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Comparison of stable isotope ratios in larval Pacific lamprey tissues and their nutritional sources when reared on a mixed diet

Evans, Thomas M., Lampman, Ralph T.
Aquaculture 2019 v.503 pp. 499-507
Entosphenus tridentatus, animals, aquaculture, biomass, carbon, diet, erythrocytes, foods, larvae, liver, mixing, muscle tissues, muscles, nitrogen, oxygen, rearing, sediments, stable isotopes, statistical models
Aquaculture of larval lampreys (ammocoetes), to help recover and maintain threatened populations, is increasingly viewed as an important management tool. Ammocoetes are filter-feeders that remain burrowed in fine grain substrates for the majority of their lives, making it difficult to determine how well diets are being supplied and in what proportions various foods are utilized. Stable isotope analysis offers the ability to distinguish which foods are being incorporated into animal biomass. While muscle tissue is most commonly used for stable isotope analysis, other tissues could also be collected to avoid lethal sampling (e.g., blood) or to provide insight into condition (e.g., liver). Muscle, red blood cells (RBC), plasma, liver, and notochord were collected from Pacific lamprey (Entosphenus tridentatus) larvae raised in the laboratory on a varied diet; δ2H, δ13C, δ15N, δ18O and δ34S were measured in food sources, animal tissues, and lipid-extracted muscle. Tissues were generally isotopically similar to one another except in a few notable cases. The δ2H of notochord was more enriched than any other tissue and the δ15N and δ34S of RBC were elevated over muscle. The δ18O of all tissues was predicted from source water, allowing this isotope ratio to provide information about regional origin of lampreys. A stable isotope mixing model found that larval biomass, even when ammocoetes were supplied with various diet items, was still primarily dependent on aquatic sediments. Therefore, the burrowing medium supplied to ammocoetes in aquaculture facilities is likely to have a strong impact on growth rate and may benefit from the inclusion of more labile organic material or feed that specifically enriches the aquatic sediment.