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    Species: Aphyosemion striatum

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    Species: Corydoras oiapoquensis

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    Species: Hypsophrys nicaraguensis

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    Species: Panaque LDA31

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    Species: Plants

Store visit: Abacus Aquatics in Southeast London

Abacus Aquatics is a brand new tropical fish shop aiming to provide a combination of bread-and-butter tropical community fish alongside less widely traded catfish, cichlids and other specialist species. One of the nice things about this shop is that it is clearly a labour of love, the owner being a dedicated hobbyist. Shoppers were provided with lots of help and advice, and we spotted lots of little things indicative of a well-run tropical fish shop, such as the absence of non-aquatic plants in the display of Dutch-grown aquarium plants. Prices were surprisingly competitive, with discounts on certain fish when bought in groups, and good-value Eheim and Juwel branded all-in-one aquarium kits.

Abacus Aquatics is at 168 Halfway Street, Sidcup about fifteen minutes walk from Sidcup railway station. Buses on Route 286 call at the Longlands, Days Lane stop just north of the shop.

Community fish

If pushed to name the best group of community fish, most aquarists would place the danios at or near the top of the list. Notably undemanding, all most danios require is good water quality, swimming space, and low to middling water temperatures. Water chemistry is generally not critical when keeping danios, though soft to moderately hard, around neutral pH water is generally preferred and in some cases required for breeding. We were pleased to see several danio species on sale when we visited Abacus Aquatics. As well as the two most widely traded species, the Zebra Danio and the Pearl Danio, we also saw the Glowlight Danio (Danio choprai), Leopard Danio (Danio frankei), Fire Ring Danio (apparently a variety of Danio kyathit) and Sondhi’s Devario (Devario sondhii). This latter species is related to the Giant Danio and has similar colours, but remains much smaller, getting to about 6 cm or so in length. It’s a bold species and kept in groups makes an excellent dither fish for medium-sized cichlids such as kribs and acaras.

For Londoners especially, the value of rainbowfish cannot be overstated. Whereas most fish from South America and Southeast Asia prefer soft, acidic water conditions, most rainbowfish do perfectly well in hard water. This means that over the long term people with hard water community tanks will find that rainbowfish maintain their health much better than soft water tetras and barbs. The downside to rainbowfish is that juveniles are notoriously lacking in colouration, and it often takes several months before fish bought from a tropical fish shop start to look like the stunning fish seen in aquarium books! We saw several rainbowfish species on sale during our visit, including the excellent Neon Dwarf Rainbowfish (Melanotaenia praecox), a small species that gets to about 6 cm long and once mature acquires an iridescent blue body with orange or red fins depending on whether they’re females or males. Another species we were pleased to see on sale was the Blue or Kutubu Rainbowfish (Melanotaenia lacustris). As its name suggests males of this medium-sized (to 12 cm) species become steely-blue in colour with a bold dark blue band along the midline of the flank. Females are similar, the body colour is less intense, so the blue band is set off against a more silvery-green body. Both sexes are attractive fish, and if kept in equal numbers the males will adopt their best colours and display to the females by strutting about and generally looking lovely.

At the peculiar end of the community fish market are things like pencilfish, hatchetfish and halfbeaks, all of which were sale during our visit to Abacus Aquatics. But one oddball that really stood out was the rarely-seen Swordtail Characin (Corynopoma riisei). This characin lives in open water near the surface, so it makes a great dither fish for tanks with peaceful dwarf cichlids and catfish. It is peaceful towards tankmates and quite adaptable, and though it prefers soft water it tolerates hard water well. What makes this species special is its sexual dimorphism: unlike the females, males have very long fins, including a tail fin with a massively extended lower lobe. Less obvious are the glands on the tail fin and gills that produce hormones apparently used during spawning. Swordtail Characins belong to a distinctive family of characins that perform internal fertilisation, the males having modified anal fins that direct sperm into females. Spawning itself is a lively affair and well worth observing in a small aquarium with soft water, feathery plants, and a gentle water current. Females retain the eggs for a while, up to a few days, and once laid the eggs soon hatch and tiny fry appear. Even if you never breed this species, its delicate gold-speckled body colouration makes it a charming addition to the shady community tank, and a fun fish to keep.

Mini fish

Because so many Londoners live in apartments or small houses, aquaria 25-45 litres (6-10 gallons) in size are very popular. Stocking these small tanks can be difficult because most community fish will not do well in them. Abacus Aquatics maintains a selection of fish suited to small tanks, some of which would be good for beginners, while others are more appropriate fish for advanced aquarists stocking a small second tank alongside their larger community system.

Beginners could do a lot worse than starting off with fancy bettas (Betta splendens). So long as the aquarium has a heater and a filter, a single male betta will do just fine in a 25-litre aquarium. Because they are quite poor swimmers, an air-powered sponge filter is recommended. Male bettas are famous for their bright colours, and in many ways they are a far superior “beginner’s fish” than goldfish. On our visit to Abacus Aquatics we saw pink, red and blue bettas on sale.

Another nifty little fish we saw on sale was the Dwarf Badis (Dario dario). This perch-like species from South Asia gets to less than 2 cm in total length. It is noted for its ability to change its colours according to mood, though settled fish tend to be silvery-blue with crimson vertical bands. Dwarf Badis are timid fish that tend to do poorly in community tanks, in part because they are shy but also because they prefer live foods but can’t compete well with more pushy feeders. But in their own small aquarium, these little fish are charming and fun to keep. Although territorial, their small size means a group can be easily kept in a densely planted aquarium with plenty of caves. They prefer gentle water currents, so air-powered filtration is ideal. Hard water should be avoided though; aim for pH 6-7.5, 3-10 degrees dH. Breeding badis is not dissimilar to breeding dwarf cichlids, though only the male guards the eggs, and his care ends once the fry become free swimming.

If you wanted to add some dither fish to an aquarium containing a pair of Badis, you couldn’t go wrong with the Dwarf Rasbora (Boraras maculatus), another species we saw in the small fish section of Abacus Aquatics. This tiny schooling fish gets to about 2 cm in length, and being so small it is easily bullied or eaten in standard community tanks. But in a peaceful planted aquarium it does very well kept in groups of six or more, and really you want to keep as many as you can if you want to appreciate the delicate beauty of this small species. Like the Dwarf Badis, the Dwarf Rasbora appreciates soft, slightly acidic water conditions.

One of the most striking small fish we saw on our visit was the Red-Striped Killifish (Aphyosemion striatum). This non-annual species comes from West Africa and does best in fairly soft water; a 50/50 mix of London tap water with RO water should produce something around 10 degrees dH that will suit the species well. Like many killifish it will be short-lived if kept too warm, so a temperature of about 22 C/72 F is recommended. It is a peaceful species, and may be kept in pairs without problems. While it can be kept with peaceful tankmates that appreciate similar conditions, for example small whiptail and Corydoras species, like most killifish it is best kept alone so that breeding can be accomplished. Red-Striped Killifish are not fussy feeders, and though small live foods such as daphnia are preferred, a good quality flake food will usually be taken as well.


We were intrigued by the selection of cichlids at Abacus Aquatics. Among the less often seen species were cichlids such as Amatitlania sp.”Honduran Red Point”, Archocentrus myrnae, Guianacara owroewefi, Hypsophrys nicaraguensis, Laetacara dorsigera, Nanochromis nudiceps and Vieja argentea. This was alongside popular cichlids like angelfish, severums, oscars, kribs and rams. Central American cichlids featured quite strongly, which is something that aquarists in London should benefit from, given the hard, alkaline water conditions of the area. In the past Central American cichlids have had a dodgy reputation because of their territoriality, and while few are truly peaceful fish, some work well in mixed species set-ups alongside robust catfish such as L-number plecs. Amatitlania sp. ”Honduran Red Point” for example is fairly small, males getting to about 12 cm when fully grown, the females a bit less. It isn’t nearly as aggressive as the closely-related Convict Cichlid, but sports lovely red and gold marking son its fins as well as the black and grey vertical bands typical of the genus.

Archocentrus myrnae is another small Central American species, males getting to about 10 cm long, females a bit less. Again, it’s Convict-like in shape but while juveniles are more or less pinkish-brown with a few black blotches along the flanks, mature fish are golden-yellow with a black patch covering the face, throat and ventral surface. Like the Honduran Red Point this species is fairly easy-going, though calling it a community fish would be overdoing it. On the other hand, Archocentrus myrnae behaves well when kept with robust catfish and suitable dither fish such as swordtails. Note that all the Convict-like cichlids have a tendency to interbreed, so Amatitlania, Archocentrus and Cryptoheros species shouldn’t be kept together in the same tank.

Sometimes called the White Cichlid, Vieja argentea is a big, largely herbivorous cichlid closely related to the popular Black-Belt Cichlid (Vieja maculicauda) but differing from that species in being iridescent silver with black spots. Sexually mature fish have red, blue and golden markings on their flanks and fins, and in good condition these fish are extremely attractive. On the downside though they are rather big, around 25 cm when fully grown, and their feeding habits veer towards the messy, so a big aquarium with robust filtration is required. They are very aggressive when spawning, but otherwise fairly mild-mannered, and work well alongside robust cichlids and catfish.

The jewel among the South American species we saw at Abacus Aquatics was the very rarely traded species Guianacara owroewefi. This small, sand-sifting species only gets to about 10 cm long and outside of spawning has proven to be fairly gregarious and well behaved. Mature fish are very pretty, essentially golden-brown with orangey-red gill covers and pelvic fins and a bold black spot halfway along the flank. Its natural habitat includes quiet, shallow streams and pools of the types also inhabited by Corydoras catfish and various small characins. Pairs work together when breeding, favouring rocky caves as spawning sites with the females looking after the eggs while the male defends the territory. Basic care is much like of geophagine cichlids, in particular the need for water that isn’t too hard and with near-zero nitrate levels.

Corydoras and L-number catfish

We spotted well over a dozen Corydoras species during our visit to Abacus Aquatics, including many unusual species that should attract catfish fans from across Southeast London and Kent. Among the less often seen species were Corydoras ambiacus, Corydoras arcuatus, Corydoras atropersonatus, Corydoras caudimaculatus, Corydoras concolor, Corydoras gossei, Corydoras metae, Corydoras oiapoquensis, Corydoras weitzmani and C150 Corydoras sp. “Mazaruni River”. Old favourites were there too, including Corydoras aeneus, Corydoras paleatus, Corydoras panda, Corydoras sterbai and Corydoras trilineatus (as Corydoras julii).

Apart from the warm-water species Corydoras sterbai, maintenance of all these catfish is much of a muchness. The Flag-Tailed Panda Catfish (Corydoras oiapoquensis) is typical. As its common name suggests this species has the same black bands on its face as the Panda Catfish but also has attractive black and white markings on its tail fin. It gets to about 6 cm in length, the females being bigger than the males, but the males having proportionally taller dorsal fins. It is happiest maintained at between 22-25 C, making it an ideal companion for Neon Tetras, Danios, Platies, Swordtails and other low-to-middling temperature community fish. All Corydoras do best in tanks with a smooth, sandy substrate; smooth silica sand purchased from a garden centre works fine. If kept in tanks with gravel their whiskers tend to get worn down, but once moved to a tank with a sandy substrate they quickly grow back. Do take care to avoid sharp sands such as Tahitian Moon Sand as these tend to abrade the whiskers just as badly as gravel, if not worse. Corydoras are not fussy about water chemistry and can be good fish for beginners, but care should be taken to ensure they get enough to eat: while they are opportunistic and will eat leftover flake food, that shouldn’t be their only source of food! Instead offer them good quality catfish pellets 3-4 nights per week.

We saw a smaller selection of L-number catfish on our visit, but the owner of Abacus Aquatics is keen to maintain a good variety of these popular fish. On sale were some very nice Ancistrus dolichopterus bristlenose plecs, among the best L-numbers for medium-sized community tanks. These catfish are notable for the odd tentacles on their heads, males tending to have more of them than the females. They are very peaceful and make first-rate algae-eaters, though they should be provided with other foods as well, including softened vegetables, algae wafers, and occasional meaty treats like seafood and frozen bloodworms. Another striking species that we saw was the Mustard Spot Plec (Panaque sp. LDA31), a close relative of the popular Clown Plec that was also on sale. Getting to about 12 cm in length this fish is a trifle shorter than the average bristlenose plec but rather more stocky. Like other Panaque catfish it consumes at least some wood in the wild, so a piece of bogwood should be kept in the aquarium for this purpose. It isn’t an especially good algae-eater, but does enjoy vegetables like carrots, sweet potato and courgette. Occasional meaty treats are valuable too, but an excessively rich diet doesn’t seem to suit Panaque well, so the accent should be on fresh vegetables and algae-based wafers.


Though still under development at the time of our visit, the marine side of the operation already included hardware, live rock, and a selection of tank-bred clownfish and Chromis damsels. All the marine tanks at Abacus Aquatics are lit with LED units rather than fluorescent tubes, a sign that the owner is clearly planning ahead and taking advantage of the best lighting technology available in terms of efficiency and long-term economics.

London tap water being notoriously hard and high in nitrates, the store also sells RO water and RO-based artificial seawater, a useful service appreciated by aquarists in this part of England. We’d recommend that any aquarist planning on keeping marines in London use RO water rather than tap water, both for making up seawater and for doing the periodic top-ups needed to offset evaporation. Corals in particular have a very low tolerance for nitrate, and even levels of 5-10 mg/l can be stressful to them over the long term. RO filters are expensive to use and maintain, so buying RO water from a store like Abacus Aquatics is one of the easiest ways hobbyists can ensure the health of their reef tank livestock.

As noted, the selection of livestock on sale during our visit was very low, but in due course the owner intends to build up the selection of fish and invertebrates to include species suitable for both FOWLR community tanks and reef tanks. Hopefully on our next visit to Abacus Aquatics we’ll be able to report back on these developments.

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