Representatives for Texas State Aquarium, which recently lost more than a tenth of its fish after a lethal chemical was introduced to its tanks rather than a parasite treatment, have filed a lawsuit against the company that provided the mislabelled carcinogen.

The chemical – believed to have been trichlorfon – actually turned out to be hydroquinone, a toxic substance used primarily for film processing and as an additive for paint and motor fuel. The container came from Florida-based Fishman Chemical, a wholesale outlet for tropical fish pharmaceuticals.

Attorney Craig Sico, with the firm Sico White Hoelscher Harris & Braugh, said the civil suit had been filed in federal court, with the aquarium seeking damages that could potentially amount to millions of dollars.

As per the aquarium’s protocol, the trichlorfon was tested for mass use in a smaller tank. With no ill effects on the fish following the test, staff treated the larger tanks with what was supposedly the same chemical but from a different but identically-labelled container, resulting in the aquarium losing around 400 fish or 13 per cent of its collection overnight.

The problem reaches beyond Texas State Aquarium, with Albuquerque BioPark Aquarium also considering a lawsuit after it lost around 200 fish in October. Upon hearing the news of the mass death at Texas State Aquarium, BioPark officials tested its trichlorfon container, discovering the batch which had killed the fish was also made up of the deadly hydroquinone. In a statement, the aquarium said it was reviewing the case and would determine whether or not to also take legal action against Fishman Chemical.

Sico said his firm is looking into five fish kills involving Fishman Chemical trichlorfon, but only named the Albuquerque aquarium and the Audubon Aquarium of the Americas in New Orleans.

In a statement, Fishman Chemical questioned the claims of mislabelling.

“Fishman Chemical's president, Dr David Fishman, has informed us that Texas State Aquarium has not co-operated with Dr Fishman to find out what the cause of the fish kill in April at the Texas State Aquarium was from,” read the statement.

“Dr Fishman has asked for both water samples and samples of the chemical in question, but as of today he has not received them. Past employees of the aquarium have told Dr Fishman that both Tom Schmid, the president and CEO, and the vice president and chief operating officer, Jesse Gilbert were both in the Yucatan on an adventure at the time of the dosing and no one of any authority or experience was present when the dosing took place. Dr Fishman is trying to verify if this is the case.

“Dr Fishman was also informed of many incidents and problems at the Texas State Aquarium, but would not elaborate until he can verify what was is true and what is just rumours. Fishman Chemical is making it a top priority to find out the truth, but first has to figure out what was going on at the Texas State Aquarium when this incident took place."

In the wake of the tragedy, more than 130 new fish have been donated by aquariums across the country, representing 30 different species. Among those lost were a sand tiger shark, tarpon, grouper, lionfish, jack crevalle, a balloon fish, redfish and many other smaller species.