In this technical field of fish medicine, you really ought to get things very spot on. One of the students queried my labelled diagram of “fork length” and its correct use. Rightly so because they were right!
There are 3 different measurements used for fish. The ‘standard length’ is from the tip of the snout to the end of the last vertebrae. The ‘fork length’ is from the tip of the snout to the distal end of the middle, caudal fin ray. The ‘total length’ is from the tip of the snout to the tip of the tail. ‘Standard length’ tends to be used with most bony fishes, ‘total length’ for eel-type fishes and ‘fork length’ for species where it is difficult to tell where the vertebral column ends. The reason why we do not use ‘total length’ at all times is because the ‘tail length’ can vary dramatically within the same species. Take for example the following species – Siamese fighting fish, guppy and swordtails. Moreover, fin damage can also reduce the apparent ‘total length’ giving the researcher an inconsistent result.
Thus, I’ve uploaded an updated page for my book, Fish Vetting Essentials –
Page 19: Fish Anatomy – FVetEssn_Anatomy.pdf
(This can be added to my being wrong about goldfish having a stomach!)
For the full list of updated pages, see https://thefishvet.com/2013/02/05/fish-vetting-series-updates/
