Chilwa is a minnow. Any small fish is called a chilwa. The trick it to find the ones that will be readily taken by predators. From what I have seen the ones with no spines and that are fleshy work better. The most common one is a Putiya or Tinfoil barb, easily identified by the dot near its tail.
Indian Gypsy help! You know most of them by name.
There are numerous species of bait fish found in the sub continent; the most commonly used are:
1) Rosy Barb (Puntius conchonius): Local names are Putthiya (Punjab, Haryana, Himachal, Uttranchal), Poothee in UP, MP and Bihar. It can be found just about everywhere in India from small roadside ditches to major rivers. Not common in the mountains though. Prefers slow moving water.
2) Gaint Danio (Devario aequipinnatus): Like the rosy barb, found just about everywhere. Larger in size than the barb. Only problem is it does not survive too long on hooks. Known as Kheengar and Dana in the North.
3) Chilwa (Aspidoparia morar ): Found in just about all hill streams. By far the best bait to use. Will not die that easly on the hook, but mis handling the bait will easily kill it. Readily taken by just about every carnivore in the water. Best way to tell if you have a chilwa in your hands is by the copius amounts of its silvery scales that easily rub off. In waters where the chilwa works well, one should also try the silver toby. When you put them side by side, you'll understand why.
4) Fresh Water Goby: There are over 2300 species of the Goby, but there is only one that is found in fresh water in the subcontinent. Have not been able to figure out the latin name so far (have not come across a latin speaking goby). Known as Chunkad in the North. Best when used around rocks. Has a tendency to keep sitting motionless on the bottom. Twitch the line with your finger every now and then like you would when using earth worms.
5) Himalayan Loach (Botia almorhae): Sold as the Yo Yo loach in the Aquarium trade, these little critters (more like critters than fish) also make awesome bait. Found at the bottom of just about all streams and nalas. Has a tendency to hide in nooks and crannies. Use in the same manner as the goby.
6) Baby Snake Heads: Any baby snakehead max 4 inches in size makes a brilliant bait no matter on what kind of water you are. Know as Solley/ Dolu in the north. Can be found everywhere. Best way to get them: give a village kid 10 bucks and some candy. They keep very well in a 'ghada' earthen pot for storing water, and can survives for months in captivity. Very tough bait. Big winner when it comes to being taken by Sol, mulley and mahseer.
The above are my favs. There are many more like the glass fish, dwarf gourami etc., but they make lousy bait. Furthermore, if nothing seems to be biting, just fry the bait. All except the goby and the loaches are brilliant when curried. Anchovies anyone?