Acosta was "no longer employed" at the school as of Thursday, NMSU spokeswoman Minerva Baumann wrote in an email. She declined to elaborate on the nature of Acosta's departure. By policy, NMSU does not discuss such personnel matters publicly.
Multiple sources within the firefighting community said Acosta was fired.
Acosta did not return phone calls from the Sun-News on Friday. He drew a salary of $82,000, according to NMSU records.
Veteran firefighter Johnny Carrillo has been named interim chief. A captain with the NMSU Fire Department for the past four years, Carrillo served 21 years with the Las Cruces Fire Department.
Carrillo will be interim fire chief, the NMSU spokeswoman said, "while we are evaluating options regarding the selection of a new fire chief."
Carrillo is the third man in less than a year to serve as NMSU fire chief. Former chief Darrell Smith retired last summer after more than 20 years with the department. Another interim chief served the six months between Smith and Acosta.
In February, NMSU announced it hired two captains in the fire department.
Established in 1921, the NMSU Fire Department employs four career firefighters and 14 student firefighters. It falls under the purview of the county fire marshal.
Acosta, in a November interview, said he started with the Farmington Fire Department in 1986, then left in 2007 as the operations battalion chief.
He worked in Arizona and California before landing at a station in suburban Seattle in 2010.
Before working at NMSU, Acosta most recently was the deputy fire chief of the Woodinville (Wash.) Fire and Rescue District until his position was eliminated last summer as part of budget cuts.
James Staley can be reached at firstname.lastname@example.org; 575-541-5476. Follow him on Twitter @auguststaley