“Blue line” is one of the few trade names that has been given by the traders themselves. It is not helpful, of course. Reasonable are only names giving locations. All species or forms which have been found and imported by experts have been given names of the locations where they have been found.
“Blue line” is an expression either of helplessness (which bintan-like Paros is not “blue lined”?) or of the intention to conceil the location (For the trade it’s a business: If you found a rich catching ground you are a fool if you speak out loudly where it is). It needed about two years to learn that the most “blue lines” come from Sumatra, in the north of the district Jambi. At that time (about 2005/06) we were far from knowledge how many bintan-like Paros were swimming in Jambi alone. Horst Linke was the first who seriously travelled there in 2008/2009 to find more than seven variants at different places, and some others clearly not bintan themselves).
Another Jambi-based bintan-variant that was given the trade name by the traders themselves is spec. Sentang. They called it “P. sintangensis” camouflaging by this that this form is not yet scientifically determined or – on the contrary – suggesting that one has found a new species by imitating the way science names them (“sintangensis”). Without a scientific description in a scientific journal including ardeous measurement work, preserved “types” stored at an institution (museum) and a clear location no latinized name is valid. So, we call this form rightly P. spec. Sentang as long science has not clarified its relation to bintan and others.
But all this is not the really crucial point with “blue line”. That is: There have been different forms sold bearing that name. It’s hardly possible to decide which was the original “blue line”. I had different fish (some with long whitish ventrals for instance, some with short bluish ventrals, …) at different times, all sold as “blue line”. The clear background is: The trade is not interested in correct names, it is interested in business. In the years from 2005 Sumatra was detected as a big catching ground for Paros. There a newly detected catching ground could not be named openly, and a insignificant name as “blue line” was helpful. And since people normally don’t look very closely at these fish several similar forms were sold bearing the same name. Then another productive catching ground was found in the north of Jambi with fish looking slightly different, not as blue and sparkling as the “blue lines” but a bit greenish and less spectacular. Ans so the trade decided: Let’s sell it as a new species, we call it as new species are named by science: P. sintangensis. That was unjustified, of course, but it helped commerce. At that time (around 2007/08) when we learned which location was meant we corrected the name to spec. Sentang.
Only science is allowed to give latinized names, but the trade should keep hands off naming fish or give the location.
However: the “blue lines” can be wonderful, beautiful fish! Especially those with that long whitish ventrals, but this with the short bluish too. Their colours are sparkling more than that of the spec. Sentang and remind of that of P. harveyi (from Western Malaysia). So, try to get some of them and breed them. In the last years the “blue lines” were sold significantly less than before, replaced by the never-ending spec. Sentang. And mixed with it. So, I hope you will be lucky a receive the original “blue line”, although it is not fully clear what the “original blue line” was 😉