By Kate Redman
With the release of Finding Dory, there is sure to be an increase in people looking to purchase ‘Dory’ fish, just as there was for clownfish after Finding Nemo . But how suitable are these fish for aquarium displays, and what are the things you need to consider before buying one of them? Here we take a look at both Dory and her friend Nemo, seeing as they are quite often exhibited together.
‘Nemos’ are Clownfish. Clownfish belong to the subfamily Amphiprioninae, in the family Pomacentridae . The subfamily is further divided into two genera, the Premnas (which contains one species commonly known as the spine-cheeked anemonefish, or the maroon clownfish ) and the Amphiprion (which contains a further 29 species ). These different species of clownfish come in a range of yellows, oranges, red, and blacks, often in combination with white bars or patches, and can range in size from around 10cms to 18cms.
The famous Nemo is an Amphiprion, more specifically an Amphiprion ocellaris, or Ocellaris clownfish (also known as a false percula clownfish, or common clownfish) . These little fish are instantly recognisable thanks to their bright orange and white banding, outlined in black, and can grow to about 11cms in length, with the females being slightly larger than the males. They are found in the Eastern Indian Ocean and the western Pacific Ocean, as well as waters off Northern Australia, Southeast Asia and Japan. Their preferred habitats are reefs and shallow, sheltered lagoons.
Of course, they are best known for where they like to call home, which also gives Amphiprioninae their other common name: anemonefish. Ocellaris clownfish inhabit three different species of anemones: Heteractis magnifica, Stichodactyla gigantea and Stichodactyla mertensii . Theirs is a mutual symbiotic relationship. Clownfish are territorial, and so this little fish will protect its home anemone from other, anemone-eating, fish. In turn, the stinging tentacles of the anemone protect the clownfish from its predators, allowing it to live and breed in relative safety . Further, it’s believed that the presence of a clownfish in the anemone boosts its health because the fanning behaviour of the fish aids in the removal of parasites . To protect itself from the anemone’s stinging tentacles, clownfish produce a special mucus.
Reproduction and gender is an interesting situation with Ocellaris clownfish. The most mundane thing about their reproduction is they are monogamous. During spawning, males will become more aggressive and territorial towards their anemone, as well as chase and bite females in a bid to attract them . Males will prepare a nest by an anemone, to be protected by its stinging tentacles, then chase a willing female to the nest to spawn and fertilise the eggs. The males will then be responsible for guarding the eggs, as well as keeping them clean, and fanning them to keep them well oxygenated. It’s after the eggs hatch that things become interesting. All baby clownfish are born gender neutral  into a social group. The most dominant fish is a female, the next dominant is a male and her breeding partner. Those ranked between them and the newborn are either other gender-neutral juveniles, or non-mating males (who, like the dominant male, will have gone through a gender change from being gender-neutral to male). If the female should die, then the dominant male will change sex, to become the new dominant female, and one of the more dominant non-breeding males will step up to become the new breeding male. Finding Nemo would have had a very different story line if it had adhered closer to clownfish biology!
Dory fish are better known as blue tangs, and are easily recognised by their royal-blue body, yellow tail and black markings. Like clownfish, they belong to the order Perciformes , but are separated from clownfish into the family Acanthuridae, of which there is only one genus: Paracanthurus. Dory is the only member of that genus; Paracanthurus hepatus. Blue Tangs are also reef fish, and share much of their range with clownfish, being present in Indo-Pacific waters from East Africa, across to the Great Barrier Reef, and up to Japan.
Blue tang reproduction is somewhat more mundane than a clownfish’s. Males aggressively court the females, and spawning and fertilising takes place at the ocean’s surface, after which the eggs are left to fend for themselves in the water .
As blue tangs and clownfish come from similar ocean regions and habitats, a reef aquarium set up for one, should be adequate for the other. If you are intending to house the two species together, you will be looking at the following water quality ranges for a fish only system [8,9,10,11,12,13]:
Salinity: 1.020 – 1.024 (specific gravity) or 35ppt
pH: 8.1 – 8.4
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: Phosphate: Carbonate Hardness (dKH) : 8 – 12°
However, if keeping anemones and other invertebrates, the following should be measured in addition [12; Chris Sturdy, personal communication, August 1st, 2016]:
Calcium: 400-450 ppm
Magnesium: 1250 – 1350 ppm
Iodine: 0.06 – 0.10 ppm
Strontium: 8 – 14 ppm
Lighting is another important factor that needs to be taken into account. If the tank is just housing tangs, then a number of different lighting options are available to maximise the display of the animals . For instance, colour-enhancing bulbs emit light from the “warmer” end of the colour spectrum, and are used to augment or enrich colour, allowing you to display the striking blue colours of your tangs to their fullest. However, a good reef tank should also contain other living (non-fish) organisms, such as coral, seaweed (though as it’s difficult to maintain in a home aquarium, this is usually reserved for large, professional aquaria), and in the case of clownfish; anemones. In which case, your lighting requirements will become more specific to allow these organisms to flourish. Seaweeds photosynthesise, and although corals and anemones aren’t photosynthetic organisms like seaweed, they do obtain essentials nutrients from symbiotic photosynthetic algae (zooxanthellae) growing in their tissues. Therefore, if you are housing clownfish with anemones, or simply including anemones and coral for show, you will need to equip your tank with a full-spectrum light , or perhaps a 50/50, or an actinic white bulb, which are blended lights that encourage photosynthetic coral growth . Additionally, anemones and corals need good water circulation to allow them to be able to absorb oxygen from the water, as well as to gather their food [15,16]. As such, most anemone species do well in tanks with low to moderate flow .
Whether installing corals, anemones, or (in the case of a large set up) algae, all good aquariums should have as their base “live rock”. The term is a bit of a misnomer, because the rock is traditionally neither a rock, nor is itself alive. Rather, it lumps of calcified skeletons of long dead corals, or other calcareous organisms (which form the majority of coral reefs) which have been collected from the ocean , although sustainable methods of curing rock from reefs has been developed . These rocks are often encrusted with coralline algae, and hold within them a host of micro and macroscopic marine life. Live rock is important to have in an aquarium, as it aids in maintaining microbial cycles, and helps keep nutrient levels down. In essence, it is a biological filter (though should not solely replace a mechanical filtration set-up).
On top of these specifics, extra considerations need to be taken into account as each species has special requirements in order for them to survive happily in their new home.
Blue tangs can grow to be nearly three times the size of a clownfish, and are very active swimmers , so any reef tank will need to be of a size to comfortably house a Dory. Therefore, you will need a tank of at least 75 gallons (approx 285 litres). Moreover, blue tangs don’t always get along, so if you want to house more than one Dory, you’ll need to get an even bigger tank (100 gallons/380 litres or more). The same goes if you want to add some clownfish as, unlike the film, they may not automatically become friends. If you’re just looking to keep clownfish, you will need a tank of at least 30 gallons .
It is also important that you don’t simply dump the tang (or indeed any fish) into its new aquarium before the tank has completed its aquarium nitrogen cycle . Doing so, before the tank contains nitrifying bacteria to break ammonia waste into less-harmful nitrogen compounds, will result in “new tank syndrome”, a situation whereby ammonia levels have reached highly stressful, or toxic, levels . A likely death sentence for your newly purchased fish! Often, the suggested method of cycling is to introduce a couple of fish, maybe a hardier species, as a way of slowly introducing ammonia to the tank, thereby allowing the necessary bacteria to flourish. This can be considered cruel, as you are putting a fish (no matter how hardy) under unnecessary stress. A more humane thing to do is carry out a fishless cycling, by adding a non-live fish source of ammonia . The cycle can also be sped up by adding sources of nitrifying bacteria . Your tank is fully cycled once nitrates are being produced, and ammonia and nitrite levels are zero .
It is essential that you make sure your tank has been set up and cycled in advance of bringing your new fish home. You’ll want to introduce your fish as soon as possible to its tank, as too long in their purchased bag/container will expose them to ammonia waste build-up. Once the tank is ready, and water ranges are within acceptable parameters (in the case of tangs, especially pH, as they are particularly sensitive to variabilities in pH ) your fish will need to be acclimatised slowly , thereby allowing it to adjust to the water conditions it will ultimately be placed into. There are several methods of introducing a fish to its new tank water, namely the Floating Bag Method, the Bucket Method, and the Drip Method . None of these procedures should be rushed. Doing so could put your fish under excess stress, and could introduce unwanted pathogens to your new tank. However, once acclimatised, and placed in its new home, blue tangs are pretty hardy fish.
In terms of diets, both blue tangs and clownfish are omnivorous, and feed on both algae and plankton [7,8]. Regarding dietary requirements, it is the tang that needs the most consideration when setting up a tank. Although omnivorous, they are primarily grazers , and will require algae-covered live rock on which to feed. In the long term, they’ll need a varied diet that includes vitamin enriched flake foods, marine seaweed (available as dried sheets similar to that used for sushi rolls), as well as frozen and live foods, all of which should help keep their colouration bright. Of these, marine seaweed is especially important for tangs. A lack of vitamin C (and possibly vitamin B complex) is believed to be a cause of a condition known as Marine Head and Lateral Line Erosion (MHLLE), something that tangs seem to be particularly susceptible to . Though rarely fatal, the disease can leave disfiguring scars on a tang. MHLLE usually begins with the development of small pits around the eye, head, and adjacent area. As the ailment progresses, the holes expand and connect, to become larger lesions, eventually extending back along the fish’s lateral line. In more advanced cases, the fins and gill covering will also often erode. Food wise, clownfish are a little simpler, and will do well on flaked foods and, like the tangs, some frozen and live foods .
The main special requirement for clownfish is, of course, anemones. To provide a suitable and secure habitat for these little fish, the presence of anemones is a must, however, not all anemones do well in captivity . As stated earlier, Ocellaris clownfish inhabit three species of anemones: Heteractis magnifica, Stichodactyla gigantea and Stichodactyla mertensii, and these organisms also have specialized requirements. Stichodactyla gigantea is from shallow water  and needs direct sunlight, and all three are capable of crawling around the tank, which could lead to them injuring themselves. Additionally, they need direct feeding in large quantities . Even capable aquarists, who can meet the needs of these anemones, are not able to keep them alive for long, with only 1 out of 32 anemones surviving for more than five years . If they do survive, they can get very big [24,25,26]. In general, reef aquariums tend to use the smaller Entacmaea quadricolor as a replacement host . Failing that, clownfish may adopt a coral species as surrogate hosts, such as Euphyllia divisa, or xenia coral .
As you can see, what may at first seem like a simple idea of getting a Dory and a Nemo, is in fact an expensive and extensive undertaking, especially if you’re just a hobbyist getting a couple of fish for the kids. To keep these animals, you will need to provide them with a large tank, proper lighting, good filtration, and adequate water circulation, not to mention corals and anemones, which even the most expert aquarists struggle to keep. All this for an animal that may only live for about five years [8,9]. Beyond these practical issues are also the environmental issues created by the desire for these fish.
Knowing where your fish has been sourced from is important. The vast majority of ornamental marine specimens continue to be collected from the wild . The clownfish, for example, is a species that makes up 43% of the global marine ornamental trade, yet only 25% of all fish making up the global trade are captive bred . This means a lot of Nemos are still being taken from their reef habitats. In the past, unregulated harvesting of tropical fish has led to the decline of many species, such as the local declines of anemonefish in Kenya [28, summarised in 27]. Blue tangs are another species regularly imported into the EU, but currently in far fewer numbers than the clownfish (4 times less ), however, this could all change now Finding Dory has been released.
Additionally, the mode of capture of these fish can greatly affect the local habitat. Cyanide fishing was, and in some places of South East Asia still is, a common method of collecting tropical fish. A report by the National Oceanic and Atmospheric Administration puts 70-80% of US tropical fish as coming from Indonesia and the Philippines, where cyanide use is the most prevalent . Cyanide is used to temporarily asphyxiate, and hence stun, fish, but its presence in the water column means it will eventually come into contact with the local corals. High doses of cyanide can cause corals to die, and medium doses cause coral to lose their symbiotic algae, leading to ‘bleaching’ events .
Using cyanide is also an unreliable method for collecting the fish themselves. The toxin not only can kill non-targeted species in the vicinity, but often kills the targeted animals too . Further, even though a fish may be brought up alive, the use of cyanide in its capture can lead to its death shortly after (as well as cause ill effects for several weeks after) . The ill effects of cyanide poisoning is further exacerbated if the animal is stressed, which is highly likely if it has just been gassed and captured.
Overall, not all the fish make it to trade, those that do could likely end up dying after purchase, and the ecosystem at the point of capture can often be irreversibly changed because of the removal of large numbers of different fish species, along with the death of corals. With the added pressure of the ‘see it want it’ desire caused by films like Finding Nemo and Finding Dory, future aquarists could unwittingly worsen the situation at these reefs.
The alternatives are fish bred through ornamental fish farms, or fish collected sustainably out of their natural habitat. Sustainable capture involves catching wild fish for aquariums by hand, using a minimum of equipment . Depending on the species, collection can involve using small hand-held nets, baited traps, or the shake-down of natural objects in which fish could be hiding. This kind of capture lets fishermen carefully select how and what they catch, allowing them to target the species of interest for which they have orders. As such, this causes a minimum of damage to the habitats where the fish live, and to the fish themselves, ensuring the habitats remain viable, and that the captured fish remain healthy. This is doubly important, as sustainable capture is often a source of valuable income for poorer communities.
If you are determined to bring Nemo and Dory into your home or display, what can be done to mitigate the environmental impact of sourcing these animals? The most important thing you can do is make sure your animals come from a reputable breeder or collector. Clownfish breed well in captivity, and even a pair in a good home tank set-up could end up producing eggs . With this in mind, choosing captive-reared clownfish is the way to go, and easily done. Unfortunately, blue tangs are the polar opposite, and only recently has a shoal been successfully bred in captivity . However, it’s early days yet in the captive breeding of tangs, and as such, any tangs currently found in shops will be wild-caught. Because of this, you will need to do your homework to ensure your future Dory was responsibly harvested. Reputable UK companies have been working for decades to make sure cyanide-caught fish do not enter the market by working closely with their suppliers, and with local charities . Additionally, as well as ensuring your fish come from good stockists, the same should be true of any live rock, corals, or anemones you use in your tanks.
It’s also worth bearing in mind that both clownfish and blue tangs are susceptible to various saltwater fish diseases and parasites , especially if wild caught . Yet another good reason to source your animals, if possible, from captive breeders.
The reefs of Nemo and Dory may be far away, out of sight and out of mind, but our actions as aquarists, whether we be public exhibitors, or home-based hobbyists, can have big and negative impacts on their habitats. Therefore, it’s crucial we exercise an important weapon, that of choice. It is up to us to choose whether we buy a captive-bred fish, or a wild caught; whether we choose a reputable trader, or no; and whether that wild-caught animal is worth it, considering the possible damage that may have been left in its wake. With Finding Dory being released in cinemas, and the likely rush on the buying of blue tangs, such decisions are more important than ever. We don’t want the next film to have to be called No More Dory!
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