CHANGES IN NUCLEIC ACID CONCENTRATION WITH STARVATION IN THE BLUE CRAB

Changes in nucleic acid concentration as a result of starvation followed by feeding were determined over a 30-day period in juvenile Callinectes sapidus Rathbun. RNA concentration decreased by 31% within three days of starvation. The decrease was continuous over the 30day starvation period and reached a level 27% of the control crabs by day 30. DNA concentration decreased by 21% between days three and six but remained stable during the rest of the starvation period. Juvenile C. sapidus exhibited a high capacity for recovery from longterm starvation. DNA concentration increased by 35% and 22% when crabs were fed for five days after being deprived of food for 15 and 30 days, respectively, while RNA concentration increased by 129% and 91%. We have found RNA concentration and the ratio of RNA to DNA to be a reliable and sensitive index of nutritional stress in view of the large and rapid changes in nucleic acid concentration, especially during the early stages of starvation. Nutritional condition and growth are often difficult to determine in crustaceans. Length-weight relationships or morphometric measurements are not suitable because growth takes place by molting and increase in size occurs in discrete increments. Other methods, such as size increase per molt or molting frequency, have the disadvantage of not being an instantaneous measurement and worse yet, the organism may not molt at all under unsuitable conditions. However, since growth has a biochemical basis, it may be feasible to monitor nutritional state and growth at the macromolecular level. Because ribonucleic acid (RNA) is produced during gene transcription and participates in protein biosynthesis, changes in cellular RNA content reflect changes in cellular activity (Brachet, 1960). The deoxyribonucleic acid (DNA) content per cell is usually constant (Leslie, 1955) and may be used as an indicator of cell number (Bulow, 1970). The quantity and ratio of RNA to DNA can then provide information about the physiological state of an organism. Organisms in good nutritional condition which are growing are expected to have high concentrations of RNA and high ratios of RNA to DNA relative to those organisms suffering from nutritional stress. Changes in nucleic acid concentration and RNA:DNA ratio have been studied in relation to various biological processes in controlled experiments and field studies. Patterns of RNA synthesis and changes in the RNA:DNA ratio have been studied in early crustacean (Sulkin et al., 1975) and molluscan development (e.g., Collier, 1976; Kidder, 1976) as well as during ontogenesis of fishes (Zeitoun et al., 1977; Buckley, 1981). Quantitative measurements of nucleic acids have also been used to estimate growth rates of fishes (e.g., Bulow et al., 1978; Buckley, 1982, 1984), marine plankton and aquatic microbial communities (e.g., Karl, 1981; Dortch et al., 1983), and macroinvertebrates (Sutcliffe, 1965, 1969; Dagg and Littlepage, 1972; Regnault and Luquet, 1974). In general, both RNA concentration and the ratio of RNA to DNA were positively correlated with growth rate. However, the RNA:DNA ratio was considered to be a more accurate index than RNA concentration alone because the ratio is independent of cell number or size in the tissue sample (Hotchkiss, 1955; Haines, 1973). In addition to serving as an index of growth or biomass, quantitative changes in nucleic acids have also been measured in fishes subjected to various stressors.