Towards sustainable freshwater prawn aquaculture – lessons from shrimp farming, with special reference to India

The annual increase in farmed freshwater prawn production in the world during the decade ending 2001 has been estimated as 29% and that during 1999–2001 as 48%, the production in 2001 being about 300 000 mt (all Macrobrachium species). Between 1999 and 2003 the annual increase in farmed Macrobrachium rosenbergii production in India was about 80%, production reaching 30 450 mt in 2002–2003. This log phase of production followed the rise and fall of shrimp farming in the country. Several shrimp farming ventures collapsed in the 1990s, owing to degraded environment and diseases, abetted by lack of awareness and inadequacy of information on the culture systems and their interactions with other human endeavours. This shrimp farming experience has made the aquafarmer and other stakeholders aware that while aquaculture has a high potential in ensuring food and nutritional security and livelihood, besides profit to the farmer and socio‐economic benefits to local communities, it is likely to slip from sustainable development pathways if adequate understanding, improved management practices, governmental policies and plans for implementation and regulation to ensure sustainability are not in place. The lessons learned from shrimp farming can help in steering the development of sustainable freshwater prawn aquaculture in India and elsewhere.     

Formulation and pharmacokinetic evaluation of hard gelatin capsule encapsulating lyophilized Vasa Swaras for improved stability and oral bioavailability of vasicine

The oral bioavailability of vasicine (1) was investigated in hard gelatin capsules of lyophilized Vasa Swaras (aqueous extract of Adhatoda vasica Nees.,Fam.: Acanthaceae) The rat pharmacokinetic profile of lyophilized Vasa Swaras, Vasa Swaras, vasicine (1) (chief marker compounds of A. vasica) and a marketed capsule formulation of A. vasica were compared. Vasicine (1) was found to be more orally bioavailable from lyophilized Vasa Swaras, with an overall minor conversion to vasicinone (2).     

Aquaculture in South East Asia: Some points of emphasis

The paper, a keynote address to the conference, addresses the aquaculture potentials which interest the international agencies. It also reviews the many production systems in aquaculture, particularly those which are of interest to or currently practised in Asian countries. Several examples are briefly described, and the need for more research is emphasised.     

Technique for visual demonstration of germinating arbuscular mycorrhizal spores and their multiplication in pots

We describe a simple technique for the germination of arbuscular mycorrhizal (AM)–fungal spores and their multiplication in pots. Glomus fasciculatum, G. mosseae, and Gigaspora margarita were used. A single wheat seedling was tied to a glass slide, previously covered with filter paper with the help of thread. One single surface‐sterilized AM‐fungal spore was placed on the middle portion of the root of the wheat seedling using a sterilized syringe. The slide was placed vertically in a 100 mL glass beaker filled with 25 mL of root exudates–water (1:4, v/v) solution, which was collected by growing twenty wheat seedlings in a 150 mL beaker filled with 100 mL sterilized distilled water for 7 d. The slide was observed daily using a compound microscope to follow the time course of germination. In this technique, the spore is directly in contact with the host root, and a visualization of spore germination, hyphal development, and appressorium formation is possible without disrupting fungal growth or the establishment of the symbiosis. The method allows to document the germination events and to assess hyphal‐elongation rates by photographing the same spore on consecutive days. The inoculated seedling was used to initiate single‐spore multiplication in a sterilized (autoclave on 3 alternate days at 120°C for 120 min at 1.05 kg cm^–2 pressure) potted sandy soil (150 mL volume) into which the slide with the inoculated seedling was inserted carefully through a previously made slit. The wheat seedlings in all pots (4 treatments and 15 replications) became colonized by mycorrhiza, confirming that the establishment of the AM‐fungal symbiosis is highly reproducible. Our technique permits the relatively undisturbed growth of the symbiotic partners, the visualization of germinating AM‐fungal spores, and their multiplication in pots. This simple and low‐cost method facilitates the production of pure lines of AM fungi from single spores, allowing for the study of intraspecific variation and potentiality for cytological, biochemical, physiological, and taxonomical studies.     

Screening of dialkoxybenzenes and disubstituted cyclopentene derivatives against the cabbage looper, Trichoplusia ni, for the discovery of new feeding and oviposition deterrents

The antifeedant, oviposition deterrent, and toxic effects of dialkoxybenzene minilibraries and of disubstituted cyclopentene minilibraries (i.e., consisting of four to five compounds) along with their pure constituent compounds were assessed against third instar larvae and adults of the cabbage looper, Trichoplusia ni, in laboratory bioassays in a search for new insect control agents. These compounds mimic naturally occurring bioactive odorants and tastants and are relatively easily prepared from commodity chemicals. Most of these libraries strongly deterred larval feeding, with some exhibiting strong toxic and oviposition deterrent effects as well. Our results suggest some structure-function relationships within these libraries. Replacement of a methyl group with larger alkyl substituents increased the feeding deterrent effects in most cases. The presence of a free hydroxyl group, irrespective of the carbon framework or alkyl substituent, served to reduce feeding deterrent effects in all series of compounds. Further, exceeding a certain group size also generally had a detrimental effect. This information will be useful in designing new insect control agents for agriculture. Some of these libraries and compounds may have potential for development as commercial insecticides.     

Management strategies associating batch-graded and size-graded postlarvae can reduce heterogeneous individual growth in Macrobrachium rosenbergii (de Man)

Two sets of adaptive trials were performed to determine the effects of size grading and batch grading on size heterogeneity in cultured Macrobrachium rosenbergii raised in the Coconut Garden channels of Kuttanad, Southern India. In the first set of trials, postlarvae were batch graded on the basis of their hatching order, segregated and grown separately as first‐hatched and second‐hatched groups. In the second set of trials, postlarvae were size graded as jumpers and laggards and were grown in separate channels. The average weight attained by prawns after 10 months of culture was highest for jumpers (83.11 g) and lowest for the prawns from the first‐hatched group (43.76 g). The percentage of males was highest in the population of jumpers (58.23%). Highest production was recorded in the channel stocked with postlarvae from the second‐hatched group (103.4 kg ha^?1) and lowest production was obtained from the first‐hatched group (63.74 kg ha^?1). The proportions of undesirable small males were highest among laggards and the first‐hatched group: 24.8% and 15.1% respectively. The level of heterozygosity within morphotypes was also high in these groups. Jumpers attained good growth by the end of culture but, because of their low survival rate, this approach was not economically feasible. However, higher production and survival in the second‐hatched group improved economic viability. Thus, for better results, stocking with later‐hatched groups would be more appropriate than stocking with the first‐hatched group.     

Analysis of genetic diversity among Indian short-day onion (Allium cepa L.) cultivars using RAPD markers.

Summary

Randomly amplified polymorphic DNA (RAPD) markers were used to estimate genetic diversity among 24 cultivars of short-day onions. Total genomic DNA was extracted and subjected to RAPD analysis using 90 arbitrary 10-mer primers. Of these, 15 primers were selected which yielded 137 bands, 91.24% of which were polymorphic. None of the primers produced a unique banding pattern for each cultivar. RAPD data were used to calculate a Squared-Euclidian Distance matrix which revealed a minimum genetic distance between cultivars ‘AFLR-722’ and ‘PBR-140’, and a maximum genetic distance between cultivars ‘PBR-139’ and ‘A.Kalyan’, and ‘MS-48’ and ‘A.Kalyan’. Based on the distance matrix, cluster analysis was done using a minimum variance algorithm.The dendrogram thus generated, based on Ward’s method, grouped the 24 onion cultivars into two major clusters. The first cluster consisted of cultivars from the northern region, and the second of cultivars from the southern region of India. The present study shows that there is high diversity among the onion cultivars selected and indicates the potential of RAPD markers for identification and maintenance of onion germplasm for crop improvement purposes.     

A novel pre‐emergence herbicide (Diclosulam) as an environmentally friendly weed management option in peanut and its phytotoxicity evaluation

A two‐season field experiment was conducted to evaluate the efficacy of diclosulam compared with recommended doses of pendimethalin and oxyfluorfen for weed management in peanut. Persistence of diclosulam in oil, de‐oiled cake, haulm of peanut, and soil was also studied. Diclosulam 22 and 26 g a.i. ha^?1, and a weed‐free check had a high pod yield due to more mature pods and their mass. Pre‐emergence application of diclosulam 26 g a.i. ha^?1 provided better weed management and enhanced peanut growth and yield with high net returns. Phytotoxicity studies indicated that the diclosulam application did not cause any phytotoxic symptoms (vein clearing, epinasty, hyponasty, wilting, and injury) on leaf tips and leaf surface of peanut. Diclosulam residues in peanut viz. oil, de‐oiled cake, haulm, and soil were below the detection level after harvesting of peanut from the experimental field. Further, germination percentage and seed cotton yield of cotton crop cultivated after peanut were also not affected significantly.     

Vulnerability of prey to predation by freshwater prawn,Macrobrachium malcolmsonii

The vulnerability of four prey species to predation by the freshwater prawn, Macrobrachium malcolmsonii, was found to be in order of decreasing vulnerability: tadpoles of frog (Rana cyanaphyctis) > minnow (Aplocheilus lineatus) > common carp fry (Cyprinus carpio) >Tilapia mossambica fry. The weight of the prey consumed per day was, respectively, 12.48 ± 1.45 g, 6.02 ± 1.15 g, 5.61 ± 0.40 and 2.89 ± 0.26 g; and the estimated 50% predation time was 1.25 ± 0.26 days, 1.66 ± 0.33 days, 2.0 ± 0.17 days, and 3.54 ± 0.72 days, respectively.     

Linear downscaling from MODIS to landsat: connecting landscape composition with ecosystem functions

Context

The open and free access to Landsat and MODIS products have greatly promoted scientific investigations on spatiotemporal change in land mosaics and ecosystem functions at landscape to regional scales. Unfortunately, there is a major mismatch in spatial resolution between MODIS products at coarser resolution (≥?250 m) and landscape structure based on classified Landsat scenes at finer resolution (30 m).

Objectives

Based on practical needs for downscaling popular MODIS products at 500 m resolution to match classified land cover at Landsat 30 m resolution, we proposed an innovative modelling approach so that landscape structure and ecosystem functions can be directly studied for their interconnections. As a proof-of-concept of our downscaling approach, we selected the watershed of the Kalamazoo River in southwestern Michigan, USA as the testbed.

Methods

MODIS products for three fundamental variables of ecosystem function are downscaled to ensure the approach can be extrapolated to multiple functional measurements. They are blue-sky albedo (0–1), evapotranspiration (ET, mm), and gross primary production (GPP, Mg C ha^?1 year^?1). An object-oriented classification of Landsat images in 2011 was processed to generate a land cover map for landscape structure. The downscaling model was tested for the five Level IV ecoregions within the watershed.

Results

We achieved satisfactory downscaling models for albedo, ET, and GPP for all five ecoregions. The adjusted R² was?>?0.995 for albedo, 0.915–0.997 for ET, and 0.902–0.962 for GPP. The estimated albedo, ET, and GPP values appear different in the region. The estimated albedo was the lowest for water (0.076–0.107) and the highest for cropland (0.166–0.172). Estimated ET was the highest for the built-up cover type (525.6–687.1 mm) and the lowest for forest (209.7–459.7 mm). The estimated GPP was the highest for the build-up cover type (8.65–9.85 Mg C ha^?1 year^?1) and the lowest for forest.

Conclusions

Estimated values for albedo, ET, and GPP appear reasonable for their ranges in the Kalamazoo River region and are consistent with values reported in the literature. Despite these promising results, the downscaling approach relies on strong assumptions and can carry substantial uncertainty. It is only valid at a spatial scale where similar climate, soil, and landforms exist (i.e., values in isolated patches of the same cover type are similar). Plausibly, the uncertainties associated with each estimation, as well as the model residuals, can be explored for other pattern-process relationships within the landscape.