David P. Ahlfeld
The effect of ramp slope and substrate grain size on the passage of juvenile American Eel (Anguilla rostrata) over indoor ramps was tested from May – August 2016. Two size classes of fish (300 glass eels 50 – 70 mm and 300 elvers 90-114 mm), five substrates varying in coarseness (Substrate 1: 0.18-0.25 mm grain size, Substrate 2: 0.25-0.60 mm grain size,
Substrate 3; 0.60-1.00 mm grain size, Substrate 4: 1.00 – 2.00 mm grain size, Substrate 5: 2.00-
4.00 mm grain size), and three ramp slopes (25, 35 and 45 degrees) were explored. Individual fish were placed at the bottom of a ramp and given 30 minutes to ascend 0.5 m. Movements over the substrate were recorded with video footage and digitized. Fish length, fish weight, water temperature, and days the fish were held in captivity before being tested were also recorded and analyzed. Results indicated that substrate had a highly significant effect on glass and elver climbing performance, and slope had an effect on elver performance but not glass eel performance. The roughest substrate yielded the highest proportion of eels ascending the entire length of the ramp and the highest climbing speed in each parameter category. Further testing with more grain sizes and longer ramp lengths are required, and mass manufacturing processes for this substrate need to be explored.