Larval abundance of Chironomus circumdatus in relation to biotic and abiotic factors

Larval abundance of Chironomus circumdatus in sewage canal and pond systems was studied during 1988–1990. Monthly changes in the morphometric features of the pond revealed that both total and littoral areas progressively decreased from 1063 and 107 m² in December 1988 to 151 and 43 m² in May '89; the decrease during the year 1989–1990 was from 1116 and 92 m² in October to 109 and 31 m² in May. A significant negative correlation (r= – 0.52) was obtained for the relation between littoral area and larval density in the pond. Larval density and biomass depended generally on the nature of the substrate and quantity of organic matter. Larval density of Ch. circumdatus was positively correlated with O₂, bacterial count and organic matter content, but negatively correlated with CO₂ level. Daily removal of organic matter by the larvae ranged from 20 to 31 % of the available organic matter in the sewage canal and from 3 to 11 % in the pond.     

Morphometry,Primary productivity and Energy flow in a Tropical Pond

Monthly changes in the morphometric features of pond Idumban reveal that total and littoral areas progressively decreased from 62.4 and 15.4 ha in October-November-December to 6.8 and 2.6 ha in September. The dominant macrophytic producers in the littoral area of the pond were Chara fragilis, Hydrilla verticillata and Ceratophyllum demersum, which flourished from October for a period of 8 to 10 months, exhibiting a typical exponential or J-shaped population growth curve. Biomass of Ch. fragilis increased to the maximum of about 420 g dry weight/m² in April, H. verticillata to 260 g/m² in June–July and that of Ce. demersum to 140 g/m² in April–May. In terms of unit weight, H. verticillata proved to be the most efficient, producing 156 mg dry substance/g plant/day; however, the mean values obtained for 1973-74 were 93, 54 and 53 mg/g/day for H. verticillata, Ch. fragilis and Ce. demersum; the corresponding NPP values 50, 29 and 30 mg/g/day. The GPP and NPP values, expressed in g dry weight/m²/day, were 7 and 4 for H. verticillata, 8 and 4 for Ch. fragilis, 3 and 2 for Ce. demersum. These values, expressed in mg C/m²/day, averaged to 8.2 and 4.6 for all the macrophytes and suggest that the macrophytes were photosynthetically faster and more efficient than phytoplankton. Total gross productivity for Idumban pond amounts to 1773 and 1449 ton (dry weight) for 1973 and 74, respectively: the corresponding values for the NPP were 953 and 825 ton. In other words, 44% of the GPP is lost on plant respiration. Plants equivalent to 56 ton (6% of NPP) are exposed to death in the periphery of the littoral area. The population of Pila globosa proved to be the dominant consumer of these macrophytes. Mean predation amounted to 64 ton/annum for Pila and 200 ton/ annum for other consumer animals. Solar energy known to enter the pond is 1,956,000 Kcal/m²/year. Of this, 24,682 Kcal/m²/year was fixed by the macrophytes, i.e. the photosynthetic efficiency is 1.3%. Of the total GPP, NPP amounted to 13,696 Kcal/m²/year; the net primary production efficiency is 56%. Consumption of the macrophytes by Pila population amounted to 2,943 Kcal/m year and the exploitation efficiency is only 21%.     

Ouabain-insensitive salt and water movements in duck red cells. II. The role of chloride in the volume response

This paper describes the effect of external chloride on the typical swelling response induced in duck red cells by hypertonicity or norepinephrine. Lowering chloride inhibits swelling and produces concomitant changes in net movements of sodium and potassium in ouabain-treated cells, which resemble the effect of lowering external sodium or potassium. Inhibition is the same whether chloride is replaced with gluconate or with an osmotic equivalent of sucrose. Since changes in external chloride also cause predictable changes in cell chloride, pH, and water, these variables were systematically investigated by varying external pH along with chloride. Lowering pH to 6.60 does not abolish the response if external chloride levels are normal, although the cells are initially swollen due to the increased acidity. Cells deliberately preswollen in hypotonic solutions with appropriate ionic composition can also respond to norepinephrine by further swelling. These results rule out initial values of cell water, chloride, and pH as significant variables affecting the response. Initial values of the chloride equilibrium potential do have marked effect on the direction and rate of net water movement. If chloride is lowered by replacement with the permeant anion, acetate, E(Cl) is unchanged and a normal response to norepinephrine, which is inhibited by furosemide, is observed. Increasing internal sodium by the nystatin technique also inhibits the response. A theory is developed which depicts that the cotransport carrier proposed in the previous paper (W.F. Schmidt and T.J. McManus. 1977b. J. Gen. Physiol. 70:81-97) moves in response to the net electrochemical potential difference driving sodium and potassium across the membrane. Predictions of this theory fit the data for both cations and anions.     

Surfacing activity and food utilization in a tropical air-breathing fish exposed to different temperatures

Reared in tubular aquaria containing different depths of water (2.5, 5.0, 15.5, 31.0 and 40.0 cm), the obligatory air-breathing fish Ophiocephalus striatus (760 mg; 4.5 cm L) was forced to swim vertically a longer or shorter distance per surfacing. Interaction of temperature (17, 22, 27, 32 and 37°C) and aquarium depth reveals that surfacing frequency of the fish, fed ad libitum on Tilapia muscle, increased with increasing aquarium depth, but the increase was significant only at 27 and 32°C; in the starving series, the frequency was not depth-dependent at any temperature. Owing to the sustained surfacing activity and the consequent fatigue, the test individuals ‘hung’ to the surface for a definite period. Hanging frequency was temperature-dependent, but not a depth-dependent activity either in the starving or feeding series. At any temperature and aquarium depth, the feeding series hung more frequently than the starving series. Hanging duration increased from about 1 hr/day in either series at 17°C to 6 and 18 hr/day in the feeding and starving series at 37°C. At any tested temperature, distance swum by the feeding and starving series was a depth-dependent activity. The feeding series at 32°C exhibited the maximum swimming speed of 2 L/sec for 4.8 hr/day in the 40 cm depth. With increasing temperature and depth, feeding rate increased (from 24 to 225 g cal/g live fish/day); between 17 and 27°C, it was more a temperature-dependent activity. The highest rate (47 g cal / g/day) and efficiency (27%) of conversion were observed at 32°C; whereas the efficiency was depth-dependent, the rate was not. Oxygen uptake was a temperature-dependent activity; aquarium depth played a secondary role. Briefly, O. striatus in deeper aquaria consumed significantly more food and converted lesser, as it surfaced more frequently and swam longer distance, dissipating more energy on metabolism and swimming activity. Hence, culturing O. striatus in shallow waters at the optimum temperature of 32°C will be advantageous. This work was supported by the University Grants Commission's (New Delhi) grant to Dr. T. J. Pandian: Grant No. F. 23-210/75 (Sr II) for which appreciation is expressed.     

Pathogenicity, antibiotic susceptibility and genetic similarity of environmental and clinical isolates of Vibrio cholerae

Isolates of Vibrio cholerae were obtained from clinical and environmental samples and the pathogenicity of these isolates was confirmed by hemolytic assay. The clinical isolates were more pathogenic than environmental isolates. Antibiotic susceptibility of V. cholerae to a set of antibiotics showed a marked variation. The environmental isolates exhibited more resistance to the antibiotics than clinical isolates. The plasmid curing technique was used to check the encoding of antibiotic resistance gene in genome. In both isolates, the resistance to vancomycin and co-trimaxazole was not mediated by plasmid and it may probably be encoded in genome. RAPD method was adopted to find out the variation in the genome of the clinical isolates and environmental isolates of V. cholerae. The genomic similarity pattern revealed that the environmental Ogawa isolates were closely related to clinical Ogawa isolates. This study confirmed the existence of the complex nature of V. cholerae in its pathogenicity, response to a set of antibiotics and genetic similarity.     

Transferability of sequence tagged microsatellite site (STMS) primers across four major pulses

The transferability of genome-specific sequence tagged microsatellite site (STMS) primers from field pea (P. sativum) and chickpea (C. arietinum) to other major pulses was examined. Overall, field pea STMS primers amplified products in most of the accessions in comparison to that of the chickpea STMS primers, which amplified products in relatively few accessions. The highest level of successful amplifications with a single primer was 89% for field pea and 33% for chickpea primers respectively. The potential transferability of the STMS primers among species, expressed as the total mean percentage of positive amplifications, was 53% for the field pea STMS primers and 9% for the chickpea STMS primers. The individual mean percentage of successful transferability of field pea STMS primers across lentil, vetch and chickpea/Cicer sp. accessions was 60%, 39% and 62%, respectively. Whereas, for the chickpea STMS primers successful transferability was 5%, 3% and 18% for lentil, vetch and field pea, respectively. The trnasferability of these STMS primers indicates a high level of sequence conservation in these regions across species. Together with their locus-specificity, co-dominant nature and potential to amplify multiple alleles, their transferability makes STMS markers a powerful tool for genetic mapping, diversity analysis and genotyping.     

Screening and evaluation of probiotics as a biocontrol agent against pathogenic Vibrios in marine aquaculture

AIMS: The present work aims at finding potential probionts from marine sources as a biocontrol agent against pathogenic Vibrio species in shrimp larval culture. METHODS AND RESULTS: A total of 109 bacterial strains were isolated from seawater, sediment and marine fish-gut samples, and were screened for their antagonistic activity against Vibrio species. Three strains (Q, Q1 and M) isolated from the marine sediment were found antagonistic against Vibrio strains. Based on 16S ribosomal DNA gene sequence analysis, the strain Q was identified as Paenibacillus spp. (EF012164); Q1 as Bacillus cereus (DQ915582); and the M as Paenibacillus polymyxa (DQ915580). Further, the two bacterial species, Paenibacillus spp. and B. cereus were challenged separately at two different concentrations of 10(4) and 10(5) CFU ml(-1) for probiotic activity in the postlarvae of Penaeus monodon against pathogenic Vibrio harveyi and Vibrio spp. CONCLUSIONS: The present study identified the probiotic activity of Paenibacillus spp., B. cereus and Pa. polymyxa against the pathogenic Vibrios in the postlarvae of P. monodon. SIGNIFICANCE AND IMPACT OF THE STUDY: In vivo study reveals that the marine bacterial species can be used as probionts against pathogenic Vibrios in shrimp larval culture practices.