PUMPING RATES AND PARTICLE RETENTION EFFICIENCIES OF THE LARVAL LAMPREY, AN UNUSUAL SUSPENSION FEEDER

¹ Department of Zoology, Washington State University, Pullman, WA 99164

The suspension feeding larvae of lampreys (ammocoetes) inhabit fine-grained sediments where particulate organic matter is concentrated, but whose low permeability limits the rate at which ammocoetes can pump water (flow rate). This study determined: 1) flow rates through the pharynges of ammocoetes, both within and out of the sediment, and 2) the ability of ammocoetes to filter particles from suspension (retention efficiency) over a wide range of algal cell concentrations (Chlorella pyrenoidosa, 1-75 mg/l).

For most suspension feeders, flow rate and retention efficiency must be measured indirectly (clearance method). Direct measurement was possible here, as ammocoetes remain apparently undisturbed in glass tubes that allow the separation of inhalent from exhalent ventilatory currents. Problems arise in attempting to use clearance methods to determine flow rates in burrowed suspension feeders, and these problems are discussed.

Ammocoete flow rates are exceptionally low compared to the rates of other suspension feeders, but retention efficiency was consistently high, even at the highest algal concentrations employed (x = 82%). While most suspension feeders rapidly process dilute suspensions, ammocoetes meet nutrient needs by slowly processing concentrated suspensions.