Alexander Adriaenssen (also spelt Adriansen; 1587–1661) was a Flemish Baroque still-life painter, particularly known for his renderings of fish.
Adriaenssen was born in Antwerp, the son of the musician Emmanuel Adriaenssen and Sibilla Crelin and the older brother of the painter Vincent Adriaenssen. He was baptised on 17 January 1587. In 1597 he was registered as the pupil of Artus van Laeck. In 1610 he became a master of the Guild of St. Luke. He paid his dues each year until 1633. He was buried on 30 October 1661 in St. James' Church, Antwerp. Works by him survive with dates from 1623 to 1661, but the peak of his career was approximately 1630–1650. The signature "A. Neck" on one oil painting is probably a badly preserved instance of Adriaenssen's.
According to Arnold Houbraken, who devoted only one line of text to him, Adriaenssen "painted still lifes, fruit, fish, etc." He was influenced in his still-life motifs by Frans Snyders, including for instance "artichokes, poultry, and live cats". He also produced pronkstillevens (ostentatious still lifes) with expensive glasses and dishware. The subgenre of pronkstillevens was developed in Antwerp during the 1640s. However, he is known particularly for his renderings of raw fish, a common topic of Dutch still-life painters which he portrayed in more than 60 works, more than any other artist in 17th-century Antwerp. Many of his fish still lifes were relatively small and inexpensive works.
Stylistically, he was influenced by the school of Haarlem. His compositions are characterised by an asymmetrical diagonal layout—a triangle standing on end flanked by ellipses—with objects overlapping over multiple planes for greater depth. He uses a "sober" palette, "tending to monochrome"; he has also been described as important for the "purity of his colour".