Studies on the bottom fauna in a tropical freshwater fish pond

Summary Quantitative samples of the bottom fauna obtained from a tropical freshwater fish pond during a period of two years were studied with regard to species composition, zonal variation and seasonal fluctuation. Two different zones with differences in faunal composition could be distinguished. The littoral zone was dominated by Mollusca, whereas Oligochaetes were predominant in the profundal zone. Most of the organisms showed their peaks in the months January to April. Breeding activities ofVivipara bengalensis, Digoniostoma cerameopoma, Melanoides granifera andPisidium clarkeanum as evidenced by presence of younger length groups in the populations were also observed during the same period (January to April). The influence of environmental factors as temperature, alkalinity and food were discussed as probable causes for the peaks in abundance. The average number of total organisms per square metre was found to be comparatively high indicating a high standing crop. Differences observed in the total number of organisms present have been attributed to inflow of water resulting in sudden alteration of the nutrient condition of the bottom mud. The seasonal variations of the standing crop of bottom fauna during both the years have been found to be influenced by fluctuations of the bivalve mollusc,Lamellidens corrianus. The availability of sufficient amount of benthic fauna for consumption by bottom feeding fishes has been indicated.This work formed part of a thesis submitted for the Degree of Doctor of Philosophy to the University of Calcutta, India in 1964.     

Fluctuations in the relative abundance of the weed fauna of a tropical freshwater fish pond

Summary The macrofauna present in the weed Eichhornia crassipes in a tropical fish pond have been studied for a two year period. Different groups of animals under the phyla Annelida, Arthropoda and Mollusca and their seasonal abundance have been recorded. The method of studying densities of organisms as related to a known volume of plant material was found to give satisfactory results. Aulophorus furcatus and Branchiodrilus hortensis were the two species of Oligochaeta which were associated with the weeds. The Ostracods Stenocypris malcolmsonii and Eucypris capensis showed almost similar seasonal trends. Larvae of the Ephemeropteran, Baetis, five species of Chironomidae and different nymphal instars of Zygoptera and Anisoptera were also encountered. Of the four species of Molluscs, three were pulmonates whose occurrence in the weeds is considered to be favourable for their growth and reproduction in view of their proximity to the water surface. The effect of nutrition on the populations of weed fauna has been discussed. Their maximum abundance during the months of November to March was found to be concurrent with the presence of other favourable environmental factors also.This work formed part of the thesis submitted for the award of the Degree of Doctor of Philosophy to the Calcutta University, in 1964.     

Diurnal variations in a shallow tropical freshwater fish pond in Shahjahanpur,U.P. (India)

Summary Diurnal variations in water chemistry and plankton in this eutrophic tropical freshwater ponds were quite apparent. Large fluctuations were noted in dissolved oxygen, pH, carbonate and bicarbonate concentrations. The pond water gets oversaturated with oxygen during day (24.2 p.p.m.) and depleted in the night (1.2 p.p.m.). Diurnal migrations of plankton were not in conformity with temperate waters.     

Secondary productivity and energy flow in a tropical pond

Monthly changes in density and biomass of a Pila globosa population were estimated in the littoral area of the pond Idumban. Mean density of active snail was 10.4, equivalent to 76 g dry weight/m² during 1973 and 6.5, equivalent to 45 g/m² during 1974. Total population size of the snail decreased from 9.2 × 10⁶ individuals, equivalent to 6.5 ton during 1973 to 6.3 × 10⁶ snails, equivalent to 4.4 ton during 1974. The period from December to May represented the time of abundance and active growth. Mortality assessed from marking and recapture as well as from monthly changes in population density, averaged to 2.7 snails/m²/month or 20% of the density. Growth estimated by marking and recapture suggested that the snail required a period of over 4 years to attain a body (wet) weight of 35 g. Laboratory experiments revealed that young (<4 g), intermediate (4 g><24 g) and old (>24 g) P. globosa grew at the rate of 4.0, 1.5 and 0.3 mg dry weight/g live weight/day. Using these values and the size-wise population density data, net productivity of the snail was estimated as 74 and 40 g/m²/year in 1973 and 74, respectively. The snail exhibited an efficiency of 70% for absorption and 10% for conversion. Using these values, it was further possible to estimate rates of feeding and absorption for the population. Consumption amounted to 1039 g/m² in 1973 and 560 g/m² in 1974. The efficiencies of exploitation, gross and net productions were 21, 7 and 10%, respectively; ecological efficiency amounted to 1.4% only.     

Studies on the ecology of a freshwater pond community

Summary Temperature of air and surface water showed a double oscillation curve. Physicochemical conditions and their diurnal amplitudes varied depending on the depth of water, amount of phyton and total activity of organisms. Permanent hardness, temporary hardness, acidity and total carbondioxide varied interdependently and also closely related to the amounts of plant matter. The abundance of gastropods was correlated with the abundance of food associated with permanent hardness. The abundance of bottom soil fauna was related to the temperature. Floral succession and abundance were correlated with the variations in silicates, phosphates and other chemical conditions. Microcystis bloom was recorded during winter months.Data formed part of Ph. D. Thesis and published with the permission of the Syndicate of S.V. University.     

Studies on the zooplankton of a tropical fish pond

Summary Seasonal abundance and the pattern of fluctuations in the zooplankton of a tropical fish pond has been studied at weekly intervals for a period of two years from September 1960 to August 1962. Except for a group of ciliates, protozoa were found only in limited numbers. Coleps, Tintinnus and Difflugia were recorded during both the years, whereas Arcella and Codonella were collected in the first year only. Other members as Centropyxis, Didinium, Paradileptus, Stentor and Bursaria were seen occasionally as few individuals. The total numbers of protozoa showed their peak from January to April and the prevailing phytoplankton abundance and temperature conditions are suggested as probable causative factors. More than thirty species of rotifers were recorded during this study, although many of them were only in limited numbers. Loricate forms showed their maximum density in summer months only, when total alkalinity values were also high. Nonloricate forms were found during September, October and December to February. The effect of temperature, total alkalinity and phytoplankton on these populations have been discussed. Five species of Copepoda were recorded. The most dominant copepod Mesocyclops hyalinus was present almost throughout the year and its fluctuation pattern closely resembled that of the copepodids and the nauplii. Definite peaks in naupliar populations were probably indicative of periods of active reproduction. Among the five species of cladocera, Diaphanosoma brachyurum was present during certain months only, in both the years. Moina brachiata was present during the first year only. The total abundance of these microcrustacea showed direct relationship with phytoplankton production. The importance of these investigations in fish cultural practices is suggested.This work formed part of a thesis submitted for the degree of Doctor of Philosophy to the University of Calcutta, India in 1964.     

Facultative aestivation in a tropical freshwater turtle Chelodina rugosa

• 1.1. Chelodina rugosa dug from aestivation sites at the end of the dry season were immediately alert and well coordinated.
• 2.2. Compared with non-aestivating animals, aestivating turtles had 20% higher plasma osmotic pressure and 7% higher sodium. Coupled with a small, but significant weight gain upon return to the water, this suggested the occurrence of minor dehydration in aestivating animals.
• 3.3. Plasma lactate levels of aestivating animals were low, averaging 1.99 mmol/l, consistent with aerobic rather than anaerobic metabolism having sustained their long period under ground.
• 4.4. No evidence was seen of dramatic physiological specialization. Aestivation in this species is interpreted as a primarily behavioural adaptation, made possible by typically reptilian abilities to tolerate a wide range in plasma electrolytes and to survive long periods without feeding.

     

Primary production in a tropical fish pond at Aligarh,India

Summary Seasonal fluctuations in gross and net primary production values were quite apparent in surface waters and showed a bimodal type of distribution. The values were generally high during post winter months (March to May) and low during winter (February) and monsoon months (July and August). At different depths the rate of primary production was always found decreasing from surface to bottom. The rate of photosynthesis was found to be highly variable from time to time and at different depths.Respiratory rate was found to be increasing from surface to bottom perhaps due to decomposition of organic matter and high bacterial growth at the increasing depths. A close relationship was found between the transparency and primary production values. Phosphate-phosphorus was found to be directly related with the gross primary production values. However, there was no relationship between nitrate-nitrogen and production values. An inverse relationship was shown between ammonia-nitrogen and the production values. Fluctuations in chlorophyll were also found significantly related with the gross primary production.     

Ecomorphology of a size-structured tropical freshwater fish community

Among nine species of a tropical community ecomorphological correlates were sought throughout ontogeny. Ontogenetic changes were distinguished by establishing six pre-defined size-classes. Morphometric data associated with feeding were compared by canonical correspondence analysis to dietary data. This analysis revealed seven significant relationships, showing 71% of the morphological variance explained 77% of the variance in diet. Based on funtional ecomorphological relationships established in other studies and results of the canonical correspondence analysis, three food characters were selected: the size of the food particles, the type of food (vegetable versus animal) and the vertical position in the water column. The morphometric data were reduced using principal component analysis into three axis explaining 83% of the variation. The morphological characters with the highest loadings were: mouth gape on the first principal component axis, length of the intestine tract on the second and the orientation of the mouth together with the presence of barbels on the third. These axis were significantly correlated with, respectively, the size, the type and the vertical position of the food. The importance of morphological changes during ontogeny in explaining dietary changes was shown because 75% of the variation in the first, and most important, morphological principal component was accounted for by differences between size-classes. Assuming functional relationships, the potential niches of the species/size-classes were established, distinguishing herbivorous, omnivorous/molluscivorous and carnivorous species which, in turn, were segregated by their potential to feed on larger prey. This revised version was published online in July 2006 with corrections to the Cover Date.     

Decomposition patterns of unprocessed and processed lignocellulosics in a freshwater fish pond

In an attempt to recycle the lignocellulosic wastes like Eichhornia crassipes, Salvinia cucullata and rice (Oryza sativa) straw as manurial inputs in freshwater fish pond ecosystem, a decomposition experiment was carried out in litter bags in an oligotrophic freshwater fish pond environment, with the above mentioned three substrates in unprocessed and microbially processed forms. The loss rates, associated microbial groups, oxygen consumption patterns and other related parameters like carbon, nitrogen, phosphorus, cellulose, hemicellulose and lignin were analysed. The mean daily dry matter loss rates (unprocessed: 10.44>6.97>1.97 and processed: 11.03>8.21>3.67) and oxygen uptake rate (unprocessed: 0.675>0.571>0.568 mg O₂ g^–1 h^–1 and processed: 0.592>0.424>0.407 mg O₂ g^–1 h^–1) in raw and processed substrates were in the sequence Eichhornia > rice straw > Salvinia. The oxygen consumption pattern almost covariated with variations in temperature of pond water, daily dry matter loss rates and fungal counts on substrates. During the decay, the percentage of N and P increased whereas that of C decreased, resulting in lowering of C/N and C/P ratios of the substrates. The structural polymeric fractions like cellulose and hemicellulose decreased along with dry matter whereas the lignin content increased after an initial decrease due to loss of other structural carbohydrates resulting in apparent per cent gain of lignin. A higher number of different heterotrophic bacterial groups was observed in the processed substrates as compared to their raw counterparts. However, cellulolytic bacterial numbers were found to fluctuate through the study period. The fungal load was found to be decreasing gradually as the decay progressed. In this study, bacteria were found to be the prominent microbial group responsible for the decay. The nitrogen-fixing, phosphatase-producing and phosphorus-solubilising bacterial groups were observed to play an important role in lowering the C/N and C/P ratios of the decomposing substrates during decay.     

Migratory benthic fishes may induce regime shifts in a tropical floodplain pond

1. Alternative states are a widely recorded phenomenon in shallow lakes, which may shift between turbid‐ and clear‐water conditions. Here, we investigate whether such shifts in a tropical floodplain pond may be related to the effect of the flood pulse regime on the community structures of fish and macrophytes. 2. Using a long‐term data set, we demonstrate how benthic fish migration together with colonisation by submerged plants affected the transition from a turbid to a macrophyte‐dominated state in a floodplain pond without top‐down control. 3. In our study, the turbid state occurred mostly during low water phases and was largely characterised by high values for the biomass of benthic fish, chlorophyll‐a and total phosphorous. 4. During the period of rising water levels, the migration of benthic fish out of the pond occurs simultaneously with the establishment of submerged plants, while water turbidity decreases along with phytoplankton and nutrient concentrations, inducing a clear‐water phase. However, when submerged plants are absent and fish migration is low, a transient state is generated. 5. We suggest that, in contrast to temperate ponds and shallow lakes, where the main driving mechanisms establishing alternative states are related to cascading effects via the food chain, in tropical ponds and shallow lakes it is resuspension of sediments by benthic fish that plays the most significant role in establishing alternative states. However, the effect of the flood pulse regime plays an important role in the temporal dynamics of fish community structure by controlling benthic fish migration.     

Starvation-induced impairment of metabolism in a freshwater catfish

Starvation induced changes in citrate synthase (CS), glucose-6-phosphate dehydrogenase (G6-PDH), lactate dehydrogenase (LDH), DNA, RNA, RNA/DNA ratio and protein were studied in the freshwater catfish Clarias batrachus. Starvation gradually decreased the activity of CS, G6-PDH and LDH in brain, liver and skeletal muscle of the freshwater catfish. The maximum reduction in these enzyme activities upto 35-45% was observed after 35 days of fasting. This shows substantial decline in aerobic and biosynthetic capacity during starvation period. DNA, RNA, RNA/DNA ratio and protein contents were also reduced from 40-67% which reflects reduction in an overall capacity of the protein synthesis. Starvation-induced macromolecular changes indicate impairment of metabolism in fish.     

Massive upstream migrations by a tropical freshwater neritid snail

While upstream movements of benthic invertebrates have been reported, gregarious upstream migrations of freshwater snails have never been described. We report a possible adaptation to downstream drift by a population of the Neritid (Archeogastropoda) snail,Neritina (Clypeolum) latissima (Broderip, 1833), in the Rio Claro, a small coastal river in Corcovado National Park, Costa Rica. We observed large numbers of these snails in gregarious upstream migration. Snails migrated in narrow lines up to 32 meters long, containing thousands of snails. The migration covered over 1 km of the stream. Larval and juvenile snails are more susceptible to washout by current, and differential mortality of these age classes in the estuarine and ocean environment may provide the selective pressure for the evolution of this behavior.     

Opportunistic top predators partition food resources in a tropical freshwater ecosystem

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Low intraspecific diversity in a polynucleobacter subcluster population numerically dominating bacterioplankton of a freshwater pond

Cultivation-dependent and -independent methods were combined to investigate the microdiversity of a Polynucleobacter subcluster population (Betaproteobacteria) numerically dominating the bacterioplankton of a small, humic freshwater pond. Complete coverage of the population by cultivation allowed the analysis of microdiversity beyond the phylogenetic resolution of ribosomal markers. Fluorescent in situ hybridization with two probes specific for the narrow subcluster C (PnecC bacteria) of the Polynucleobacter cluster revealed that this population contributed up to 60% to the total number of bacterioplankton cells. Microdiversity was investigated for a date at which the highest relative numbers of PnecC were observed. A clone library of fragments of the ribosomal operon (16S rRNA genes, complete 16S-23S internal transcribed spacer 1 [ITS1], partial 23S rRNA genes) amplified with universal bacterial primers was constructed. The library was stepwise screened for fragments from PnecC bacteria and for different ITS genotypes of PnecC bacteria. The isolated PnecC strains were characterized by sequencing of the 16S rRNA genes and the ITS1. Both the clone library and the established culture collection contained only the same three ITS genotypes, and one of them contributed 46% to the entire number of clones. Genomic fingerprinting of the isolates with several methods always resulted in the detection of only one fingerprint per ITS genotype. We conclude that a Polynucleobacter population with an extremely low intraspecific diversity and an uneven structure numerically dominated the bacterioplankton community in the investigated habitat. This low intraspecific diversity is in strong contrast to the high intraspecific diversities found in marine bacterial populations.