Friday, 27 January 2012

Roach Length/Weight Curve - A New Record is out There, Somewhere...

In the last post I made a video of a roach trip to a local stream where a fish was banked, that on capture and before weighing, I really thought would make at least a pound and four ounces, if not slightly more. I thought it would be the largest roach I had ever caught from the river but the scales gave only a pound and one ounce, which was much less than I would have thought.  Luckily, I measured the fish and took a reading of 12 inches from fork in tail to snout...

The day before the trip I'd just re-read a chapter of an old book, Faddist's 'Roach Angling', 1949 edition. Faddist had included a table of roach weights against their length which held my attention and so that evening I went to work creating a length/weight curve from the data. I finished the curve off with Ray Clarke's once record roach of four-pounds three-ounces because we have exact measurements on record for that stupendous fish (17.5 inches) and found that the curve, from fry to record, was accurate all the way, excepting the small fish under a pound and down to just a few ounces where the curve just could not be made to work for some reason, all the fish in that range exceeding the mean in terms of length. 

The curve is logarithmic and is a perfect one generated by computer. It can't be tweaked to create a hump in the lower weight range because then the rest of the curve in the higher, and more reliable ranges beyond a pound, will either duck or soar, and that can't happen. Therefore, I concluded that the weights below a pound are probably unreliable due to the fish being weighed on unreliable scales, but not measured with unreliable rulers, because weighing is far more prone to error than measuring ever is. The alternative is that the figures are indeed accurate and that a growth curve for roach must be an imperfect one with a sharp rise in the lower parts followed by a smooth curve thereafter when the fish begin to assume their adult form. Whatever the truth is, the perfect curve in the graph below (click for a closer look) shows a useful mean average against which to plot the actual truth of the matter ~

I then went to work measuring a few of my own captures by creating rulers in photoshop from objects included in mat shots of fish, the brass scales I use for instance -- the tube that contains the spring including the knurled zeroing knob on top being exactly seven inches in length. The resulting figures were plotted on the graph also. Of course photographs are unreliable because of lens distortion and the fact that a picture taken from an angle even slightly lower than directly above will tend to shrink the object placed above, or enlarge those placed below, so I only used pictures that were perfectly square to gain measurements from.

The results once plotted on the graph are interesting because the variations are quite remarkable. The most violent disruption of the norm is with a fish I caught suffering from an infestation of the tapeworm, Ligula intestinalis, a worm that can grow to more than the total weight of the fishes own flesh. This fish was found to be the length of an average fish of just one-pound three-ounces but had ten ounces of tapeworm in its poor unfortunate gut taking the combined weight of host and parasite to an astounding one-pound thirteen-ounces.

Roach with Ligula intestinalis infestation. The dislodged scales are a recognised symptom of infestation, the fish bloating beyond the capacity of its own skin and the scales loosening. The scales have actually grown as the fish has grown, and they are enlarged greatly compared to normal scales, but now the disease is advanced they cannot grow further. The last stage in the parasitic cycle is infection of the skin, rupture and death. The corpse is eaten by birds, the worm passing into the bird's gut, laying eggs and these excreted back into water to take up host inside more fish.  

The fish caught in the stream also turned out to be something of an irregular, it being the length of a one-pound four-ounce fish but turning in three-ounces under the mean average for its 12 inch length. No wonder I was confused on the bank as the fish had all the appearance of a larger fish flank on, but little of the girth of one, and that's a measurement that I didn't take. It also has a discontinuity in its lateral line, something I have never seen before in a roach, though that probably has nothing to do with things...

Long and lean

Out of interest, the next green dot along the scale is one for a fish caught from the same stream at 11.5 inches, but here's one that exceeds the average the other way, being far shorter than it should be for its one-pound three-ounce weight, but it is an exceedingly fat fish in the picture I have of it.

Girth is clearly important when it comes to catching big fish! Or is it...?

I mean to carry on with this, measuring more fish on the bank and especially in the lower ranges just  to clarify the situation there. I also intend to create sub curves for still water, river and canal records because I am sure that these would show the potential of those fisheries in terms of expected growth rates, curves that end up at or above Ray Clarke's record being the fisheries that might well produce a very big fish, and those below, those that never could.

Ray Clarkes record roach. Two and a half times the length of my brass scales...

Whilst on the subject of records, the graph also shows quite clearly that the growth potential for roach is not exhausted at Clarke's record because the curve continues smoothly upwards, another half inch of growth yeilding an extra half pound or more!

However, the German record for roach is an incredible fish of just under five pounds eight ounces. From the Rhine, I believe...

Monster roach. The German record at just under 5lb 8 ounces

Is it really that big?  Well, it's certainly a very big roach indeed, and if it's really the weight stated then it would be well off my scale but only an inch longer than Clarke's fish, coming in at around 18.5 inches. However, the stated size of the boilies used is 14mm, so from that I worked out that the fish is actually between 19 and 20 inches in length. Get out a tape measure and see for yourself just how enormous a roach that is!

The Germans obviously have a better growth curve (red line in graph above) than us because plotted on the graph, its length for weight ratio would take the curve well above the British one at all weights, 'long and lean', in the end producing a far greater maximum potential weight than 'short and fat'. And this fish doesn't look that old, but Clarke's fish certainly was! Just how big can they go over there? Six pounds? More? Not only do they make better and faster cars than us, but faster growing and better roach too, it seems...

Not exactly Cricket though -- four rods, three strawberry boilies and caught by accident ! Purists would sniff, but I might book a holiday...

Vorpsrung Durch Technik!

PS. The roach that started me thinking about all this is the only one that intersects the German curve. Its great, great grandparents must have fallen out of a Luftwaffe plane back in 1940... Perhaps I should go back, catch it and rear little monsters from it? Obviously good brood stock, that fish...


  1. Brilliant post Jeff.
    One of my targets for 2012 is a 2lb roach - i have a few local waters which can produce the goods.
    I was thinking of measuring and weighing each fish - I definately will be now after reading this.

  2. Steve in Colorado28 January 2012 at 03:30

    Huge Hun roach?! Dr. Mengele has the last laugh... ;)

  3. Great article. I will be printing the curve off, laminating it and using it at the my fishery/angling lake :)

  4. That's great, glad you find it that useful and interesting that customers might want to see it at your fishery! Which fishery is this by the way?