Preference by juvenile Chinese sucker Myxocyprinus asiaticus, for substrate colour in zero versus slow velocity regimes suggest a change in habitat preference of wild juveniles after damming the Yangtze river

Abstract

Habitat preference of benthic riverine juvenile Chinese sucker, Myxocyprinus asiaticus, a protected species in China, is poorly understood. This situation makes it difficult to evaluate the potential impacts on juveniles after river alteration. To better understand the impact of damming, we studied preference of cultured juvenile Chinese sucker (7.90-8.55 cm, standard length) for dark versus light substrate colours in 2 velocity regimes: zero velocity (like on a reservoir bottom) and in a slow water current of 0.15-0.19 cm/s (like on the bottom of a slow flowing stream). In the slow current regime, juveniles chose black substrate during the day and night. This likely represents the natural substrate preference by wild suckers in a river. However, in the zero velocity regime, juveniles chose a black substrate during the day, but switched preference to a white substrate at night. The results suggest wild juveniles in the natural Yangtze River have evolved a preference for a black substrate during the day and night. However, after the river was impounded by the Three Gorges Dam and bottom velocity changed to a static regime, juveniles in the reservoir changed substrate colour preference and now prefer a light-coloured substrate colour at night. Thus, damming likely caused a major behavioural change by juveniles.The adaptive significance and effect on fitness of this change in habitat preference is not known but should be investigated as wild Chinese sucker continue to decline in abundance. KEYWORDSdamming effects on fish, fish behaviour, fish life history, habitat preference

Substrate type and brightness preference ofSchizothorax wangchiachiiandPercocypris pingijuveniles

“…Therefore, P. pingi's preference for black substrate is likely due to its need to hide and ambush prey, with its grey-black body being relatively well camouflaged against the black substrate. Shi et al (2017) found that there were different preferences for substrate colour during the day and night in juvenile Chinese suckers.…”

“…Therefore, P. pingi's preference for black substrate is likely due to its need to hide and ambush prey, with its grey‐black body being relatively well camouflaged against the black substrate. Shi et al (2017) found that there were different preferences for substrate colour during the day and night in juvenile Chinese suckers . The present study was undertaken during the daytime, and therefore, subsequent studies should conduct nocturnal experiments to determine any day and night preference differences.…”

“…In addition, brightness preference may change in varying conditions. For example, juvenile Chinese sucker ( Myxocyprinus asiaticus ) preferred a black substrate in water with low flow velocity, while they preferred black substrate during the day and white substrate at night when in still water (Shi et al, 2017). Pelteobagrus vachelli significantly preferred black substrate in flowing water and no preference for a particular substrate colour in still water under artificial light (Lu et al, 2012).…”