Methods for rearing the invasive zooplankter Bythotrephes in the laboratory

The invasive spiny water flea's (Bythotrephes longimanus) current North American distribution encompasses the Laurentian Great Lakes as well as a number of inland lakes, particularly on the Canadian Shield. In the past, poor survival in the laboratory has precluded controlled long-term studies on Bythotrephes. Here we investigated field collection techniques and choices of culture media, temperature, and diet that led to the successful maintenance of Bythotrephes from birth to reproduction. Gravid parthenogenic females were collected from invaded lakes. Resulting offspring were reared in source lake water filtered through 20 or 80 mu m, or a fully defined artificial culture medium, FLAMES. Individuals raised in FLAMES produced significantly larger broods than those in lake water, indicating that it is an appropriate culture medium. We next conducted a 96-h temperature bioassay on juvenile Bythotrephes. Survival was comparable at 16 degrees C, 20 degrees C, and 24 degrees C but decreased after 48 h at 28 degrees C, and most animals died after 24 h at 32 degrees C. We also reared Bythotrephes at 16 degrees C, 19 degrees C, 22 degrees C, and 25 degrees C. Corresponding intrinsic rates of natural increase (r) for animals maintained to first brood release were 0.02, 0.05, 0.06, and 0.03 d(-1), suggesting that Bythotrephes should be reared at similar to 22 degrees C to benefit from maximum population increases. Feeding trials confirmed that young Bythotrephes prefer small, slow-moving prey. Finally, we devised a protocol for rearing Bythotrephes that yielded 100% survival to reproduction and r = 0.10 d(-1) (for animals maintained to first brood release). Given these results, it is now possible to conduct long-term laboratory studies on this invader.