Effect of incremental salinity on survival and behaviour of zebrafish (<i>Danio rerio</i>)

Freshwater ecosystems in coastal regions are occasionally flooded with saline water due to tidal, seasonal and catastrophic water movements, thereby affecting physiology and behaviour of freshwater fishes. The aim of the present study was to determine the tolerance limit of salinity in zebrafish as a freshwater fish model, to characterize and quantify their behavioural response under mild to high incremental salinity exposure. Wild-type zebrafish (Danio rerio) individuals were maintained and exposed from fresh water to increasing NaCl concentration up to 20 g L–1 with a repeated exposure schedule for 96 h. Observation was made per tank for their mortality and for cumulative behavioural patterns under defined time frames. The estimated LC50 value was 14.122 g L–1 NaCl. Abrupt shifts of behavioural expression were found from 10 g L–1 of NaCl, with predominant stress movements followed by aggression and fighting as well as diminishing feeding and playing movements. The incremental salinity concentration and exposure time both were found to control the key behavioural indicators in a defined pattern.