Effect of salinity acclimation on routine activity rate in two closely related species of blennies from different habitats

The freshwater blenny, Salaria fluviatilis, and the marine peacock blenny, S. pave, are closely related and can survive in both freshwater acid seawat er. Salaria fluviatilis is widespread in rivers and lakes in the vicinity o f the Mediterranean basin, including Lake Kinneret (Sea of Galilee), and S. pave is distributed in rocky parts of the Mediterranean coast. This study investigated the effect of salinity acclimation on routine activity level. Fish were acclimated for three months in 0%, 40%, and 100% seawater mixed w ith 100%. 60%. and 0% dechlorinated tap water (<2, 14.4, and 36 ppt sea sal t, respectively). The fish were then placed in aquaria equipped with IR bea m projectors and detectors set up to count their activity level in the diff erent salinities under a photoperiod of 14:10 L:D. S. pave demonstrated a s imple daily rhythm of activity, being active during the light phase, wherea s S. fluviatilis was also active in the light phase. but demonstrated a bim odal activity pattern. In both species, activity decreased during the accli mation period. The bimodal daily activity pattern of S. fluviatilis might b e a result of the daily wind regime on Lake Kinneret in summer (May-October ). The activity reduction in lower or higher salinities (in relation to nat ural habitat) is suggested to be a tertiary stress response.