Abstract
Four tissues that can be removed nonlethally were evaluated for their effectiveness in estimating recent growth rates of Atlantic salmon Salmo salar smolts using RNA-DNA ratios (R/Ds). Weight-based growth rates were calculated for smolts reared in the laboratory for 4 weeks. Gill, muscle, scale, and caudal fin tissues were sampled to evaluate sampling ease during fieldwork, the quantity of RNA and DNA available for analysis, and the correlation of R/D with growth rate. Muscle provided adequate tissue for nucleic acid analysis, was strongly correlated with recent growth rates, and could be easily sampled in the field using a biopsy punch. Gill tissue did not provide adequate RNA for analysis with an ethidium-bromide-based microplate fluorometric assay, and R/Ds from scale and fin tissues were poorly correlated with growth rate.