Water column production and nutrient characteristics in mangrove creeks receiving shrimp farm effluent

Water column processes in undisturbed mangrove creeks and in creeks receiving effluent from shrimp farms in North Queensland, Australia, were studied. Small scale discharges into tidal creeks did not elevate dissolved nutrient concentrations compared with non‐impacted creeks, but did elevate concentrations of particulate nutrients, chlorophyll and suspended solids proximal to the site of the effluent discharge. Rates of primary and bacterial production downstream from the discharge exceeded rates in the shrimp ponds because of the synergistic effects of turbulent mixing and eutrophication. In the lower reaches of the mangrove creeks and immediately offshore, standing stocks of particulate material and rates of primary and bacterial production were within the range of values found in non‐discharge areas. Our results suggest that water column production by phytoplankton and bacteria strips nutrients from shrimp farm effluent and repackages them in more bioavailable forms.     

Reducing rice field algae and cyanobacteria abundance by altering phosphorus fertilizer applications

In California’s water-seeded rice systems, algal/cyanobacterial biomass can be a problem during rice establishment and can lead to yield reductions. Laboratory, enclosure, and field-scale experiments were established to evaluate the effects of fertilizer P management on algal/cyanobacterial growth. Two field-scale experiments evaluated the response of algal/cyanobacterial growth to three P management strategies: conventional surface applied, incorporated into the soil, and delaying P applications by 30 days. Results from these experiments indicated rice fields that received conventional surface-applied P fertilizer had 4–8 times more algal/cyanobacterial biomass and 3–11 times higher concentrations of soluble reactive phosphate (SRP) than those in which P fertilizer was incorporated or delayed. Laboratory experiments evaluated the ability of field water to support growth of Nostoc spongiaeforme. Results indicate that water from the incorporated or delayed P application fields was P limited for N. spongiaeforme growth. Water from the surface-applied fields was not P limited. Enclosure experiments evaluated the effects of delayed P applications on algal/cyanobacterial biomass and rice yields. Algal/cyanobacterial cover and biomass increased in enclosures which received added P. Soluble reactive phosphate concentrations were also significantly greater in these enclosures. Delaying the application by up to 28 days did not reduce rice yields in the enclosures. One management implication is that reducing SRP concentrations early in the season in rice field water will result in reduced algal/cyanobacterial biomass. Strategies to reduce water SRP include incorporating fertilizer P or delaying the P application by up to 30 days.     

Soil water content,carbon, and nitrogen determine the abundances of methanogens,methanotrophs, and methane emission in the Zoige alpine wetland

Journal of Soils and Sediments - Alpine wetland ecosystems can contribute large amounts of methane (CH4) to the atmosphere; however, their emissions vary with environmental conditions. Microbial...     

Plasma cortisol and hypothalamic monoamine responses in yellow perch <Emphasis Type="Italic">Perca flavescens</Emphasis> after intraperitoneal injection of lipopolysaccharide

The concentrations of monoamines in the hypothalamus were determined in yellow perch Perca flavescens before and after injection with lipopolysaccharide (LPS; 3 mg kg⁻¹ fish weight) or saline to test for the presence of neurochemical changes potentially associated with changes in plasma cortisol characteristic of intraperitoneal (ip) challenge with LPS. In the first experiment, yellow perch were injected with saline or LPS and the hypothalamus removed and plasma sampled before and at 0.5, 1.5, 3.0, and 6 h after injection. Plasma cortisol was elevated in both saline- and LPS-injected fish through 1.5 h after injection and returned to levels resembling pre-injection by 3 h after injection. Significantly higher amounts of cortisol in plasma from LPS-injected relative to saline-injected fish were observed 6 h following injection. A significant decrease relative to levels observed 0.5–3 h after handling was observed in serotonin concentrations at 6 h following LPS and saline injection with a concomitant increase in the ratio of 5-hydroxyindoleacetic acid:serotonin. In the second experiment, hypothalamic monoamines were sampled before and at 3, 6, 9, 12, and 24 h after injection with LPS or saline. Significant increases from pre-injection levels were observed in the ratio 5-hydroxyindoleacetic acid:serotonin at 9, 12, and 24 h after injection, but no differences were detected between LPS- and saline-injected fish. These results support a model linking serotonergic system activation following handling stress, but no correlations with the sustained elevations of plasma cortisol associated with inflammatory challenge were observed.     

Long-term catch trends and risk assessment of the Critically Endangered white-spotted wedgefish (Rhynchobatus djiddensis) from South Africa

1. The white-spotted wedgefish (Rhynchobatus djiddensis) is a Critically Endangered shark-like ray in the family Rhinidae. Throughout its Western Indian Ocean distribution, it is targeted for its valuable meat and fins and is reported to have undergone major population declines. However, there remains a need for species specific time-series data to accurately assess localized population declines.
2. This study used two independent long-term (37 and 40 years) time-series catch data from competitive shore angling and shark nets to investigate the size composition and catch per unit effort (CPUE) and conduct a risk assessment for the population on the east coast of South Africa.
3. From 1977 to 2017 the competitive shore fishery captured 7,703 individual R. djiddensis, whilst shark nets in the same region captured 2,856 individuals from 1981 to 2017. Individuals captured in the nets had a sex ratio of 1.8:1 females to males, and were larger than those caught by the anglers. Although the mean annual sizes of net-caught individuals were above the size of reported sexual maturity, there was little evidence to suggest that any individuals captured were reproductively active.
4. Both the competitive shore fishery and shark net catches exhibited strong seasonal trends with the majority of R. djiddensis catches occurring from October to May peaking in austral summer. Standardized CPUE from the competitive shore fishery declined substantially between 1977 and 2017 and shark net catches exhibited a significant (p < 0.05) fourfold decline in annual nominal CPUE from 1981 to 2017.
5. Ultimately, a risk assessment showed a 65.1% decline in abundance over a period of three generation lengths, which indicates that the sampled population of R. djiddensis in South Africa should be classified as Endangered according to the IUCN Red List using criterion A2b. The conservation implications of this are discussed.

     

Do swimming fish always grow fast? Investigating the magnitude and physiological basis of exercise-induced growth in juvenile New Zealand yellowtail kingfish, <Emphasis Type="Italic">Seriola lalandi</Emphasis>

There is a wealth of evidence showing that a moderate level of non-stop exercise improves the growth and feed conversion of many active fishes. A diverse number of active fish are currently being farmed, and an optimal level of exercise may feasibly improve the production efficiency of these species in intensive culture systems. Our experiments have set out to resolve the growth benefits of juvenile New Zealand yellowtail kingfish (Seriola lalandi) enforced to swim in currents at various speeds over two temperatures (14.9 and 21.1°C). We also probed potential sources of physiological efficiency in an attempt to resolve how growth is enhanced at a time of high energetic expenditure. Results show that long-term exercise yields a 10% increase in growth but this occurs in surprisingly low flows (0.75 BL s⁻¹) and only under favourable environmental temperatures (21.1°C). Experiments using a swim flume respirometer indicate that exercise training has no effect on metabolic scope or critical swimming speeds but it does improve swimming efficiency (lower gross costs of transport, GCOT). Such efficiency may potentially help reconcile the costs of growth and exercise within the range of available metabolic energy (scope). With growth boosted in surprisingly low flows and elevated water temperatures only, further investigations are required to understand the bioenergetics and partitioning of costs in the New Zealand yellowtail kingfish.     

Concentration of 17α-Methyltestosterone in HormoneTreated Feed: Effects of Analytical Technique, Fabrication, and Storage Temperature

Feed treated with 17α-methyltestosterone (MT) is used to manipulate the gender of early tilapia fry. In the USA, hormone-treated feed is used by selected producers under an Investigational New Animal Drug (INAD) program. While monitoring the fabrication and on-farm use of this treated feed, concerns were raised about the high performance liquid chromatography (HPLC) analytical procedure for detecting MT in feeds, the incorporation of MT in feeds during fabrication, and effects of storage temperature on MT concentration. A series of experiments demonstrated that the analytical procedure for detecting MT in feeds lacked high precision, and, on average, biased results low. MT was uniformly mixed with feed by spraying an MT-alcohol solution on feed while it was blended in an industrial ribbon mixer. Alcohol volumes ranging from 15 mL/kg to 150 mL/kg were equally effective at dispersing MT in feed. The concentrations of MT in feeds consistently declined over time if the storage temperatures were 25 C or higher. Freezing preserved the MT in feed, and the refrigeration of feed fabricated to contain 60 mg MT/kg maintained acceptable MT concentrations during 6 mo of storage.     

The killing fields: Science and politics at Berkeley, California, USA

Over the past several decades, a group of scholars at the Berkeley campus of the University of California have frequently challenged many of the dominant themes of contemporary agricultural research. In their work, they have organized curricula questioning the assumptions of conventional agriculture and its sciences while encouraging the development of alternative agricultural practices based on principles of ecology. Their collective critique has stimulated an intellectual climate calling forth a scrutiny of the university's role in the production of knowledge and the social consequences of its works. The result of this intellectual project has been a group that has also largely challenged the dominant themes of the modern university. In place of a setting where ideas are a passive currency, the modern university is a place where knowledge and power are manifest in a dialectic that is revealed not simply by the production of knowledge, but its destruction as well. It is in this context that the recent history of a group of scholars at the University of California provides a striking testimony concerning the disturbing character of science in the modern university. The ecological and social dimensions of “killing fields” that captures the contemporary hazards of food and fiber production in California is also reflected in the gradual demise of a group of researchers at Berkeley who have endeavored to provide an alternative vision of agriculture.     

Simplified calculation of the NRC estimates for net energy for maintenance in beef cattle diets

Calculation of dietary intake for beef cattle using the equation outlined by the NRC (1984) is confounded by the need to know the net energy for maintenance content of the diet (NEmkg). Intake cannot be calculated until NEmkg is specified, but intake must be indicated before performance can be predicted. To calculate NEmkg, dietary intake must be known or estimated, or it can be calculated using a complicated quartic equation. This quartic equation, when solved, gives the percentages of selected feedstuffs necessary to balance a diet. Placing the resulting percentages of feedstuffs necessary back into the generalized net energy equation solves for NEmkg. The quartic equation may be simplified by inserting imaginary nutrient values that optimize the equation for simplicity. It remains a quartic equation, but the coefficients for the first three factors of the equation are fixed, with only the unary X term and the coefficient containing variables. A modified version of Newton's method of approximating roots of equations estimates the percentage of feed necessary and when incorporated into the generalized net energy equation solves for NEmkg. The final reduced form results in simplified equations for NEmkg for each of the classes of beef cattle that are easily solved by the hand-held calculator.     

Ecosystem health as a clinical rotation for senior students in Canadian veterinary schools.

We describe 4 years of an experimental rotation in ecosystem health offered to senior veterinary students in Canada. Faculty from the 4 Canadian veterinary colleges collaborated in offering the rotation once annually at 1 of the colleges. The 1st rotation was held in Guelph in 1993, followed in successive years by rotations at Saskatoon, Saint-Hyacinthe, and Charlottetown. The rotation is a predominantly field-based experience that allows students to work with veterinary and other role models who are actively engaged in clinical research related to ecosystem health. Five specific field studies that worked particularly well during the rotations are presented. These studies involved investigating mortality in wildlife due to botulism, designing an environmental surveillance system around herds of beef cattle, using belugas to evaluate the health of the St. Lawrence River, dealing with competition for water use by aquaculture and agriculture, and exploring the role of veterinarians during major coastal oil spills. The experience has resulted in our developing the subject matter, field examples, teaching approach, and confidence necessary to make ecosystem health the focus of a productive clinical rotation for senior year veterinary students.