Investors shouldn't believe in market rumors or invest speculatively with regards to trading shares of special-treatment listed firms, the bourse said in a notice to investors amid its on-going education campaign.

Special treatment companies, or ST counters, refer to those that have lost money for two straight years and face the risk of being de-listed if they can't turn around in the following year.

Share prices of these poor-quality firms can rise or fall by five percent each session, compared with a 10 percent daily band for normal mainland-listed firms. Rumors over shareholding restructuring in ST firms often make them target of speculative trading.

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"A majority of ST firms can't avoid being de-listed although some can survive through revamps," the notice said. "We advised investors to focus on corporate fundamentals rather than on market talk."

Yuan-backed equities on China's mainland, which have nearly tripled in value since early 2006, have seesawed in recent months with wider volatility daily amid worries of overheating and possible regulatory moves to cool the market.

The fluctuations have prompted the stock regulator and two exchanges in China - the other being the Shanghai bourse - to launch nationwide programs to educate investors against investment risks as the authorities are jittery that a sudden tumble in shares may spark social unrest as people lose their savings.

The Shanghai Stock Exchange late last month ordered ST firms to issue fortnightly statements to detail whether they have price-sensitive information to unveil as it tries to curb speculation.

Yesterday's notice by the Shenzhen bourse also suggested people pay close attention to whether a listed company's profit growth is sustainable rather than just to its rosy financial figures.

If a firm is in a fiercely competitive industry, the room for prices of its products to rise is limited with increases in raw-material costs and with higher capacity among the firms in that industry, the notice cautioned.

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