Ethogram of zebrafish (Danio rerio) after exposure to nitrates.

Nitrate pollution is one of the most widespread forms of contamination, and in high concentrations has adverse effects on aquatic ecosystems. Fish are susceptible to this contaminant and are known to modify their behaviour in a variety of ways when exposed, but most information regarding changes in behaviour pertains only to long-term or chronic exposure. Therefore, this study aimed to use zebrafish (Danio rerio) as a model fish species to create a specialized ethogram relevant to acute nitrate contamination and identify any immediate changes in behaviour (within the initial 10 min of exposure). Three water treatments were created in a laboratory setting: water with optimum conditions to support D. rerio, and water with two levels of nitrate concentration: 11 mg/L NO3 --N and 100 mg/L NO3 --N. Fish were filmed in each treatment group, and visual review of the footage identified nine unique behaviours. These behaviours were measured in frequency, duration and latency per fish, and the values were compared between treatments. From those, repetitive long movement, repetitive short movement and freezing increased in occurrences in conjunction with sweeping decreasing in occurrence when fish were exposed to higher concentrations of nitrates. The findings suggest that four behaviours (repetitive long movement, repetitive short movement, freezing and sweeping), which immediately change in the presence of high concentrations, may be relevant in indicating exposure to acute nitrate contamination.