I have notice that the shape and size of the tail on my male botia is different and bigger than on the female botias. It is also apparent with cweg71's fish that he calls " Big Tail". See link http://forums.loaches.com/viewtopic.php?t=4135
Here is an illustration I made to show the difference. These fish are approximately same body size with the exception of the female being stockier and having more girth.
120 gallon planted aquaponic tank with 10 clown loachs, first one since 1994, 1 modesta and 3 striadas.
Yes, the tail size and shape has been linked to possible sexual differences for many years now. My adult males clearly have a bigger tail in relation to those of the females of a similar size. They also appear more deeply forked.