Relating nucleic acid and protein indices to growth in Mysis relicta: ration, cycling temperature, and metabolism

We investigated growth rate, nucleic acid (DNA, RNA) and protein indices and respiration in juvenile (8.5 to 12 mm total body length, 7 to 20 mg wet wt) and young adult (12 to 14 mm, 20 to 30 mg wet wt) Mysis relicta, as a function of temperature, body mass and molt stage in order to develop methods to assess condition or growth in the field. Mysids were exposed to either a preferred temperature (6.5C) and 3 ration levels, or a range of constant and dielly-cycling (DC) temperatures with ad libitum feeding. Mysid growth parameters (specific rates of growth [SGR], respiration [MO sub(2)], and RNA content cell super(-1)) integrated the DC temperature experienced as averaged responses weighted by the time spent at each temperature. MO sub(2) peaked at 12.7C on acute temperature exposure from 4.2C. MO sub(2) compensation with prolonged temperature exposure occurred at mean diel temperatures less than or equal to 8.5C. Mysids could not survive at 16C even for 5 h d super(-1). These results confirm behavioral observations of temperature preferences. RNA concentration in M. relicta increased with ration and decreasing temperatures. Protein:DNA ratio, %protein and SGR increased with ration and then plateaued. Protein:DNA ratio, %protein and DNA:weight ratio did not change with temperature with unlimited feeding. Forward, stepwise, multiple regression models for each experiment and the combined data accounted for 31 to 72% of variability in SGR. Our experimental data provide guidance, a preliminary temperature-correction factor for RNA, and benchmarks for use of nucleic acid and protein indices in assessing growth or condition of M. relicta in the field.