Crawfish Ponds Research Articles

Fate of high-risk antibiotic resistance genes in large-scale aquaculture sediments: Geographical differentiation and corresponding drivers

Antibiotic resistance genes (ARGs), emerging environmental contaminants, have become challenges of public health security. However, the distribution and drivers of ARGs, especially high-risk ARGs, in large-scale aquaculture sediments remain unknown. Here, we collected sediment samples from 40 crayfish ponds in seven main crayfish culture provinces in China and then investigated the distribution and risk of ARGs based on high-throughput sequencing and quantitative PCR techniques. Our results suggested that aquaculture sediment was potential reservoir of ARGs and the abundance of aadA-02 was the highest. High-risk ARG (floR) was also prevalent in the sediment and was the most abundant in Jiangsu Province, where opportunistic pathogens were also enriched. The abundance of floR was positively correlated with different environmental factors, such as total phosphorus in water and total carbon in sediment. In addition, Mycobacterium sp., opportunistic pathogenic bacteria, might be potential host for floR. Furthermore, the potential propagation pathway of ARGs was from sediment to crayfish gut, and Bacteroidetes and Proteobacteria might be the main bacterial groups responsible for the proliferation of ARGs. Generally, our results illustrate that pond sediment may be an ARG reservoir of aquatic animals. Meanwhile, our study helps develop valuable strategies for accessing risks and managing ARGs.

Occurrence, distribution, and ecological risks of antibiotics in Honghu Lake and surrounding aquaculture ponds, China.

Antibiotics are largely applied in aquaculture to increase production and control diseases, while how the antibiotics used in pond farming influence the distribution of antibiotics in receiving water seasonally is still not well understood. In this study, the variations of 15 frequently used antibiotics in Honghu Lake and surrounding ponds were investigated seasonally to figure out the impact of pond farming on antibiotics distributions in Honghu Lake. Results showed that the antibiotic concentrations in fish ponds ranged from 11.76 to 389.8ng/L, while in crab and crayfish ponds were lower than 30.49ng/L. The predominant antibiotic in fish ponds was florfenicol, followed by sulfonamides and quinolones, with generally low concentrations. Sulfonamides and florfenicol were the main antibiotics in Honghu Lake, affected by the surrounding aquaculture water partially. The antibiotics residue in aquaculture ponds showed obvious seasonal characteristics, with the lowest in spring. From summer, the concentrations of antibiotics in aquaculture ponds gradually increased and reached a peak in autumn, and the seasonal variation of antibiotics in the receiving lake was also related to the antibiotics in the aquaculture ponds. Risk assessment analysis showed that antibiotics such as enrofloxacin and florfenicol in fish ponds posed a medium and low risk to algae, and Honghu Lake acted as a natural reservoir of antibiotics and poses increased risks to algae. In general, our study demonstrated that aquaculture represented by pond farming brought significant risks of antibiotic pollution to natural water bodies. Therefore, reasonable control of the fish antibiotics usage in autumn and winter, as well as the rational use of antibiotics in aquaculture and the use of antibiotics before pond cleaning, is required to reduce the migration of antibiotics from aquaculture surface water to the receiving lake.

Antibiotic resistance genes and their links with bacteria and environmental factors in three predominant freshwater aquaculture modes

Rapid development of aquaculture industry and increasing demand of various inputs (especially antibiotics), are suspected to promote the occurrence and spread of ARGs in aquaculture related environments. However, the occurrences of ARGs under different freshwater aquaculture practices are rarely known. Here, we investigated the seasonal profiles of the main ARGs, intI1 and bacteria in waters from three kinds of predominant freshwater aquaculture practices around the Honghu Lake (China), as well as their co-occurrences and interrelationships with antibiotics, heavy metals and general water quality. The results indicate that quinolone resistance genes (qnrB), tetracycline resistance genes (tetB and tetX) and sulfonamide resistance genes (sul1 and sul2) were the top five predominant ARGs with seasonal variations of abundance. Fish ponds were of the highest absolute abundances of tested ARGs than the other two modes. Crayfish ponds and their adjacent ditches shared similar ARGs profile. Different subtypes of ARGs belonging to the same class of resistance were varied in abundances. Some bacteria were predicted to carry different ARGs, which indicating multi-antibiotic resistances. Moreover, the combined environmental factors (antibiotics, heavy metals and water quality) partially shaped the profiles of ARGs and bacteria composition. Overall, this study provides new comprehensive understanding on the characterization of ARGs contamination in different freshwater aquaculture practices from the perspectives of environmental chemistry, microbiology and ecology. The results would benefit the optimization of aquaculture practices toward environmental integrity and sustainability.

Patterns of phytoplankton community structure and diversity in aquaculture ponds, Henan, China

In aquaculture, phytoplankton contribute to primary productivity, helping maintain fishery harvests and water stabilization. To better understand the drivers controlling phytoplankton communities, sampling was conducted during two seasons in 185 aquaculture ponds that cultured five species of aquatic animals (channel catfish, common carp, grass carp, crayfish and largemouth bass). Principal coordinate analysis (PCoA), redundancy analysis (RDA), and generalized linear model (GLM) were applied to quantify the relative importance of multiple factors to phytoplankton species composition and diversity. The PCoA results demonstrated that in spring, phytoplankton species composition showed no distinct differences among the 5 cultivated-animal ponds. In summer, phytoplankton species composition had a distinct pattern, which was clustered into three distinct groups. The RDA results revealed that the variation in the phytoplankton composition was closely correlated with the water temperature, conductivity, dissolved organic carbon (DOC), alkalinity, and nitrate in spring. In summer, different variables, including cultivated animals, alkalinity, pH and dissolved oxygen (DO), were responsible for explaining species composition patterns. In spring, no significant difference in phytoplankton α-diversity was found among the 5 cultivated-animal ponds. In summer, significantly higher α-diversity was found in the channel catfish and crayfish ponds than in the other ponds. GLM analysis showed that phytoplankton density, cultivated animals, and conductivity can be used to explain phytoplankton diversity. Although no effect of cultivated animals was found during the early aquaculture stage, the results from the summer samples demonstrated that cultivated animals have an important influence on phytoplankton communities. Therefore, we suggest that in intensive fish-stocking ecosystems, top-down effect is an important strength on phytoplankton communities. In terms of preventing algal blooms, a low density of phytoplankton is important for maintaining high phytoplankton diversity and water stabilization in aquaculture. Our results can provide useful information for water management practices in aquaculture ponds.

Detection of water quality in crayfish ponds with IoT

Data from the Central Bureau of Statistics shows that during the first quarter of 2014 to 2019, the tendency of Indonesian crayfish export increases by an average of 3.54% in 2019 and reach 7.09 million USD. This number still fails to meet the global market demand caused by poor water quality due to cultivators’ lack of experience and education. Two parameters measured in water quality are temperature and pH. Thus, a device was made using IoT to maintain those conditions in order to increase the viability of the crayfish in the pond. The perceptron method is used to classify water quality based on those parameters. To send the data, ESP8266 is used as an intermediary for Arduino and cloud server. The result is that the information about the ponds’ condition can be seen via a smartphone. The method gives a value of 98.06% accurate in determining water quality.

Using the biochar produced from spend mushroom substrate to improve the environmental condition of aquaculture pond

This study aims to probe the potential adsorbent of the biochar produced from spent mushroom substrate (SMS), of which pyrolysis temperature is 400°C, in improving the qualities of sediment and water quality in aquaculture pond. In the first trial, the adsorption of biochars to the ammonia-N and nitrite-N in water was evaluated, and the results showed that the SMS-derived biochars had the ability to adsorb ammonia-N rather than nitrite-N. Additionally, the adsorption capability of biochars to ammonia-N decreased as ambient salinity was increased. The SMS-derived biochars can also increase the pH of water. In view of the improvement of sediment, SMS-derived biochars was able to increase sediment pH and decrease the levels of ammonia-N and sulphite in sediments. In field trial, SMS-derived biochars was applied to a red claw crayfish farming. As the SMS-derived biochars had been thrown to the crayfish pond, pond conditions were improved because the pH of water and sediment increased, and the level of ammonia-N in water decreased, and the levels of ammonia-N and sulphide in sediment decreased. Therefore, the SMS-derived biochars was considered great potential as sorbents to adsorb the toxic substances, such as ammonia-N and sulphide in water and sediment.

Patterns of Sediment Fungal Community Dependent on Farming Practices in Aquaculture Ponds.

Despite fungi playing an important role in nutrient decomposition in aquatic ecosystems and being considered as vital actors in the ecological processes, they received limited attention regarding the community in aquaculture pond sediments which are extremely important and typically disturbed habitats. Using an ITS1 region of fungal rDNA, this study aimed to investigate sediment fungal communities in fish, crab, and crayfish ponds for decades of farming practices at representative aquaculture regions in the middle Yangtze River basin, China. We then aimed to explore the community patterns associated with species-based farming practices in the ponds at 18 farms. The results showed that the pond sediments harbored more than 9,000 operational taxonomic units. The sediments had significantly higher alpha diversity in crab ponds compared to that in fish and crayfish ponds. The fungal phyla largely belonged to Ascomycota and Chytridiomycota, and the dominance of Rozellomycota over Basidiomycota and Aphelidiomycota was observed. The majority of sediment fungal members were ascribed to unclassified fungi, with higher proportions in fish ponds than crab and crayfish ponds. Further, the fungal communities were markedly distinct among the three types of ponds, suggesting divergent patterns of fungal community assemblages caused by farming practices in aquaculture ponds. The community diversity and structure were closely correlated to sediment properties, especially sediment carbon content and pH. Thus, the distribution and pattern of fungal communities in the sediments appear to primarily depend on species-based farming practices responsible for the resulting sediment carbon content and pH in aquaculture ponds. This study provides a detailed snapshot and extension of understanding fungal community structure and variability in pond ecosystems, highlighting the impacts of farming practices on the assembly and succession of sediment fungal communities in aquaculture ponds.

Use of Aquaculture Ponds and Other Habitats by Autumn Migrating Shorebirds Along the Lower Mississippi River

Populations of many shorebird species are declining; habitat loss and degradation are among the leading causes for these declines. Shorebirds use a variety of habitats along interior migratory routes including managed moist soil units, natural wetlands, sandbars, and agricultural lands such as harvested rice fields. Less well known is shorebird use of freshwater aquaculture facilities, such as commercial cat- and crayfish ponds. We compared shorebird habitat use at drained aquaculture ponds, moist soil units, agricultural areas, sandbars and other natural habitat, and a sewage treatment facility in the in the lower Mississippi River Alluvial Valley (LMAV) during autumn 2009. Six species: Least Sandpiper (Calidris minutilla), Killdeer (Charadrius vociferous), Semipalmated Sandpiper (Calidris pusilla), Pectoral Sandpiper (C. melanotos), Black-necked Stilt (Himantopus himantopus), and Lesser Yellowlegs (Tringa flavipes), accounted for 92% of the 31,165 individuals observed. Sewage settling lagoons (83.4, 95% confidence interval [CI] 25.3-141.5 birds/ha), drained aquaculture ponds (33.5, 95% CI 22.4-44.6 birds/ha), and managed moist soil units on public lands (15.7, CI 11.2-20.3 birds/ha) had the highest estimated densities of shorebirds. The estimated 1,100ha of drained aquaculture ponds available during autumn 2009 provided over half of the estimated requirement of 2,000ha by the LMAV Joint Venture working group. However, because of the decline in the aquaculture industry, autumn shorebird habitats in the LMAV may be limited in the near future. Recognition of the current aquaculture habitat trends will be important to the future management activities of federal and state agencies. Should these aquaculture habitat trends continue, there may be a need for wildlife biologists to investigate other habitats that can be managed to offset the current and expected loss of aquaculture acreages. This study illustrates the potential for freshwater aquaculture to provide habitat for a taxa at risk. With the rapid growth of aquaculture worldwide, the practices of this industry deserve attention to identify benefits as well as risks to wildlife.

Prevalence of a Potentially Lethal Parasite of Wading Birds in Natural and Agricultural Wetlands in South Louisiana

Abstract Gambusia affinis (Western Mosquitofish) were sampled from 18 sites representing marsh, forested wetlands, and agricultural wetlands in south Louisiana to determine distribution and infection parameters of Eustrongylides ignotus, a potentially lethal nematode parasite of wading birds, (n = 400 per site). Overall, prevalence of infection was 0.3%, with significantly higher prevalence in agricultural wetlands than in marshes or swamps. Our findings are similar to work in Florida suggesting parasite prevalence is higher in disturbed wetlands, and suggest that birds foraging in crayfish ponds and rice fields may be at increased risk of exposure.

Superabundant Food at Catfish Aquaculture Facilities Improves Body Condition in American White Pelicans

Abstract. Few studies have investigated the use of aquaculture-produced foods by piscivorous birds. American White Pelicans (Pelecanus erythrorhynchos) were collected from four locations (two aquaculture, one riverine and one coastal) in the southeastern United States during winter and spring 1998–1999 to assess the contribution (biomass, frequency of occurrence) of aquaculture-produced foods and their effect on body condition. Pelican diets reflected opportunistic foraging across locations. Diet near catfish ponds consisted mostly of Channel Catfish (Ictalurus punctatus). Diets along the Mississippi River had similarly high biomass of catfish, but otolith counts suggested lower use of catfish. Diets near crawfish (Procambarus spp.) ponds included shad (Dorsomis spp.), crawfish and sunfish (Lepomis spp.); whereas diets from coastal Louisiana were predominantly salt water fish. Pelican body condition, as indexed by percent omental fat, was similar between seasons but higher at catfish ponds. Foraging at cr...

Evaluation of Baits for Harvesting Procambarid Crawfishes with Emphasis on Bait Type and Bait Quantity

ABSTRACT Two crawfish baits and several bait quantities were evaluated in 2 trials conducted from January through May in four 2.0–2.5-ha experimental earthen crawfish (Procambarus clarkii and Procambarus zonangulus) ponds at the Aquaculture Research Station, Louisiana State University Agricultural Center, Baton Rouge, LA. In the bait-type trial, a freshwater cluepid, gizzard shad (Dorosoma cepedianum), a commercially formulated bait, and a shad + formulated bait combination were evaluated. Highest daily crawfish catch per unit trap effort (CPUE) and bait margin (gross value of crawfish less bait cost) was with gizzard shad at water temperatures less than 20°C (January, February, March), and with formulated bait at 20°C and higher (April, May). The shad + formulated bait combination was effective in attracting crawfish over a wide range of water temperatures from February through May. In the bait quantity trial, both gizzard shad and the formulated bait were evaluated singly at 113 g/trap, 150 g/trap, 227 ...

Waterbird Nest Density and Nest Survival in Rice Fields of Southwestern Louisiana

Rice fields in southwestern Louisiana provide breeding habitat for several waterbird species; however, little is known about nest density, nest survival and the importance of landscape context of rice fields in determining breeding activity. In 2004, 42 rice fields were searched for nests, and 40 were searched in 2005. Land uses surrounding rice fields, including irrigation canals, trees, crawfish ponds, rice, fallow and soybean fields, were examined to determine influence on nest density and survival. Nest densities were 13.5–16.0 nests/km2 for Purple Gallinules (Porphyrio maitinica), 3.0–13.7 nests/km2 for Fulvous Whistling Ducks (Dendrocygna bicoloi), 2.6–2.8 nests/km2 for Common Moorhens (Gallinula chloropus), 0.3–0.92 nests/km2 for Least Bitterns (Ixobiychus exilisi) and 0–0.6 nests/km2 for Mottled Ducks (Anas fulvigula). Nest survival was 52–79% for Purple Gallinules and 39–43% for Fulvous Whistling Ducks. Apparent nest success of Common Moorhens was 73–75%, 83% for Least Bitterns and 33% for Mottled Ducks. Purple Gallinule and Common Moorhen nest densities were highest in fields with a larger proportion of irrigation canals surrounding rice fields. Purple Gallinule nest densities were greater in fields devoid of trees and landscapes dominated by rice fields and pasture, rather than landscapes containing soybean fields and residential areas. Fulvous Whistling Duck nest densities were higher in agriculturally-dominated landscapes with few trees.

Determination of cadmium copper, iron, nickel, lead and zinc in crawfish [Procambrus clarkii] by inductively coupled plasma optical emission spectrometry: a study over the 2009 season in Southwest Louisiana

Following a mini-review of crawfish aquaculture, the concentrations (mean in micrograms of analyte per gram of dried sample ± 95% confidence interval, range) determined by inductively coupled plasma-optical emission spectrometry of cadmium (0.49 ± 0.14, 0.34–0.79 ), copper (34.9 ± 5.3, 23.8–44.2), nickel (1.83 ± 0.54, 1.08–3.39), lead (18.0 ± 4.0, 9.9–23.), iron, and zinc (47.3 ± 4.6, 41.3–55.8) were relatively constant with a slight increase in iron (620.4 ± 205.8, 328.8–1072.8) in whole crawfish in a season of 4 months (February through May 2009) in Southwest Louisiana. The temperature of the crawfish ponds was monitored weekly but had no effect on the metal concentration in the crawfish trial. The copper and zinc concentrations in the crawfish pond soil decreased with increasing temperature. The other four metals showing no effect of temperature variations (increase). A comparison with a previous study showed no significant changes in the metal concentrations in the crawfish.

Water Budgets for a Rice–Crawfish Aquaculture System

AbstractRed swamp crawfish Procambarus clarkii and white river crawfish P. zonangulus are raised mostly in southern Louisiana, usually in association with commercial rice cultivation. Shallow ponds (fields) are flooded in the fall after the rice harvest (usually in October) and drained at the end of the crawfish production cycle the following spring–summer (usually in May–July). The water use and effluent volume associated with crawfish aquaculture have not been quantified. This study was conducted to determine water use and effluent release in crawfish aquaculture under simulated commercial conditions. Water inflow and outflow were measured in experimental crawfish ponds from 1999 to 2002 (three consecutive crawfish production seasons) that simulated rice–crawfish rotational production practices. The mean water inflow from groundwater pumping and precipitation was 228 cm per production season (range, 223–233 cm). Total water use (groundwater plus precipitation) and groundwater consumption averaged 21.5 and 15.2 m3 per kilogram of crawfish harvested, respectively. The amount of groundwater used for filling ponds, replacing losses from evaporation–evapotranspiration and seepage, and flushing ponds to maintain satisfactory dissolved oxygen levels averaged 139 cm (range, 97–165 cm). The contribution from precipitation averaged 90 cm. Effluent discharge averaged 59.5 cm. Of this, 36.9% was accounted for by pond drainage at the end of the production season, 29.4% by precipitation overflow and temporary levee failures, 22.1% by lateral seepage and minor leaks of the perimeter levees, and 11.6% by intentional flushing to maintain an acceptable concentration of dissolved oxygen. On average, 74% (172.5 cm) of the water input was lost as a result of evaporation, evapotranspiration, and percolation through the pond‐bottom sediments.

Effects of Paddlewheel Aeration on Water Quality in Crawfish Ponds

ABSTRACT Six experimental ponds (1.8–2.2 ha each) were planted with rice Oryza sativa in August as forage for red swamp crawfish, Procambarus clarkii, and flooded in October. From late October through May, three ponds were aerated nightly for 10 hours (2200–0800 hours) with two 2.2-KW (3 hp) paddlewheel aerators per pond. The other three ponds were not mechanically aerated. Dissolved oxygen (DO) less than 3 mg/L in non-aerated ponds occurred four to five times more frequently than in aerated ponds. Chlorophyll a, biochemical oxygen demand, turbidity, nitrite, and total ammonia were significantly higher in aerated ponds. The DO, free carbon dioxide, total ammonia-nitrogen, and nitrite-nitrogen were within acceptable levels for crawfish in both aerated and non-aerated ponds. Mean crawfish harvest from aerated ponds (2,300 kg/ha) did not differ from non-aerated ponds (2,396 kg/ha). Paddlewheel aerators effectively mixed and circulated pond water but mechanical aeration was not effective in increasing crawfish yield in ponds planted with rice in late summer.

Potential Effluent Quality from Commercial Crawfish Ponds

AbstractSeventeen commercial and two demonstration crawfish ponds in southern Louisiana that were either planted with rice Oryza sativa or a sorghum‐sudangrass hybrid (Sorghum bicolor × S. sudanese) or colonized with volunteer terrestrial or semiaquatic vegetation were evaluated for potential effluent quality. Nutrients and solids concentrations in potential crawfish pond effluents increased significantly in spring and summer from fall and winter levels. Potential effluent quality was poorest during the annual summer drawdown and is likely to have the greatest impact on receiving waterways. Total suspended solids and turbidity most frequently exceeded Louisiana water quality standards. Ponds with volunteer vegetation had significantly lower concentrations of chemical oxygen demand, turbidity, total suspended solids, total volatile suspended solids, and total Kjeldahl nitrogen than ponds with rice and sorghum‐sudangrass. Soluble reactive phosphorus, total phosphorus, total ammonia, nitrite, and nitrate were highest in ponds with sorghum‐sudangrass. Nutrient and solid concentrations were generally lower in ponds with volunteer vegetation, presumably as a result of nutrient uptake by aquatic macrophytes and reduced suspended sediment loads. Establishing limited stands of aquatic macrophytes inside crawfish ponds or using effluent to replenish water in adjacent ricefields may reduce the amount of suspended solids and nutrients entering receiving waters.

Water Quality Simulation of Rice/Crawfish Field Ponds within Annualized AGNPS

Rice and crawfish are important agricultural commodities in Louisiana and they are often managed as integrated cropping systems. The effluent from rice/crawfish ponds is an environmental concern because of potentially high sediment and nutrient concentrations. However, current available models used for TMDL development such as BASIN, SWAT, and AnnAGNPS do not have the capability of simulating rice/crawfish farming and their impact on water quality. The objective of this study was to develop a rice/crawfish module which can be integrated into the Annualized Agricultural Non-point Source Pollution (AnnAGNPS) model to simulate rice/crawfish farming and its impact on water quality. Both hydrologic and pollutant mass balances are maintained for the crawfish ponds in AnnAGNPS. Inflows, outflows, precipitation, infiltration (or seepage), and evaporation (or evapotranspiration) are considered for hydrologic mass balance. Water release from the pond is added to the receiving reach of the AnnAGNPS cell in which the rice/crawfish pond is located. Pollutant mass balances are maintained based on the inflows and outflows to the crawfish pond and water quality characteristics of the flows. The dynamics of complicated nutrient reactions in the pond are not considered at this development stage. Water quality constituents considered in the model are suspended sediment, total nitrogen, total phosphorus, dissolved nitrogen, and dissolved phosphorus. Based on a detailed review of rice/crawfish management practices and their impact on water quality, a water quality database of rice/crawfish ponds has been built into AnnAGNPS and a user interface was designed to quantify the rice/crawfish farming processes. This water quality database provides an estimate of water quality in the crawfish pond effluent during simulations, and a more accurate quantification of effluent water quality can be achieved through analysis of water samples of the water released from the pond. Model testing of proof of concept showed that the model performed appropriately and provided logical results.

Engineering considerations for water circulation in crawfish ponds with paddlewheel aerators

Engineering considerations for paddlewheel aeration in vegetated shallow water ponds for the production of procambarid crawfish is necessary to ensure cost-effective application. Three experimental ponds (approximately 2 ha each) were planted with rice in August as forage for the resident pond population of red swamp crawfish, Procambarus clarkii, and flooded in October. Two 2.2 kW (3 hp), single-phase electric motor (110 V ac) paddlewheel aerators were placed in each pond. The aerator rotors were 160-cm long and 95-cm in diameter. The aerator rotor had 36 paddles with half the paddles 27.3-cm long and half 34.9-cm long. Rotor speed was set at 83 rpm and operated at three paddle submergence settings: 7.6, 12.7, and 17.8 cm below the water surface. Over a 20-week period between November and April, channel velocity, head difference, and aerator amperage was measured for both one and two aerators in operation in each pond. Results indicated that circulation of oxygenated water from the aerators can be accomplished as efficiently with a single aerator set at a lower paddle depth (7.6-cm) compared to operating two aerators set at a greater paddle depth (12.7 or 17.8-cm). However, based on the apparent efficiency of the aerators and the calculated channel roughness coefficients values obtained from the channel velocities, paddlewheel aerators are an inefficient option for circulating the pond water especially when rice foliage dominants the total vegetative biomass of the pond.

A PERSPECTIVE ON ECOLOGICAL CONSIDERATIONS IN CRAWFISH POND AQUACULTURE

The suite of resident, migrant, breeding, and wintering waterbirds depending on this region includes grebes, pelicans, cormorants, anhingas, wading birds, waterfowl, coots, rails, gallinules, shorebirds, gulls, and terns. All taxa now use the artificial freshwater wetland habitat provided by the ag wetlands. These taxa include local, regional, continental and hemispherical populations. Crawfish ponds are especially valuable cool season habitat for predaceous waterbirds because they provide shallow water systems rich in invertebrate and small vertebrate prey during the period from midautumn through midspring when most ricefields are drained. Numerous other bird species use riparian areas around ag wetlands either as residents or seasonal visitors. Over 280 bird species have been identified in and around crawfish-rice systems in Louisiana. Whereas birds are conspicuous species associated with ag wetlands, numerous other vertebrate species including mammals, reptiles and turtles use the habitat. In addition, fishes in waterways receiving pond effluents receive significant food resources when water is released from the ponds.

Effects of a native crayfish (Orconectes virilis) on the reproductive success and nesting behavior of sunfish (Lepomis spp.)

While crayfish are traditionally considered fish prey, they are capable of feeding on substrate-bound fish eggs and their introductions have been blamed for the decline in fish populations in Europe and North America. To investigate their potential effects on fish reproductive success we measured the effects of a native crayfish (Orconectes virilis) on the reproductive success of two substrate-nesting sunfish, pumpkinseed (Lepomis gibbosus) and bluegill (Lepomis macrochirus), in replicated pond experiments. Crayfish were observed feeding on eggs in both experiments. Crayfish presence delayed successful reproduction by pumpkinseeds in densely vegetated ponds, resulting in lower young-of-the-year biomass in ponds with crayfish. In the second experiment, with bluegills in less-vegetated ponds, crayfish prevented successful reproduction entirely. However, when we added crayfish-proof exclosures to the crayfish ponds late in the summer, bluegills located the crayfish-free habitat and successfully reproduced inside the exclosures (1 month after first successful reproduction in control ponds). The results of these experiments demonstrate the potential strong negative effects of crayfish on sunfish reproduction and suggest that the spatial distribution of crayfish and other egg predators may influence fish nesting behaviors and habitat choices. Further studies are needed to determine the magnitude of crayfish effects in natural lakes and ponds where sunfish and crayfish co-occur.