Locomotor activity (% of the two-hour interval) of adult armoured catfish Pterygoplichthys spp. from the Da Rang River during six hours after transfer to test apparatus Type 1 with different water salinities (0 PSU, 5 PSU, 10 PSU, 15 PSU). Different letters (a vs b) indicate statistical differences by Mann–Whitney U test between two values of locomotor activities during two hours. Standard error (|).