Executive chairman Peter George shelled out £470,000 to buy 1mln shares at a price of 47p apiece.
He completed the purchase on Friday, Benchmark said in a statement on Monday, his first stake in the company.
Yngve Myhre, the Norwegian aquaculture veteran who is a non-executive director of the company, also snapped up £135,240 worth of shares.
He scooped up 225,000 shares at 44.44p and another 75,000 at 46p, to take his total holding to 400,000 shares, or 0.07 of the company’s total share capital.
Last week Benchmark said it was accelerating a programme of disposals and structural efficiencies after discussions with third parties about licensing its non-core animal vaccines were subject to delays.