GROWTH ESTIMATES FROM RIBONUCLEIC ACID CONTENT IN SOME SMALL ORGANISMS1

RNA concentrations were determined on whole amphipods (O&estia platensis) of dif-fcrcnt sizes and a relationship bctwccn RNA and dry weight established by least squares. The smallest (and fastest growing) individuals had ten times the RNA concentration of the largest. Growth rate in the amphipods was estimated by length-frcquencics in a time series and then related to RNA concentration. Growth rate and RNA concentrations were dctermincd on a laboratory population of the brine shrimp Artemin salinn. Growth prcdic-tions for A. salina made by using the growth-RNA relation for amphipods wcrc in rcason-able agrccmcnt with the actual growth. Growth rate of larvae of the mud snail, Nassasius &sol&us, estimated from RNA determinations was consistent with observed values under laboratory conditions. Thcsc results inclicate that the RNA-growth relationship might be useful in estimating growth or productivity in other spccics or in mixed populations of animals