Respirometer in a box: development and use of a portable field respirometer for estimating oxygen consumption of large-bodied fishes

This study developed a portable, low-cost field respirometer for measuring oxygen consumption rates of large-bodied fishes. The respirometer performed well in laboratory tests and was used to measure the oxygen consumption rates ( O₂) of bull sharks Carcharhinus leucas (mean: 249.21 ± 58.10 mg O₂ kg⁻¹ h⁻¹ at 27.05°C). Interspecific comparisons and assessments of oxygen degradation curves indicated that the respirometer provided reliable measurements of O₂. This system presents a field-based alternative to laboratory respirometers, opening opportunities for studies on species in remote localities, increasing the ability to validate physiological field studies.     

Age and growth of the bull shark (Carcharhinus leucas) around Reunion Island,South West Indian Ocean

Sharks exhibit varied demographic strategies depending on both the species and the population location, which make them more or less vulnerable to fishing. Accurate evaluation of local age and growth parameters is therefore fundamental for the sustainable management of their stocks. Although demographic parameters have been assessed for bull shark (Carcharhinus leucas) populations in several locations of the world, this information is missing so far around Reunion Island, in the south-west Indian Ocean. To fill this gap of knowledge, age and growth data were gathered from the vertebrae of 140 individuals of C. leucas (77 females and 63 males, mostly adults) fished around the island between 2012 and 2019. After verification of the annual deposition of growth band pairs on these structures using relative marginal increment analysis on 40 individuals, band pairs were counted along the vertebral centrum for each individual. Thanks to this approach, growth was shown to significantly differ between male and female C. leucas around Reunion Island, with respective von Bertalanffy growth model equations of L_t =  and L_t = . Indeed, the females of the species fished in this area were significantly (P < 0.001) larger than local males, with an estimated difference in size of ~16.1 cm at 20 years old. They also apparently reach older ages, with an estimated maximum age of 33.50 years, against 29.75 years only for the males. The estimated size at birth around the island is larger than elsewhere in the world, varying from 92.30 to 100.00 cm depending on the method used. These results confirm that the population of C. leucas around Reunion Island exhibits a K-selected strategy, which makes it highly vulnerable to fishing pressure.     

Spatial pattern of distribution and reproductive strategy of vermiculate electric-rays Narcine vermiculatus

In the study, the authors evaluate the spatial distribution pattern of vermiculate electric-ray Narcine vermiculatus using geostatistical techniques to predict its spatial distribution and indicate its reproduction strategy. From January 2008 to December 2009, 3333 specimens of vermiculate electric-ray were caught. Total length (L_T), sex, maturity stage, catch location and depth were recorded for each specimen. The L_T of vermiculate electric-ray ranged from 6.7–24.6 cm. The authors estimate an irregular spatial structure, with a high-density patch ( 53 ind. ha⁻¹) located on the east coast, which concentrates 65.2% of the specimens. The high-density patch consists mainly of large juveniles (13.3–19.5 cm L_T), sub-adults (14.0–19.8 cm L_T) and young adults (14.7–21.3 cm L_T). Data indicate that adults migrate to the high-density patch to reproduce. Males reached maturity at 14.5 cm L_T, whereas females reached maturity at 19.3 cm L_T. Vitellogenesis in female vermiculate electric-ray begins in June; ovulation, mating, fertilization and gestation in October and birth begins in February. This indicates an annual cycle with vitellogenesis and consecutive gestation, in females synchronized in reproduction. Fecundity was 1–8 ( 4), and the sex ratio of embryos was 1:1. The birth occurred between February and April, with an average size at parturition of 6.3 cm L_T. Incidental capture of sub-adults and adults of N. vermiculatus by bottom trawls threatens the survival of this species.     

Developmental changes in oxygen consumption and hypoxia tolerance in the heat and hypoxia-adapted tabasco line of the Nile tilapia Oreochromis niloticus,with a survey of the metabolic literature for the genus Oreochromis

The genus Oreochromis is among the most popular of the tilapiine cichlid tribe for aquaculture. However, their temperature and hypoxia tolerance, if tested at all, is usually tested at temperatures of 20–25°C, rather than at the considerably higher temperatures of 30–35°C typical of tropical aquaculture. We hypothesized that both larvae and adults of the heat and hypoxia-adapted Tabasco-line of the Nile tilapia Oreochromis niloticus would be relatively hypoxia-tolerant. Oxygen consumption rate (), Q₁₀ and aquatic surface respiration (ASR) was measured using closed respirometry at 2 (c. 0.2 g), 30 (c. 2–5 g), 105 c. (10–15 g) and 240 (c. 250 g) days of development, at 25°C, 30°C and 35°C. at 30°C was inversely related to body mass: c. 90 μM O₂ g⁻¹/h in larvae down to c. 1 μM O₂ g⁻¹/h in young adults. Q₁₀ for was typical for fish over the range 25–35°C of 1.5–2.0. ASR was exhibited by 50% of the fish at pO₂ of 15–50 mmHg in a temperature-dependent fashion. However, the largest adults showed notable ASR only when pO₂ fell to below 10 mmHg. Remarkably, p_crit for was 12–17 mmHg at 25–30°C and still only 20–25 mmHg across development at 35°C. These values are among the lowest measured for teleost fishes. Noteworthy is that all fish maintain equilibrium, ventilated their gills and showed routine locomotor action for 10–20 min after ceased at near anoxia and when then returned to oxygenated waters, all fish survived, further indicating a remarkable hypoxic tolerance. Remarkably, data assembled for from >30 studies showed a > x2000 difference, which we attribute to calculation or conversion errors. Nonetheless, p_crit was very low for all Oreochromis sp. and lowest in the heat and hypoxia-adapted Tabasco line.     

Excess post‐hypoxic oxygen consumption in Atlantic cod Gadus morhua

Atlantic cod Gadus morhua experienced oxygen deficit () when exposed to oxygen levels below their critical level (c. 73% of p_crit) and subsequent excess post‐hypoxic oxygen consumption (C_EPHO) upon return to normoxic conditions, indicative of an oxygen debt. The mean ± s.e . C_EPHO: was 6·9 ± 1·5, suggesting that resorting to anaerobic energy production in severe hypoxia is energetically expensive.     

Precision of the age–length increments of three cyprinids: effects of fish number and sub‐sampling strategy

The effects of number of fish that are aged and scale sub‐sampling strategies on the precision of estimates of mean age–length increments from populations of Rutilus rutilus, Leuciscus leuciscus and Leuciscus cephalus were tested. Analyses used data derived from river fish communities in eastern England, U.K.. Regarding the number of fishes analysed in each age group, for each species and mean fork‐length increment at age, significant relationships were detected between sample size (n) and the coefficient of variation of the mean (Z) and mean length increment and measured variance (s²). This enabled calculation of the number of scales for producing a mean length increment at age according to . Outputs indicated that the number of scales requiring ageing increased substantially as precision increased, but with little variation between species per age category. Ageing between seven and 12 scales per age group would thus provide estimates at 10% precision. As the ages of fishes are not known in advance of scale ageing, the effect of scale sub‐sampling regime on precision was also tested using randomized strategies of 10 fish per 5 mm, five per 5 mm, three per 5 mm, 10 per 10 mm, five per 10 mm and three per 10 mm. These were applied to the datasets and the consequences of their reduction in the number of scales for precision were determined using . When compared to no sub‐sampling, three per 10 mm always significantly reduced data precision, whereas 10 per 5 mm never significantly reduced precision. These outputs can thus be applied to the design of fish sampling protocols where age and growth estimates are required, with the randomized sub‐sampling likely to be the most useful strategy.     

The effects of hurricanes on the stochastic population growth of the endemic epiphytic orchid Broughtonia cubensis living in Cuba

We carried out a posthurricane evaluation of Broughtonia cubensis (Lindl.) Cogn., an endemic Cuban epiphytic orchid, after Hurricane Ivan (2004). We studied the transient responses in the stochastic dynamics of the species at three different sites over 13 successive years (2006–2019), monitored plot inventories (464 individuals in 10 transects) and built stochastic population models. The deterministic stochastic growth rate values () did not significantly differ (F = 2.76; p > 0.076) among the three sites over the 2006–2019 period. The long-term stochastic growth rate was 0.973 [0.932, 1.034]. The matrix elements that had the largest effect on were the transition to and stasis within the largest size class. Transient responses explained an average of 86% of the variation in the observed population growth rates , compared to 4% of the variation in the vital rates . Because transient dynamics are dependent on the population size composition, we ran extinction risk analyses under two scenarios: a population composed mainly of juveniles and another composed mainly of adults. There was little risk of falling below the quasi-extinction threshold before 25 year for both juveniles and adults. However, the risk of quasi-extinction was almost certain for both size classes by 80 year. We also simulated the effect of increasing the hurricane occurrence probability over 80 year on the population. There was little risk of extinction before 20 year in the baseline model, but there was a significant risk of extinction within 5 year when 90% of the individuals were affected by a new hurricane event.     

An estimator of the Opportunity for Selection that is independent of mean fitness

Variation among individuals in number of offspring (fitness, k) sets an upper limit to the evolutionary response to selection. This constraint is quantified by Crow's Opportunity for Selection (I), which is the variance in relative fitness (I = σ²_k/(u_k)²). Crow's I has been widely used but remains controversial because it depends on mean offspring number in a sample (). Here, I used a generalized Wright-Fisher model that allows for unequal probabilities of producing offspring to evaluate behavior of Crow's I and related indices under a wide range of sampling scenarios. Analytical and numerical results are congruent and show that rescaling the sample variance (s²_k) to its expected value at a fixed removes dependence of I on mean offspring number, but the result still depends on choice of . A new index is introduced, Δ_I = Π– E(Î_drift) = Π– 1/, which makes Î independent of sample without the need for variance rescaling. Δ_I has a straightforward interpretation as the component of variance in relative fitness that exceeds that expected under a null model of random reproductive success. Δ_I can be used to directly compare estimates of the Opportunity for Selection for samples from different studies, different sexes, and different life stages.     

Valid oxygen uptake measurements: using high r2 values with good intentions can bias upward the determination of standard metabolic rate

This analysis shows good intentions in the selection of valid and precise oxygen uptake (O₂) measurements by retaining only slopes of declining dissolved oxygen level in a respirometer that have very high values of the coefficient of determination, r², are not always successful at excluding nonlinear slopes. Much worse, by potentially removing linear slopes that have low r² only because of a low signal-to-noise ratio, this procedure can overestimate the calculation of standard metabolic rate (SMR) of the fish. To remedy this possibility, a few simple diagnostic tools are demonstrated to assess the appropriateness of a given minimum acceptable r², such as calculating the proportion of rejected O₂ determinations, producing a histogram of the r² values and a plot of r² as a function of O₂. The authors offer solutions for cases when many linear slopes have low r². The least satisfactory but easiest to implement is lowering the minimum acceptable r². More satisfactory solutions involve processing (smoothing) the raw signal of dissolved oxygen as a function of time to improve the signal-to-noise ratio and the r²s.     

Inverse problem approach to regularized regression models with application to predicting recovery after stroke

Regression modelling is a powerful statistical tool often used in biomedical and clinical research. It could be formulated as an inverse problem that measures the discrepancy between the target outcome and the data produced by representation of the modelled predictors. This approach could simultaneously perform variable selection and coefficient estimation. We focus particularly on a linear regression issue, , where is the parameter of interest and its components are the regression coefficients. The inverse problem finds an estimate for the parameter , which is mapped by the linear operator to the observed outcome data . This problem could be conveyed by finding a solution in the affine subspace . However, in the presence of collinearity, high-dimensional data and high conditioning number of the related covariance matrix, the solution may not be unique, so the introduction of prior information to reduce the subset and regularize the inverse problem is needed. Informed by Huber's robust statistics framework, we propose an optimal regularizer to the regression problem. We compare results of the proposed method and other penalized regression regularization methods: ridge, lasso, adaptive-lasso and elastic-net under different strong hypothesis such as high conditioning number of the covariance matrix and high error amplitude, on both simulated and real data from the South London Stroke Register. The proposed approach can be extended to mixed regression models. Our inverse problem framework coupled with robust statistics methodology offer new insights in statistical regression and learning. It could open a new research development for model fitting and learning.     

Body shape and robustness response to water flow during development of brown trout Salmo trutta parr

Domesticated brown trout Salmo trutta parr were subjected to increased, variable flow under controlled experimental conditions. Using geometric morphometric analyses, (a mass–length index) and caudal fin area–body length ratio, this study assessed morphological responses in lateral body depth, growth and robustness and propulsive potential, respectively, of parr over the course of 32 weeks. Geometric morphometric analyses did not reveal an effect of exercise on either lateral body depth or caudal fin area. However, improved overall robustness and growth trajectories in exercised parr showed a positive adaptive response to the enriched habitat. Exercise and habitat heterogeneity thus have the potential to improve survivability of domesticated salmonids in the wild.     

Reproductive biology of female bigeye tuna Thunnus obesus in the western Pacific Ocean

The reproductive biology of female bigeye tuna Thunnus obesus was assessed by examining 888 fish (ranging from 84·9 to 174·4 cm fork length, L_F) caught by Taiwanese offshore longliners in the western Pacific Ocean from November 1997 to November 1998 and November to December 1999 and 258 gonad samples from these fish. The overall sex ratio of the catch during the sampling differed significantly from 0·5, but males were predominant in sizes >140 cm L_F. Reproductive activity (assessed by histology), a gonado‐somatic index, and the size‐frequency distributions of whole oocytes indicated that spawning occurred throughout the year and the major spawning season appeared to be from February to September. The estimated sizes at 50% maturity (L_F50) of females was 102·85 cm (95% c.i .: 90·79–110·21 cm) and the smallest mature female was 99·7 cm L_F. They are multiple spawners and oocytes develop asynchronously. The proportion of mature (0·63) and reproductively active (0·70) females with ovaries containing postovulatory follicles indicated that they spawn almost daily. Batch fecundity for 15 females with the most advanced oocytes (>730 µm) ranged from 0·84 to 8·56 million eggs (mean ± s.d . = 3·06 ± 2·09). The relationships between batch fecundity (F_B, in millions of eggs) and L_F (cm) and round mass (M_R, kg) were (r² = 0·84) and (r² = 0·80), respectively. The parameters estimated in this study are key information for stock assessments of T. obesus in the western Pacific Ocean and will contribute to the conservation and sustainable yield of this species.     

Age and growth of mangrove red snapper Lutjanus argentimaculatus at its cool‐water‐range limits

This study investigates the age and growth of Lutjanus argentimaculatus at its southern (cooler) range limits in eastern Australia. Specimens were collected from New South Wales and southern Queensland between November 2011 and December 2013. Fork lengths (L_F) ranged from 190 to 1019 mm, and ages ranged from 2+ to 57+ years. Growth was described by the von Bertalanffy growth function with coefficients L_∞ = 874·92 mm, K = 0·087 year^?1 and t₀ = ?2·76 years. Estimates of the instantaneous natural mortality rate (M) ranged from 0·072 to 0·25. The L_F (mm) and mass (W; g) relationship was represented by the equation: . The maximum age of 57+ years is the oldest reported for any lutjanid and comparisons with tropical studies suggest that the age‐based demography of L. argentimaculatus follows a latitudinal gradient. High maximum ages and low natural mortality rates indicate considerable vulnerability to overexploitation at the species' cool‐water‐range limits. These results demonstrate the need to identify underlying processes driving latitudinal gradients in fish demography.     

Enhanced temporal and spatial resolution in super-resolution covariance imaging algorithm with deconvolution optimization

Based on the numerical analysis that covariance exhibits superior statistical precision than cumulant and variance, a new SOFI algorithm by calculating the n orders covariance for each pixel is presented with an almost -fold resolution improvement, which can be enhanced to 2ⁿ via deconvolution. An optimized deconvolution is also proposed by calculating the (n + 1) order SD associated with each n order covariance pixel, and introducing the results into the deconvolution as a damping factor to suppress noise generation. Moreover, a re-deconvolution of the covariance image with the covariance-equivalent point spread function is used to further increase the final resolution by above 2-fold. Simulated and experimental results show that this algorithm can significantly increase the temporal–spatial resolution of SOFI, meanwhile, preserve the sample's structure. Thus, a resolution of 58 nm is achieved for 20 experimental images, and the corresponding acquisition time is 0.8 seconds.     

Determination of the diameter of simulated human capillaries using shifted position-diffuse reflectance imaging

Multiple diseases are associated with a wide spectrum of microvascular dysfunctions, microangiopathies and microcirculation disorders. Monitoring the microcirculation could thus be useful to diagnose many local and systemic circulatory disorders and to supervise critically ill patients. Many of the scores currently available to help identify the condition of a microcirculation disorder are invasive or leave scope for interpretation. Thus, the present study aims to investigate with Monte-Carlo simulations (as numerical solutions of the radiative transfer equation) whether shifted position-diffuse reflectance imaging (SP-DRI), a non-invasive diagnostic technique, reveals information on the capillary diameter to assess the state of the microcirculation. To quantify the SP-DRI signal, the modulation parameter K is introduced. It proves to correlate almost perfectly with the capillary diameter (), making it a valid parameter for reliably assessing microcirculation. SP-DRI is emerging as an important milestone on the way to early and conveniently diagnosing microcirculation associated diseases.     

Optimal rotation of insecticides to prevent the evolution of resistance in a structured environment

Several strategies have been used in insecticide resistance management to prevent the evolution of resistance, but the spatial aspects of insecticide application are crucially important among these strategies. Here, we consider a structured environment that consists of on-farm and off-farm fields where crops are planted periodically in on-farm fields during cultivation periods. We define the basic reproduction rate () of resistance as the expected number of offspring of a resistant individual divided by that of a susceptible individual under the condition that the proportion of resistance is extremely small; it is measured as the quantity per cycle of the cultivation period. We calculate using realistic dose-survival curves under a given fitness cost of resistance genes. The evolution of resistance occurs if and only if the value is larger than 0. Then, we propose a procedure for calculating the optimal design of rotational spraying that prevents the evolution of resistance, that is, the evolutionary stable strategy (ESS) for farmers, satisfying the mortality required for managing the abundance of insects. We consider the following controllable factors in calculating the optimal design: the dose of insecticide, the number of sprays, the number of different types of insecticides and potentially, the size of on-farm fields.     

Long-Term Spatiotemporal Dynamics and Factors Associated with Trends in Bare-Nosed Wombats

Geographically widespread species present challenges for conservation assessment. We used long-term spotlight surveys to assess spatiotemporal dynamics of bare-nosed wombats (Vombatus ursinus), encompassing 34 years of surveys for the Tasmanian mainland sub-species (V. u. tasmaniensis, 1985–2018) and 25 years for the Flinders Island sub-species (V. u. ursinus, 1994–2018). Wombat populations increased on the Tasmanian mainland by 2.59 times and on Flinders Island by 3.51 times ( = 1.05 and 1.1 times increase/yr, respectively). At smaller spatial scales on mainland Tasmania, increases in wombat counts generally occurred within meteorological regions and regional zones, except for the Central North (West Tamar) region where a decrease in wombats is linked to a sarcoptic mange disease epizootic. We used generalized additive models to assess relationships between variables and wombat counts. The most supported variables at the mainland Tasmania scale were (in order of importance) year, positive associations with time-lagged minimum temperature, Tasmanian devil (Sarcophilus harrisii) counts, and moonlight, and a negative association with time-lagged rainfall. Among meteorological regions, variables associated with wombat counts exhibited some heterogeneity, with temperature and rainfall the most frequently associated variables. Our long-term, large-scale, and ecologically diverse analysis of bare-nosed wombats supports spotlight monitoring as a valuable, relatively simple, and affordable survey method in Tasmania and beyond. © 2021 The Wildlife Society.     

Dual‐ and single‐shot susceptibility ratio measurements with circular polarizations in second‐harmonic generation microscopy

Polarization‐resolved second‐harmonic generation (P‐SHG) microscopy is a technique capable of characterizing nonlinear optical properties of noncentrosymmetric biomaterials by extracting the nonlinear susceptibility tensor components ratio , with z‐axis parallel and x‐axis perpendicular to the C₆ symmetry axis of molecular fiber, such as a myofibril or a collagen fiber. In this paper, we present two P‐SHG techniques based on incoming and outgoing circular polarization states for a fast extraction of : A dual‐shot configuration where the SHG circular anisotropy generated using incident right‐ and left‐handed circularly‐polarized light is measured; and a single‐shot configuration for which the SHG circular anisotropy is measured using only one incident circular polarization state. These techniques are used to extract the of myosin fibrils in the body wall muscles of Drosophila melanogaster larva. The results are in good agreement with values obtained from the double Stokes‐Mueller polarimetry. The dual‐ and single‐shot circular anisotropy measurements can be used for fast imaging that is independent of the in‐plane orientation of the sample. They can be used for imaging of contracting muscles, or for high throughput imaging of large sample areas.     

Satiation meal and the effects of meal and body sizes on gastric evacuation rate in brook trout Salvelinus fontinalis fed commercial pellets

Gastric evacuation (GE) experiments were performed on brook trout Salvelinus fontinalis fed commercial food pellets. The experiments included small fish (36 g; 15 cm total length, L_T) fed meals of 0·2, 0·4 and 0·8 g and large fish (152 g; 23 cm) fed meals of 0·8, 2·0 and 4·0 g at temperatures ranging from 15·1 to 18·2° C. The stomach contents were thereafter sampled and weighed at 3 h intervals until the first empty stomach was observed. The course of GE was examined by use of a general power function of the data that revealed that the square‐root function described the GE rate (GER) by the current stomach content mass independently of original meal size. Using the square‐root function, the relationship between GER and fish size was described by a power function of fish length, whereas the effect of temperature was described by a simple exponential function. GER of the commercial pellets fed to S. fontinalis could thus be described by (g h^?1), where S_t is stomach mass (g) at time t (h), L is total fish length (cm) and T is temperature (° C). The result of this study should provide a useful tool for planning of feeding regimes in production of S. fontinalis by optimizing growth and minimizing food waste.     

Important role of genetic drift in rapid polygenic adaptation

We analyzed a model to determine the factors that facilitate or limit rapid polygenic adaptation. This model includes population genetic terms of mutation and both directional and stabilizing selection on a highly polygenic trait in a diploid population of finite size. First, we derived the equilibrium distribution of the allele frequencies of the multilocus model by diffusion approximation. This formula describing the equilibrium allele frequencies as a mutation‐selection‐drift balance was examined by computer simulation using parameter values inferred for human height, a well‐studied polygenic trait. Second, assuming that a sudden environmental shift of the fitness optimum occurs while the population is in equilibrium, we analyzed the adaptation of the trait to the new optimum. The speed at which the trait mean approaches the new optimum increases with the equilibrium genetic variance. Thus, large population size and/or large mutation rate may facilitate rapid adaptation. Third, the contribution of an individual locus i to polygenic adaptation depends on the compound parameter , where is the effect size, the equilibrium frequency of the trait‐increasing allele of this locus, and . Thus, only loci with large values of this parameter contribute coherently to polygenic adaptation. Given that mutation rates are relatively small, this is more likely in large populations, in which the effects of drift are limited.