Substrate Preference of Parazacco Spilurus and Cirrhinus Molitorella: Role of Sediments In River Ecological Restoration

In natural rivers, fish have certain preference for bottom substrate types and will select where they prefer to stay. To investigate the substrate preference of target fish - predaceous chub (Parazacco spilurus) and mud carp (Cirrhinus molitorella), four duplicated experimental trials were carried out in laboratory. A rectangular test flume (7.2 m long×0.6 m wide×0.3 m deep) was divided into four equal areas and paved with four different bottom materials. Each striped substrate is 1.8 m long and 0.6 m wide. A natural part (NA) was set up at upstream of the flume to represent habitat in natural rivers. By deploying artificial turf, sand, pebbles, cobbles and vegetation (Winged star fern) randomly in this part, heterogenous flow conditions and habitat were then created. As most of urban streams have been channelized and concrete-lined, it is hoped to study fish preference for such surface. Therefore, at the end of the flume, an artificial part (AR) was characterized by polymethyl methacrylate (PMMA). Besides, two other bottom materials were tested, including the sediment- dominant substrate (SED) and the pebble-dominant substrate (PEB). To maintain the physical properties of sediments, natural sediment (<2 mm) collected from rivers was paved on one of the four sections. And the PEB region was covered with pebbles ranging from 31 to 64 mm. Flow rate in the flume was set at 3 L/s and water depth was kept at 25 cm by adjusting a tail gate. A group of 10 fish individuals (including 3 Parazacco spilurus and 7 Cirrhinus molitorella) were released into the flume and recorded by a monitoring system for one hour. Fish preference for various part of the flume was estimated by the distribution on every one-min video footage. Results show that fish population spent 34%-35% of the entire time on both NA and SED. On AR, the percentage of time is approximately 22%, while fish show little interest on PEB (~9%). The findings reveal the significance of sediments on fish habitat conservation. To better understand the role of sediments in fish habitat reestablishment, in addition to fish laboratory experiments, future research should also include numerical simulation of sediment transport and physical habitat modeling.