Accumulation of Chemical Elements in Texas Shrimp Pond Soils

Abstract— This study evaluated changes in chemistry of shrimp pond soils over one production cycle. Several soil nutrients, pH, organic matter, and total soluble salts were analyzed in the upper 10 cm of pond-bottom soil on two Texas shrimp farms in two consecutive years. Soil concentrations of S, P, Ca, Mg, K, Na, Mn, and Zn increased from one year to the next, S increased by 400 ppm. Organic matter did not accumulate. The pH decreased in all pond soils, owing perhaps to the oxidation of organic matter and/or inorganic compounds. There was no statistical difference in shrimp yield between the two consecutive years. These results indicated that the accumulation of S and soluble salts derived from seawater and feed should be monitored and evaluated to prevent excessive chemical element loading of pond soil and discharge water.     

Low-cost experimental unit and growth medium for testing soil effects on shrimp culture

PVC pipes, 10 cm in diameter and 46 cm long, sealed at one end and filled with 18 ppt of artificial seawater and a 6-cm layer of substrate, were tested as experimental units for the culturing of penaeid shrimp. The growth substrate was prepared by mixing 70% quartz sand, 24% Georgia kaolin, 5% Gonzales bentonite and 1% Bermuda grass hay. One juvenile Penaeus vannamei was placed in each container and shrimp weight gain was monitored. In the first study (four replicates), shrimp grew to 8.15 g within 8 weeks at a rate of ≈1 g week⁻¹ with no mortality; thereafter, growth decreased and 25% mortality was observed. In the second study (seven replicates), the average weight of shrimp was 8.66 g in 10 weeks, with 29% mortality occurring between the seventh and eighth week. Experimental unit cost was $3.30.     

The importance of bare marine sedimentary habitats for maintaining high polychaete diversity and the implications for the design of marine protected areas

• 1. Bare intertidal sedimentary habitats have received relatively little attention compared with their neighbouring vegetated habitats. An ecological comparison of benthic faunal assemblages inhabiting tropical intertidal seagrass beds and bare sediments has been made to assess the faunal similarity between the two habitats in south‐east Asia.
• 2. The poorly developed taxonomy of most invertebrate taxa in the region precluded the full identification of many faunal groups. Only the polychaetes — which accounted for 76% of all the macrofaunal organisms collected — were identified to the lowest possible taxonomic level, yielding 177 nominal species belonging to 35 families. Ecological analyses suggested that although each habitat had a distinct polychaete assemblage, there were few differences between habitats based on a range of calculated assemblage diversity metrics.
• 3. Further analyses were applied to the data to test the performance of three strategies for optimizing the selection of sites for inclusion in potential marine protected areas. Strategies were based either on the total number of species, the number of rare or endemic species, or on the level of species richness (used as a surrogate for community structure).
• 4. All three strategies consistently captured above average numbers of species at most levels of conservation intensity. The merits of each strategy are considered in turn.

Copyright © 2009 John Wiley & Sons, Ltd.     

Ion regulation in the larval lepidopteran midgut and the response to Bacillus thuringiensis δ-endotoxin

Fourth-instar Bombyx mori (silkworm) was used as a model insect to study the effects of Bacillus thuringiensis (Bt) on ion homeostasis in the larval lepidopteran midgut. The K⁺ chemical gradient across the midgut of B. mori larvae is quite small, sustained by a lumen/haemolymph activity ratio of only 1.6. More than 95% of the driving force causing K⁺ flux from lumen to haemolymph is electrical. In contrast to K⁺, the H⁺ chemical gradient is exceedingly large, with luminal pH values of 11–12 and haemolymph/lumen H⁺ ratios as high as 10⁵. At equilibrium, the steep proton gradient is consistent with a passive distribution of H⁺ across the midgut epithelium as predicted from the Nernst equation. In B mori larvae, ingestion of a lethal dose of Bt δ-endotoxin produces an increase in K⁺ conductance in the midgut apical epithelium, causing a decrease in the electrical gradient and dissipation of the pH gradient. Larval morbidity can be correlated with a rise in haemolymph K⁺ and pH and a decline in luminal pH. Midgut K⁺ activity, however, remains unchanged. An important factor in the pathogenesis of Bt is irreversible alkalization of the epithelial cells as H⁺ is redistributed across the midgut to reach a new Nernst equilibrium.     

Factors Affecting Yield and Composition of Zein Extracted from Commercial Corn Gluten Meal

Twelve corn gluten meal samples obtained from six wet-milling plants were processed into zein. Zein was extracted using 88% aqueous isopropyl alcohol at pH 12.5, followed by chilling. Protein recovery ranged from 21.3 to 32.0%, and protein purity ranged from 82.1 to 87.6%. Protein recovery increased as the protein purity increased (r = 0.76) (P < 0.01). One of the major factors influencing extraction yield was protein composition; especially α-zein content, which ranged from 53.4 to 64% of the total protein in the corn gluten meal samples. The intensity of red color of the corn gluten meal was negatively correlated with protein recovery and zein purity (r = -0.66 and -0.72, respectively) (P < 0.02).     

Effects of autumn and spring defoliation management on the dry‐matter yield and herbage quality of perennial ryegrass swards throughout the year

A small‐plot experiment was conducted in south‐west Ireland to investigate (i) the effects of pre‐closing regrowth interval and closing date on dry‐matter (DM) yield and sward structural and composition characteristics, during the autumn–winter and spring opening periods, and (ii) subsequent carryover effects. The study used a randomized block design with a factorial arrangement of treatments (4 closing dates × 2 opening dates) with a split plot (two pre‐closing regrowth intervals). The long pre‐closing (LPC) interval began on 9 August, and the short pre‐closing interval (SPC) started on 15 September. The autumn closing dates were as follows: 1 October (CD1), 15 October (CD2), 1 November (CD3) and 14 November (CD4). Plots were defoliated again on 1 February (EOD) or 1 March (LOD). On the LPC treatment, herbage yield increased from CD1 (2463 kg DM ha^?1) to CD3 (3185 kg DM ha^?1). On the SPC treatment, herbage yield was similar for CD3 and CD4, indicating a ceiling in herbage accumulation. For each 1‐d delay in closing date between CD1 and CD4, the opening herbage yield was reduced by 10 kg DM ha^?1. Herbage quality decreased as the closing date was delayed; DMD and CP decreased by 0·06 and 12 g kg DM^?1, respectively, between CD1 and CD4. The EOD resulted in increased leaf and decreased dead proportions over the LOD treatments. A balance between autumn CD and spring OD needs to be achieved to ensure a sufficient supply of high‐quality grass in spring.     

Variation Among Physical,Compositional, and Wet‐Milling Characteristics of the F1 Generation of Corn Hybrids of Introgressed Exotic and Adapted Inbred Lines

Hybrids with high grain yield and higher starch, protein, or oil content are available to corn growers; however, they result from crossing adapted Corn Belt inbred lines that rarely include exotic germplasm. This study was conducted to determine whether Corn Belt lines introgressed with exotic materials from Argentina, Chile, Uruguay, Cuba, and Florida have appropriate wet‐milling characteristics in their hybrids. Ten lines from the Germplasm Enhancement of Maize (GEM) project with different starch contents were crossed to three adapted inbred lines used as testers. The B73×Mo17 hybrid was used as a control. The F₁ generation of these 30 experimental hybrids was analyzed using both near‐infrared transmittance (NIT) technology and a 100‐g modified wet‐milling procedure, and measuring test and 1,000‐kernel weight. There was great variation among physical, compositional, and wet‐milling characteristics of the experimental hybrids, suggesting that exotic germplasm can be used to improve wet‐milling characteristics of Corn Belt hybrids.