting the female, and would not stop chasing her around the tank. I went back and bought a second female in order to give the first some peace, and then started adding other fish species to the tank. Fry did not survive in the community tank.

In order to raise fry, I moved the cherry barbs to a 5 gallon tank containing Java moss and Java ferns. I did not succeed in raising any fry from the first spawnings due to an inadequate food supply. It was the middle of winter; all green water sources were frozen and I could not buy any food aimed at egglayer fry in the local pet store. When I tried again later, the weather had warmed and I had also taken to creating green water indoors which gave me a food source for the young fish. I only succeeded in raising one fish the first time, but the fish was a healthy female. I believe the scarcity of offspring in this case may have been due to a poor spawning.

I later left the three fish together in the 5 gallon tank. I had not intended to raise any offspring, but when I looked inside a jar of dirty fish tank water I was about to pour on my houseplants I discovered a young fish swimming inside. I then moved the adults to the main tank and proceeded to add green water 2 to 3 times a day to the little tank, graduating to egg yolks squished through nylon stocking and crushed flake food as the fry grew. Some 40 or so young fish from that spawning survived.

While cherry barbs have a reputation for being shy and rather timid fish, I found that this was untrue of the male so long as there were both females and hiding places around. Under these circumstances the male spent the majority of his time displaying and chasing the females. He was in fact the most aggressive fish in the tank, chasing my neon tetras and occasionally attempting to chase the corydoras catfish which were larger than he was. They ignored him, but his harassment of the female Cherry barbs appeared to cause them stress. One developed a fungus patch on her side which disappeared after I separated her from the male, and one female jumped out of the 5 gallon tank with fatal results. I believe she did this in an attempt to escape the male’s attentions, and any future breeding of cherry barbs will be done with a cover on the tank.

The male’s aggressiveness in this regard severely surprised me as nothing I had read about this species suggested this level of aggression. It is notable that his aggressiveness only occurred when females were present; in the absence of females he usually hid in the darker corners of the tank.

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Fry have a reputation for being sucked into filter intakes. The question is, how does this occur and is it actually a problem?

The most often recommended type of filter for the fry tank is the sponge filter. This type of filter works by pulling water through the sponge. The holes in the sponge are small enough and the water current is weak enough that fry and eggs are unharmed and cannot be pulled inside. The microorganisms growing on the sponge are also considered to be a source of food for fry. This makes these filters doubly valuable in the fry tank.

When rearing fry I used a box filter since it was what I happened to have handy. Fry got into the filter, but they seemed completely unharmed by the experience, being healthy and about the same size as fry living outside the filter. I merely check for fry when I clean the filter and move any that I find into the main tank.

Undergravel filters should not pose a problem in drawing fry into themselves as water intake occurs through the gravel bed. I suppose it is potentially possible that eggs could get sucked down and any resulting fry be stuck in the gravel bed, but I could not say if or how often this happens.

I suspect the main complaints about fry being sucked into filters involve power filters where there is quite a strong a current to draw fry into the intake tube. The danger to fry could be reduced by placing something over the filter intake that has very small holes - such as a piece of nylon ladies stocking attached with an elastic band. The holes should be too small for the fry to be sucked through into the filter. However, if current at the intake is extremely strong the filter could still potentially harm the fry by holding them against the nylon stocking by a current of water too strong for them to swim against. I have no personal experience using this sort of filter with fry, but based on other people’s comments I would not recommend it.

Sponge filters are usually very cheap to buy so you may find the best solution for a fry rearing tank is to buy one of them and leave the power filters for tanks with adult fish. A simple sponge filter may cost around $5-10 CAN, or it is possible to make your own. However, in addition to the filter you will also need plastic tubing and an air pump. An air pump for a small tank is usually under $20.00 CAN, but you may already have one so check before buying. With a little extra tubing and valves you can often hook more than one thing up to the same air pump.

In short, fry getting into the filter is only a problem with certain filter types. With box, undergravel, or sponge filters fry either won’t enter the filter, or are unlikely to be harmed if they do.

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This small barb comes originally from Sri Lanka and is a popular fish in the aquarium hobby. It is designated as low vulnerability conservation dependent by the IUCN, which means that there are some conservation programs in place to protect it without which it would be considered vulnerable (Pethiyagoda, 1996). There are some indications that the most brightly colored population may be being reduced in number by export for the aquarium trade (fishbase.org). Overall, this situation is very similar to that of the cherry barb, Puntius tittaya, which lives in many of the same habitats in Sri Lanka. Both fish are present in the Sinharaja forest reserve (Sinharaja forest reserve).

The black ruby barb is bred in captivity in Sri Lanka as well as being wild caught for export (Ekaratne, 2000). It is also bred in hobbyist’s tanks and instructions for breeding can be found in such places as Mongabay.com. I am not certain to what extent it is bred commercially outside of Sri Lanka.

References:

Ekaratne, S. 2000. A Review of the status and trends of exported ornamental fish resources and their habitats in Sri Lanka. Published by Y.S. YADAVA for the Bay of Bengal Programme.ftp://ftp.fao.org/docrep/fao/007/ad920e/ad920e00.pdf

Fishbase.org

Butler, R. San Francisco, CA Mongabay.com. 1999-2008. Retrieved 09 March 2009 http://fish.mongabay.com/species/Puntius_nigrofasciatus.html

Pethiyagoda, R. 1996. Puntius nigrofsciatus. In: IUCN 2008. 2008 IUCN Red List of Threatened Species.www.iucnredlist.org. Downloaded on 03 March 2009.

Sinharaja forest reserve. World heritage sites. United Nations environment programme and the world conservation union monitoring center. Appears to have been written post-2003. Retrieved 4 March 2009.

http://www.unep-wcmc.org/sites/wh/pdf/Sinharaja.pdf

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There are three main types of filtration: mechanical, biological and chemical. Mechanical filtration removes particles from the water by forcing the water through a medium with holes. Particles larger than the holes get stuck in the filter and are removed from the tank. Biological filtration uses bacteria to transform ammonia into less toxic substances. Chemical filtration usually involves the use of activated carbon to remove chemical substances from the water. There are also certain specialized methods of changing the water’s chemical makeup such as reverse osmosis, protein skimming and peat filtration. However, these are special cases that are not used or required for the vast majority of freshwater tanks.

Many aquarium filters use all three types of filtration to clean the water, while others may use two or even one. A simple corner box filter performs all three functions and can be used as an example. The filter consists of a box containing a layer of activated carbon and a larger layer of filter wool. The filter wool is not actually wool, but is usually made of polyester batting.

 Air enters through a tube that opens at the bottom of the box. The air bubbles rise through the layer of activated carbon and then through the filter wool before leaving through the holes in the top of the box. Because the air moves through the water, the movement of the air causes the water to move upwards through the filter.

The water carries with it chemicals and particulate matter. The activated carbon adsorbs some of the chemicals (Lenntech), which removes them from the water, while the filter wool traps some of the solid particles. On the filter wool live bacteria that convert ammonia into nitrite, and other bacteria that convert nitrite into nitrate. These bacteria are aerobic, which means that they require oxygen. The movement of the water allows oxygen to reach them easily and provides a constant stream of water containing the ammonia to be converted.

The box filter described here is one of the cheapest and simplest filters available. They work very well in small tanks, but other types of filters are more common in larger tanks.

References:

Lenntech Water treatment & air purification Holding B.V. Retrieved March 3, 2009
http://www.lenntech.com/adsorption.htm

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The Cherry Barb originally comes from Sri Lanka. It is very common in the aquarium trade, as it is hardy, easy to breed, peaceful, small and quite pretty. The vast majority of individuals seen in pet stores are captive bred.

In the wild it is threatened by habitat destruction (Ekaratne, 2000). The cherry barb lives in forest streams in Sri Lanka and much of Sri Lanka has been deforested. There are also problems with introduced fish species in Sri Lankan freshwater habitats (Ekaratne, 2000), although I am not sure if the cherry barb is affected by this directly. The IUCN lists the Cherry Barb as being lower risk but conservation dependent. This means that it would be listed as vulnerable except that there are programs in place to protect it (Pethiyagoda, 1996). It was listed as vulnerable prior to the conservation initiatives being implemented. However, its status has not been updated since 1996, which makes it difficult to determine how well the fish is doing now.

According to fishbase.org, some especially colorful varieties may be being overfished for the aquarium trade, although some of the cherry barbs exported from Sri Lanka are hatchery bred (Ekaratne, 2000). The Cherry barb is present in the Sinharaja forest reserve, which is the last large area of primary tropical rainforest on the island. The status of this reserve as the largest on the island is rather startling to me, as it is only 21×4km in extent (Sinharaja forest reserve). Still, the cherry barb is a very small schooling fish so it may be big enough to preserve the species provided that the fish are efficiently protected within the park. The protection of the specific especially colorful varieties is another question.

 Overall, I would probably avoid buying wild caught cherry barbs but there’s certainly no problem with buying the captive bred ones.  Of course, telling the origin of the fish is difficult when most pet shop workers do not necessarily know where the fish come from.  This is a standard problem with the aquarium hobby for far too many species.

References:

Ekaratne, S. 2000. A Review of the status and trends of exported ornamental fish resources and their habitats in Sri Lanka. Published by Y.S. YADAVA for the Bay of Bengal Programme. ftp://ftp.fao.org/docrep/fao/007/ad920e/ad920e00.pdf

Fishbase.org. Retrieved 27 February 2009.http://www.fishbase.org/Summary/SpeciesSummary.php?id=6147

Pethiyagoda, R. 1996. Puntius titteya. In: IUCN 2008.2008 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Retrieved 27 February 2009.

Sinharaja forest reserve. World heritage sites. United Nations environment programme and the world conservation union monitoring center. Appears to have been written post-2003. Retrieved 27 February 2009. http://www.unep-wcmc.org/sites/wh/pdf/Sinharaja.pdf

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