Your fish houses: Mark Walters


  Corydoras eversi  may not even exist in the wild any more, so it’s a species that fishkeepers should try and breed to ensure its continued existence.  Corydoras eversi may not even exist in the wild any more, so it’s a species that fishkeepers should try and breed to ensure its continued existence. 
Rare catfish, a scratch built fish house, and a holotype preserved in acetone – just a few things you’ll find in one of the UK’s top fish collections. 

Corydoras eversi may not even exist in the wild any more, so it's a species that fishkeepers should try and breed to ensure its continued existence.


Meet the fishkeeper

Name: Mark Walters. 
Age: 48.
Occupation: Project manager.
Time keeping fish: 35 years.
Number of tanks: 40.
Most spent on a fish: £195 each for Hypancistrus zebra.

Mark Walters is a name recognised by anyone immersed in the aquarium hobby. He’s Chairman of the Catfish Study Group (CSG), and among his many breeding accolades you’ll find rare Scleromystax and Loricariids. 

While there’s no such thing as a bad reader visit, we just know that some are going to truly shine, and as well as being an exceptional fishkeeper, Mark also has a wonderful openness and lucidity that’s as rare as it is charming. 

So, without any further amble from me, here’s more of the man, the method, and indeed the fish behind the CSG’s top spot…

  Spectracanthicus  L354.

Spectracanthicus L354.

As hobbyists go, you’ve got quite the pedigree with an M.Sc. in Aquatic Biology. Was that something that came before the hobby, or was it a result of existing fish love? 

I kept various pets as a youngster and always had a keen interest in the natural world, but it was a surprise Christmas present of a three-foot tank from my parents that really took the hobby off. Not an empty tank and equipment from a pet shop – a fully stocked aquarium from an ad in the local press, which was carried half-filled up the stairs and into my bedroom for Christmas morning! 

I spent the next few months learning about the fish in the tank and regularly discovering new ones as they emerged as fry from the substrate! After this I was hooked and at 13 I was working in my first job at a local fish shop, had joined an aquarium society and took a much greater interest in science at school. This led to a more serious academic pursuit through degrees at University and my first ‘real’ job as a Fisheries Scientist.

  Scleromystax barbatus.

Scleromystax barbatus.

Of all the fish you could have gotten involved with, why catfish? And why Scleromystax and suckermouths in particular?

I remember as a young fishkeeper absorbing as much information as I could, mainly through very old aquatic books and bundles of aquatic magazines picked up at aquatic club sales. I also subscribed to PFK in the early 80s and recall being mesmerised by an article by a well-known north western aquarist who had kept and bred the bearded cory we now know as Scleromystax barbatus. Back in the day, they were unavailable to the average fishkeeper and it wasn’t until the mid ’90s during a resurgence in my fishkeeping that I picked up a group. They definitely were the catalyst for my love of catfish, and managing to spawn them just increased my desire to find out more about Corydoradinae and other cats.

Joining the Catfish Study Group (CSG) in 2005 opened the next chapter in my fishkeeping life and species became available that I’d only read about, through their availability at club auctions from experienced breeders. I quickly started collecting groups of Corydoras, which seemed to respond to my care and before long had spawned a few dozen species. During this time I realised that there were plenty more species of my beloved Scleromystax and started to collect groups through auctions and specialist shops. Of the 13 known species, I’ve kept nine and bred eight. I still have barbatus in my tanks plus a very special species — CW038, which I first wrote about in PFK back in 2008.

My move to Loricariidae came about through the CSG breeders award programme, and my desire to breed more and more species. After knocking off 50-odd cory species I needed to move onto different genera to get the necessary points, so I bred a few woodcats and moved to suckermouth catfish. I got as far as I could with the breeders award programme but haven’t really stopped and have now bred over 20 species of suckermouth catfish from nine genera. I still keep plenty of corys though!

  Scleromystax prionotus.

Scleromystax prionotus.

Scleromystax are beautiful – why don’t we see more of them available in stores? 

Many of the most desirable Scleromystax originate from critically threatened habitats in south west Brazil. Some may even be extinct now. Imports of CW038, C112, C113, and CW042 haven’t been seen for over ten years. It is reported that the occurrence of S. barbatus is now very restricted due to pollution and habitat destruction, which makes them scarce and expensive when imported. It’s important that hobbyists continue to breed some of these species, and make them more available; it’s equally important for shops to support local breeders and not rely on wild caught fish as the sole source of such desirable species.

Where do you source yours?

My groups of Scleromystax come from a variety of sources, including other hobbyists in the UK and abroad, as well as specialist retailers.

What’s the trick to spawning them?

Typically, Scleromystax enjoy cooler waters than most tropical fish. In captivity, tank temperatures tend to creep back up again, especially in a fish house, so the best trigger for spawning is a large water change with cooler water, simulating a rainy season. Good food is also important, with plenty of live or frozen foods in their diet. Most of my breeding fish have their own species tanks, reducing competition from other species and minimising stress on the fish I want to breed.

  Pseudancistrus  L259.

Pseudancistrus L259.

Which other cats should more people be breeding? 

Lots of the fish we’re used to seeing in shops are becoming more restricted due to export bans from their native countries. Species we may not see imported from the wild in the future include Leopard frog plecos, Peckoltia compta; Zebra plecos, Hypancistrus zebra, and many of the black and white striped Loricariidae of the Xingu and Tapajos Rivers of Brazil. These are reasonably easy to breed and demand will be high in the future. 

There are also a few Corydoras and, of course, Scleromystax that people could try to maintain — one beautiful cory is the recently described C. eversi, named after famed German aquarist Hans Georg Evers. Hans brought the first specimens into Europe over ten years ago, and all the fish available originate from this import. It’s unlikely the fish remains in the wild but it’s great that it has been described to science and is still in existence in aquariums, at least.

What are the material and intellectual challenges of catfish keeping? 

For me, the greatest challenge is finding time to devote to fish breeding. I have a busy job, a young family, and other outside commitments. I also devote a lot of time to the Catfish Study Group as Chairman, Convention Manager and a host of other responsibilities. It’s important to me to share the knowledge, spread the hobby as wide as possible and bring new people into the fishkeeping family, especially young people. My hobby gave me a fantastic grounding in science and DIY and eventually led to a career. I hope others can experience the rewards.

  Corydoras boesemani.

Corydoras boesemani.

And what are those rewards? 

With so many catfish to choose from, I’ve been lucky enough to breed a few ‘world-firsts’ and written loads of articles for the CSG Journal and other publications, which gives me a lot of kudos. The main rewards though are the fantastic people in the hobby, many of whom I regard as close friends. Through social media, the hobby transcends international borders and social conventions, such that hobbyists can communicate directly with professional ichthyologists around the world, sharing their experiences and learning from each other.

What’s the fish you want but can’t get?

There are a couple of Scleromystax species, which although reasonably common haven’t been imported yet. Similarly there are a few Corydoras species which seem to only find their way to Japan.

What’s the most difficult fish you’ve ever spawned successfully?

I managed to breed one of the cactus plec species a few years ago and was successful in raising a few hundred youngsters from five or six spawnings. The experience gave me the chance to work out the best way to raise the fry, and some of the pitfalls of working with quite an aggressive species of Loricariid. Pseudacanthicus have quite serious dentition and the male will routinely rough-up the female during spawning and even youngsters will bite chunks out of each other during their raising!

 One of Mark’s  Scleromystax  fry.

One of Mark’s Scleromystax fry.

What’s the rarest? 

I came across a pair of Scleromystax at Pier Aquatics in Wigan back in 2008. They had been imported with a bigger group, but the rest hadn’t survived. I kept them and recorded their development and brought them along to a CSG Convention where they were identified as a new species — CW042. These were the only known examples of the species imported. Unfortunately, straight after their first spawning, the male died and the eggs failed. The species hasn’t been seen since. 

Where do you think the greatest breeding advances are being made?

The future of some species probably rests with commercial fish farms in South East Asia, rather than amateur fish tanks. Literally thousands of Zebra plecs are now being produced every week in Indonesia, for export around the world. The same fish farms have expanded to breed other rare plecos including Hypancistrus L174. It was good to meet up with some of the biggest commercial zebra producers, when I went to the L-Welse event in Germany in 2015, it changed my perception of South East Asian aquatic fish production. 

What do you think the best conservation approaches are for wild fish? 

I’m afraid it’s probably too late for many species impacted by habitat destruction, pollution and hydro-electric dams. The best we can do is maintain what we have in the best environments possible, and try to breed them.

  Spatuloricaria puganensis.

Spatuloricaria puganensis.

What are the greatest perils for an aspiring breeder? 

Many people start fish breeding thinking they will make a fortune, then drop out of the hobby after a year when they realise it’s not so easy! I probably make about enough to pay the electricity bills, from sales of my baby fish. I’m never going to retire on the proceeds!

All fish are different, we know, but what are your bare essentials for successful catfish breeding?

My top tips are single species tanks, strong flow, the correct temperature, the best food and patience. Many of my fish have been sat in their tanks for years without any obvious signs of spawning, but they often surprise you when you least expect it!

  Spatuloricaria puganensis  juveniles.

Spatuloricaria puganensis juveniles.

What’s the plan for all these Spatuloricaria fry you’re rearing?

I was lucky enough to have these amazing giant whiptails spawn for me, on two occasions now. Most recently over 400 eggs were successfully brooded by the male, through to hatching. The trouble is they will take a good year before they are big enough to transport, let alone move to other fishkeepers’ tanks, with the added complication that they are extremely skittish. I may just end up with a 100 gal tank full of giant whiptails!

If you weren’t keeping catfish, what would be your next choice? 

I’d actually like to keep more livebearing fish, as dither fish in my tanks. The trouble is I use only rainwater during water changes which makes my water too soft for most. That’s why I have a few chalk pebbles in most of my tanks to prevent pH crashes. Having said that, I have a plague of Endlers livebearers through most of my tank systems, which act as useful canaries in case water conditions are less than ideal. 

 Mark’s fish house is paradise for any cory or suckermouth catfish fan.

Mark’s fish house is paradise for any cory or suckermouth catfish fan.

How much maintenance does your fish house require? Are you a daily, weekly or monthly kind of aquarist?

I’m a ‘do as much as I can’ kind of aquarist. If I have an easy month, I will keep up regular water changes and my fish will reward me with spawns. If I have a hectic month, then the water changes go on hold and my fish suffer a ‘dry’ season! 

The worst times for me are if we go away on holiday — fry don’t get fed, eggs don’t get harvested and I spend most of my time on the beach fretting about my sump tanks running dry!

  Peckoltia braueri.

Peckoltia braueri.

Being the chairman of the Catfish Study Group, running a fish house and working a full time job must make some demands on your personal life. How do you juggle the fish world/rest of the world balance?

Fishkeeping is important to me, but not at the expense of my family. I’ve seen lots of aquarists for whom the hobby has tipped too far in one direction and their home lives have suffered with terrible consequences. I used to go to fish shows most weekends and spend a couple of hours a night in the fish house but as my kids grew up and work pressure increased I eased off some of those activities and automated some of the fish house chores. The increase in use of social media has actually made the CSG management much easier in recent years, although as Chairman, Convention Manager and Auctioneer at club events there is still plenty of demand on my time. Thankfully, I have a great committee at the CSG who assist with the running of the club, producing a world-class Journal and the best Catfish Convention in the world (in my biased opinion)!  

Talk us through the filtration in your fish house. 

In recent years I’ve actually reduced the number of tanks in my fish house from 50-odd down to 30-odd, but the volume of water has increased! The consequence is three centralised systems, each filtered through a trickle filter and sump which pumps water back to the tanks within that system. It helps reduce water change time, keeps tanks more balanced and reduces power consumption. The disadvantage is the increased potential for disease to spread through each system, although I’ve also installed UV sterilisers to kill any nasties.

  Scleromystax  CW038.

Scleromystax CW038.

Do you need to alter your water chemistry for the fish you keep? 

I used to test my water weekly. I can’t remember the last time I checked, or even where the nearest thermometer is! I assume from the rainwater changes, copious bogwood and associated brown water, that my fish are swimming in perfect Amazonian conditions!

 Preserved specimens aren’t something you come across in every fish house...

Preserved specimens aren’t something you come across in every fish house...

What’s the deal with the preserved fish on the shelf? 

Actually, it started with the death of the Scleromystax CW042 I mentioned earlier. Being the only known specimen, I thought it my duty to preserve it, in case I met a Corydoradinae scientist who might like to study it. I did actually take a DNA sample for sequencing which has been used to assign the species in the Corydoradinae ‘tree’, so its death wasn’t in total vain! To preserve it I needed to buy some acetone, so a beauty technician friend got me 5 l of nail polish remover (which is basically acetone). Of course I didn’t need that much, but since have preserved interesting specimens using jars from a popular brand of coffee!

What’s currently at the top of your fish literature reading list?

The most thumbed book on my desk is Ingo Seidel’s Back to Nature guide to L-Catfishes. It’s a must-have for any keeper of plecos. 

Are you a lumper or a splitter? 

Catfish present some of the most interesting families of vertebrates on the planet for evolutionary biologists, which means we are lucky to see lots of scientific research and descriptions of our favourite fish. It’s the subtle differences between seemingly similar fish which add an extra dimension to the hobby once you’ve worked out the difference between a Corydoras napoensis and a Corydoras bilineatus.

Corys are a case in point, with research due to split the group into many more genera, based on relatively subtle morphology. I’m all for it!

  Leporacanthicus  L263.

Leporacanthicus L263.

Do you try to replicate seasonality?

Only in so much as it gets a bit colder and darker in my fish house during winter! I should try even harder to trigger some of my fish to spawn, but I don’t have the time, or enough rainwater!

Biggest fishy disaster? 

I had a bad case of white spot through one of my centralised systems a few years ago which wiped out some of my favourite fish and knocked back my breeding efforts by about four years. Since then, I’ve installed UV and rigorously quarantine new fish. Plus I now know how to treat whitespot! 

Best homemade piece of kit you’ve ever made? 

I’m really pleased with my automatic top-up system on my sumps. After drilling the glass, I installed mini cistern-filling devices to each tank linked to a header tank — the same as a ball-cock in a toilet cistern. It has made holidays slightly more bearable!

At a guess, how much do you think your fish house cost?

I only really paid for the construction of the building and insulation materials,
which cost around £6k. After that it was salvaged wood for stands, DIY fibreglassing of walls and ceiling, second hand tanks and DIY plumbing. 

Tell me three bits of essential fish house kit you’d not want to be without. 

Drinks crate – doubles as a stool and a seat; freezer – I keep all my dried foods in the freezer, keeping them fresh, plus all manner of frozen mussels, shrimps, runner beans etc. Radio – tuned into Radio 5 Live so I can listen to the match while doing my water changes!