Excrement examination with a test for blood detection as a tool to study the post-metamorphic feeding in lampreys

Abstract

The aim of this study was to investigate the potential use of a commercial test for blood detection (Hemastix®, Siemens Healthcare Diagnostics) as a non-invasive tool for inferring active haematophagous feeding in post-metamorphic lampreys, by analysing their excrement. We investigate the onset of the parasitic phase in recently transformed sea lamprey Petromyzon marinus L. 1758 captured in freshwater. Excrement from haematophagous feeding was identified by the presence of haemoglobin. The presence of faeces was detected in 68% of the post-metamorphics (n = 244) captured in a preliminary study and carried out in April 2012. Subsequently, 164 individuals were captured (December 2014 to June 2015), and 36 provided excrement (22%) to test for the presence of haemoglobin. Haemoglobin was detected in eight of the animals with faeces, indicating the onset of parasitic feeding. Excrement samples containing haemoglobin were characterised by being relatively voluminous, dense and white, red, orange, black or dark green. Excrement without haemoglobin was less dense, lower in volume and light green (in some cases dark green). Results presented in this study support the use of a test for blood detection for revealing active feeding and investigating different aspects of the poorly understood post-metamorphic trophic ecology of lamprey species.