Silly fish measuring question

[Guppysnail]

As a kid I learned to measure fish when we went fishing. Tip of lip to end of tail fin. 
I recently was looking at fish ads from sellers selling lemon blue eyed plecos to get an idea of what my pleco kids should be selling for rather than me trying to adopt them out. 
Shortfin ones from all sellers were listed as max adult size 4-5 inches and the longfin 4-5 inches also.  Well there is a good 1-2 in difference in size if the tail fin is included. 
Are these sellers just copy and pasting the ad for both types or have I been measuring hobby fish wrong?

Edited November 30, 2022 by Guppysnail

[Janoš Bećar Pecaroš]

I think that the hobby fish are measured without the tail, but take this with a grain of salt.

[TOtrees]

The question isn’t how to measure fish, the question is what method the seller is using to measure their fish. There are different methods, depending on whether you are farming or hunting or researching fish. 

source: http://www.fsl.orst.edu/geowater/FX3/help/9_Fish_Performance/Measures_of_Fish_Length.htm

[Guppysnail]

On 11/30/2022 at 8:32 AM, TOtrees said:

The question isn’t how to measure fish, the question is what method the seller is using to measure their fish. There are different methods, depending on whether you are farming or hunting or researching fish. 

source: http://www.fsl.orst.edu/geowater/FX3/help/9_Fish_Performance/Measures_of_Fish_Length.htm

This was very helpful. It explains why fish are listed different approximate sizes on different sites. Do you know which is most commonly used by hobby fish sellers or fish clubs? 

[TOtrees]

On 11/30/2022 at 8:34 AM, Guppysnail said:

Do you know which is most commonly used by hobby fish sellers or fish clubs? 

Can’t answer that precisely, but I suspect most people do what I usually do, which is describe the length from tip to tip. It just seems to make more sense. It’s not like I’m trying to follow this rule or that rule or whatever, it’s just that in the absence of defining which method of measuring you’re using, tip to tip seems to be the most descriptive and logical.

[Janoš Bećar Pecaroš]

In my experience with the local fish stores they all messer without the tail. But this is how local to me shops do. Also any literature I found on how many fish to put in an aquarium, talks about the length of fish without the tail. Like one inch of fish without the tail per gallon of water.

I wonder what coop does when it comes to this?

[Pepere]

Measuring standard length gives a better indication of bioload than tip to tip.

[lefty o]

body length is most common in the hobby. now if you were out fishing and caught something you would measure from tip of nose to tip of tail as its longer and therefore sounds more impressive, and thats before adding 30% to its actual size 🤪.

[Odd Duck]

You may find abbreviations of SL for standard length, and TL for total length (tip to tip).  Back when I began fish keeping, SL was, well, standard.  But I’ve noticed over the years that TL is becoming more common.  If in doubt when ordering, ask the seller if the result will make a difference on whether or not you order from them.

[nabokovfan87]

I definitely only use total length. Very weird but I understand why SL exists (long fin species make things weird)

[Biotope Biologist]

We in the biology field almost exclusively use Fork Length. Total length  for sharks. And standard/ventral length for rays and skates as some species can have 4 foot tails.

 

Reason being is some species of fish have modified caudal fins ie: swordtails that would make it very inaccurate to measure total length.
 

Also interesting tidbit is the sport fisheries use total length for legal lengths but we still use fork length for data purposes. Also depending on if the caudal fin is stretched or squished you can squeeze a few centimeters out of it. Saw it all the time with people trying to convince fishery enforcement that “it was bigger when they caught it.”

Edited December 1, 2022 by Biotope Biologist