As for the so-called bottom-fishing, we just need to follow the main force!
Generally speaking, at the end of a downward trend, if the "volume starts to increase significantly", you can follow the position, and the probability of reversal is very high.
Because in a general downward trend, the volume is very large, and short positions are closed, so naturally you have to open long positions to close them.
As for how to tell whether the downward trend is at the end, you just need to look at the length, and the length depends on your own feeling!
Be cautious when bottom-fishing, and bring stop loss and risk control!