RNA: DNA ratio as an indicator of growth, nutritional status and condition of fish: A review

The changes in the growth rate of fish with respect to nutrition, disease and environment are well documented. The growth rate in fish is estimated by simple length-weight calculations to complicated radiocarbon-dating methods. These growth estimation methods although commonly used but the factors like false indications, time consumption, labour and cost make most of the techniques less reliable. The RNA: DNA ratio is a simple estimator that provides a short-term measure of the condition of fish. The method is based on the notion that within individual cells, DNA concentrations remain constant and RNA varies, which in turn increases the protein synthesis. In general, the ratio is relatively high in a well-fed, metabolically active, growing fish compared to a starving, sluggish and metabolically inactive individual. The methodology to calculate the RNA: DNA ratio is simple, ranging from the extraction of nucleic acids to quantification. The post-processing of these methods is not needed, which make the technique simple, efficient and cost-effective. The present review highlights the importance, variations as well as the effects of nutritional status, stress and environment on the RNA: DNA ratio of culture and captured fishes.