A review and assessment of the potential use of RNA:DNA ratios to assess the condition of entrained fish larvae

Abstract

a b s t r a c tIn rivers, lakes, and other aquatic systems throughout the world, intake pipes withdraw huge volumes of water for industrial purposes, including power plant cooling. During this process, large numbers of small-bodied, early life-stages of fish are pulled into pipes (i.e., entrained) and may be subjected to physical, thermal and chemical stress. As a result of such entrainment, these organisms can suffer direct or indirect mortality. However, given that the vast majority of larval fish are likely to die during early life due to natural processes, it is not obvious that entrainment-related mortality will have a strong influence on subsequent adult population sizes. The ability to evaluate if larval fish are dead on arrival, moribund, or in poor condition (i.e., likely to die through natural processes) at the time of entrainment could shed light on likely population-level impacts. To this end, we review the potential use of RNA:DNA ratios to index condition of entrained larval fish. Through a meta-analysis of published research studies, we demonstrate that RNA:DNA ratios of larval fish are responsive to starvation stress, with effect size increasing with duration of starvation. We relate these results to a surrogate measure of irreversible long-term negative impacts to fish populations, and demonstrate that the timescale over which RNA:DNA ratios respond to stress may not be long enough to reflect before-and-after entrainment stress. We also highlight the diverse factors contributing to variation of RNA:DNA ratios, including methodological, ontogenetic, and thermal influences. We believe that the need to account for these influences when comparing among RNA:DNA values limits the utility of broadly using RNA:DNA ratios to evaluate entrainment effects. However, the method shows promise as a quick and efficient means of determining fish condition and, used in proper context (e.g., specific to a given set of environmental conditions; in conjunction with other assessment techniques), may provide a powerful tool in assessing the effects of entrainment on fish populations. Assuming that researchers can account for sources of background variation, RNA:DNA analyses may be most useful for assessing the condition of fish larvae susceptible to entrainment (i.e., physically in the vicinity of the water intake) and/or evaluating whether fish larvae are likely to die from natural processes independent of entrainment.

Thermal stress altered growth performance and metabolism and induced anaemia and liver disorder in Labeo rohita

“…During extreme temperature stress, organisms try to cope up the situation by altering metabolism so that energy can be channelled to vital organ like brain vis-a-vis compromise with other physiological performances such as growth (Eldridge, Sweeney, & Law, 2015) as documented here. Previously, different researchers also referred RNA-DNA ratio as an environmental stress indicator for aquatic animals (Chícharo & Chícharo, 2008;Foley, Bradley, & Höök, 2016).…”

Determination of optimal feeding rates for juvenile lake sturgeon ( Acipenser fulvescens) fed a formulated dry diet

“…The current results support the reliability of RNA/DNA ratio in muscle as a parameter to estimate growth status because estimated optimal feeding rates were similar based on either the growth performance of fish or the RNA/DNA ratio in muscle tissues. Furthermore, an increased RNA/DNA ratio can be an indication of increased protein synthesis because DNA concentrations within individual cells remain fairly constant while RNA concentrations increase as protein synthesis increases (Buckley et al, ; Ferron & Leggett, ; Foley, Bradley, & Höök, ; Suthers, Cleary, Battaglene, & Evans, ). In the current study, the RNA/DNA ratio reached a plateau level when sturgeon were fed at 3%–4% and 1%–3% BW/day for trial I and trial II, respectively, suggesting that protein synthesis could have peaked in those fish.…”

Diet Effects on Growth, Mortality, RNA: DNA Ratio and Gene Expression of Zebrafish Danio rerio

“…This approach has demonstrated especially appropriate for investigations of larval fish, which show conceivably fast, almost ceaseless development of absolutely somatic tissues (i.e., energy accessible for larval fish development isn't directed to shedding or gonadal tissue). The quality and quantity of RNA and DNA and its sources of variation in a fish especially in larval fish depends on some factors like the ontogenetic stages, effects of temperature and methodology (Foley, Bradley, & Hook, 2016).…”