A mislabelled chemical has been blamed for the loss of more than a tenth of Texas State Aquarium fish last week.

As per the aquarium’s protocol, the commonly-used parasite treatment, Trichlorfon, was tested for mass use in a smaller tank. With no ill effects on the fish, staff treated the larger tanks with what was supposedly the same chemical but from a different, identically labelled, container.

The result was that 400 fish or around 13 per cent of the aquarium’s total collection, died overnight. Initial tests carried out by the aquarium after the investigation show that the chemical used was actually hydroquinone – a chemical used as a stabiliser in paint and motor fuel, and for film processing. In living creatures, the chemical causes blood poisoning and acts as a carcinogen.

"For further verification, we have also sent samples to the Texas Veterinary Diagnostic Medical Lab, and we will share additional information as it becomes available,” said a statement from the aquarium. “At this time, we are not prepared to release the name of the company from which we acquired the drug.

"We are in the process of cleaning all of the impacted systems to remove any trace of the toxin. Once we have established the water is safe, we will begin adding new fish."