In afternoon trade, the $S&P/ASX 200 (.XJO.AU)$ is on course to record a decline. At the time of writing, the benchmark index is down 0.6% to 7,965.9 points.

Four ASX shares that are not letting that hold them back today are listed below. Here's why they are rising:

$ARB Corp Ltd (ARB.AU)$

The ARB share price is up 6% to $42.21. This follows news that the 4×4 automotive parts manufacturer is increasing its presence in the United States. According to the release, its US based associate, ORW USA, has announced a conditional agreement to acquire the US-based 4 Wheel Parts business from Hoonigan for US$30 million. 4 Wheel Parts owns 42 retail stores and associated online stores. Should the acquisition proceed, ORW USA will settle the purchase using additional funding provided by its shareholders. This will see ARB increase its shareholding in ORW from 30% to 50%. ARB will separately acquire the Poison Spyder brand from Hoonigan for US$1 million.

$Guzman y Gomez Ltd (GYG.AU)$

The Guzman Y Gomez share price is up 5% to $40.40. This has been driven by news that the quick service restaurant operator will be added to the ASX 200 index at the next quarterly rebalance. The company's shares are one of three that will join the benchmark index on 23 September. This is good news for two reasons. One is that its inclusion in a major index means that index funds have to buy shares to reflect the change. The second is that fund managers with strict investment mandates may now be free to invest in Guzman Y Gomez should they want to.

$Opthea Ltd (OPT.AU)$

The Opthea share price is up 8.5% to 58 cents. This biopharmaceutical company's shares will be added to the ASX 300 index at the next rebalance later this month. This may have given its shares a boost today. In addition, the release of a corporate presentation may have caught the eye of investors. Opthea estimates that it has a $15 billion market opportunity for the VEGF-A Inhibitor it is developing.

$Yancoal Australia Ltd (YAL.AU)$

The Yancoal share price is up 4% to $5.50. This is another share rising thanks to its inclusion in the ASX 200 index at the quarterly rebalance. The coal miner's CEO, David Moult, was pleased with the news. He said: "We see the Company's inclusion in the S&P ASX indices providing a further opportunity to expand our investor base and bolster the trading liquidity of our shares."