Can We Predict Joint Effects Of Hypoxia And Metals On Fish Survival?

Fish are suddenly exposed to hypoxic conditions during diverse events such as seiche- or turnover-related water movements, bottom water release from reservoirs, ice-over of eutrophic arctic lakes, and rapid shifts in respiration: photosynthesis associated with cultural eutrophication. In each case, chemical equilibria established under hypoxic conditions that result in metal dissolution and accumulation suddenly shift toward chemical equilibria of oxic conditions. Critical changes in speciation include those determining the free ion activity that, as expressed by the Free Ion Activity Model (FIAM), is often the most bioactive form of a dissolved metal. Metal phase can also change rapidly and, in some cases, result in a precipitate on respiratory surfaces. Exposure of fish gills to metal (and integument of larval or small fish) changes O2 exchange dynamics. Changes in mucus quality and production and lamellae morphology decrease the amount of effective gill exchange surface and increase the diffusive layer thickness. These changes exacerbate those associated with the reduced O2 partial pressure gradient. Consequent shifts in blood chemistry (e.g., pH and ion composition) and ventilation also affect metal transport and deposition within fish tissues. Some of these changes have immediate consequences, but others can continue for long periods after the hypoxic conditions pass. Long-term metal effects can influence fish tolerance during future hypoxic episodes. A joint, similar action model can be applied if the parsimonious assumption is made that asphyxiation constitutes a common mode-of-action for both acute metal effects and hypoxia. Joint action models are applicable based on either conventional dose-effect or survival time approaches. Expansion of such models to a physiologically-based toxicokineticstoxicodynamics framework (e.g., framed around the Fick equation) would be desirable, provided that model parameter requirements remain realistic. Long-term effects may be better addressed with models such as the binary logistic models used by epidemiologists.https://scholarworks.wm.edu/vimsbooks/1013/thumbnail.jp

Bedside differentiation of vestibular neuritis from central "vestibular pseudoneuritis".

Acute unilateral peripheral and central vestibular lesions can cause similar signs and symptoms, but they require different diagnostics and management. We therefore correlated clinical signs to differentiate vestibular neuritis (40 patients) from central ‘‘vestibular pseudoneuritis’’ (43 patients) in the acute situation with the final diagnosis assessed by neuroimaging. Skew deviation was the only specific but non-sensitive (40%) sign for pseudoneuritis. None of the other isolated signs (head thrust test, saccadic pursuit, gaze evoked nystagmus, subjective visual vertical) were reliable; however, multivariate logistic regression increased their sensitivity and specificity to 92%

Uniqueness of Ground States for Short-Range Spin Glasses in the Half-Plane

We consider the Edwards-Anderson Ising spin glass model on the half-plane $Z \times Z^+$ with zero external field and a wide range of choices, including mean zero Gaussian, for the common distribution of the collection J of i.i.d. nearest neighbor couplings. The infinite-volume joint distribution $K(J,\alpha)$ of couplings J and ground state pairs $\alpha$ with periodic (respectively, free) boundary conditions in the horizontal (respectively, vertical) coordinate is shown to exist without need for subsequence limits. Our main result is that for almost every J, the conditional distribution $K(\alpha|J)$ is supported on a single ground state pair.Comment: 20 pages, 3 figure

Variability in spawning frequency and reproductive development of the narrow-barred Spanish mackerel (Scomberomorus commerson) along the west coast of Australia

The narrow-barred Spanish mackerel (Scomberomorus commerson) is widespread throughout the Indo-West Pacific region. This study describes the reproductive biology of S. commerson along the west coast of Australia, where it is targeted for food consumption and sports fishing. Development of testes occurred at a smaller body size than for ovaries, and more than 90% of males were sexually mature by the minimum legal length of 900 mm TL compared to 50% of females. Females dominated overall catches although sex ratios within daily catches vary considerably and females were rarely caught when spaw n ing. Scomberomorus commerson are seasonally abundant in coastal waters and most of the commercial catch is taken prior to the reproductive season. Spawning occurs between about August and November in the Kimberley region and between October and January in the Pilbara region. No spawning activity was recorded in the more southerly West Coast region, and only in the north Kimberley region were large numbers of fish with spawning gonads collected. Catches dropped to a minimum when spawning began in the Pilbara region, when fish became less abundant in inshore waters and inclement weather conditions limited fishing on still productive offshore reefs. Final maturation and ovulation of oocytes took place within a 24-hour period, and females spawned in the afternoon-evening every three days. A third of these spawning females released batches of eggs on consecutive days. Relationships between length, weight, and batch fecundity are presented

Joint Effects of Fragmentation and Mercury Contamination on Marsh Periwinkle (Littoraria irrorata) Movement

There are different ways contaminants can interact and enhance the effects of habitat fragmentation, such as modifying the movement of organisms. The present study tested the hypothesis that mercury exacerbates the effects offragmentation by affecting the movement of the marsh periwinkle Littoraria irrorata and reducing the probability of snails crossing fragmented microlandscape experimental systems. How these changes could affect the search efficiency of organisms in the long term was assessed using hidden Markov models and random walks simulations. Bayesian nonlinearmodels were used to analyze the effects of fragmentation and contamination on the mean speed and mean directional change of organisms. Snail movement for control and two mercury‐exposure treatments were recorded in microlandscapeswith six different levels of habitat cover and three landscape replicates. The results indicated that exposed organisms had lower probabilities of crossing the landscape, reduced speed, and shifts in step length distributions. Both mercury exposure and habitat fragmentation affected the movement of the marsh periwinkle. Mercury exacerbated the effects of habitat fragmentation by affecting the cognition (e.g., route planning, orientation, and spatial learning) and movement of L. irrorata. Hence, the interaction of these stressors could further reduce the functional connectivity of landscapes and reduce the searchefficiency of organisms

Regression or significance tests: What other choice is there?—An academic perspective

Both the no-observed-effect concentration and its null hypothesis significance testing foundation have drawn steady criticism since their inceptions [1–5]. Many in our field reasonably advocate regression to avoid conventional null hypothesis significance testing shortcomings; however, regression is compromised under commonly encountered conditions (Green, present Perspective’s Challenge). As the debate to favor null hypothesis significance testing or regression methods continues into the 21st century, a sensible strategy might be to take a moment to ask, Are there now other choices? Our goal is to sketch out 1 such choice

Biological characteristics and mortality of western butterfish (Pentapodus vitta), an abundant bycatch species of prawn trawling and recreational fishing in a large subtropical embayment

The western butterfish (Pentapodus vitta) is numerous in the bycatch of prawn trawling and recreational fishing in Shark Bay, Western Australia. We have thus determined crucial aspects of its biological characteristics and the potential impact of fishing on its abundance within this large subtropical marine embayment. Although both sexes attained a maximum age of 8 years, males grow more rapidly and to a larger size. Maturity is attained at the end of the first year of life and spawning occurs between October and January. The use of a Bayesian approach to combine independent estimates for total mortality, Z, and natural mortality, M, yielded slightly higher point estimates for Z than M. This result indicates that P. vitta is lightly impacted by fishing. It is relevant that, potentially, the individuals can spawn twice before recruitment into the fishery and that 73% of recreationally caught individuals are returned live to the water