POLYCULTURE INCREASES GROWTH AND SURVIVAL OF LARVAL PACIFIC LAMPREY Entosphenus tridentatus

Healthy wild river environments sustain large communities of fishes, invertebrates, and microorganisms. Laboratory environments are largely homogenous, providing little  habitat complexity, few interspecies interactions, and semi-sterile conditions resulting from disinfection to  control  harmful bacteria or other pathogens. T o  test the effects of microbial inputs to our recirculating system, we examined growth and survival of lab-propagated larval Pacific lamprey (Entosphenus tridentatus ) held in culture with speckled dace (Rhinichthys osculus) . For the purposes of population supplementation and research, l arval Pacific Lamprey   have been propagated and reared at Confederated Tribes of the Umatilla Indian Reservation (CTUIR) facilities since 2012, mainly  in  monoculture  (only lamprey). As larval lamprey are closely associated with the benthic environment in the wild, they likely have an important ecological relationship with the microbial community in substrate .

Average instantaneous growth rates for larvae reared in polyculture in 2018 were higher (7.2x10^-3 mm/day) than those of monoculture larvae reared in 2016 and 2017 (2.1 x 10^-3 mm/day; Figure 1A ). Laboratory monoculture of larval lamprey in 2016 resulted in a 29.0%  survival  rate, adjusted to 90 days post-fertilization, while polyculture resulted in  a  57.1%  adjusted survival  rate (Figure 1B). These results suggest that the presence of dace provided some improvement in the growth and survival of lab-propagated larval lamprey.  Potential mechanisms for these results include direct consumption by lamprey of microorganisms or increased ecosystem services provided by the microbial community. F urther research is needed to identify mechanisms of microbial interaction s and their implications for production- scale  lamprey aquaculture.