RNA-DNA Ratio Research Articles

Thermal windows supporting survival of the earliest life stages of Baltic herring (Clupea harengus)

Abstract Peck, M. A., Kanstinger, P., Holste, L., and Martin, M. 2012. Thermal windows supporting survival of the earliest life stages of Baltic herring (Clupea harengus). – ICES Journal of Marine Science, 69: 529–536. Projecting climate-driven changes in marine systems will require knowledge on how thermal windows affect the vital rates of key species. To examine the potential, direct effect of climate-driven warming on southwest Baltic herring, we quantified the survival, development, and biochemical condition of embryos (eggs and yolk-sac larvae) at ten temperatures between 2.9 and 21.7°C. Viable hatch was highest from 7 to 13°C, <20% at 2.9°C and 0% at 21.7°C. Between 5 and 19°C, increasing temperature (T) decreased the time to 50% hatch (Ht, h,): Ht = 4461.9 × T − 1.24 (r2 = 0.98, p < 0.0001). Using degree-days [°d = T (°C) × age (d)] could normalize some (but not all) thermal effects. Most hatching occurred 90–120°d post-fertilization, unfed larvae lost 0.33 µg dry mass (DM) °d−1, larvae did not survive >160°d post-hatch. RNA–DNA ratios rapidly decreased between 50 and 80°d post-hatch, whereas DNA ×DM−1 increased throughout the yolk-sac phase and likely provides a stronger indicator of irreversible starvation. The critical, “mixed feeding” stage is likely 60–100°d post-hatch. The broad thermal tolerance of herring embryos makes “direct”, negative effects of warming unlikely; however, a lack of common methods among studies makes it difficult to project how climate warming will affect embryos of different fish populations and species.

Pacific salmon (Oncorhynchus spp.) runs and consumer fitness: growth and energy storage in stream-dwelling salmonids increase with salmon spawner density

We examined how marine-derived nutrients (MDN), in the form of spawning Pacific salmon, influenced the nutritional status and δ15N of stream-dwelling fishes. We sampled juvenile coho salmon ( Oncorhynchus kisutch ) and Dolly Varden ( Salvelinus malma ) during spring and fall from 11 south-central Alaskan streams that ranged widely in spawning salmon biomass (0.1–4.7 kg·m–2). Growth rate (as indexed by RNA–DNA ratios), energy density, and δ15N enrichment in spring-sampled fishes increased with spawner biomass, indicating the persistence of spawner effects more than 6 months after salmon spawning. Point estimates suggest that spawner effects on nutrition were substantially greater for coho salmon than Dolly Varden (268% and 175% greater for growth and energy, respectively), indicating that both species benefitted physiologically, but that juvenile coho salmon accrued more benefits than Dolly Varden. Although the data were less conclusive for fall- than spring-sampled fish, they do suggest spawner effects were also generally positive during fall, soon after salmon spawned. In a follow-up analysis where growth rate and energy density were modeled as a function of δ15N enrichment, results suggested that both increased with MDN assimilation, especially in juvenile coho salmon. Our results support the importance of salmon runs to the nutritional ecology of stream-dwelling fishes.

Sublethal effects of alizarin complexone marking on Baltic cod ( Gadus morhua) eggs and larvae

Standard, single-exposure alizarin complexone- (ALC) marking was conducted on early life stages of Baltic cod ( Gadus morhua L.) to examine acute and chronic effects. Embryos and yolk sac larvae were marked using different concentrations of ALC (0, 50, 100 and 200 mg l − 1 ). Experiments included control groups for treatment and handling effects. In agreement with previous studies, long-lasting, distinct otolith marks were produced by immersion of yolk sac larvae in ≥ 50 mg l − 1 ALC for 24 h. Mortality of eggs and larvae was low during the marking procedure. Hatching success of ALC marked embryos was significantly reduced and hatching was delayed with increasing ALC concentration. Growth rates of larvae through 21 dph (exogenous feeding stage) were significantly reduced in ALC marked fish compared to controls. Biochemical condition (RNA–DNA ratio) was not affected. Subtle changes in activity and metabolism were indicated by reduced first feeding success and yolk absorption rates. Our results reveal that batch marking of finfish early life stages using ALC can have not only significant, acute impacts on survival but, despite long-standing assumptions to the contrary, also sublethal effects on other vital parameters like growth. We discuss these acute and chronic effects and give recommendations for assessment of life stage- and species-specific ALC immersion marking procedures.

On the edge of death: Rates of decline and lower thresholds of biochemical condition in food-deprived fish larvae and juveniles

Gaining reliable estimates of how long fish early life stages can survive without feeding and how starvation rate and time until death are influenced by body size, temperature and species is critical to understanding processes controlling mortality in the sea. The present study is an across-species analysis of starvation-induced changes in biochemical condition in early life stages of nine marine and freshwater fishes. Data were compiled on changes in body size (dry weight, DW) and biochemical condition (standardized RNA–DNA ratio, sRD) throughout the course of starvation of yolk-sac and feeding larvae and juveniles in the laboratory. In all cases, the mean biochemical condition of groups decreased exponentially with starvation time, regardless of initial condition and endogenous yolk reserves. A starvation rate for individuals was estimated from discrete 75th percentiles of sampled populations versus time (degree-days, Dd). The 10th percentile of sRD successfully approximated the lowest, life-stage-specific biochemical condition (the edge of death). Temperature could explain 59% of the variability in time to death whereas DW had no effect. Species and life-stage-specific differences in starvation parameters suggest selective adaptation to food deprivation. Previously published, interspecific functions predicting the relationship between growth rate and sRD in feeding fish larvae do not apply to individuals experiencing prolonged food deprivation. Starvation rate, edge of death, and time to death are viable proxies for the physiological processes under food deprivation of individual fish pre-recruits in the laboratory and provide useful metrics for research on the role of starvation in the sea.

Physiological condition status and muscle‐based biomarkers in rainbow trout (Oncorhynchus mykiss), after long‐term exposure to carbamazepine

Recently, residual pharmaceuticals are generally recognized as relevant sources of aquatic environmental pollutants. However, the toxicological effects of these contaminants have not been adequately researched. In this study, the chronic toxic effects of carbamazepine (CBZ), an anticonvulsant pharmaceutical commonly present in surface and ground water, on physiological condition status and muscle-based biomarkers of rainbow trout were investigated. Fish were exposed at sublethal concentrations of CBZ (1.0 microg l(-1), 0.2 mg l(-1) and 2.0 mg l(-1)) for 42 days. Compared with the control, there was a significant lower (P < 0.05) condition factor in fish exposed at the highest concentration of CBZ (2.0 mg l(-1)), but the hepatosomatic indices in all groups were not significant changes. At lower CBZ concentration (1.0 microg l(-1), 0.2 mg l(-1)), the antioxidant enzyme activities were induced slightly, except catalase, while at the highest concentration (2.0 mg l(-1)) oxidative stress was apparent as reflected by the significant higher lipid peroxidation and protein carbonyls in the fish muscle, associated with a significant inhibition of antioxidant enzymes activities. Moreover, energy metabolic parameters (RNA-DNA ratio, Na(+)-K(+)-ATPase) were significantly inhibited in muscle of the fish exposed at the highest concentration (2.0 mg l(-1)), compared with the control. In short, CBZ-induced physiological and biochemical responses in fish were reflected in parameters measured in this study, which suggest that these biomarkers could be used as potential indicators for monitoring residual pharmaceuticals present in aquatic environment.

RNA-DNA Ratios as an Indicator of Fish Growth in Golden Mahseer (Tor putitora)

RNA-DNA Ratios as an Indicator of Fish Growth in Golden Mahseer (Tor putitora)

Growth and condition of 0-group European flounder, Platichthys flesus as indicator of estuarine habitat quality

The purpose of this present study was to use the growth rates, RNA–DNA ratio and morphometric (Fulton’s K) condition indices measured on 0-group juveniles European flounder, as a means of comparing the quality of estuarine nursery habitats. The Seine estuary, heavily impacted by manmade modifications and one of the most contaminated in Europe, was compared to two smaller estuaries considered as clean (low domestic, agricultural and industrial effluents). Indicators of human disturbance (sediment chemical contaminants) as well as biotic data (macrobenthos abundances) were used to establish between-site differences in environmental quality. The abundance of macrobenthos (potential preys for juvenile) was high and not significantly different among the three estuaries confirming the important role played by estuaries as feeding grounds. Sediment metal concentrations (Cd, Cr, Cu, Pb, Zn) were significantly higher in the Seine than in the Canche and Authie estuaries. Otolith growth was closely related to somatic fish growth, and we used daily otolith increments from the previous 10 days before capture as an indicator of 0-group flounder recent growth (RG). RG did not vary significantly among flounders from the Canche and Authie estuaries and individuals from the Seine had slower RG. RNA–DNA ratio and K values were also significantly lower in individuals from the Seine compared to those of the Authie or the Canche. Pollution (e.g. metal contaminants) is the most likely cause of growth and condition differences among estuaries. The results of this study suggest that habitat-specific fish growth and condition are useful proxies for habitat quality since they integrate the effect of multiple environmental factors.

The influence of food quality and availability on trophic position, carbon signature, and growth rate of an omnivorous crayfish

Fourteen sites in 13 streams were surveyed to address the importance of food quality and quantity on trophic position, carbon signature, and growth rate of noble crayfish ( Astacus astacus ) by combining the analyses of gut content, stable isotopes, and RNA–DNA ratio. The gut content analysis showed an omnivorous feeding habit, but total animal food sources contributed more to the nitrogen and carbon isotope signals of this species. The biomass of invertebrates (i.e., high quality food) influenced the trophic position, carbon signature, and growth rate. Our results show that crayfish in streams with a high biomass of invertebrates were at a higher trophic position and had a higher growth rate than crayfish in streams with a low biomass of invertebrates. A high biomass of relatively sedentary invertebrates indicates a habitat with high algae biomass, which is reflected in the more autochthonous carbon signature of crayfish. Further, noble crayfish in temperate streams seem to have dual functional roles by acting as predator and as shredder by processing large amounts of detritus.

Does skimming flow reduce population growth in horse mussels?

Skimming flow was induced in a field flow-through flume with model and live horse mussels as roughness elements. A growth experiment was conducted in the flume with locally available seawater and natural seston. Horse mussel population growth was compared in turbulent isolated element (control) and skimming flow (treatment) and with regulated natural seston levels, indicated by C = bulk flow seston concentration, C 1 = seston concentration in the benthic boundary layer, near the inhalant, which just meets the maintenance ration of the mussel population. We were able to control the bulk seston within the range: 1.2 to 5 times of C 1 during the growth experiment. No significant difference between control and skimming flow treatments was found in: tissue growth, RNA–DNA ratios, or condition factor. Extrapolating from the experimental results we predict that under minimum growth enhancing seston concentrations at a high horse mussel density (71 m 2), skimming flow does not reduce population growth.

Habitat specific growth rates and condition indices for the sympatric soles Solea solea (Linnaeus, 1758) and Solea senegalensis Kaup 1858, in the Tagus estuary, Portugal, based on otolith daily increments and RNA-DNA ratio

Habitat specific growth rates and condition indices were estimated for Solea solea and Solea senegalensis, in two nursery areas within the Tagus estuary, at the end of the estuarine colonization process, in 2005. While in the uppermost nursery area the two species of sole live in sympatry, in the lower nursery only S. senegalensis is present. Daily increments of left lapillar otoliths were used to estimate age (in days) and determine growth rates (mm per day). Condition indices were assessed through RNA-DNA ratio in muscle samples. Growth rates were higher for S. senegalensis (0.970and 1.180 mm per day in nursery A and B, respectively) than for S. solea (0.767 mm per day in nursery A). Growth rates of S. senegalensis from the uppermost nursery area were lower when compared to those obtained for the other nursery. The RNA/DNA condition index followed the general trend given by the growth rate estimates, i.e. values were higher for S. senegalensis than for S. solea. However, no significant differences were detected in S. senegalensis from the two nurseries. Larger variations in salinity (10‰ amplitude in the uppermost nursery vs 0.2‰ in the lower nursery) and highest pollution loads may be important factors lowering the habitat quality of the uppermost nursery in comparison to the lower nursery. The use of growth rate estimates based on otolith readings and the RNA/DNA index as tools for habitat quality assessment was discussed.

Length and Weight Reduction in Larval and Juvenile Yellow Perch Preserved with Dry Ice, Formalin, and Ethanol

AbstractDue to the increasing interest in biochemical indices such as the RNA–DNA ratio used to measure fish growth, fish often need to be stored frozen with dry ice (i.e., −80°C). The objectives of this study were to (1) quantify the effects of dry ice on both the length and weight of larval and juvenile yellow perch Perca flavescens preserved for storage periods of 15 d and 7–8 months, (2) compare these effects with those of two commonly used preservatives (a 10% solution of formalin and a 75% solution of ethanol), and (3) provide equations to convert the lengths and weights of larval and juvenile yellow perch preserved with dry ice, formalin, and ethanol back to their initial unpreserved values. For all preservation methods, fish weight was more affected than length. The smallest length reduction was observed with formalin (short term: 2.1% and 0.1% for larvae and juveniles, respectively; long term: 10.1% and 1.2%), followed by dry ice (short term: 4.0% and 1.4%; long term: 7.2% and 3.9%) and ethanol (short term: 9.6% and 1.2%; long term: 11.7% and 1.2%). The smallest weight reduction was also observed with formalin (short term: 21.9% and 2.2%; long term: 23.2% and 3.9%), followed by dry ice (short term: 54.0% and 11.1%; long term: 52.8% and 8.4%) and ethanol (short term: 61.1% and 22.0%; long term: 66.0% and 26.0%). Except for one case, all of the regression equations that were built to convert the lengths and weights of larval and juvenile yellow perch preserved with dry ice, formalin, and ethanol back to initial measurements were highly significant.

Ontogenetic changes in RNA, DNA and protein contents of laboratory-reared Pacific bluefin tuna Thunnus�orientalis

The ontogenetic changes in the growth potential of larval and juvenile laboratoryreared Pacific bluefin tuna were examined based on RNA-DNA and protein-DNA ratios. Experimental fish were reared at the Ohshima Experiment Station of Kinki University Fisheries Laboratory in August 2002. Samples were taken from 13 to 35 days after hatching (DAH). Metamorphosis from larva to the juvenile stage was observed around 23 DAH. Somatic growth of Pacific bluefin tuna was accelerated after metamorphosis. The value of the RNA-DNA ratio from 13 to 19 DAH increased slightly from 3.77±0.58 (mean±SD) to 7.28±2.23. After that, the ratio markedly increased from 13.89±3.71 on 21 DAH to 19.11±4.27 on 23 DAH, which was the end of the metamorphic period. After 25 DAH, the ratio remained at a high level of 15–20. The protein-DNA ratio showed a similar tendency to the RNA-DNA ratio. These results suggest that the rapid increase in the RNA-DNA ratio in the metamorphic period supports the consequent rapid somatic growth in the juvenile stage. The high ratio after the metamorphic period could be because of the species-specific traits large prey exhibit for their survival and because of the tuna’s fast-growth after the juvenile stage.

Are fish early growth and condition patterns related to life-history strategies?

Life-history studies provide a global framework for comparison of fish species responses and trade-offs facing ecological and environmental constrains. A broad comparison among fishes’ early growth and condition traits is performed in order to determine ecological patterns of early development regarding latitudinal distribution, habitat use and life-history strategies. Based on Winemiller and Rose (1992) classification of life-history strategies, data on early growth and condition indices of 46 fish species worldwide was analysed. Available information on fishes’ early features, namely first year length percentage (relative to species maximum theoretical length), age at maturation and Fulton’s condition index (K), provided a good segregation of species by latitudinal distribution and habitat use, and evidenced the categories of the three-endpoint model. Higher larvae and juvenile growth rates and condition indices (K, mean RNA–DNA ratios and protein contents) were associated with tropical and temperate fish species that occur in complex or variable habitats (respectively coral reefs and estuaries). These species selected for the opportunistic and periodic strategies, investing highly in rapid growth in order to increase survival probability to counter high mortality rates during early stages or unstable habitat conditions. Later age at maturation, slower larvae and juvenile growth as well as lower mean condition indices were consistent with fish species from more stable or predictable environments, as polar regions and freshwater habitats, which selected for the equilibrium strategy. Nonetheless, differences in energy allocation strategies during early stages were not observed, evidencing the scarcity of available data regarding condition indices and/or the importance of integrating life-history intermediate strategies. Future research into condition indices and other physiological processes, for a broader set of species and for a wider latitudinal and habitat range including seasonal variability (particularly for species from tropical and polar regions), is essential to better understand or test current theories of species ecological patterns. The use of direct quantitative measures of young fishes’ metabolic investment and fitness constitutes a new approach for life-history studies, and should be fundamental for predicting species’ responses to acute environmental or human constrains, especially in a global climate change scenario that is expected to affect distribution and abundance of fish species worldwide.

Direct and indirect effects of the herbicides Glyphosate, Bentazone and MCPA on eelgrass ( Zostera marina)

Eelgrass beds are important habitats for many organisms, but there has been a decline in the area covered by eelgrass during the last decades due to increased eutrophication resulting in increased shading from phytoplankton. The use of herbicides in terrestrial agriculture has also increased over the last century, and while the effects of herbicides on non-target organisms have been well studied in freshwater they are overlooked in coastal waters. It is not known if herbicides have any effect on the distribution of eelgrass ( Zostera marina), or how natural phytoplankton communities respond to the same herbicides. Direct and indirect effects of the herbicides Glyphosate, Bentazone and MCPA both as single toxicants and as mixtures, on the eelgrass plants were investigated in this study. The direct effects on eelgrass were examined by measuring the four different endpoints; the relatively growth rate as length and weight, the chlorophyll a and b ratio, as well as the RNA–DNA ratio, at the end of a 3 days exposure period. The indirect effect was investigated by measuring the effect on a natural phytoplankton production from Roskilde Fjord six times during 1 year. The results showed that the chlorophyll a– b and RNA–DNA ratios were the most sensitive endpoints in single herbicide experiments. The effects of herbicide mixtures on eelgrass were much larger compared to the single substances. Nearly a halving was found for both the relatively growth rate in length and weight, and the RNA–DNA as well as the chlorophyll a– b ratios were also significant reduced. This indicates a possible synergistic effect, and calculations based on the concentration addition model indicate that the low concentrations mixture has a synergistic effect, whereas the high concentration mixture has an antagonistic effect on eelgrass ( Z. marina). The low concentrations mixture is the one with the highest relevance for coastal areas. The effect on phytoplankton showed some variation over the year but mainly in a stimulation in primary production. This means that herbicides affect eelgrass both directly and indirectly.

Temperature and diet effects on omnivorous fish performance: implications for the latitudinal diversity gradient in herbivorous fishes

Herbivorous fishes show a clear latitudinal diversity gradient, making up a larger proportion of the fish species in a community in tropical waters than in temperate waters. One proposed mechanism that could drive this gradient is a physiological constraint due to temperature. One prediction based on this mechanism is that if herbivorous fishes could shift their diet to animal material, they would be better able to grow, survive, and reproduce in cold waters. We tested this prediction on the omnivore Girella nigricans under different temperature and diet regimes using RNA–DNA ratios as an indicator of performance. Fish had increased performance (100%) at low temperatures (12 °C) when their diet was supplemented with animal material. In contrast, at higher temperatures (17, 22, and 27 °C) fish showed no differences between diets. This indicates that omnivorous fishes could increase their performance at low temperatures by consuming more animal matter. This study supports the hypothesis that a relative increase in the nutritional value of plant material at warmer temperatures could drive the latitudinal diversity gradient in herbivorous fishes.

The Effects of Feeding Restriction on Metallothionein Levels and Ethoxyresorufin-O-Deethylase Activities in Mummichogs

Pollution exposure is thought to affect animals through increased maintenance costs, which lead to a decrease in the energy available for other production processes. This can cause weight loss in animals that are chronically exposed to sublethal pollution levels. Starvation and food deprivation have been shown to affect the expression of commonly used bioindicators in fish. The experiments reported in this article were designed to examine the effect of dietary restrictions (in the absence of pollution exposure) on metallothionein and ethoxyresorufin-O-deethylase (EROD; an indicator of CYP1A1 expression) levels in mummichogs Fundulus heteroclitus, a fish that has been extensively examined as an environmental bio-indicator species. Dietary restriction over a 35-d period led to weight loss and alterations in physiological indicators (condition index, liver glycogen, and RNA–DNA ratio) consistent with a reduction in available food. Liver EROD activity increased up to 20-fold on a gram basis and 7-fold on a total-liver basis after 35 d of food restriction. The induction of EROD activity was dependent on the level of caloric restriction. Metallothionein levels initially decreased but then increased slightly to near baseline levels after 35 d of dietary restriction. These results are discussed in the context of using mummichogs as bioindicators of pollution exposure.

Larval development of silver sea bream (Sparus sarba): ontogeny of RNA-DNA ratio, GH, IGF-I, and Na(+)-K(+)-ATPase.

To ascertain some of the important biochemical and molecular events that take place during early larval development of silver sea bream (Sparus sarba), we undertook a study of changes in the morphology as well as the ontogeny of the RNA-DNA ratio, growth hormone (GH), insulin-like growth factor I (IGF-I) messenger RNA abundance, Na(+)-K(+)-ATPase subunit mRNA abundance, and Na(+)-K(+)-ATPase enzyme activity. Larvae samples were collected at 1 to 46 days posthatch (dph). At 7 dph the yolk sac was fully absorbed, and from 28 dph onward larvae underwent rapid developmental changes to the juvenile stage. The RNA-DNA ratio was highest at 1 dph, decreased to low levels between 7 and 21 dph, then increased by 28 dph, and then again by 46 dph. The ontogenetic profiles of GH, IGF-I, and Na(+)-K(+)-ATPase alpha1 and beta1 subunits were studied using reverse transcriptase polymerase chain reaction, coupled with radioisotope hybridization of immobilized DNA. Growth hormone abundance reached a constant and high level from 35 dph onward, whereas the IGF-I level reached a peak at 35 dph and then significantly decreased. Both Na(+)-K(+)-ATPase alpha1 and beta1 subunit mRNAs increased up to 35 dph, however, at 46 dph the alpha1 subunit remained high whereas the beta1 subunit decreased. Na(+)-K(+)-ATPase activity was low in 1-dph larvae but increased rapidly as development progressed. The importance of these findings is discussed within the context of larval development.

RNA–DNA Ratio in Scales from Juvenile Cod Provides a Nonlethal Measure of Feeding Condition

Abstract We removed scales from juvenile Atlantic cod Gadus morhua, extracted RNA and DNA from tissue associated with the scales, and found that the ratio of RNA to DNA (R/D) reflects the feeding condition and growth of the fish. Moreover, R/D was found to be a more sensitive indicator of feeding condition than either weight or length. We performed a series of experiments in which the diets of juvenile cod (mean total lengths, 10.4–18.8 cm) were manipulated. At regular intervals, the fish were weighed and measured, and scales were removed from each individually marked fish. In fish that were either fed or starved for 49 d, R/D was significantly correlated with growth in length for individual fish (r 2 = 0.27, P < 0.0001) and tank means (r 2 = 0.59, P < 0.0001). The ratio of RNA to DNA was also sensitive to changes in feeding condition. Fish that were initially starved had significantly (P < 0.05) higher R/D after 2 d of feeding, and fish that were initially fed had significantly (P < 0.05) lower R/D after...

Availability of phosphorus from selected inorganic phosphate to juvenile abalone,Haliotis discus hannai ino.

The availability of phosphorus to juvenile abalone,Haliotis discus hannai from primary, secondary and tertiary calcium phosphate, primary sodium or potassium phosphate separately or in combination was determined in a 120-day feeding trial. Seven semi-purified diets were formulated to contain relatively constant dietary phosphorus, ranging from 0.78%–0.82%. The concentrations of dietary phosphorus were presumed to be slightly below the requirement for abalone. A brown alga,Laminaria japonica, was used as a control diet. Abalone juveniles of silimar size (average weight 1.18 g; average shell length 18.74 mm) were distributed in a single-pass, flow-through system using a completely randomized design with eight treatments and three replicates each treatment. The survival ranged from 71.1% to 81.1%, and was not significantly (P>0.05) related to dietary treatment. However, the weight gain rate (41.72%–65.02%), daily increment in shell length (36.87–55.07 μm) and muscle RNA-DNA ratio (3.44–4.69) were significantly (P<0.05) affected by dietary treatment. Soft body alkaline phosphatase activity (10.9–19.8 U/g wet tissue) and carcass levels of lipid (7.71%–9.33%) and protein (46.68%–49.35%) were significantly (P<0.05) responsive to available phosphorus of the diets. Dietary treatment had significant effect (P<0.05) on concentrations of phosphorus in the whole body (WB) and soft body (SB). Apparent digestibility coefficients (45%–97%) of phosphorus were also significantly (P<0.05) different between dietary treatments. The results indicated that among these inorganic compounds, primary calcium, potassium and sodium phosphates separately or in combination could be utilized effectively by juvenile abalone as dietary phosphorus sources (availability ranging from 87%–97%). However, secondary and tertiary calcium phosphates were found to be low in availability, the values being 45% and 77%, repectively.

Relationship between nucleic acid ratios and growth in Listeria monocytogenes.

Listeria monocytogenes is a pathogen whose distribution in a range of foodstuffs requires the development of methods for sensitive and rapid detection. Molecular biological methods usually rely on specific detection of L. monocytogenes rDNA directly amplified by the application of PCR to DNA extracts. Information on the metabolic status of L. monocytogenes populations would be valuable and can, in theory, be provided by quantitative detection of rRNA itself. Both fluorometry and oligonucleotide probe assays were applied to L. monocytogenes cultures to quantify RNA and DNA and produced more meaningful data than previous estimates for bacteria based on eukaryotic nucleic acid standards. In batch culture, the RNA-DNA ratio was found to be greatest at the end of exponential growth, after which RNA became degraded in accordance with the rapid decrease in viability. When the pH of the medium was controlled at neutrality, culture viability was dramatically extended and although RNA was degraded, intact DNA was maintained for the duration of the experiment. Ribosome numbers per cell were estimated to decrease from about 25000 observed during mid-exponential growth to about 600 during stationary phase, under pH-controlled conditions. Like Escherichia coli, therefore, L. monocytogenes loses viability and rRNA rapidly once exponential growth has ceased in batch culture. However, much improved survival of a culturable L. monocytogenes population when pH is controlled has clear implications for the persistence of this species in buffered environments such as dairy products.