How to weigh fish!

How to weigh fish!

Paul Arden | Monday, 23 September 2019

Following on from Mika’s page about how to measure fish by length, I thought I would write something about how to measure them by weight. It’s interesting how we are a little bit different in this regards. Certainly when it comes to trout, continental Europeans and strange people from the USA measure fish by length (cm and inches respectively). In the UK, NZ and the rest of the world we tend to go by weight. This is not a new thing by any means; books I’ve read written hundreds of years ago in England had authors measuring fish by weight.

I’ve always been a weight measurer myself too, principally because you can catch trout that have the proportion of eels and others that look like rugby balls. It’s quite possible that 5lb trout and 10lb trout have exactly the same length yet one is a trophy and the other isn’t worth catching!

Small fish - I don’t even bother weighing - not only can I guess them to a relatively high degree of accuracy but also I don’t think it matters. Let’s say you are fishing a reservoir and you catch 8 fish weighing between 1 and 1 1/2 lbs, then you’ve caught eight fish between 1 and 1 1/2 pounds! The distribution between these weights is pretty irrelevant to me and everyone else.

Where is matters, I think, is only the big ones. Is it 6, 10 or 25lbs? And for that knowledge, while I’m pretty good at guessing, I really need a net and a set of balances to be certain. Like you, I’ve seen many photos of fish that are claimed to be much heavier than they really are. We are all optimists - that goes with fly fishing territory! But for myself, I really want to know the true weight instead of what I would like it to have been.

So electronic weighing scales or “balances”, like the tape measure, really are essential. I used to use a McLean Weighnet, but the problem with this otherwise great invention, is that it has a wide variation for error. You can test this for yourself: weigh the same fish several times and you can get widely different results. I also don’t like the standard tail-splitting mesh, that can and really must be changed.

Nowadays I use electronic luggage scales and a very large net for the enormous fish that I catch and release. Once landed, I keep the fish in the net, submerged in the water, where the net acts as a cage, until I’m ready to weigh. Then I weigh the fish and the net together, release the fish and finally weigh the net (because I can never remember what it is even thought it’s all always 1KG). and subtract that from the first measurement in order to establish the true, genuine, weight of the fish.

You might think to yourself, “what is the point, Paul?” And you’re right. But for me, I find it interesting; I used to use the numbers in NZ to compare rivers to previous seasons. Here in the jungle in Malaysia I’m still trying to find out how big these fish actually grow! I’m getting better at guessing and I always try to guess the weight first, but it takes thousands of fish to become reasonably accurate. I doubt I’ve seen a thousand Snakehead to my boats yet - getting there but still a long way from “thousands”.

Incidentally, if you are weighing fish, make the out-of-the-water part for them very fast - no more than a couple of seconds max. Make sure that the net has soft knotless close-knit mesh. Make sure that the net is wet before landing your fish - trout in particular are very susceptible to being out the water. I always try to unhook them in the water and I never lift them into the boat to unhook. The net should be large enough that it can act as a cage once the fish is netted. The welfare of the fish must always come first. Without them, fishing is kind of pointless - I’m sure you’ll agree! If you ever need any advice on this matter then please please ask. This is perhaps the most important skill that you and I will ever need and use.


Now, we have a few big things happening at the moment. We are starting the flyline measuring database; weighing flylines to find out their true AFFTA rating and not the one printed on the box.

Flavio is over in Malaysia for three weeks of fishing. One in the jungle and two on the lake. Flavio always catches his fish on the first cast.

I have some videos to finish and upload. I’ve been flat out recently but hope to catch up fully this week. Also, now that I have some more time again, I’ll get this year’s Sexyloops HT competition fully buzzing. Ooh ooh ooh maybe I can win a new 10WT Hot Torpedo?  I sure need one, since Piffen sold my last one to the gypsies.

I’ll be back on the lake by the time you read this and probably will have had a big fish in the boat. Yay!!!

Cheers, Paul