EFFECTS OF TIMING OF FIRST FEEDING ON GROWTH AND SURVIVAL OF CULTURED PACIFIC LAMPREY Entosphenus tridentatus LARVAE  

Pacific lamprey populations have declined from historic levels in the Pacific Northwest. The decline of this species of great ecological significance has raised concern among tribal, state and federal management agencies. Conservation efforts involving this native species include habitat restoration, improvements to fish passage systems, and development of culture techniques for this species. This research focused on refining the culture methods for the early larval stage of the species, a stage where culturists in the past have observed high mortality. There were two objectives to this study. The first was to test different timing for administering the critical first feeding. We suspected that administering feed too early could lead to mortality by fouling the tank at a time when the fish cannot utilize the feed, and that feeding too late could reduce growth and survival. The second objective was to closely monitor the first month of the larval stage to characterize the timing and magnitude of mortality events at this stage and to monitor larval development.

Fish were cultured according to methods used previously at the Abernathy Fish Technology Center. Four treatments of first feed timing were tested. Each treatment was applied to 3 replicate tanks containing 150 larvae that were 16 days post hatch (DPH).  The first treatment was offering feed immediately after stocking. The next treatment was offering feed at 24 DPH. Another began at 31 DPH. The fourth treatment was not fed during the experiment. Water quality was assessed on each tank at the end of the 4 week study. All fish were captured, counted and measured at 43 DPH. To monitor larval development and characterize mortality during this stage three additional tanks were stocked with 150 larvae at 16 DPH, were offered first feeding at 24 DPH and were collected, enumerated and photographed with a digital stereo microscope weekly over a 28 day period to assess survival, growth and development.  The results of this research will increase our understanding of what is occurring during this critical period in lamprey culture, and greatly improve our ability to produce quality lamprey for conservation purposes.