Hi Bobby. What is Ravas???
Niel and Freddy answered your questions however let me take this a bit further.
There are about 5 different types of Threadfin Salmon, my father in law has borrowed (and not returned) on of my books so I do not have access to that information just now so I am quoting from another. Knowledge is good, so for those of you who are interested:
King Threadfin - Polynemus Sheridani
Blue Threadfin - Eleutheronema Tetradactylum
Seven Fingers Threadfin - Polynemus heptadctylus
Striped Threadfin - Polynemus Plebejus
Giant African Threadfin - Polydactylus quadrifilis
Typically if all these fish were available in India they would all be called "Ravas" by the locals.
I believe we have 3 types available in India that I have seen first hand, may be there are more:
Blue Threadfin - Most commonly caught in India and what everyone have been referring to on this site.
Striped Threadfin - Very Rare, a small fish growing to about a 19 inches only.
Giant Threadfin - That have seen and trying to track down for the last 5 Years, we may not have exactly the same species in India may be slightly different. But they grow to that size as in the picture and larger. Though unlikely, it could very well be the same Blue Salmon growing to these monsterous propotions in Indian waters. Another thing, if memory serves me correctly, the head of these monsters I saw in India were more like the head of the Blue Threadfin Salmon.
There is another Ravas that locals refer to Dhara, but I believe that it may be just the same Blue Threadfin though they tend to be slightly darker in colour (this could come with age), in India it is common to call the larger fish of the same species by another name, good example is the Spanish Mackrel, small ones are called Surmai and large ones are called Towar.
The King Threadfin is a popular sports fish in Northern Australia, Among anglers in Bombay they commonly believed/speculated this fish is/was the Dhara, this is not correct. There is no evidence of this fish in India.
Won't blame you if you fell asleep reading through this..