Use of RNA: DNA ratios as an indicator of nutritional stress in the American oyster Crassostrea virginica

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Abstract
Hatchery spawned oysters approximately 1 1/2 yr old were subjected to starvation stress by exposing them to 1 .mu.m seawater over an 8 wk period. Control (fed) oysters were exposed to unfiltered flowing seawater. RNA:DNA ratios in mantle tissue from fed and starved oysters were monitored throughout, together with shell length, width, height, whole specimen displacement and shell displacement. Wet weight was estimated from whole weight determinations made before and at the end of the experiment. From Day -4 (before the start of the experiment) to Day 52, there was a 32% increase in mean weight of fed animals and a 12.6% loss in wet weight of starved animals. Rate of wet weight growth was significantly less in starved oysters than in fed oysters after Day 3. Shell height increased in fed oysters, but remained more constant in starved specimens. Shell lengths were significantly different from Day 42. Condition index, defined as ratio of wet tissue weight to cavity volume, decreased rapidly in starved oysters and became significantly less than in fed oysters. Two sample t-tests between treatments showed that there was a significant difference in RNA:DNA ratio between treatments on all sampling days except Day 0. By Day 55, starved oysters had 36.5% lower ratios than fed oysters. Over the 55 day experimental period the RNA:DNA ratio correlated highly with condition index, but was lower in response to starvation than in reported studies on vertebrates.