After a couple of disappointing days for investors, the S&P/ASX 200 (Index: ^AXJO) (ASX:XJO) has managed to eke out a small gain today, rising 0.13% to 5,214 points.

The financial and healthcare sectors have been the biggest contributors to today’s gains, with the energy and materials sectors lagging behind.

Four shares that have delivered solid share price gains today, include:

Platinum Asset Management Limited (ASX: PTM)

Shares of the fund manager have rocketed more than 12% higher today after it announced its intention to commence an on-market share buy-back for up to 10% of its shares. Platinum’s share price has been under serious pressure over the past few weeks and this move is perhaps an attempt to flush out the short sellers that have been targeting the stock recently. The company noted that no target price has been set for the buy-back and it will only buy back shares if the they trade at a significant discount to their underlying value.

BigAir Group Limited (ASX: BGL)

BigAir shares have surged more than 23% today after announcing it would be merging with fellow junior tech company, Superloop Ltd (ASX: SLC). Investors are being offered two options for their shares, both of which offer a significant premium to yesterday’s closing price of 84 cents. The merger is expected to deliver $4 million in savings each year and is being marketed as an opportunity for the combined entity to “become a leading independent provider of connectivity services across the Asia Pacific region”.

Nearmap Ltd (ASX: NEA)

Shares of Nearmap have climbed around 4% today on the news that boutique fund manager, Paradice Investment Management, has become a substantial holder in the company. The fund manager has taken a 5% stake in the aerial imaging company and this will no doubt be seen by some investors as a vote of confidence in Nearmap’s growth strategy, particularly into the lucrative US market. Although the shares have been volatile over the past 12 months, they have still managed to gain more than 12% during that time.

Medibank Private Ltd (ASX: MPL)

Shares of Medibank Private have risen by 2.2% today after the private health insurer announced a number of key changes to its executive management team. Most significantly, the current Chief Financial Officer (CFO) will be leaving the company after serving for four years and a new position of chief customer officer will be created in an effort to improve customer outcomes and reduce policyholder churn. This has been a major issue for Medibank over the past 12 months and has been one of the biggest reasons the shares have slumped more than 15% since the release of its full year results last August.

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Motley Fool contributor Christopher Georges owns shares of Platinum Investment Management Limited. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.