Boyle's Law ignores dynamic processes in governing barotrauma in fish.

The expansion and potential rupture of the swim bladder due to rapid decompression, a major cause of barotrauma injury in fish that pass through turbines and pumps, is generally assumed to be governed by Boyle's Law. In this study, two swim bladder expansion models are presented and tested in silico. One based on the quasi-static Boyle's Law, and a Modified Rayleigh Plesset Model (MRPM), which includes both inertial and pressure functions and was parametrised to be representative of a fish swim bladder. The two models were tested using a range of: (1) simulated and (2) empirically derived pressure profiles. Our results highlight a range of conditions where the Boyle's Law model (BLM) is inappropriate for predicting swim bladder size in response to pressure change and that these conditions occur in situ, indicating that this is an applied and not just theoretical issue. Specifically, these conditions include any one, or any combination, of the following factors: (1) when rate of pressure change is anything but very slow compared to the resonant frequency of the swim bladder; (2) when the nadir pressure is near or at absolute zero; and (3) when a fish experiences liquid tensions (i.e. negative absolute pressures). Under each of these conditions, the MRPM is more appropriate tool for predicting swim bladder size in response to pressure change and hence it is a better model for quantifying barotrauma in fish.

The effects of simulated hydropower turbine rapid decompression on two Neotropical fish species.

Barotrauma is a major cause of injury and mortality of fish as they pass through hydropower turbines. Current understanding of hydropower related barotrauma is biased towards northern temperate and southern subtropical species with single chambered swim bladders, specifically North American and Australian species, respectively. Today, unprecedented hydropower development is taking place in Neotropical regions where many species have complex multi-chambered swim bladder architecture. This study investigated barotrauma in two dual-chambered physostomous Neotropical fish (pacu, Piaractus mesopotamicus, and piracanjuba, Brycon orbignyanus) exposed to rapid (< 1 s) decompression at different Ratios of Pressure Change (RPC), using a hypo-hyperbaric chamber. The incidence and intensity (percentage surface area of organ affected) of injury and physiological and behavioural response (hereafter just response) of each species immediately after decompression was assessed. Twenty-two injury types (e.g. gill haemorrhage and exophthalmia) and eight response categories (e.g. rising to the surface and loss of orientation) were identified and the influence of: 1) species, 2) RPC, and 3) swim bladder rupture on each was quantified. There was considerable interspecific difference with emboli type injuries occurring more frequently in piracanjuba, but injury intensity tending to be higher in pacu. Both swim bladder chambers tended to rupture in piracanjuba but only the anterior chamber in pacu. RPC was positively correlated with response, incidence and intensity of several injury types for both species with some injuries occurring at very low RPC (e.g. 50 % probability of swim bladder rupture at 2.2 and 1.75 for piracanjuba and pacu, respectively). Multiple responses (e.g. loss of orientation) and injuries (e.g. eye haemorrhage) were correlated with swim bladder rupture suggesting gas venting into the body cavity likely causes secondary injury. When directly comparing our results with those available in the published literature, both pacu and piracanjuba appear to be more susceptible to barotrauma than previously studied subtropical and temperate species.

Applying appropriate frequency criteria to advance acoustic behavioural guidance systems for fish.

Deterrents that use acoustics to guide fish away from dangerous areas depend on the elicitation of avoidance in the target species. Acoustic deterrents select the optimum frequency based on an assumption that highest avoidance is likely to occur at the greatest sensitivity. However, such an assumption may be unfounded. Using goldfish (Carassius auratus) as a suitable experimental model, this study tested this as a null hypothesis. Under laboratory conditions, the deterrence thresholds of individual goldfish exposed to 120 ms tones at six frequencies (250-2000 Hz) and four Sound Pressure Levels (SPL 115-145 dB) were quantified. The deterrence threshold defined as the SPL at which 25% of the tested population startled was calculated and compared to the hearing threshold obtained using Auditory Evoked Potential and particle acceleration threshold data. The optimum frequency to elicit a startle response was 250 Hz; different from the published hearing and particle acceleration sensitivities based on audiograms. The difference between the deterrence threshold and published hearing threshold data varied from 47.1 dB at 250 Hz to 76 dB at 600 Hz. This study demonstrates that information obtained from audiograms may poorly predict the most suitable frequencies at which avoidance behaviours are elicited in fish.

Selective fish passage: Restoring habitat connectivity without facilitating the spread of a non-native species.

River managers are challenged to address two key threats to freshwater biodiversity. The first is the effects of habitat fragmentation by instream structures, such as dams and weirs, that disrupt migrations and impact species distributions. The second is the impact of non-native species on native species and ecological processes. However, mitigating anthropogenic habitat fragmentation through the installation of passage facilities can facilitate the invasion and spread of non-native species. This study compared the potential of two existing low-cost fish passage technologies designed for sloping weirs, a cylindrical bristle cluster (CBC) array and horizontally oriented studded tiles, to facilitate upstream movement of native European fish while preventing dispersal of non-native American signal crayfish (Pacifastacus leniusculus); thus providing a selective fish passage solution. Crayfish movement and passage was experimentally quantified at a Crump weir installed in a recirculating flume under two velocity regimes (low and high), without (control) and with the addition of either a CBC array or studded tiles. Results were compared to passage efficacy (PE) data for native fish species for both technologies (existing data). Most (84.4%) crayfish were active during the trials, exhibiting frequent up and downstream movements below the weir. During control conditions under the high velocity regime, high velocities (ca. 2.39 m s-1) prevented crayfish reaching the foot of the weir (PE: 0%). Under the low velocity regime, relatively low velocities (ca. 0.74 m s-1) at the weir crest prevented most crayfish from passing (PE: 10-16%). Crayfish movement speed and total distance moved were lower under the high than the low velocity regime. Neither fish pass technology improved crayfish maximum distance of ascent on the downstream weir face or PE under either velocity regime. Under comparable conditions to the high velocity regime tested here, previous studies have shown both technologies improve PE for native fish. Hence, both CBC arrays and studded tiles would likely function as suitable selective fish passes where the conservation objective is not to aid the spread of non-native crayfish. Additional passage inhibiting technologies will be required at sites where complete blockage of crayfish movement is required.

Rethinking swimming performance tests for bottom-dwelling fish: the case of European glass eel (Anguilla anguilla).

Systematic experiments on European eel (Anguilla anguilla) in their juvenile, early life stage (glass eel), were conducted to provide new insights on the fish swimming performance and propose a framework of analysis to design swimming-performance experiments for bottom-dwelling fish. In particular, we coupled experimental and computational fluid dynamics techniques to: (i) accommodate glass eel burst-and-coast swimming mode and estimate the active swimming time (tac), not considering coast and drift periods, (ii) estimate near-bottom velocities (Ub) experienced by the fish, rather than using bulk averages (U), (iii) investigate water temperature (T) influence on swimming ability, and (iv) identify a functional relation between Ub, tac and T. Results showed that burst-and-coast swimming mode was increasingly adopted by glass eel, especially when U was higher than 0.3 ms-1. Using U rather than Ub led to an overestimation of the fish swimming performance from 18 to 32%, on average. Under the range of temperatures analyzed (from 8 to 18 °C), tac was strongly influenced and positively related to T. As a final result, we propose a general formula to link near-bottom velocity, water temperature and active swimming time which can be useful in ecological engineering applications and reads as [Formula: see text].

Stability and safety of MA50 intraocular lens placed in the sulcus.

PURPOSE: To describe the safety and stability of sulcus placement of the MA50 intraocular lens (IOL). PATIENTS AND METHODS: Consecutive patients with MA50 IOLs placed in the sulcus at the University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA, from 1997 to 2012 were identified. Inclusion criteria included patients with over 4 weeks of follow-up data. AEL was compared with incidence of IOL decentration using at two-tailed Student's t-test. RESULTS: Fifty eyes of 49 patients meeting the inclusion criteria were identified. Four weeks post-operatively, the average best-corrected visual acuity was 20/30. IOL decentration occurred in 14% of patients; patients with decentered IOLs had a significantly longer average AEL (25.37 mm) than patients whose IOL remained centered (23.94 mm, P=0.017). Other complications included uveitis-glaucoma-hyphema syndrome (12%), iritis (8%), and glaucoma (6%). There were no cases of pigment dispersion syndrome or need for lens exchange. Twelve eyes (24%) had intra-operative optic capture by the anterior capsule, none of which had post-operative decentration. CONCLUSION: The MA50 IOL is a reasonable, stable option for placement in the sulcus, with a low-risk profile; however, in eyes with longer AEL and presumably larger anterior segment, surgeons should consider placing an IOL with longer haptic distance than the MA50 to maintain centration. Optic capture of the MA50 IOL by the anterior capsule should be considered for longer eyes, as it is protective against decentration.

Relationship between European eel Anguilla anguilla infection with non-native parasites and swimming behaviour on encountering accelerating flow.

The effect of Anguillicola crassus, Pseudodactylogyrus bini and Pseudodactylogyrus anguillae infection on the behaviour of downstream migrating adult European eels Anguilla anguilla as they encountered accelerating water velocity, common at engineered structures where flow is constricted (e.g. weirs and bypass systems), was evaluated in an experimental flume. The probability of reacting to, and rejecting, the velocity gradient was positively related to A. crassus larval, adult and total abundance. High abundance of Pseudodactylogyrus spp. reduced this effect, but A. crassus was the strongest parasitic factor associated with fish behaviour, and abundance was positively related to delay in downstream passage. Delayed downstream migration at hydraulic gradients associated with riverine anthropogenic structures could result in additional energetic expenditure for migrating A. anguilla already challenged by A. crassus infection.

Experimental quantification of the swimming performance and behaviour of spawning run river lamprey Lampetra fluviatilis and European eel Anguilla anguilla.

Using a large-scale open-channel flume, the swimming ability and behaviour of individual adult European eel Anguilla anguilla and river lamprey Lampetra fluviatilis, species that exhibit anguilliform locomotion, were quantified under complex hydraulic conditions created by a 0·2-0·3 m high under- or overshot weir during four discharge regimes. Fishes were allowed to approach the weirs from both up- and downstream. All fishes passed the undershot weir, independent of discharge and direction of movement, and under high flow (mean ±S.E. 194·63 ± 6·48 l s(-1)) moved upstream against velocities that ranged between 1·75 and 2·12 m s(-1), suggesting greater maximum swimming capability than previously reported. In comparison, passage efficiency during upstream movement was lower for the overshot weir for both L. fluviatilis and A. anguilla. Downstream moving A. anguilla took longer to pass the over- than undershot weir. This study describes a methodology to attain realistic measures of swimming ability and behavioural performance required to develop multispecies fish passage criteria.

Efficient spatiotemporal analysis of the flagellar waveform of Chlamydomonas reinhardtii.

The 9 + 2 axoneme is a microtubule-based machine that powers the oscillatory beating of cilia and flagella. Its highly regulated movement is essential for the normal function of many organs; ciliopathies cause congenital defects, chronic respiratory tract infections and infertility. We present an efficient method to obtain a quantitative description of flagellar motion, with high spatial and temporal resolution, from high speed video recording of bright field images. This highly automated technique provides the shape, shear angle, curvature, and bend propagation speeds along the length of the flagellum, with approximately 200 temporal samples per beat. We compared the waveforms of uniflagellated wild-type and ida3 mutant cells, which lack the I1 inner dynein complex. Video images were captured at 350 fps. Rigid-body motion was eliminated by fast Fourier transform (FFT)-based registration, and the Cartesian (x-y) coordinates of points on the flagellum were identified. These x-y "point clouds" were embedded in two data dimensions using Isomap, a nonlinear dimension reduction method, and sorted by phase in the flagellar cycle. A smooth surface was fitted to the sorted point clouds, which provides high-resolution estimates of shear angle and curvature. Wild-type and ida3 cells exhibit large differences in shear amplitude, but similar maximum and minimum curvature values. In ida3 cells, the reverse bend begins earlier and travels more slowly relative to the principal bend, than in wild-type cells. The regulation of flagellar movement must involve I1 dynein in a manner consistent with these results.