22 MARCH 2022 • WORLD AQUACULTURE • WWW.WA S .ORG Broodstock holding has indicated that adult lampreys can be kept at extremely high densities when provided with cold, oxygenated water. Fertilization and incubation experiments revealed that gamete contact times are very short and that embryos are resilient to low flow and poor water quality. Early prolarvae are also resilient to these factors, can tolerate abrupt changes in temperature and extended periods of starvation. However, they cannot survive sudden changes in water quality, excessive disturbance and lack of adequate microbial communities. These observations have resulted in more efficient and effective lamprey propagation and have yielded important information about the early life stage requirements of lampreys in the wild. Further study is needed on a broader array of species to allow inter-specific comparisons of early life history. However, information from lampreys receiving the most attention to date (European river lamprey Lampetra fluviatilis, sea lamprey and Pacific lamprey) indicates that culture and environmental requirements of the early life stages are remarkably similar, allowing for generalization across lamprey species. Optimization of Feeding Frequency for the Intensive Culture of Larval Pacific Lamprey James Barron, Racheal Headley and Ann Gannam The Pacific lamprey is an ancient fish of great importance to the ecosystems and indigenous cultures of the U.S. Pacific Northwest. Pacific lamprey have declined in abundance and range from historic levels, thus leading to increased conservation efforts for the species. Efforts to conserve this native fish include development of culture techniques. The larval stage of this species occurs in freshwater and can take up to seven years to reach metamorphosis in the wild. During the larval stage, lamprey are filter feeders and a slurry of active dry yeast paired with a fine larval fish diet (4:1) is commonly used as a standard diet in the hatchery. Larval lamprey have been successfully cultured with two feeding events per week; however, more frequent feedings could optimize fish growth and condition. This project tested two levels of feeding frequency (two feedings per week, five feedings per week) through two 8-wk trials with 65 days post hatch (DPH) larvae (Trial 1) and 803 DPH larvae (Trial 2). The high feeding frequency treatment represented a 150 percent increase in feeding events relative to the control. At the end of Trial 1, larvae fed a high frequency were 21 percent heavier on average relative to control fish. Feeding frequency had no significant effect on final length, condition factor or survival. In Trial 2, high feeding frequency increased length and weight relative to the control fish but did not affect survival or condition factor (Fig. 4). Feeding at a high frequency increased larval weight by 32 percent relative to control fish. High frequency also elevated whole body lipid content by 51 percent relative to the control fish and altered the fatty acid profile. The fatty acid profile of the high frequency fish indicated a build-up of depot lipids in these fish with increased saturates relative to the control fish. Their long chain polyunsaturated fatty acids also decreased relative to the control fish possibly through dilution by the increased depot lipids. Increasing feeding frequency can increase the growth of the larval lamprey. The effects were more pronounced in older larvae so larger fish may benefit more from increased frequency than young larvae. As the accumulation of sufficient lipid reserves are thought to be critical to reaching metamorphosis in lamprey, the high frequency regime could facilitate a shorter duration of larval rearing. Increased feeding frequency will increase costs and tank fouling so those considerations need to be balanced as a trade-off with increased growth and lipid deposition. Polyculture Increases Growth and Survival of Larval Pacific Lamprey Alexa N. Maine, Mary L. Moser, Aaron D. Jackson and Frank Wilhelm Healthy rivers sustain diverse communities of microorganisms, while aquaculture environments are typically homogenous. FIGURE 4. Larval Pacific lamprey at the conclusion of Trial 2. FIGURE 5. Subsample of larval Pacific lamprey used in this study.
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