A series of bizarre and fatal mishaps—including the vanishing of a “mutant rabbit” and the killing of more than 11,000 zebrafish with bleach—plagued an animal testing laboratory at the University of Michigan last year, according to federal documents.

They reveal that, within a six month period in 2018, the laboratory accidentally bleached more than 11,000 zebrafish, killed 53 mice of dehydration, and mistakenly allowed nine mice to develop cancer.

The records were obtained through a Freedom of Information Act (FOIA) request submitted by the advocacy group Stop Animal Exploitation Now (SAEN), and were reported on Friday by Michigan news site MLive.

Each of the strange events was described by the university in a separate letter to the National Institutes of Health (NIH) Office of Laboratory Animal Welfare, which provides oversight to recipients of grant funding.

In one letter, dated May, 7 2018, officials described the rabbit incident, saying that “an animal caretaker noted that a transgenic rabbit was missing from the vivarium.” After conducting a search for the animal in other rooms and even the ventilation system, they determined that “the location of the animal is unknown.”

The exact project involving the rabbit was not specified in the letter.

The killing of 11,548 zebrafish with bleach was blamed on a reverse osmosis system accidentally flooding the tank with the chemical solution instead of water.

Additionally, 53 mice were deprived of water when a rack of cages was dislodged from an automatic water supply system. Afterwards, animal husbandry staff at the laboratory underwent “intense retraining” to prevent such a mistake from happening again.

Another nine mice were euthanized when a protocol breach in a gastrointestinal cancer study led to the animals developing tumors, having been “inadvertently left in the study too long,” MLive noted.

"Upon discovery in 2018, these incidents were corrected immediately by our animal care team, and corrective action plans were put into place to prevent any future issues," a spokesperson for the University of Michigan told Motherboard.

"As part of that oversight, and in the interest of full transparency, the [university] self-reported each of these events to the National Institute of Health’s Office of Laboratory Animal Welfare...[which] found [the university] took all necessary steps to self-report and correct these isolated incidents," the spokesperson added.

SAEN routinely “makes FOIA requests to many sources to obtain documents” and focuses “solely on the animal experimentation issue,” the organization’s executive director Michael Budkie told Motherboard in an email.

Budkie said that very few laboratories have zero-compliance issues. “However, I am not presently aware of any labs that have killed so many animals through negligence in such a short period of time,” he added.

After obtaining the documents, Budkie wrote the University of Michigan regents asking for an independent investigation into the incidents.

“As you know from reviewing the documents, upon discovery in 2018, these incidents were corrected immediately by the university’s animal-care team and corrective action plans were put into place to prevent future issues,” the regents said in a response to Budkie viewed by Motherboard.

“No further review is deemed necessary,” they added.

The laboratory has been scrutinized for other animal deaths in the past.

Between 2012 and 2013, a baboon was left unattended with a toy and strangled itself. Additionally, “a researcher performed an unapproved emergency surgery on a guinea pig,” and a hamster that had escaped from its cage and was found dead in a drain, according to a 2014 report from MLive.

Both revelations also stemmed from FOIA documents obtained by SAEN.