Canada's main stock index fell on Monday, touching a six-week low as energy and other resource shares tumbled alongside commodity prices.

The Toronto Stock Exchange's S&P/TSX composite index ended down 144.5 points, or 0.89 per cent, at 16,094.72.

The index hit a session low of 16,090.66, its weakest intra-day level since Dec. 15. All but one of the index's 10 main sectors were in negative territory.

The energy group retreated 1.8 per cent as U.S. crude prices settled down 58 cents at US$65.56 a barrel, driven lower by a stronger U.S. dollar and rising crude output.

Enbridge Inc (ENB.TO) was the biggest drag on the index, down 1.5 per cent at $46.35, followed by Suncor Energy (SU.TO), which declined 1.5 per cent to $45.53.

The firmer greenback also weighed on gold prices, sending gold producers in Toronto down 3 per cent. Barrick Gold (ABX.TO) fell 2.9 per cent to $17.68.

Cannabis company Aphria Inc (APH.TO) fell 5.8 per cent to $18.99 after it said it would buy rival Nuuvera Inc (NUU.V) for $826 million. Nuuvera jumped 10.4 per cent to $7.73.

Shares of cannabis companies generally came under pressure following last week's deal between Aurora Cannabis Inc (ACB.TO) and CanniMed Therapeutics Inc (CMED.TO), which would create the world's top marijuana producer by market value. Canopy Growth (WEED.TO) was down 5.7 per cent at $33.10

The TSX posted nine 52-week highs and three new lows. Across all Canadian issues, there were 73 new 52-week highs and 43 new lows.

Among the most active Canadian stocks by volume, Bombardier (BBDb.TO) was up 1.7 per cent at $3.60 after a U.S. trade commission on Friday backed the Canadian plane maker in a trade dispute with Boeing (BA.N).

Volume on the TSX index was 200.16 million shares.