Observations of Chaceon affinis, from the French deep submersible Nautile, were made at the Menez Gwen hydrothermal vent site (Mid-Atlantic Ridge, 37°50′N) in June 1994. This was the first time that specimens of this species were seen in the inner periphery of an active vent field. Almost all specimens were observed very near mytilid mussel beds, and on one occasion a crab was seen eating the remains of one of these vent mussels. In addition, baited fish traps were deployed in the close vicinity of the active vent field for periods of 24 h. The yield of these catches was much higher than the one obtained at a similar depth in a place without any influence of an active vent field. It is suggested that the population of C. affinis living in the vicinity of this vent field can profit from the amount of biomass available inside it.