A prison staff member at HMP Nottingham has been arrested and seven others suspended after a police investigation was launched.
A 28-year-old man was arrested by Nottinghamshire Police on suspicion of conspiracy to cause actual bodily harm and has since been bailed.
The jail, in the Sherwood area of the city, is a men's Category B prison with a capacity for 1,060 inmates.
In a statement the force said: "Nottinghamshire Police have arrested a member of prison staff from HMP Nottingham.
"The 28-year-old man was arrested on suspicion of conspiracy to cause actual bodily harm and has been bailed pending further inquiries.
"A further seven members of staff have been suspended from duty while an investigation is carried out."
The most recent report by the prison's independent monitoring board identified problems with staff levels, psychoactive substances which were having "a destabilising effect", and levels of violence and number of serious assaults on prisoners and staff.
Monitors, in its most recent annual report, further concluded that the prison's discrimination incident logging system had not been used for eight months, up until November last year, indicating "the prison's priorities were elsewhere".
The report also stated: "The board receives relatively few complaints from prisoners of unfair treatment relating to ethnicity."
In the 12-month period covered by the report to February 2016, there were 205 assaults on staff, 284 prisoner-on-prisoner incidents, with 31 of that total being classed as serious.
The report also noted an inmate was killed by another prisoner at the jail during that time, with the culprit later convicted of murder.