Feeding and Growth of Larval Pacific Lamprey Reared in Captivity

Pacific Lampreys Entosphenus tridentatus are declining in the Columbia River basin as well as in much of their broader range. To mitigate for reductions in abundance, strategies such as hatchery propagation and captive rearing of lamprey larvae are currently being considered. We conducted a series of experiments using captive larval Pacific Lampreys at EagleCreek National Fish Hatchery to investigate the effect of different food types and different food concentrations on the growth of larvae. In our first experiment, we evaluated the growth of larvae (TL range, 59-145 mm) given four different food types (algae, leaves, yeast-larval fish food, and salmon carcass analogs) and a control group that was not fed. Assimilation of food types was evaluated by tracking unique stable isotope signatures of delta C-13 and delta N-15 within larval tissues. Results from experiment 1 indicated that lampreys fed a diet of salmon carcass analog or algae had positive growth (up to 0.16 mm/d and 42% proportional change in length) over approximately 6 months. Isotopic analyses of larval tissues showed unique signatures that matched those of their specific food treatment. Based on the results of experiment 1, we conducted a second experiment to evaluate the growth of larvae fed four different quantities of salmon carcass analog. Results from this experiment indicated larval growth rate increased with increasing rations of food, but positive growth was observed in all feeding treatments. The highest dose of salmon carcass analog resulted in the highest growth (up to 0.15 mm/d and 36% proportional change in length) over 6 months. We successfully reared larval Pacific Lampreys in captivity with minimalmortality and positive growth, which highlights the potential to use captive rearing and propagation as a conservation tool for this ecologically and culturally important species.