[1] This species is a small notothen with lemon yellow caudal, pectoral and pelvic fins.

All fins are lighter at the tips and the body is generally colored gray, with the snout and the top of the head being darker.

[1] This species is very similar to congener Patagonotothen brevicauda, however, it has more gill rakers (26 to 39 in total compared to 22 to 27 in total) and the difference between the number of pectoral fin rays (23-26 compared to 22–25, with a mean of 24.8 for P. guntheri and a mean of 23.0 for P. brevicauda) can also be used to distinguish between the two species.

[1] This species is a benthopelagic predator which mainly feeds on krill (comprising 89% of total prey mass), but also takes amphipods.

[2][1] This species was once very important to commercial fisheries, with 12, 000 tonnes (13, 228 tons) being landed in 1979 from the Shag Rocks alone.