WINDERMERE, Fla. ( Stockpickr) -- Professional traders running mutual funds and hedge funds don't just look at a stock's price moves; they also track big changes in volume activity. Often when above-average volume moves into an equity, it precedes a large spike in volatility.>>Outwit the S&P in 2013 With 5 Hated Stocks Major moves in volume can signal unusual activity, such as insider buying or selling -- or buying or selling by "superinvestors." Unusual volume can also be a major signal that hedge funds and momentum traders are piling into a stock ahead of a catalyst. These types of traders like to get in well before a large spike, so it's always a smart move to monitor unusual volume. That said, remember to combine trend and price action with unusual volume. Put them all together to help you decipher the next big trend for any stock. >>5 "Magic Formula" Stocks for 2013 With that in mind, let's take a look at several stocks rising on unusual volume today. Tronox ( TROX) This company is a producer and marketer of titanium dioxide pigment, which is an inorganic white pigment used in paint, coatings, plastics, paper and many other everyday products. This stock is trading up 8.6% at $17.13 in recent trading. Today's Volume: 3.25 million Average Volume: 1.63 million Volume % Change: 259% From a technical perspective, TROX is gapping higher here right above some near-term support at $15 with heavy upside volume. This move has pushed TROX into breakout territory, since the stock has pushed above some near-term overhead resistance at $16.64. Traders should now look for long-biased trades in TROX as long as it's trending above $16.64 with strong upside volume flows. I would consider any upside volume day that registers near or above 1.63 million shares as bullish. If TROX can maintain that trend, then this stock has a great chance of re-testing or taking out its next major overhead resistance levels at its 50-day of $18.58 to $19. Repros Therapeutics ( RPRX) This is a development stage biopharmaceutical company focused on the development of oral small molecule drugs for major unmet medical needs in male and female health. This stock is trading up 5.5% at $14.54 in recent trading.