Experimental Ponds Research Articles

Effects of Nitrogen Input on Community Structure of the Denitrifying Bacteria with Nitrous Oxide Reductase Gene (nosZ I): a Long-Term Pond Experiment.

Excessive nitrogen (N) input is an important factor influencing aquatic ecosystems and has received increasing public attention in the past decades. It remains unclear how N input affects the denitrifying bacterial communities that play a key role in regulating N cycles in various ecosystems. To test our hypothesis-that the abundance and biodiversity of denitrifying bacterial communities decrease with increasing N-we compared the abundance and composition of denitrifying bacteria having nitrous oxide reductase gene (nosZ I) from sediments (0-20 cm) in five experimental ponds with different nitrogen fertilization treatment (TN10, TN20, TN30, TN40, TN50) using quantitative PCR and pyrosequencing techniques. We found that (1) N addition significantly decreased nosZ I gene abundance, (2) the Invsimpson and Shannon indices (reflecting biodiversity) first increased significantly along with the increasing N loading in TN10-TN40 followed by a decrease in TN50, (3) the beta diversity of the nosZ I denitrifier was clustered into three groups along the TN concentration levels: Cluster I (TN50), Cluster II (TN40), and Cluster III (TN10-TN30), (4) the proportions of Alphaproteobacteria and Betaproteobacteria in the high-N treatment (TN50) were significantly lower than in the lower N treatments (TN10-TN30). (5) The TN concentration was the most important factor driving the alteration of denitrifying bacteria assemblages. Our findings shed new light on the response of denitrification-related bacteria to long-term N loading at pond scale and on the response of denitrifying microorganisms to N pollution.

Effect of mixed leaf litter of four mangrove species on shrimp post larvae (Penaeus monodon, Fabricius, 1798) performance in tank and mesocosm conditions in Bangladesh

Mangrove leaf litter is a potential source of nutrients for shrimp post larvae. To introduce mangrove trees in shrimp farms it is necessary to identify the combination of trees which is most beneficial for shrimp. The present study evaluated the effects of mixed leaf litter of four mangrove species (Avicennia officinalis (Ao), Sonneratia apetala (Sa), S. caseolaris (Sc) and Heritiera fomes (Hf) on shrimp post larvae performance and water and soil quality. Leaf litter with and without supplemental feed was applied to shrimp culture tanks according to a 4 × 2 factorial design and followed by testing a subset of treatments in mesocosm pond conditions. Shrimp post larvae of 15-days old (PL15) with an average weight of 0.01 g were used for both experiments, each with a 4-week duration without water exchange. Under controlled conditions in the tanks, leaf litter and feed resulted in 22 to 32% higher weight gain of PL shrimp than combined weight gain realized when receiving only leaf litter or only feed, indicating synergism. Based on this, the pond experiment was designed with combined application of leaf litter and feed. The pond experiment resulted in higher shrimp weight gain than realized in the tanks. In tanks, the highest average individual weight gain of PL was observed for the leaf litter mixture SaAoHf (0.23 g)followed by SaScHf (0.21 g), ScAoHf (0.21 g) andSaScAoHf (0.20 g). Paralleling the results of the tank experiment, SaAoHf leaf litter also gave the highest average individual weight gain (1.2 g) of PL shrimpin the ponds but other leaf litter treatments followed by SaScAoHf (0.95 g), ScAoHf (0.84 g) and SaScHf (0.69 g) leaf litter. The different mixtures of mangrove leaf litter also resulted in significant differences in biological oxygen demand (BOD5), phytoplankton and zooplankton concentrations in pond water and organic carbon in soil. Both phytoplankton (P < 0.01, Pearson correlation r = 0.910)and zooplankton (P < 0.05, r = 0.535) abundance was positively correlated to shrimp weight gain. The low feed conversion ratio (FCR) in the treatments combining leaf litter and supplemental feed as compared to treatments using only feed indicated extra food benefits for shrimp PL from decomposing leaf litter. Overall, mixed mangrove leaf litter had a positive effect on shrimp performance and this effect was highest for SaAoHf leaf litter.

Dimensionality Reduction Analysis of the Integrated Solar and Hydraulic Jump Enhanced Waste Stabilization Pond Model Parameters

The study investigated the structure of the integrated solar and hydraulic jump enhanced waste stabilization pond (ISHJEWSP) variables. Also, to determine the cluster of the most important variables that account for the performance of the ISHJEWSP using principal component analysis (PCA). Three sets of experimental ponds were constructed with varying locations of point of initiation of hydraulic jump. Wastewater samples collected from the inlet and outlet for varying inlet velocities were examined for physicochemical and bacteriological characteristics for a period of nine months. The Pearson’s R-matrix and KMO statistic were used in evaluating the structure of the variables. Consequently, the variables of temperature, pH, algae concentration, solar radiation, and locations of the point of initiation of hydraulic jump were subjected to PCA. Two components had eigenvalues above the Jolliffe’s criterion and in combination explained 90.66% of the total variance. The inflexion of the scree plot justified the retained components. The analysis after rotation revealed that the parameters of pH, temperature, solar radiation, and algal concentration loaded highly to component 1. This underscores the precedence of ambient climatic conditions, alongside the state of the wastewater in general, to the inlet velocity and location of point of initiation of hydraulic jump.

The effectiveness of using the synbiotic drug “ProStor” as additives in compound feed when growing carp fingerlings in pond conditions

The stimulating effect of the synbiotic drug “ProStor” on the body weight gain of fish and their physiological state was previously considered in various scientific sources when growing various fish species in swimming pools, cages and experimental aquariums. With the intensification of pond fish cultivation with compacted carp plantings, the percentage of natural forage organisms in the food lump is minimized, and, accordingly, the main weight gain of fish is carried out by feeding with compound feeds. In such conditions, the importance of using probiotic supplements in carp feeding becomes relevant. For a more complete description of the stimulating effect of probiotics, studies were conducted on feeding carp fingerlings in pond conditions of the Saratov region using the synbiotic drug “ProStor”. As a result of the conducted studies, it was revealed that the fish productivity of the outgrowth pond, where young carp were fed mixed feed with the drug “ProStor”, was 20% higher than in the control pond. Higher fish productivity was accompanied by better indicators of carp fingerlings by their average weight, which was 29.6 g and 26.4 g, respectively, in the experimental and control outgrowth ponds. In addition, the use of the developed drug by the company “STC BIO” LLC allowed to reduce feed costs when growing carp fingerlings, which indicates an increasing factor on the quality of compound feed of the synbiotic drug used. On average, the economic efficiency of the use of “ProStor” additives allows you to get an additional profit from one hectare of pond area compared to the control up to 22.5 thousand rubles.

Analysis of ancestry heterozygosity suggests that hybrid incompatibilities in threespine stickleback are environment dependent.

Hybrid incompatibilities occur when interactions between opposite ancestry alleles at different loci reduce the fitness of hybrids. Most work on incompatibilities has focused on those that are "intrinsic," meaning they affect viability and sterility in the laboratory. Theory predicts that ecological selection can also underlie hybrid incompatibilities, but tests of this hypothesis using sequence data are scarce. In this article, we compiled genetic data for F2 hybrid crosses between divergent populations of threespine stickleback fish (Gasterosteus aculeatus L.) that were born and raised in either the field (seminatural experimental ponds) or the laboratory (aquaria). Because selection against incompatibilities results in elevated ancestry heterozygosity, we tested the prediction that ancestry heterozygosity will be higher in pond-raised fish compared to those raised in aquaria. We found that ancestry heterozygosity was elevated by approximately 3% in crosses raised in ponds compared to those raised in aquaria. Additional analyses support a phenotypic basis for incompatibility and suggest that environment-specific single-locus heterozygote advantage is not the cause of selection on ancestry heterozygosity. Our study provides evidence that, in stickleback, a coarse-albeit indirect-signal of environment-dependent hybrid incompatibility is reliably detectable and suggests that extrinsic incompatibilities can evolve before intrinsic incompatibilities.

Mariculture of Indian white shrimp Penaeus indicus (H. Milne Edwards): Optimization of stocking density in modified extensive shrimp farming (MESF) system

Shrimp culture has become a part and parcel for continuing sustainable livelihood of the farmers in the coastal villages of Bangladesh. This study aimed to optimize stocking density for a disease-free and profitable Indian white shrimp (Penaeus indicus) farming. The experiment was conducted under three treatments each with three replications. Stocking density of 10 individuals m-2 was considered as treatment one (T1), 20 individuals m-2 as treatment two (T2) and 30 individuals m-2 as treatment three (T3) for farming Indian white shrimp. Generally, all the water quality parameters of the experimental ponds except the salinity were found within the optimum condition for Indian white shrimp culture. In modified extensive shrimp farming (MESF) system, T2 showed higher survival rate than any other treatments at a low salinity level. Besides, total production values were revealed very tiny gap between T2 and T3. Though the highest value of production was found in T3 but survival rate was lower than T2. Moreover, values of shrimp’s average body weight (ABW), daily weight gain (DWG), and specific growth rate (SGR) were the highest in T2. During 90 days of culture, the growth of the Indian shrimp was negative allometric (2.86), which value was about to the value (3.00) of isomerism. This study recommends MESF culture system for growing Indian white shrimp for a greater output in brackishwater farms. This investigation also suggests some future research by considering MESF system for other important indigenous shrimp species.

Does Fish Conditioning in Aquaculture Increase Survival Success in the Wild? A Case Study on a Cyprinid Fish

Many endangered fish species in the wild are artificially bred, and their populations are strengthened by the stocking of aquaculture-raised juveniles. Because fish from aquaculture are generally not well prepared for the challenging life in the wild, we tested whether training for selected challenges could improve fish survival after stocking. We chose conditioning on predation pressure (by learning predator image of northern pike Esox lucius using predator chemical cues and visual stimuli), increased rearing water velocity 20 cm × s−1, and direct exposure to predation. The juvenile cyprinid fish asp (Leuciscus aspius) was used as a model prey species. A total of 7949 asp were reared in four groups using a combination of high flow, predation, and control treatments (low flow, no predation; 2018, 2149, 1929, and 1856 individuals, respectively). Of these, 1800 individuals were released into three ponds with pike, and their mortality rates were monitored in relation to predation for two months after stocking using passive telemetry arrays. The remaining 6149 aquaculture-reared individuals were released directly into a large reservoir, while 1426 individuals that survived pike predation for two months were released after the pond experiment ended. Fish survival in a reservoir was monitored in 2020 and 2021 by boat electrofishing and passive telemetry. The effect of training in aquaculture was not detected in pond conditions, but the fish that survived direct predation from pike for two months in the semi-natural treatment were more likely to survive in the wild than their aquaculture-reared counterparts. In the laboratory environment, asp responded to predator chemical cues with an increase in shoal cohesion and swimming activity, which demonstrate their ability to detect chemical cues. However, exposure to more fluvial conditions did not result in increased critical swimming speed. The study suggests that conditioning tested in aquaculture may not be sufficient to prepare fish for the wild, while exposing fish to direct predation could increase fish survival.

Histological changes in the gills, livers and muscles of Oreochromis niloticus fed with steriod, natural hormone and pawpaw seed based diets

This study was conducted to evaluate the histological changes of 17αmethyl-testosterone (MT), wet testes of bull (Bos indicus), boar (Sus domesticus), bull/mud catfish testes (B. indicus/C. gariepinus) and pawpaw (Carica papaya) seed powder-based diet on the Nile tilapia fry in an indoor experimental pond. Histological changes and efficacies in producing monosex males were determined after four months. Fifty-five fry were assigned randomly to three experimental ponds in triplicates. Five experimental feeds composed of soya-bean, fish meal, wheat bran, cassava flour were formulated by adding 0.06g of 17α- methyl-testosterone, 17.47g of bull wet testes, 25.59g of boar wet testes, 20.48g of bull/catfish and 20g of pawpaw seed powder per kg of feed to group 1, 2, 3, 4, 5 respectively. Obtained results from the morphological examination revealed a significant difference (p &lt; 0.05) in phenotypic males of the Nile tilapia fry fed with the experimental diets. The highest indistinct percentage was recorded in the 17αmethyl-testosterone-treated diet while the lowest was recorded in diets 3 and 4 with no significant differences. All the groups showed histopathological differences in the livers, gills, and muscles. However, the liver histology of groups 1 and 5 showed central vessels that are mildly congested with abundant glycogen vacuolation and somewhat fat infiltration, while the histology of the muscles of group 5 showed pathological lesions including moderate to severe necrosis. These alterations can be considered an indication of the performance and health of fish in monosex culture medium indicating effects of plant extract and MT.

MANGROVE ASSOCIATE BASED SHRIMP FEED: AN INNOVATION IN THE AQUACULTURE SECTOR

The traditional method of shrimp culture is a common practice in Indian Sundarbans which is done without any sound scientific back-up, proper feed, and water quality management. The shrimp farmers use a traditional feed of animal origin that often results in deterioration of water quality and disease outbreaks in cultured species. The present paper highlights the effect of the total replacement of animal ingredients in shrimp feed with floral ingredients on water quality and shrimp health. Weight gain, condition index, feed conversion ratio (FCR), survival, body pigmentation (astaxanthin level) were analyzed in shrimps along with pond water quality. Higher condition index (C.I.) values, survival rate, and gain in shrimp weight were observed in the experimental pond (E) compared to the control pond (C). Low FCR values were observed in the experimental pond than in the control pond. Astaxanthin values in shrimps of the experimental pond were also higher than the control pond which points towards Suaeda maritima as the source of carotenoid in the shrimp tissue.

Effects of GnRH and Anti-Dopamine on Gonad Maturation of Osteochilus melanopleurus (Bleeker, 1852)

The Osteochilus melanopleurus (Bleeker, 1852) is one of the endogenous fish in the Siak River waters of Riau province which has high economic value. However, the fulfillment of needs still depends on the catch in nature. Efforts to overcome these problems are the availability of mature gonads. Broadly to accelerate the maturation of gonads through hormone induction until the fish are ready to be spawned to produce fish fry continuously. The purpose of this study was to analyze the effect of gonadotropin and anti-dopamine hormone induction with the trademark “Oodev” on the final gonad maturity (TKG) of the prospective broodstock of O. melanopleurus. The research was conducted from April to August 2021 in the fish rearing column and the experimental pond, Faculty of Fisheries and Marine Science. The research method was a Completely Randomized Design with 4 treatment levels and 3 replications, while the treatments were P0 (without Oodev injection), P1 (Oodev dose 0.5 mL/kg), P2 (0.7 mL/kg), and P3 (0,9 mL/kg). Measured responses: percentage of broodstock that reached TKG and egg diameter. The results of the research that have been carried out, the measurement of the diameter of the eggs produced showed that the use of the Oodev hormone at a dose of 0.7 mL/kg body weight of O.melanopleurus given every week for twelve weeks was able to stimulate the development of the gonads of O.melanopleurus. Ovaprim injection of 0.7 mL/kg body weight produced 89,566 eggs with a latency of 4 hours. oodev injection dose of 0.7 ml/kg BW or P2 treatment has succeeded in achieving a TKG of 82%.

Decreasing toxicity of un-ionized ammonia on the gastropod Bellamya aeruginosa when moving from laboratory to field scale

Along with a steady increasing use of artificial nitrogen fertilizer, concerns have been raised about the effects that high nitrogen loading may have on ecosystems. Due to the toxicity of unionized ammonia (NH3), tolerance criteria have been proposed for ambient water management in many countries; however, these are mainly based on acute or chronic tests carried out under lab conditions run with purified water. Aiming at understanding the responses of organisms to natural exposure to high ammonia concentrations, a Viviparidae gastropod, Bellamya aeruginosa, was tested at three experimental scales: standard 96-h lab test, one-month cage test in 6 experimental ponds with continuous nitrogen inputs, and intensive investigation of the B. aeruginosa from these ponds in spring and winter. The results were: 1) 96-h LC50 in the standard lab test was 0.56 mg NH3-N/L and 343.3 mg TAN/L (total ammonia expressed as N, standardized at pH 7 and 20 ℃). 2) In the one-month cage test, the survival rate was 97% when NH3-N was 0.61 mg/L (i.e., a higher concentration than the lab 96-h LC50) and the body size of the gastropods actually increased with increasing NH3-N concentrations. 3) In the winter-spring investigation, little effect of ammonia on the standing crops of gastropods was found, and the body size of the gastropods tended to increase with increasing ammonia concentrations (NH3-N concentration range of 0.05 ~ 2.06 mg/L). Thus, B. aeruginosa showed higher tolerance to ammonia exposure (NH3-N concentration < 0.81 mg/L) in the field than under laboratory conditions. Our study points to the necessity of considering the relevant scale when determining criteria for ammonia toxicity in water management.

Growth and survival of diploid and triploid bata, Labeo bata (Hamilton, 1822)

AbstractBata (Labeo bata), an indigenous, freshwater minor carp, is a great delicacy in Bangladesh. In its natural fishery, bata contributes significantly to the health and nutritional security of a large section of the fisher communities in Bangladesh. However, it is not a popular farmed fish because of its small size and slow growth rate. The induction of triploidy, aimed at providing faster growth and larger body size, could be appropriate for L. bata to enhance its aquaculture potential. In the present study, we induced triploidy in L. bata by applying heat shock on fertilised eggs (that were maintained at the ambient temperature of 26–28°C), 3 to 5 min post fertilisation and for durations ranging from 1 to 2 min. Four different temperatures, namely, 38, 39, 40 and 41°C, were tested as heat shock treatments. The optimum treatment combination for triploidy induction in L. bata was found to be 39°C for the 1 min duration, 3 min after fertilisation, yielding 100% triploidy. Karyotyping revealed 72 chromosomes in the triploid fish (3n), whereas the diploid control (2n) had 48 chromosomes. The growth performance of the triploid hatchlings was compared against the diploid control in experimental ponds. After 12 weeks of rearing, the triploid fish were significantly heavier (p &lt; 0.05) than their diploid counterparts. The survival rate of the triploids was also better (69%) than that of diploids (56%). Overall, results revealed better performance (growth and survival) of triploid bata over diploids, indicating that the farming of triploid bata can be a viable practice in Bangladesh.

STUDY ON GROWTH PERFORMANCE, PRODUCTION, AND RETURN OF VIETNAMESE KOI (Anabas testudineus) FOR SOCIO-ECONOMIC UPLIFTMENT OF RURAL YOUTH IN MANIPUR, INDIA

The climbing perch fish Anabas testudineus, locally known as Ukabi, is one of the important freshwater small indigenous fish of Manipur. It is very popular in the state for its delicious taste and flavor. A study was carried out in nine experimental ponds (each size 0.25 ha) to assess survival rate, specific growth rate, absolute growth, production, and benefit-cost ratio of climbing perch (Anabas testudineus) for four months period during the year 2020. The experiment consists of three treatments T1 (P1&amp; P2- stocking density with 80000 nos. fry/ha), T2 (P3 &amp; P4 stocking density with 100000 nos. fry/ha), and T3 (P5 &amp; P6 stocking density with 120000 nos. fry/ha). Water quality parameters of the test ponds were within the normal range for fish culture. As compared to T2 and T3, T1 was significantly higher in the specific growth rate (5.021±0.001%), absolute growth (113.25±0.18 g), production (1709.4±1.97 kg/0.25 ha), and benefit-cost ratio (3.28±0.19). Therefore, the present study was very important for the proper stocking density of its culture in the Manipur and NE region. It will help in the commercialization of its technique in maximization of production and income for the socio-economic upliftment of rural youth in the state.

The nursery of Litopenaeus vannamei at different density using aeration system on pond

The nursery of shrimp is an intermediate effort to connect hatchery and grow-out process, wherein shrimp fry was rear in a controlled process in a certain time before reared on pond. The study was aimed to evaluate the growth and, survival rate of white shrimp (L. vannamei) under different stocking density in nursery phase on pond. The nursery of L. vannamei was carried out at experimental pond installation of Research Institute for Coastal Aquaculture and Fisheries Extension (RICAFE) in Maros-South Sulawesi using a 5.5 x 11 m2 size of ponds, which was equipped with a bottom aeration system. The water depth of pond was 40 cm. Pond preparation was done by pond repairing, maintaining, drying, and eradicating using 20 ppm of saponin, flushing and water filling gradually until maximum of water level. The fry of L. vannamei (PL-10) with an average initial weight of 0.002g, which obtained from hatchery, were stocked. The treatments were stocking density of L. vannamei fry namely 1,653 individuals/m3 or 40,000 individuals/pond (A) and 909 individuals/m3 or 22,000 individuals/pond (B). Commercial powdered feed was given 3 times/day in 50–100% of biomass weight calculation base. The parameters observed were growth rate, survival rate of white shrimp and water quality condition. The results showed water quality variables including temperature, dissolved oxygen, pH, salinity, and alkalinity were in a suitable range for growth and survival of L. vannamei. The survival rate of L. vannamei in 21 days nursery was 86.40-95.61% and the final weight ranging from 0.292 to 0.320g/ind.

Вирощування цьоголіток коропа із застосуванням суспензії хлорели (Chlorella (Beijerinck,1890))

Purpose. Investigate ecological conditions and determine fish productivity of ponds when growing young-of-the-year carp using a suspension of chlorella. Methodology. During the study, we used methods generally accepted in hydrochemistry, hydrobiology and fish farming. Findings. The article presents the results of the study on the use of chlorella suspension in the cultivation of carp. It was found that the use of chlorella suspension created favorable hydrochemical conditions resulting in intensive development of zooplankton, which had a positive effect on the growth of young-of-the-year carp and fish productivity of the pond. The development of the natural food supply was sufficient to meet the nutritional needs of juvenile carp. The average seasonal biomass of zooplankton in the experimental pond was 28.68 g/m3 that was 1.5 times higher than in the control. The share of cladocerans in the total biomass of zooplankton in the experimental pond was 76.6%, versus 36.8% in the control. The average biomass of zoobenthos for the growing season in the experimental was 1.3 times higher than in the control, and was formed by chironomid larvae, which are valuable in the food chain. Originality. The study investigated ecological conditions and fish productivity of growing ponds under conditions of the application of cattle manure and suspension of chlorella when growing carp in monoculture. Practical value. It was found that the use of chlorella suspension promotes the intensification of the development of zooplankton organisms in ponds. The obtained data can be used to develop practical recommendations for optimizing the conditions for growing carp seeds and increasing the biological productivity of ponds. Key words: nursery ponds, natural food supply, phytoplankton, zooplankton, zoobenthos, young-of-the-year carp, chlorella suspension, fish productivity.

Ефективність використання в годівлі коропа пребіотика на основі мананових олігоcахаридів

Purpose. Analysis of productive and economic indicators in the cultivation of age-1+ carp as a result of the use of prebiotics based on mannan oligosaccharides (MOS) in feeding. Methodology. Four ponds were used, two of which were experimental and two control ponds, which were stocked with age-1 scaly carp with an average weight of 76–77 g at a stocking density of 2200 specimens/ha. Fish of Experiment 1 and Control 1 were fed with extruded feed with a protein content of 23%, fish in Experiment 2 and Control 2 were fed with a grain mixture with a protein content of 19%. 0.05% prebiotic based on MOS "Actigen" was added to the diet of experimental groups of carp throughout the growing season. Optimal conditions for carp farming were ensured including control over oxygen, hydrochemical and hydrobiological regimes in ponds, which were measured according to the generally accepted methods in fish farming. Fishery and economic indicators of growing age-1+ were determined after harvesting fish in autumn. Findings. Major hydrochemical parameters in all ponds were within the normative values. The average seasonal biomass of forage organisms of zooplankton and zoobenthos during the growing season did not differ in the experimental ponds and amounted to 10.33-16.23 g/m3 and 1.23-2.96 g/m3. A positive effect of the use of prebiotics based on MOS in the feeding of age-1+ carp was established. When the prebiotic was given as a part of the extruded feed, the average weight of fish was higher by 11.5%, and fish productivity by 22.7% relative to the control group, while the cost of feed for cultivation was lower by 20%. When it was added to the grain mixture, these values were higher by 12.9%, 16.3% and 16.7%, respectively. The profit, as a result of the use of the prebiotic based on MOS in the composition of the extruded feed increased by 43.3% compared to Control 1, and by 19.1% compared to Control 2 when it was added to the grain mixture. Originality. For the first time, a comparative analysis of the effectiveness of the use of the prebiotic based on MOS in the composition of extruded feed and grain mixtures was performed taking into account productivity and economic indicators. Practical value. The obtained results indicate the feasibility and effectiveness of the use of prebiotics based on MOS in the feeding of age-1+ carp. Introduction of experimental additives to feeds of different composition helps to obtain additional growth and increase the economic component in the cultivation of carp to marketable condition. Key words: carp, prebiotic, feed, productivity, efficiency, profit hydrochemical and hydrobiological indicators.

Effect of Stocking Density on Growth Performance and the Survival of Golden Mahseer, Tor putitora (Hamilton) Fry

Growth performance and survival of Tor putitora fry under different stocking densities were evaluated fry rearing system. The experimental period was 10 weeks from 31 December to 10 March 2019. The experiment was carried out in nine earthen ponds of 0.04 ha each under three treatments with three replications. Thirty days old fry were stocked at the rate of 1.0X105/ha was designated as treatment- 1 (T1), 1.5X105/ha` as treatment- 2 (T2) and 2.0X105/ha as treatment- 3 (T3), respectively. Fry were fed with commercially available nursery feed containing 32% crude protein. It was observed that, lower stocking density showed highest daily weight gain in T1 (growth 0.066 ± 0.006 g/day) compared with higher stocking density in T2 (growth 0.044 ± 0.004 g/day) and T3 (growth 0.024 ± 0.003 g/day), respectively. It is also noticed that, the lower stocking showed the highest survival rate (79.66 ± 4.34 %) than the other two treatments (66.97±3.67 and 54.67± 3.12 %). The values of different water quality parameters were within the optimum ranges for the rearing of carp fry. Water quality parameters did not show significant variations in the experimental ponds under different stocking densities. Among these three stocking densities lower stocking density (T1) showed the best result compare with the other two higher stocking densities.

Top predator introduction changes the effects of spatial isolation on freshwater community structure.

Current conceptual metacommunity models predict that the consequences of local selective pressures on community structure increase with spatial isolation when species favored by local conditions also have higher dispersal rates. This appears to be the case of freshwater insects in the presence of fish. The introduction of predatory fish can produce trophic cascades in freshwater habitats because fish tend to prey upon intermediate predatory taxa, such as predatory insects, indirectly benefiting herbivores and detritivores. Similarly, spatial isolation can limit dispersal and colonization rates of predatory insects more strongly than of herbivores and detritivores, thus generating similar cascading effects. Here we tested the hypothesis that the effect of introduced predatory fish on insect community structure increases with spatial isolation by conducting a field experiment in artificial ponds that manipulated the presence/absence of fish (the redbreast tilapia) at three different distances from a source wetland. Our results showed that fish have direct negative effects on the abundance of predatory insects but probably have variable net effects on the abundance of herbivores and detritivores because the direct negative effects of predation by fish may offset indirect positive ones. Spatial isolation also resulted in indirect positive effects on the abundance of herbivores and detritivores but this effect was stronger in the absence rather than in the presence of fish so that insect communities diverged more strongly between fish and fishless ponds at higher spatial isolation. We argue that an important additional mechanism, ignored in our initial hypothesis, was that as spatial isolation increases fish predation pressure upon herbivores and detritivores increases due to the relative scarcity of predatory insects, thus dampening the positive effect that spatial isolation confers to lower trophic levels. Our results highlight the importance of considering interspecific variation in dispersal and multiple trophic levels to better understand the processes generating community and metacommunity patterns.

Widespread agrochemicals differentially affect zooplankton biomass and community structure.

Anthropogenic environmental change is causing habitat deterioration at unprecedented rates in freshwater ecosystems. Despite increasing more rapidly than many other agents of global change, synthetic chemical pollution-including agrochemicals such as pesticides-has received relatively little attention in freshwater community and ecosystem ecology. Determining the combined effects of multiple agrochemicals on complex biological systems remains a major challenge, requiring a cross-field integration of ecology and ecotoxicology. Using a large-scale array of experimental ponds, we investigated the response of zooplankton community properties (biomass, composition, and diversity metrics) to the individual and joint presence of three globally widespread agrochemicals: the herbicide glyphosate, the neonicotinoid insecticide imidacloprid, and nutrient fertilizers. We tracked temporal variation in zooplankton biomass and community structure along single and combined pesticide gradients (each spanning eight levels), under low (mesotrophic) and high (eutrophic) nutrient-enriched conditions, and quantified (1) response threshold concentrations, (2) agrochemical interactions, and (3) community resistance and recovery. We found that the biomass of major zooplankton groups differed in their sensitivity to pesticides: ≥0.3mg/L glyphosate elicited long-lasting declines in rotifer communities, both pesticides impaired copepods (≥3µg/L imidacloprid and ≥5.5mg/L glyphosate), whereas some cladocerans were highly tolerant to pesticide contamination. Strong interactive effects of pesticides were only recorded in ponds treated with the combination of the highest doses. Overall, glyphosate was the most influential driver of aggregate community properties of zooplankton, with biomass and community structure responding rapidly but recovering unequally over time. Total community biomass showed little resistance when first exposed to glyphosate, but rapidly recovered and even increased with glyphosate concentration over time; in contrast, taxon richness decreased in more contaminated ponds but failed to recover. Our results indicate that the biomass of tolerant taxa compensated for the loss of sensitive species after the first exposure, conferring greater community resistance upon a subsequent contamination event; a case of pollution-induced community tolerance in freshwater animals. These findings suggest that zooplankton biomass may be more resilient to agrochemical pollution than community structure; yetall community properties measured in this study were affected at glyphosate concentrations below common water quality guidelines in North America.

The effects of intraguild interactions (or lack of) on prey diversity in experimental ponds food webs

The interactions between top- and intermediate-level predators can have significant effects on community structure of food webs. The direct and indirect effects of top predators not only affect prey communities both negatively (e.g. predation) and positively (e.g. thinning effects), but can also impact intermediate-level predators (via intraguild predation [IGP]). These IGP interactions can have especially far-reaching implications when predators of increased ecological importance, such as keystone predators, are involved. Yet, the strength of these interactions are often context-dependent with relationships that are highly variable, and little is known about the factors that shape the outcomes. We conducted a mesocosm experiment to test for the potential IGP interactions among top (invertebrate) and intermediate (amphibian) predators and their effects on a diverse prey community. We used larval Boyeria vinosa (Fawn Darner), a rarely studied member of the family Aeshnidae, and Ambystoma opacum (Marbled Salamander), a known keystone predator in parts of its range, in a mesocosm study with an additive experimental design. Each mesocosm received an equal assemblage of five anuran prey species. Total prey survival was lowest when both predators were present, but A. opacum overwhelmingly reduced the survival of three prey species, lowering species diversity in all food webs when present. Species diversity was highest in the B. vinosa food web, with one prey species (Anaxyrus americanus) emerging smaller and sooner than from other food webs. We did not detect any interactions between predator species, indicating that B. vinosa may not be as voracious as other members of Aeshnidae. Our findings suggest that density mediated IGP interactions are non-existent among our focal species. Ultimately, we also demonstrate the importance of examining variability in keystone predators and how abundant, but less-known predator species affect community structure.