Economic characteristics of extensive shrimp farms in the Mekong delta

Abstract

Extensive forms of shrimp aquaculture have become an important source of income for farm households in the brackish water region of the Mekong Delta, Vietnam. The economic and production characteristics of farms are discussed in this paper, based on a 1997 farm survey, with particular emphasis on shrimp farming practices. Two types of shrimp fanning practice were observed, one based on natural recruitment of seedstock with few supplementary inputs, and the other based on relatively high cash investments in Penaeus monodon seedstock and other inputs. Households practising monodon culture made significantly more income, but faced high risk associated with shrimp mortality. An investigation of the factors affecting monodon yields indicated that investment in higher quality inputs had a positive effect on yield and income. However, further research is needed on the extent to which management can reduce risk of shrimp mortality by investing in such premium quality inputs.     

Lowering seed gossypol content in glanded cotton (Gossypium hirsutum L.) lines

Cottonseed is a rich source of high quality protein, but its value as an animal feed is limited by gossypol, a toxic polyphenolic compound contained in glands located throughout the plant. This compound helps protect the plant from pests. Totally glandless varieties have been developed, but not adopted as these plants are left vulnerable to pests. This study describes a breeding strategy to decrease the levels of gossypol in the seed while maintaining a high enough concentration of toxin in vegetative plant parts to offer protection from pests. Preliminary studies indicated that crosses between varieties with different gland densities and distributions produced a range of glanding patterns. By selecting within the resulting progeny, we have identified F₇ generation progeny that have <0.30% total gossypol in the seed, while still possessing glands at critical locations on the vegetative plant parts. These new lines will be a valuable source of germplasm for developing low seed gossypol varieties. Seed from these varieties would provide a new source of inexpensive protein for animal feeding rations.     

Expression of the “<Emphasis Type="Italic">glanded-plant</Emphasis> and <Emphasis Type="Italic">glandless-seed</Emphasis>” trait of Australian diploid cottons in different genetic backgrounds

The expression of the “glanded-plant and glandless-seed” trait was assessed using High Performance Liquid Chromatography (HPLC) analysis methods in different Gossypium hybrids obtained by crossing Australian diploid cottons and various diploid and tetraploid species. Significant variation in the gossypol content in the seed was observed among the analyzed genotypes. HPLC data demonstrated that the gossypol synthesis repression mechanism in the Australian diploid species belonging to C and G genomes was dominant but did not confirm its preferential functioning against A genome species bearing GL₂ locus. About 10% of the produced seeds had total gossypol content lower than the limit imposed by the World Health Organisation (600 ppm) for the use of cotton flour in food and feed. HPLC analysis of the terpenoids aldehyde (TA) contents in the aerial parts of the hybrids showed important qualitative and quantitative variability. This result could indicate a certain separation between pigment gland morphogenesis and terpenoid synthesis mechanisms in cotton.     

United States Department of Agriculture-Agricultural Research Service research on natural products for pest management

Recent research of the Agricultural Research Service of USDA on the use of natural products to manage pests is summarized. Studies of the use of both phytochemicals and diatomaceous earth to manage insect pests are discussed. Chemically characterized compounds, such as a saponin from pepper (Capsicum frutescens L), benzaldehyde, chitosan and 2-deoxy-D-glucose are being studied as natural fungicides. Resin glycosides for pathogen resistance in sweet potato and residues of semi-tropical leguminous plants for nematode control are also under investigation. Bioassay-guided isolation of compounds with potential use as herbicides or herbicide leads is underway at several locations. New natural phytotoxin molecular target sites (asparagine synthetase and fructose-1,6-bisphosphate aldolase) have been discovered. Weed control in sweet potato and rice by allelopathy is under investigation. Molecular approaches to enhance allelopathy in sorghum are also being undertaken. The genes for polyketide synthases involved in production of pesticidal polyketide compounds in fungi are found to provide clues for pesticide discovery. Gene expression profiles in response to fungicides and herbicides are being generated as tools to understand more fully the mode of action and to rapidly determine the molecular target site of new, natural fungicides and herbicides.     

An experimental evaluation of castellated laryngofissure and bilateral arytenoid literalisation for the relief of laryngeal paralysis in dogs

The aim of this study was to compare the efficacy of 2 surgical procedures for providing an adequate laryngeal airway in dogs after surgically induced laryngeal paralysis. The laryngeal function of 10 healthy, adult experimental dogs was assessed by clinical examination, laryngoscopy, arterial blood gas measurement and analysis of tidal breathing flow-volume loops before, and after, bilateral recurrent laryngeal neurectomy. A castellated laryngofissure with vocal fold resection was done on 5 dogs and bilateral arytenoid cartilage lateralisation performed on the remaining 5 dogs. Six weeks later, the laryngeal function of the 10 dogs was reassessed, before the dogs were killed and a necropsy performed. The visible changes in laryngeal structure were recorded. Both surgical procedures alleviated some of the airway obstruction caused by the bilateral recurrent laryngeal neurectomy, but bilateral arytenoid cartilage lateralisation produced more consistent clinical improvement, a wider rima glottidis, increased inspiratory air flow and a significant increase in post-operative arterial oxygen tension.