Producing some of the finest coarse fish for the waters that need it most, the National Coarse Fish Rearing Unit at Calverton, Nottinghamshire is a fascinating place to see our favourite fish species produced in their tens of thousands. Dom Garnett presents a revealing look at the pioneering work of the centre.

It’s a curious fact that while anglers spend countless hours trying to catch fish, we give little thought to how these creatures develop and grow, let alone how stocks are artificially reared. Even as a proper angling geek, I must admit that my knowledge is limited in this respect and so it is with 101 questions that I arrive at Calverton on an autumn afternoon.

The first impression you get is how busy the site is, with holding tanks, tunnels and pools galore, not to mention our team of experts. Over a cup of tea in the staff room, I’m introduced to the gang who make it all happen, while an aquarium of crucians and tench gape at us in the corner. Along with biscuits there are also, tellingly, containers of boilies as the talk ranges from current flood warnings to favourite barbel baits!

With hundreds of thousands of precious fish on site, it’s a necessity that team members live either on site or very close. After all, a sudden change in conditions or emergency could require all hands on deck within the hour! It’s no surprise that they’re a tight-knit bunch who are passionate about what they do and keen to show me the good use they make of Environment Agency rod licence funds.

Behind the scenes

With the bewildering array of equipment and holding areas, I’m already intrigued to see what goes on. Autumn is an exciting time of year, as fish of 18 months are sorted and carefully harvested to be sent off to fisheries around the country. With nine species grown at the farm (including crucians and barbel), it is a crucial and hectic time of year.

First, however, come bio security measures. Impressively, they have clean waterproof boots to fit my size 14 feet, along with sterile fishery wear. Nobody is exempt; and hilariously, the General, my six-inch specimen angling prop is also obliged to take a dip to make sure he carries no nasties. It might seem extreme, but any breech could result in disaster and the whole site having to be decontaminated and every stock fish terminated!

Fish farming has been called “the most risky business in the world” and so it’s perhaps no surprise there is high level security and monitoring. Parts of the complex are like a Bond villain’s base, with cameras and emergency alarms poised to alert staff at a moment’s notice should an intruder arrive or oxygen levels drop.

Looking at some of the fish now ready for transit, they are beautifully fit looking and I’m already wondering just how they reach this condition. “We use a wide gene pool for brood fish- and as you’ll see, we condition them carefully” says Technical Officer Richard Pitman. “If you simply raised fish in a concrete tank they would struggle to adjust, so our aim is to make them only one step away from wild fish.”

Close to nature…

The stock ponds at Calverton are an interesting exercise in trying to replicate natural conditions found in the wild. Far from being sterile, the stock pools have proper vegetation growing around them. If you removed features like the feeders and canopies, in fact, they would resemble a pleasant corner of your local fishery!

Flow is another feature that is key to every stock pond, especially with river species such as barbel, chub and dace.
“ The fish have to be fit for purpose and used to flow” says Richard. “They wouldn’t survive in a river otherwise, so we want them to be strong.” The proof can be seen when they are released into the wild. Young Barbel speed off strongly into river currents where EA staff find it hard to keep their footing!

Other details are also critical, from feeding to getting the fish used to a natural environment. The various ponds are prepared carefully with conditions that promote natural food such as daphnia and midge larvae. This is crucial as it gives the fish a taste for natural food, not just artificial pellets. Nor are natural “guests” discouraged- and in fact the local herons and kingfishers are very useful for getting the fish alert to the reality of predators and teaching them to take cover.

Another interesting aspect is the balance of species in each pool. While I half expect species to be kept separate, this isn’t the way to get the best from them. In fact, with fish occupying different niches- preferring different food and levels in the water- the best results come from mixing. So while they are raised with their own kind during their first summer at the farm, after a year they will be mixed into pools of up to six species. This is called “Polyculture” and the coexistence and competition boost growth much more effectively!

To make matters more complicated, spawning times of coarse fish vary quite a lot; so with dace and grayling doing this as early as February and tench anything up to late June, the breeding times are anything but uniform between species.  Nor are they all equally easy to raise. Of the 500,000 fish that are produced by the Calverton team every year, roach are the most prolific, while tench are perhaps the trickiest to get up to a reasonable size due to their slow early growth rates.

All very impressive, but the part of the puzzle that still baffles me are the sheep wandering round the complex. I thought this was a fish farm, so what are Dolly and her mates doing here? The answer is simple: “obviously electric lawnmowers and other tools are not a great idea with so much water around, so the sheep do a grand job of keeping everything in check. They are our living lawnmowers and verge trimmers!”

A treasury of coarse fish

With literally hundreds of thousands of fish passing through Calverton each year, the guys on site have an incredible knowledge of coarse fish and the character of each species. Some are easier than others to rear and keep, it must be said.  I wonder which are the most challenging? Dan Clarke, another of the site’s expert Technical Officers has some interesting revelations.

Chub are the greatest escape artists, it seems. “They are adept at jumping through any gap, even finding gaps in the mesh- and we’ve had to scoop them up off dry land and send them back to the pools lots of times!”.

As for the most aggressive and greedy, tench and barbel take the prize. You wouldn’t believe what they get up to, in fact! “We’ve had tench suck the heads off smaller fish!” Dan says. The barbel can be guilty of GBH too, if you’re not careful, and have sucked parts off other fish!

Another curious aspect from the angler’s point of view is that not all fish are created equal. A small number from every batch will be much darker or lighter than their shoal mates. Meanwhile, one in every few hundred will show dramatically higher growth rates than its brothers and sisters; these will be tomorrow’s specimen fish and record breakers.

Deliveroo for fish!

Back at the holding tanks, it’s time to sort out today’s deliveries of fish, and so we watch the staff counting and sorting fish by the hundreds. It’s a quickfire process with fish being checked through computerised counters before sliding into containers by the dozen.

There’s enough time for me to be a nuisance, too, though, as I cannot resist a closer look at some of the fish. The skimmers and roach are as perfect as you’ll ever see, shimmering with health. The barbel are great to see, too, with a more speckled coloration than bigger fish, presumably to help the youngsters blend in and grow larger.

It’s the crucians that get the prize for me, however. With this classic species disappearing around the country, Calverton has been a vital part of the National Crucian Conservation Project. What fish they are too! At just two summers growth, they are already half pound plus, thick in the shoulder and glowing with health.

Pretty much all the fish have had two growing seasons when they move on. This is for the simple reason that it’s the ideal size for them to go and find a new home. They are big and strong enough to give them a chance to survive, but young enough to adjust, grow on and, critically, have young of their own.

Where next?

Once sorted for transit, our fishy cargo will proceed into specially adapted vehicles with storage tanks on board. First, however, I am intrigued to see a little trio of potions that will be added to the water. The first is Vidalife- described as a “liquid sticking plaster for fish” this stuff will help mitigate any bumps and scratches during transit and keep the fish in top condition. Virkon-Aquatic comes next, an agent that will protect the stock from bacteria and viruses, because we don’t want to take any chances.

Last but not least, we also have Pro-Tex, which is made from Prickly Pear extract, among other things. Aside from healing properties, this stuff alleviates stress in animals. In other fields, it has been used to keep racehorses calm. Bizarrely, it is also been sold as a hangover cure in Australia!

Where the fish end up next is always a carefully judged decision. Top priority are rivers and fisheries that could use a helping hand; such as a waterway in recovery after pollution, or a venue where it is hoped that habitat improvements will allow fish a chance to bounce back.

All in all, it is a huge and impressive operation that every angler should be proud to support via their rod licence money. Daft social media comments aside, the team can testify the value of what they do here, too. Indeed, over the past 35 years, rivers and stillwater across the country have received a welcome shot in the arm from Calverton. Whether it’s the revival of barbel and chub on the River Rother, or genuine crucian carp across dozens of club lakes, these young fish are quite literally tomorrow’s net fillers and the very future of fishing in England.

It only remains for me to thank the team and return to my corner of Devon. It has been a fascinating visit; I’m not sure I’ll ever look at a roach or crucian quite the same way ever again.