Seven fish best left in the wild


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Forum moderator Bob Mehen looks at some freshwater and marine fish that he thinks are best left in the wild...

There are literally thousands of species of fish imported for the aquarium hobby, and the majority can live a perfectly healthy and long life in the artificial confines of aquaria, many living far longer than they would in their natural environment and displaying their health through breeding.

However the hobby is also the end destination for many species that are entirely unsuitable for life in captivity for a number of reasons.

Pangasius catfish

Shark catfish or Pangasius are sadly a common site in dealers' tanks. Generally the species imported appear to be Pangasianodon hypophthalmus and Pangasius sanitwongsei - both usually sold as Iridescent sharks.

These fish are mass produced for the food industry - you may have seen "Vietnamese River Cobbler" fillets for sale at supermarkets - this is usually the same fish. The babies seen in your local aquarium shop are just a profitable sideline.

There is a reason they are commercially farmed other than taste. They are fast growing, large fish. When the fish are harvested for food they are probably less than a year old but already well over 30cm long.

Given that wild P. hypophthalmus have been recorded at over 1.3 metres and 44 kg and P. sanitwongsei 3 metres and 300 kg, you can see that there are probably few major public aquaria that can satisfactorily house these fish as adults, let alone hobbyists.

Add to this massive potential size the fact they are a fast swimming, nervous fish then it's little surprise most of the fish seen in aquaria have damaged noses and eyes from crashing into the aquarium glass.


The Pacu, Colossoma macropomum (and its relatives) is another giant best left chomping on nuts in the flooded forest of the Amazon. Again often imported as a by product of the food industry it can rapidly grow to over 1 metre and 40 kg.


A possibly controversial choice here, but I think Synchiropus splendidus, the Mandarin fish warrants inclusion. This is a very commonly seen species in the hobby and this is hardly surprising as they must be amongst the most beautiful. They do however have a dreadful record for long term survival due to their specific dietary needs, namely a constant supply of copepods.

A large tank with copious live rock, limited stock which doesn't compete for this food source and a refugium is really needed or you are in all likelihood condemning these stunning creatures to death by starvation.

Red-tailed cat

The Red-tailed catfish, Phractocephalus hemioliopterus is usually seen in shops at the "kitten" stage – all whiskers and anthropomorphic face – making these very tempting to the unwary.

These majestic fish can however grow to over 1.3 metres long and require expert care and huge tanks beyond the means of most hobbyists.

Moorish idol

The Moorish idol, Zanclus cornutus – better known to many as Gill from Finding Nemo – is a surprisingly common and popular import – surprising because of just how poorly these fish fare in captivity.

On the reef they eat largely sponges and tunicates – it is simply not possible for the average tank to produce enough of these to sustain these fish, so as a result most quickly starve. If you like the look of these fish then please try the similar looking Bannerfish, Heniochus sp. instead.

Puntius denisonii

Going off at a slight tangent we have the Red-line torpedo barb, Puntius denisonii. What? I can hear you say, but let me explain my reasons. Although these fish make attractive, hardy aquarium subjects, the wild population is at risk of extinction as a direct result of the aquarium trade if reports are accurate.

Fortunately these fish are being commercially bred, so this is a plea to be sure that any fish you are considering buying are farmed stock or this fish may disappear from the wild just a few short years after its introduction to the hobby.

Cleaner wrasse

Cleaner wrasse, Labroides dimidiatus are another species imported in large numbers, despite having a poor record for survival in captivity through being a largely "obligate" feeder – in this case on parasites carried by the fish they clean.

The removal of these easily caught fish from their reef cleaning stations can also have a detrimental effect on reef health - only now are we beginning to understand just how important a role these fish play.

Other species

The species I mention are all commonly seen for sale – there are many other species that suffer from similar problems in captivity that are thankfully less often seen.

The basic message I'm trying to get across here is one of thorough research and self regulation. There are three main factors at play in my recommending you avoid these species: difficulty feeding in captivity, unsuitable adult size and impact on the species and its environment in the wild as a result of collection.

There are an increasing number of voices questioning the ethics of the hobby we love, and the unthinking collection and sale of the species mentioned can only give more ammunition to their arguments.

The hobby and industry that supports it has made considerable strides in recent years to be more ethically minded. There is still a long way to however, go but we can help greatly by becoming more informed of the issues surrounding our pastime. The less people that buy these fish, the less of them that will be imported.

This is an item from the Practical Fishkeeping website's archives. It may not be reproduced without written permission.