Just came across this old post that i had missed.
Yes there should be a limit to the number of fish that any self respecting angler should take for the pot. Of course trying to monitor this on a river is out of the question.
On the other hand how many fish a day does one need for the pot ? I guess that would depend a lot on the number of people in camp (if you are camping independently). Taking fish home is where there needs to be some rules laid down.
On the subject of murral the amount of baby mahseer they will get to eat in a river is debateable.
However in a lake with significant numbers of murral, the odds could be stacked in favour of the murral.
They both prefer very different habitat, and that usually keeps them apart when they are bigger. However the mahseer fingerlings live in slower waters till they can fend for themselves, and that's where the depletion of mahseer fingerlings by the larger murral begin, and that's where i have an issue in stocking rivers and lakes designated for mahseer protection with murral.