Tests carried out in the wake of the accident on Total's Elgin installation have shown they are "untainted" by the pollution after no hydrocarbons were found in the samples.
Over the weekend Marine Research Vessel Alba na Mara collected fish, water and sediment samples from the edge of a two-mile exclusion.
The first-stage testing of the fish samples involved the specially trained panel of sensory testers at Marine Scotland Science in Aberdeen, who can detect the taint of hydrocarbon contamination in fish.
Full chemical testing of all environmental samples is continuing, with initial results expected by the end of this week.
Scottish Environment Secretary Richard Lochhead said: "The environmental impact of this gas leak has been minimal so far, however it's important we take precautions and analyse all available data.
"Therefore it's reassuring that sensory testing of the fish samples gathered by the Alba na Mara have found they are untainted by hydrocarbons.
"Full chemical analysis work - including water and sediment samples - is ongoing and will provide further clarification on any impact. Marine Scotland Science have the necessary knowledge, skills and experience to carry out this work effectively, including the UK's only specially trained sensory panel.
"We will continue our monitoring activities for the duration of this incident, so we can assess any impact on the marine environment and respond as needed."
Marine Research Vessel Alba na Mara collected environmental samples on April 6-7 from close to the 2 mile vessel exclusion zone.
Samples covering seven species of fish, both pelagic and demersal, were gathered using a bottom trawl. Seawater samples were taken at one and ten metre depths. Sediment samples were collected using a grab sampler.
A total of 210 individual taint tests were carried out using the collected fish samples. The trained sensory panel use a 1-6 scale for the presence of hydrocarbons, using both taste and smell, and testing concluded that the samples were untainted.
The Marine Scotland Science laboratory, based in Aberdeen, includes world-leading expertise, knowledge and facilities for analysing the impact of the gas leak.
The same sensory panel and marine scientists who undertook analysis work relating to the Shell Gannet incident last year are involved in the environmental testing work for the Elgin platform.