Frontiers in Marine Science (Nov 2015)
Excrement examination with blood detection tests as a novel method to study the postmetamorphic feeding in lampreys
Abstract
After several years in freshwater, sea lamprey Petromyzon marinus L. 1758 ammocoetes undergo metamorphosis that allows postmetamorphic individuals to migrate to the sea and start the haematophagous feeding. Very little and fragmented information, based on scarce captures of lampreys or wounded preys, is available concerning the postmetamorphic phase of the life cycle. For example, although it was previously considered that postmetamorphics do not start feeding until they reach the estuary or the sea, recent studies have shown that in European populations some individuals start feeding in freshwater. Therefore, it is necessary to develop, calibrate and standardize new methods to advance in the knowledge of the trophic ecology of postmetamorphic lampreys. According to that, the aim of this study is to investigate the usefulness of a commercial test for blood detection based on an advanced modification of the Kastle-Meyer test (Hemastix, Siemens®) as a non invasive method to notice active haematophagous feeding in postmetamorphic lampreys (analysing excrements), and in our particular case to study the onset of feeding in newly transformed P. marinus. For this purpose, 170 postmetamorphic sea lampreys were captured in a fixed trap located in the River Ulla (NW Spain) since December 2014 until June 2015. Thirty six individuals presented excrements (21%), which were analyzed. Positive blood tests were obtained in March (1 of 84 individuals; 1.2%), April (5 of 23 individuals; 22%), May (1 individual, 100%) and June (1 individual, 100%). Excrements with positive results were characterized by being abundant, usually of dense consistency and white, red, orange or dark green. Less abundant light green faeces of liquid consistency (and dark green faeces in some cases) provided negative results. Thus, this study reveals the test for blood detection as a suitable tool to notice active feeding in postmetamorphic lampreys. The presence and visual analysis of excrements can provide an approximate view in this regard, being necessary to test doubtful cases (e.g. dark green faeces) with the test for blood detection to confirm active feeding.
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