Thoracoscopic-assisted diaphragmatic hernia repair using a thoracic rib resection

OBJECTIVE: To describe the surgical treatment of a dorsal diaphragmatic hernia in an adult horse using thoracic rib resection aided by thoracoscopy and a flank incision. STUDY DESIGN: Case report. ANIMAL POPULATION: One client-owned horse. RESULTS: A six-year-old Dutch warmblood gelding was admitted for colic-associated colonic incarceration in a diaphragmatic hernia. Seven weeks after the initial colic surgery, the gelding underwent surgery to repair the defect. Thoracoscopy and a flank incision were used to identify the location of the hernia and the subsequent site of rib resection. The stomach was adhered to the edges of the defect, leaving only a small residual hole. Resection of the 14th rib provided excellent exposure of the defect and closure of the remaining hernia. CONCLUSION AND CLINICAL RELEVANCE: Thoracic rib resection can provide access to diaphragmatic hernias in adult horses. Thoracoscopy or a flank incision, or both, may aid in determining which rib is best resected.     

Linear versus Monod representation of ammonia oxidation rates in oligotrophic recirculating aquaculture systems

Monod kinetics are widely used to model nitrifying biofilters. However, these kinetics are incapable of representing the collapse of volumetric TAN conversion rate (VTR) under high organic loadings. Failure to recognize the underlying heterotrophic interference can lead to calibration issues as a single Monod function is applied across contrasting levels of carbon loading. This, plus an historic bias towards the analysis of peak carrying capacities leave modelers poorly prepared to serve the needs of a mariculture industry demanding oligotrophic designs for broodstock maturation and larval/fingerling production. Consequently, data was generated by a Monte Carlo technique under the assumption of heterotrophic inhibition to nitrification. The data was used to compare the accuracy of calibration of the Monod relationship using the traditional Lineweaver–Burke and Eadie–Hofstee calibration methods against direct linear regression for low substrate (mesotrophic/oligotrophic) regimes. The results indicate that a simple linear relationship with a zero intercept, calibrated on data ranging from 0.1 to 0.5 g-TAN m⁻³, is most suitable for the representation of the mesotrophic/oligotrophic performance of nitrifying biofilters based on a comparison of SSE for both the Monte Carlo and field data analyzed herein. Additionally, the coefficient of variation was found to be between 7 and 8% for the parameter τ, which is the slope of the linear relationship between total ammonia nitrogen (TAN) and VTR while the CV for the Monod parameters ranged between 22 and 143% for VTR_max and between 29 and 137% for the apparent half-saturation constant showing the improved stability of the linear model to that of the Monod model.     

Nitrification performance of a propeller-washed bead clarifier supporting a fluidized sand biofilter in a recirculating warmwater fish system

A propeller-wash bead filter (PWBF) and a fluidized sand filter (FSF) on a 28 m³ recirculating system stocked with tilapia maintained favorable water quality at five different feed rates, ranging from 0.9 to 4.5 kg feed per day. TAN removal rates ranged up to about 200 g TAN/m³ of media per day for each of the units. Peak rates of 244 g TAN/m³ of media per day were observed when the recirculating flow was boosted by 20%. Roughly 75% of the removal was accomplished by the fluidized sand filter an observation that is consistent with the difference between the fluidized sand filter volume (0.92 m³) and the bead filter media volume (0.28 m³). The bead filter's primary function was clarification. At the highest daily feed load, over 570 g dry weight of solids were removed during each daily bead filter backwashing event. A 20% increase in flow, at the same daily feed rate, improved solids removal to over 670 g dry weight per bead filter backwash event. The PWBF and FSF combination provided suitable water quality for fish production; however, further increases in feed loading were limited by carbon dioxide buildup and oxygen limitations.     

Rating fixed film nitrifying biofilters used in recirculating aquaculture systems

Predicting the performance of biofilters is an engineering challenge that is critical to both designers and managers. The task is complicated by the wide variety of water quality expectations and environmental conditions displayed by a recirculating aquaculture system (RAS). A myriad of biofilters designs have been generated reflecting approaches of engineers attempting to maximize specific surface area and oxygen transfer within the context of a biofilm management strategy. A rating strategy is presented for biofilters to facilitate the identification of appropriate matches between biofiltration formats and RAS applications. As a foundation, a previously proposed RAS classification system based upon salinity, temperature and trophic levels is upgraded to create 17 systems classifications. A biofilter classification system identifies seven combinations of trophic level and pH which should be sufficient to serve the RAS demands. Temperature and salinity are neglected as a means of simplifying the approach. An experimental methodology based upon chemical feeds is proposed to represent the steady-state RAS performance of the biofilters. Data is summarized by linear analysis of filter performance for concentration ranges below 1.0 g TAN m⁻³ and simple averaging is proposed for higher trophic levels. Input from the aquacultural engineering community and RAS aquaculturists is required to further refine the approach prior to endorsement.     

Mapping forest dynamics under climate change: A matrix model

Global climate change may be affecting forests around the world. However, the impact of climate change on forest population dynamics, especially at the landscape or regional level, has hardly been addressed before. A new methodology was proposed to enable matrix transition models to account for climate impact on forest population dynamics. The first climate-sensitive matrix (CSMatrix) model was developed for the Alaska boreal forest based on observations from over 15 years of forest inventory. The spatially explicit model was used to map climate-induced forest population dynamics across the region. The model predicted that the basal area increment in the region under natural succession would be hindered by global warming, more so for dry upland areas than for moist wetlands. It was suggested that temperature-induced drought stress could more than offset a predicted increase of future precipitation in the region to lower overall forest productivity. At the same time, stand diversity would increase across the region through transient species redistribution. Accounting for climate conditions made the CSMatrix model more accurate than conventional matrix models.     

High and dry in days gone by: Life-history theory predicts Appalachian mountain stream fish assemblage transformation during historical drought

Understanding the ecological dimensions of drought is critical for predicting how humans and nature will be affected by the expected increased prevalence of drought in the future. We tested life-history-based predictions for fish assemblage responses to drought using retrospective analysis of long-term (1986–2003) fish surveys from two streams in the Appalachian Mountains of North America. We hypothesised that (1) fish assemblage composition would correlate with wet and dry hydrologic conditions as assemblages fluctuated within a loose equilibrium and (2) life-history traits of fishes would correlate with dry versus wet periods such that opportunistic life-history strategists would dominate during drought. Results showed fish assemblage changes in Little River and Cataloochee Creek correlated with drought severity measured one year prior to fish surveys. Fish assemblages at all three sampling sites in Little River and two sites in Cataloochee Creek fluctuated within a loose equilibrium, while the remaining two sites in Cataloochee Creek indicated directional change. Life-history traits for fishes in Cataloochee Creek correlated with one-year time lag fluctuations in drought caused by opportunistic species being dominant during drought and periodic/equilibrium species dominant during wet periods. Time series plots of fish abundances aggregated by life-history strategy revealed dominance of opportunistic species emerged at the onset of a multi-year drought spanning 1998–2004, particularly for the two sites undergoing directional change. Our work provides empirical evidence for theoretical linkages between life history and environmental fluctuations and can ultimately be used to predict stream fish community response to future drought regimes.