Something fishy is going on in northern Spain. The waters of the port of Gijon are shortly to be invaded – by robots.

Scientists are building a shoal of robot fish to be let loose in the port to check on the quality of the water. Modelled on carp and costing about £20,000 ($29,000) each to make, the fish are to be lifelike in appearance and swimming behaviour so they will not alarm their fellow marine inhabitants.