Mackerel barb, Opsarius pulchellus

Nathan Hill spotlights a lovely, active fish that's ideal for a fast-flowing sub-tropical aquarium.

Alternative common names: Royal Opsarius, Butterfly trout, Green-barred danio.

Synonyms: Barilius pulchellus, Daniops macropterus.

Origin: China, Laos and possibly Thailand.

Size: To 11cm/4.3”.

Diet: This fish is a ready feeder and takes almost anything that hits the surface of the tank. These are surface and midwater feeders that are less inclined to take any food once it reaches the bottom of the tank.

Offer dried foods along with frozen treats such as bloodworm and Daphnia.

Live foods will be snapped up within seconds and insects are also appreciated.

Water: Preferred pH sits between 6.5 and 7.5. KH is accepted between 8-12. This tropical/sub tropical fish prefers things slightly cooler at 21-24°C/70-75°F and will rapidly lose weight if kept at higher temperatures.

Habitat: This fish comes from fast moving and clear streams.

Aquarium: Ensure a good-sized tank for this incredibly active species and avoid any shy tank mates that may be spooked by Opsarius’ incessant and rapid swimming behaviour.

As active fish go, these are larger than many typically offered for sale and a tank of 1m/3.3’  length should be the minimal size you should consider.

A good, open swimming area is required, ideally with laminate flows of water they can fight against. Oxygen levels should be very high.

Opt for a sandy and cobbly base, with longer grasses for décor. Opsarius will swim at all levels and have no requirement for caves or other hiding places.

Tank mates can be made up of almost any fish that enjoy the same water parameters but, if opting for a biotope set-up, other fishes found alongside wild Opsarius include Puntius rhombeus, Rhinogobius taenigena, Schistura and Sewellia species, plus Rasbora paviana.

Notes: Opsarius pulchellus is a rare find in the UK hobby, which is a shame as it’s both easy to keep and a unique, bright attraction.

Early indications are that this fish is easy to breed, although keeping the adults from consuming their eggs is something more of a challenge.

Sexing is performed by observing the contrasting shapes of individual fish, with females being plumper as well as deeper bodied than males.

Despite the moderately high price of these fish, efforts should be made to keep a shoal of six or more, although anecdotal evidence hints at these fish being content even when in pairs.

Availability: This is the first time I have seen these fish on a PFK shoptour and the specimens photographed were found at Abbey Aquatics and Reptile Centre in Suffolk.

Price: £15 each.

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