The feeding activity of Colossoma macropomum larvae (tambaqui) in fishponds with water hyacinth (Eichhornia crassipes) fertilizer.

Analysis of macrophyte water hyacinth (Eichhornia crassipes) as an organic fertilizer of Colossoma macropomum (tambaqui) larvae in ponds is provided. Water hyacinth produce an organic fertilizer at the ratio of 100 g x m(-2) in tambaqui ponds. Two groups of 5,000 larvae were transferred to two fishponds with and without water hyacinth fertilizer and reared until day 43. The fertilized pond evidenced more plankton abundance during the entire production period when compared with the control pond (P < 0.001). The phytoplankton community in the pond was not significantly different than in gut contents (P > 0.05) in both ponds (with and without organic fertilizer). Fish larvae failed to show any preference or selectivity in relation to the different algae (P > 0.01) in the pond, but exhibited high ingestion selectivity for zooplankton (P < 0.05). Application of fertilizer increased (P < 0.05) the abundance of phytoplankton and zooplankton in the treatment pond. Since water hyacinth fertilizer is quite cheap and easily available, it may be conveniently used to enhance fish yield in ponds.     

Use of water flow direction to provide spatial information in a small-scale orientation task

Experiments were designed to investigate whether three-spined sticklebacks Gasterosteus aculeatus can use direction of water flow as an orientation cue. The fish had to learn the location of a food patch in a channel where water flow direction was the only reliable indicator of the food patch position. Fish from two ponds and two rivers were trained and tested in the spatial task to determine whether river three-spined sticklebacks are more adept at using water flow as a spatial cue than fish from ponds. All fish were able to use water flow to locate the food patch but one of the two river groups was significantly faster at learning the patch location. When the task was reversed so that fish that had formerly been trained to swim downstream now had to learn to swim upstream and vice versa both river groups learned the reversed task faster than the two pond groups. In a second experiment, to investigate whether fish from ponds or rivers vary in the type of spatial cue that they prefer to use, fish from one pond and one river were given a choice between two different types of spatial cue: flow direction or visual landmarks. A test trial in which these two cues were put into conflict revealed that the river population showed a strong preference for flow direction whilst the pond population preferred to use visual landmarks.     

Flexible antipredator behavior in a dragonfly species that coexists with different predator types

Two of the main predators of dragonfly larvae, insectivorous fish in communities with fish and large dragonfly species in communities without fish, differ markedly in their mode of predation. In general, dragonfly species coexist successfully with one predator or the other, but larvae of the dragonfly Pachydiplax longipennis can coexist successfully with both. I examined the behavioral response of these larvae to a simulated predator attack to determine whether their response (1) differs between the two communities, and (2) is sensitive to waterborne cues about the type of predator present. I compared larvae from two different communities: fish ponds where insectivorous fish were the top predators, and fish-free ponds where large dragonflies were the top predators. Larvae from fish-free ponds actively moved away from an attack significantly more than did larvae from fish ponds, provided each was attacked in its native pond water. Larvae collected from a fish-free pond but then attacked in fish water moved less than did controls (larvae attacked in fish-free water). Likewise, larvae collected from a fish pond but attacked in fish-free water moved more than did controls (larvae attacked in fish water). Larvae attacked first in water from their native pond and then in water from the contrasting pond changed their response in the expected direction. These results indicate that escape behavior in P. longipennis differs between communities with different predator types and is sensitive to waterborne cues in a manner consistent with the mode of predation employed by each predator.     

The Effects of Periphyton, Fish and Fertilizer Dose on Biological Processes Affecting Water Quality in Earthen Fish Ponds

The potential of periphyton-based aquaculture in South Asia is under investigation in an extensive research program. This paper is a further analysis of data from four experiments carried out in that framework, to explore periphyton, fish and fertilizer dose effects on water quality. Factor analysis and ANOVA models applied to a data matrix of water quality parameters in ponds with and without artificial substrates (bamboo poles and kanchi sticks), with and without fish (filter feeders catla and rohu, with and without bottom feeder kalbaush), and with a standard or 50% increased fertilizer dose, allowed us to identify the underlying ecological processes governing this novel periphyton-based pond system, and construct conceptual graphic models of the periphyton–environment relationships observed. We clearly established that the phosphorus flow is mainly linked to phytoplankton activity in the water column and decomposition on the pond bottom, while nitrogen flow is mainly linked to autotrophic (photosynthesis) and heterotrophic (decomposition and nitrification) processes that take place in the periphyton in addition to the water column and pond bottom. Consequently, disruption of the pond bottom by bottom feeding fish primarily promoted phosphate cycling and phytoplankton, while periphyton development on the supplied substrates and fertilization mainly improved oxygen balance and nitrogen related processes developing in the water column. The use of bamboo poles led to better results than kanchi sticks, related to the greater autotrophic periphyton development on bamboo and to the larger surface of bamboo poles that facilitate fish grazing and periphyton dislodgment that in turn have a renewal effect on periphyton. Stocking bottom feeding fish produces a fertilizing effect through the food web that benefits the filter-feeding fish and that makes it unnecessary to increase the dose of inorganic and organic fertilizers applied to the ponds. Thus, the output of this analysis will help the fish farmers in resource constrained countries to improve their production in periphyton-based ponds just by choosing bamboo substrates, stocking a bottom feeder fish together with the filter feeders, and saving money on fertilizers.     

Environmental capacity of receiving water as basis for regulating intensity of milkfish (Chanos chanos Forsskal) culture

This paper presents the results of the assessment of the environmental condition of a receiving water and demonstrates how the environmental capacity of the system can be estimated based on effluent discharge from milkfish ponds and water criteria from scientific literature and other studies. An estuary (average volume, 295 333 m³; average depth, 1.9 m) in Punta Pulao, Dumangas, Iloilo, Philippines served as discharge and irrigation system for commercial milkfish ponds and experimental/verification ponds owned by the Southeast Asian Fisheries Development Center. Total ammonia nitrogen, nitrite, nitrate, phosphate, and chlorophyll a (chl a) were determined monthly (during spring tide) for 4 months. Samples were taken at low and high tides that coincided with the draining and flooding of ponds, respectively. Monthly concentrations of these water quality variables generally increased from the first to fourth month of sampling (April–July 2001) during low tide. Very slight increases were observed during high tide. The magnitude of changes in the diurnal patterns of phosphate, chl a, and dissolved oxygen appeared to be higher at spring tide than at neap tide. This indicates that the inflowing river at low tide (during spring tide) brought effluents containing high amounts of nutrients from ponds located upstream. The water, salt, dissolved inorganic nitrogen (DIN), and phosphate (DIP) budgets of the entire estuary were determined following the one‐box model by LOICZ‐IGBP (2000, LOICZ biochemical budgeting procedure: a tutorial pamphlet. L. T. David, M. L. San Diego‐McGlone, C. J. Crossland and S. V. Smith (Eds). Publ. for LOICZ International Project Office, the Netherlands, 29 pp.). The budgets indicate that the system is net heterotrophic and nitrogen (N) fixing during the dry months, but that there could be no environmental impact during the rainy months because of short water exchange time. Results further suggest that the system is a source of N and phosphorus (P) during the dry and rainy months; the condition is largely influenced by the high amount of nutrient inputs in to the river. Linear regression analysis was performed to determine relationship between nutrient concentrations in the system and total DIN or DIP input to the system at low tide. Environmental capacity in terms of the maximum amount of DIN or DIP input to the system was predicted using regression analysis and following set criteria for nutrients, i.e. nitrite, nitrate, and phosphate. At present, the estuarine water quality has already reached its environmental capacity during the dry months. About 945 ha of commercial milkfish ponds are operating upstream, mostly as extensive systems. If these ponds are converted to semi‐intensive or intensive systems, it is recommended that the pond area be reduced to 122 ha if the DIP criterion is to be followed so as not to exceed the environmental capacity. Exceeding this environmental capacity may affect production through reduction of fish growth, occurrence of diseases, and fish mortalities.     

Seasonal variation in the water quality and chlorophyll a of semi-intensive shrimp ponds in a subtropical environment

Twelve water quality variables were measured at different intervals (biweekly and twice a week) in two ponds during two consecutive production cycles in a semi-intensive shrimp farm on the Northwest coast of Mexico. The average harvest during dry season (March–July, a 95 days period) was 1822 kg ha^-1, with an average size of 16.0 g; while the harvest in the rainy season (August–January, a 165-day period) was 2125 kg ha^-1, with an average size of 11.9 g. In the rainy season, dissolved oxygen concentration tended to decrease as the feeding rates and shrimp and phytoplankton biomass were increasing until harvest. During both culture cycles, mean values of temperature, salinity and ammonium in ponds were not significantly different from those in inlet water, whereas pH levels in ponds were higher than in incoming water.Nitrogen nutrients, pH and particulate organic matter levels in ponds and inlet water did not exhibit seasonal differences; the better yield and feed conversion obtained during rainy season reflect the fact that temperature and mean chlorophyll a were higher during the rainy than in the dry season; salinity and total suspended solids were lower during the dry than in the rainy season. The mean levels of the water quality variables in the two ponds were not significantly different in both grow out cycles. Therefore, the differences in productivity between ponds cannot be explained by the water quality.     

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.     

Changes in sediment phosphate composition of seasonal ponds during filling

Most ponds from the Doñana National Park are shallow temporary freshwater bodies on eolian sands. The total phosphate concentration and the fractional P-composition of the sediments from two small ponds were studied before and inmediately after they were filled (autumn, 1996). Total phosphorus concentration was measured in 2 different size fractions: 2–0.1 mm (coarse) and <0.1 mm (fine). In both ponds, the total phosphorus concentration of the fine sediment increased by 20% at the beginning of the filling period, whereas 5 weeks later it did not increase further. The percentage of organic matter of the fine sediment was relatively high (between 13–18%) and did not change significantly during filling. The concentration of sediment total iron and Fe(OOH) increased significantly in both ponds during filling. The sequential P fractionation of the fine sediment included, besides the determination of two inorganic fractions (Ca-bound P and Fe-bound P), an organic-P fraction extracted with acid, another extracted with alkali, two organic-P fractios from the Ca-EDTA/dithionite and the Na₂-EDTA extracts which contained high concentrations of humic substances. The pond sediments were rich in organic P compounds as the sum of all organic-P fractions ranged between 267 and 320 g g^-1 (68% and 79% of the sum of all fractions). Significant changes (P<0.01) in the fractional P-composition of sediments were found after filling. Acid soluble organic phosphate increased about 30% in both ponds. Iron-bound phosphate increased significantly (about 40%) only in the pond where a higher concentration of Fe(OOH) was measured after filling. An adsorption experiment was carried out for each sediment to simulate P input during filling. Both the iron-bound phosphate and Ca-bound P increased significantly (P<0.01) suggesting that these two fractions were involved in the P-adsorption during the laboratory experiment.     

Comparison of various water replenishment and fertilization schemes in brackishwater milkfish ponds

The study was undertaken to determine the optimum combination of the frequency of water replenishment and fertilization that can yield the highest growth, survival, and gross production of milkfish. Results indicated that mean body weight and survival were not significantly different (P > 0.05) among the treatments. Gross fish production was higher in biweekly fertilization if considered as a single factor. However, when this was in combination with the weekly or biweekly water replenishment, similar gross fish production was attained. In any case, because biweekly fertilization has a better effect than a weekly schedule, the former should be used in combination with any other level of replenishment. A weekly water replenishment, however, is impractical in big pond areas of 5–10 ha compartments which are still common in some milkfish ponds in the Philippines. Therefore, biweekly water replenishment and fertilization with 16–20–0 at 50 kg ha^-1 would be reasonable.     

Phosphorus cycling in urban aquatic ecosystems: connecting biological processes and water chemistry to sediment P fractions in urban stormwater management ponds

Phosphorus (P) dynamics in urban landscapes may differ from that in natural landscapes due to different P sources and unique environmental conditions. However, many aspects of P cycles in urban areas, especially within engineered aquatic ecosystems, remain largely unknown. Through this work, we aim to contribute to better understanding of P cycling in urban aquatic ecosystems by investigating P fractions in sediment and their relationship with ambient chemistry in surface water from six urban stormwater management ponds located in Ontario, Canada. We found that organic P contributed up to 75% of total P in pond sediment, but this percentage decreased significantly between our two sampling events in June and September 2012. This decrease coincided with increased rates of extracellular enzyme (especially phosphatase) activities, which is indicative of fast mineralization processes in these ecosystems. Moreover, the decreased sediment organic P was matched by increased water column P concentration. This inverse relationship suggests that the large organic P pool in pond sediment, and its fast decomposition, contributed to internal release of P from sediment and increased water column P concentrations. The dominance of organic P in sediment and the putative role of relevant biological processes (i.e., decomposition and productivity) in urban ponds found in this study strongly contrast with classic water management expectations of physicochemically controlled P dynamics and long-term P storage in sediment of aquatic ecosystems. This difference suggests that urban stormwater ponds may perform poorly in terms of P retention and thereby contribute to poor water quality in terms of P pollution to downstream urban watersheds. Thus, stormwater pond design and future management strategies should consider these biogeochemical features of urban ponds, including internal P release, to help prevent eutrophication of downstream ecosystems.     

Factors affecting the predation of otter (Lutra lutra) on European pond turtle (Emys orbicularis)

In this case study, the ecological background of an unusual hunting behaviour was investigated, when otters Lutra lutra preyed upon European pond turtles Emys orbicularis in a Hungarian fish pond system during an 18-month period. Predation on turtle was found only during cold periods (established by spraint analysis and also by the collection of 182 turtle carcasses in 2003). The relationship was not close between fish availability and turtle consumption ( r _P =−0.325, P =0.19). The crude protein content of the turtle head and leg was higher than that of fish, frog and turtle body, whereas the energy content of the samples was similar. The mean body weight of the killed turtles (460 g) fell within the range of the optimal prey size of the otter. Turtles were used as cache foods by otters during extreme environmental conditions (as in the long winter), but occurred only rarely as buffer foods during moderate winter. In fish ponds, the conservation of the coexistent otter and turtle depends on pond management. The maintenance of a higher fish availability in ponds during winter makes it possible to avoid the need to acquire a proper hunting technique on turtle, indicated by the scarcity of primary fish food.     

Integrated vermi-pisciculture--an alternative option for recycling of solid municipal waste in rural India

Vermicomposts as a biofertilizer can be a great option for pond manuring as they never cause any long term harm to the soil like chemical fertilizer. In this study vegetable and horticulture waste was used as an important media for vermiculture. Three separate cemented tanks (6 m(3) each) were used in the system as control tank, vermicompost fertilized tank and inorganic fertilizer manured tank. Monoculture of fish was carried out with cat fish, Clarias batrachus. The produced earthworms were used as fish feed. Regular monitoring of water parameter was conducted in three different ponds. Specifically, the algal biomass variation was quite helpful in analyzing the behavior of the ponds. NPK value of soil samples were analyzed intermittently to know the eutrophication level. Despite the hot summer temperature in northern part of India, which is not ideal for fish growth, we have recorded an encouraging growth performance in organic manured pond along with inorganic fertilizer treated and control pond. Among eutrophicated pond, the fish biomass from vermicompost fed pond showed an increasing trend compared to inorganic fertilizer treated pond. Water retention capacity of vermicompost pond soil was better in comparison to other ponds. Result shows that the low cost model by integrating two production system vermiculture and pisciculture could be a commercially and environmentally viable option.     

Pathways of ornamental and aquarium fish introductions into urban ponds of Epping Forest (London,England): the human vector*

To examine the role of humans in the non‐native fish introductions, we measured the frequency of occurrence and density of non‐native fishes in ponds (Epping Forest, Essex, England) that had been restored (drained of water and voided of fish or treated with rotenone) on a known date and into which no piscivorous or non‐native fishes had subsequently been stocked intentionally. For each pond, the period of time since pond restoration, pond area, distance to nearest residential housing, distance to nearest footpath, distance to nearest water body or stream, and the proportion of pond vegetated were measured. The occurrence of both non‐native and unexpected native fish species was non‐random, and the number of ornamental varieties was found to increase as pond distance from the nearest road decreased. Variety richness of each of three categories of fish (non‐native, goldfish Carassius auratus and native) was significantly correlated with at least two of the following variables: distance from nearest road, nearest footpath and nearest pond. The rate of non‐native fish introductions (adjusted variety richness per year) could also be estimated from pond distance to the nearest road, being about 3.5 ornamental varieties introduced per year in ponds adjacent to roads, but the rate appears to be much greater in ponds that had recently (<1.5 years) undergone restoration. Implications for conservation and management, as well as the potential role of societal issues such as recreational activities, cultural and religious practices, are discussed.     

Inorganic transformation of applied phosphorus in brackishwater fish pond soil under different water salinity levels

Transformation of applied phosphorus in a brackishwater fish pond soil was studied under different water salinity levels, as occurring in such ponds, in presence and in absence of added organic matter. Added phosphorus was found to disappear rapidly from the water phase with some variations under different water salinities. The amount of added phosphorus in saloid-bound form increased with increase in water salinity but the same in Bray's (No. 2) extractable form showed a reverse trend. Applied phosphorus was transformed mostly into insoluble calcium phosphate form which increased with increase in water salinity. Transformation was intermediate into iron phosphate and the least into aluminium phosphate form. Application of organic matter reduced the fixation of added phosphorus into the iron phosphate form during the initial period of study and thus increased availability of phosphorus both in water as well as soil phases.This work formed a part of a thesis submitted for the Degree of Doctor of Philosophy to Bidhan Chandra Agricultural University, West Bengal in 1978This work formed a part of a thesis submitted for the Degree of Doctor of Philosophy to Bidhan Chandra Agricultural University, West Bengal in 1978     

Spatial and seasonal distribution of heterotrophic bacteria in pond water and sediments under different management practices

Population densities and generation time of heterotrophic bacteria were estimated in water and sediments of fish ponds used for polyculture, monoculture and traditional systems of fish farming over a period of two and a half years. Spatial differences in microbial densities in the ponds were related to the organic loadings of the farm site and farm management. A number of environmental factors such as nitrogen, dissolved organic carbon, bicarbonate and phosphate of water were found to be responsible for the seasonal changes of heterotrophic bacteria in these ponds.     

Vegetation fluctuation in mediterranean dune ponds in relation to rainfall variation and water extraction

Abstract. The structure of dune ponds hygrophytic vegetation has a spatial organisation in belts around the pond basin, closely related to water level and flooding regime. Doñana National Park has an important representation of temporal dune ponds, which are subjected to rainfall fluctuations and may be suffering the impact of water extraction from the neighbouring tourist resort. Permanent transects in a vegetation complex of five dune ponds have been monitored during a eight year period (1990-1997). This period was characterised by a number of dry years (annual rainfall around 300 mm), located between two wet cycles (800-900 mm). Transects were analysed in 1990 (wet period), 1994 (dry) and 1997 (wet) by hierarchical agglomera-tive clustering. During the dry period hygrophytic species showed regression, with a high mortality of some species like Ulex minor, while the xerophytic species advanced to lower areas. Seedlings of some xerophytic species colonised the dry surface of the pond basin. The lowering of the water table varied in the different ponds, ranging from 312 to 190 cm depending on topography and the distance to the pumping area. The new period of flooding during 1995-96 and 1996-97 cycles provided the opportunity for hygrophytic spe cies to re-establish themselves in their original places. This study suggest that changes in vegetation are caused by the interaction between weather conditions and human disturbance (water extractions). In our example man-made disturbance is more marked during the dry periods while wet periods tend to obscure the effects of water extractions. From a management perspective, long-term monitoring of water table and vegetation structure is revealed as a key procedure to the management of land-water ecotones on pressured areas and threatened habitats.     

EVOLUTION OF GIGANTISM IN NINE‐SPINED STICKLEBACKS

The relaxation of predation and interspecific competition are hypothesized to allow evolution toward “optimal” body size in island environments, resulting in the gigantism of small organisms. We tested this hypothesis by studying a small teleost (nine‐spined stickleback, Pungitius pungitius) from four marine and five lake (diverse fish community) and nine pond (impoverished fish community) populations. In line with theory, pond fish tended to be larger than their marine or lake conspecifics, sometimes reaching giant sizes. In two geographically independent cases when predatory fish had been introduced into ponds, fish were smaller than those in nearby ponds lacking predators. Pond fish were also smaller when found in sympatry with three‐spined stickleback (Gasterosteus aculeatus) than those in ponds lacking competitors. Size‐at‐age analyses demonstrated that larger size in ponds was achieved by both increased growth rates and extended longevity of pond fish. Results from a common garden experiment indicate that the growth differences had a genetic basis: pond fish developed two to three times higher body mass than marine fish during 36 weeks of growth under similar conditions. Hence, reduced risk of predation and interspecific competition appear to be chief forces driving insular body size evolution toward gigantism.     

Does the morphology of beaver ponds alter downstream ecosystems?

Differences among lake morphologies often explain variation in characteristics of lentic ecosystems. Although beaver ponds also vary in morphology, previous studies have not examined the effects of such variation on downstream ecosystems. This study evaluated downstream effects of multiple beaver ponds in the Colorado Rocky Mountains during one low and one high-flow year. Beaver pond morphology was described as the natural log transformed ratio of beaver dam height (which determines hydraulic head) to pond surface area and related to pond spillover phytoplankton and characteristics of the ecosystem downstream (nutrient concentrations, limiting nutrients, periphyton, benthic organic matter (BOM), and benthic invertebrate consumers). Nitrate concentration increased systematically downstream of beaver ponds, but only in the low flow year when groundwater influences predominated. Effects of beaver ponds on soluble reactive phosphorus concentration depended on pond morphology, increasing downstream of small ponds with high dams, but only during the low-flow year. In situ experiments showed that neither beaver activity nor pond morphology predicted periphyton-limiting nutrients downstream. Both periphyton biomass and BOM decreased downstream of small ponds with high dams but pond morphology did not predict abundance of invertebrate grazers or detritus-feeding consumers. While suspension feeding invertebrates increased downstream from small ponds with high dams, variation in chlorophyll a from water spilling over beaver dams did not follow a similar pattern. We conclude that the effects of beaver ponds on downstream nutrients, resources and consumers are rarely systematic, but instead depend on variation in pond morphology and on annual hydrologic variation.     

Ecological aspects between Contracaecum sp. (Nematoda, Anisakidae) and the host Serrasalmus spilopleura Kner, 1860 (Pisces, Characidae) in natural populations of northeastern Argentina

From February 1987 to February 1989, the populational biology of Contraceacum sp. (larvae) in its paratenic host, the fish Serrasalmus spilopleura Kner, 1860, was studied in two ponds in a subtropical permanent habitat northeastern of Argentina. Fishes from Ramada Paso pond presented 80% of prevalence and 1 to 132 larvae per fish while fishes from Aeroclub pond presented 63% of prevalence and 1 to 184 larvae per fish. Fishes collected from Aeroclub pond have shown a high prevalence of infection during the first period of study (1987), diminishing the following year. In fishes from Ramada Paso pond the prevalence varied not significatively during the two years. Prevalence and mean intensity of infection increase with body length and weight of the hosts. Sex of hosts is not an influential factor in parasitic level. The lenitic "closed" environmental (Ramada Paso pond) evidenced the greatest larvae mean intensity and prevalence. Although, the lenitic "open" environmental (Aeroclub pond) showed the greatest parasitic number of individuals in an infrapopulation. The spatial dispersion in both ponds were aggregated and fit well a negative binomial model. Nevertheless, the Aeroclub pond presented the greatest overdispersion.     

Biological Control of Culex pipiens pattens (Diptera, Culicidae) by the Release of Fish Muddy Loach, Misgurnus mizolepis in Natural Ponds, Korea

ABSTRACT An assessment on the biological control potential with the fish muddy loaches (Misgurnus mizolepis) was conducted against naturally bred Culex pipiens pollens larvae in four ponds (A, B, C and D) in Busan from July through September, 2001. Predation of the fish at 3 different release rates of 4,5, and 6 fish/m² resulted in mostly over 90% mosquito control from the first week after treatment through the end of the survey period for 11 weeks. There were no significant difference among the release rates of fish at the 5% level of probability. However, substantial controls of 43.0% and 25.9% were obtained from pond C during the 3rd and 7th weeks after the fish introduction, respectively. The results of those two weeks showed a lower biological control by the introduced larvivorous fishes. This might be due to the presence of heavy organic matters including aquatic weeds and/or severely polluted water from sewage in pond C. The aquatic weeds covered the pond's water surface which may have affected the deterioration of mosquito preying in favor of aquatic weeds. Also, the fishes were observed to avoid severely contaminated sewage water in some parts of ponds A and C where more mosquito larvae were found.