Investigating the Ability of Edwardsiella ictaluri and Flavobacterium covae to Persist within Commercial Catfish Pond Sediments under Laboratory Conditions.

Two prevalent bacterial diseases in catfish aquaculture are enteric septicemia of catfish and columnaris disease caused by Edwardsiella ictaluri and Flavobacterium covae, respectively. Chronic and recurring outbreaks of these bacterial pathogens result in significant economic losses for producers annually. Determining if these pathogens can persist within sediments of commercial ponds is paramount. Experimental persistence trials (PT) were conducted to evaluate the persistence of E. ictaluri and F. covae in pond sediments. Twelve test chambers containing 120 g of sterilized sediment from four commercial catfish ponds were inoculated with either E. ictaluri (S97-773) or F. covae (ALG-00-530) and filled with 8 L of disinfected water. At 1, 2, 4-, 6-, 8-, and 15-days post-inoculation, 1 g of sediment was removed, and colony-forming units (CFU) were enumerated on selective media using 6 × 6 drop plate methods. E. ictaluri population peaked on Day 3 at 6.4 ± 0.5 log10 CFU g-1. Correlation analysis revealed no correlation between the sediment physicochemical parameters and E. ictaluri log10 CFU g-1. However, no viable F. covae colonies were recovered after two PT attempts. Future studies to improve understanding of E. ictaluri pathogenesis and persistence, and potential F. covae persistence in pond bottom sediments are needed.

The Use of Kaolin as a Prophylactic Treatment to Prevent Columnaris Disease (Flavobacterium covae) in Commercial Baitfish and Sportfish Species.

Aquaculture farms in Arkansas, USA routinely battle columnaris disease caused by Flavobacterium covae. Columnaris is prevalent during stressful events such as feed training and when fish are stocked at high densities in holding vats before sale. Kaolin clay was effective in laboratory trials as a treatment for columnaris in catfish. As a result, fish farmers are interested in applying kaolin products but were hesitant as they feared that the high doses of kaolin clay in vats might negatively affect the gills and overall health of fish. Therefore, we evaluated potential clay concentrations that might be used to prophylactically treat fish in vats. The effects of low to excessively high doses (0, 1, 2, 4, or 8 g/L) of kaolin clay (AkuaProTM, Imerys, GA, USA) were evaluated using a 72 h bioassay conducted in static tanks using Micropterus salmoides, Pomoxis nigromaculatus, Lepomis macrochirus, Ictalurus punctatus, Notemigonus crysoleucas, and Pimephales promelas. Results of these trials revealed a 100% survival rate across all six fish species exposed to kaolin clay at concentrations of up to 8 g/L for 48 h (followed by a 24 h recovery period in clean water) with no adverse effects to eyes, skin, gastrointestinal tract, or liver histology noted at any treatment. In addition, Micropterus salmoides analyzed for heavy metals due to exposure to the clay indicated that concentrations did not differ from control fish.

Persistence of a Wild-Type Virulent Aeromonas hydrophila Isolate in Pond Sediments from Commercial Catfish Ponds: A Laboratory Study.

Virulent Aeromonas hydrophila (vAh) is a major bacterial pathogen in the U.S. catfish industry and is responsible for large-scale losses within commercial ponds. Administering antibiotic feeds can effectively treat vAh infections, but it is imperative to discern new approaches and better understand the mechanics of infection for this bacterium. As such, the persistence of vAh in pond sediments was determined by conducting laboratory trials using sediment from four commercial catfish ponds. Twelve chambers contained sterilized sediment, vAh isolate ML-09-119, and 8 L of water maintained at 28 °C and were aerated daily. At 1, 2, 4, 6, and 8 days, and every 7th day post-inoculation for 28 days, 1 g of sediment was removed, and vAh colony forming units (CFU) were enumerated on ampicillin dextrin agar. Viable vAh colonies were present in all sediments at all sampling periods. The vAh growth curve peaked (1.33 ± 0.26 × 109 CFU g-1) at 96 h post-inoculation. The population plateaued between days 14 and 28. No correlations were found between CFU g-1 and physiochemical sediment variables. This study validated the ability of vAh to persist within pond sediments in a laboratory setting. Further research on environmental factors influencing vAh survivability and population dynamics in ponds is needed.

Effects of Different Feeding Regimes on Growth Rates and Fatty Acid Composition of Largemouth Bass Micropterus nigricans at High Water Temperatures.

As the northern Largemouth bass (LMB) (Micropterus nigricans) industry shifts toward fingerling production, implementing practical feeding strategies to ensure efficient growth during high water temperatures is paramount. Twenty (12.7 ± 0.2 g) (Trial 1) and fifteen (7.2 ± 0.1 g) (Trial 2) LMB fingerlings were stocked in two recirculating systems (each containing nine tanks), acclimated to 30 °C, with one system fed daily rations of 3, 5 and 7% body weight (Trial 1), and the second system fed to satiation daily, every second day, or every third day (Trial 2), for 28 days each. All treatments were triplicated. Multiple growth metrics and lipid composition were analyzed. The 3% treatment yielded the lowest final average weight (36.05 g) and FCR (0.83), with no difference in final biomass in Trial 1 treatments. Fish fed to satiation daily and every second day produced FCRs and biomasses of 0.83 and 356.78 g, and 0.93 and 272.26 g, respectively. There were no differences in total lipid concentration, however, fatty acid profiles differed significantly between all treatments within their respective trials. Feeding LMB fingerlings 3% of total body weight or feeding daily to satiation allows for efficient growth at 30 °C and implements cost-effective feeding strategies.

System design and production practices of aquaponic stakeholders.

Aquaponics is an agricultural practice incorporating aquaculture and hydroponic principles. This study assesses the current system design and production practices of the aquaponic industry, compares these metrics by stakeholder group, identifies trends, and provides recommendations for future development. An electronic survey of aquaponic stakeholders was conducted from December 2019 to June 2020 targeting hobbyists, producers, and educators from various aquaponic-focused professional associations, email and social media groups. Of 378 total responses, 84% came from the United States and were clustered in plant hardiness zones five to nine. Aquaponic systems were commonly homemade/do-it-yourself (DIY), many of which incorporated commercially available (turn-key) technology. Most growers used coupled systems that integrated recirculating aquaculture systems and either deep-water culture (DWC) or media bed hydroponic units. Common plant lighting sources were sunlight and light emitting diode (LED). Water sources were typically municipal or wells. Personal labor input was typically less than 20 hrs/wk. Funding sources were primarily personal funds, followed by government grants, and private investor funds. System sizes varied greatly, but the median area was 50 to 500 ft2 for hobbyists and educators and 500 to 3,000 ft2 for producers. Respondents commonly sold vegetable produce, training and education, food fish, and microgreens. Tilapia and ornamental fish were commonly grown, with 16 other species reported. Common crops were lettuce, leafy greens, basil, tomatoes, peppers, and herbs with many additional lesser-grown crops reported, including cannabis. Overall, the industry still growing, with a large portion of stakeholders having less than two years of experience. However, veteran growers have remained in operation, particularly in the producer and educator groups. The survey results suggest a shift away from outdoor systems, media beds, tomatoes, ornamental fish, and perch production, and a shift toward decoupled systems, DWC, drip irrigation, and wicking beds, larger system area, leafy greens, and trout/salmon production compared to previous industry surveys. The reduced diversity of plant species grown suggest some level of crop standardization. Commercial producers tended to sell more types of products than other stakeholders, suggesting that diversification of offerings may be key to profitability. The combined production area specified by respondents indicates the industry has grown substantially in recent years. Finally, the presence of bank loan-funded operations suggests increased knowledge and comfort with aquaponics among lenders.

Branchial carbonic anhydrase activity and ninhydrin positive substances in the Pacific white shrimp, Litopenaeus vannamei, acclimated to low and high salinities.

The Pacific white shrimp, Litopenaeus vannamei, acclimated to 30 ppt salinity, was transferred to either low (15 and 5 ppt), or high (45 ppt) salinity for 7 days. Hemolymph osmolality, branchial carbonic anhydrase activity, and total ninhydrin-positive substances (TNPS) in abdominal muscle were then measured for each condition. Hemolymph osmotic concentration was regulated slightly below ambient water osmolality in shrimp acclimated to 30 ppt. At 15 and 5 ppt, shrimp were strong hyper-osmotic regulators, maintaining hemolymph osmolality between 200 and 400 mOsm above ambient. Shrimp acclimated to 30 ppt and transferred to 45 ppt salinity were strong hypo-osmotic and hypo-ionic regulators, maintaining hemolymph osmolality over 400 mOsm below ambient. Branchial carbonic anhydrase (CA) activity was low (approximately 100 micromol CO(2) mg protein(-1) min(-1)) and uniform across all 8 gills in shrimp acclimated to 30 ppt, but CA activity increased in all gills after exposure to both low and high salinities. Anterior gills had the largest increases in CA activity, and levels of increase were approximately the same for low and high salinity exposure. Branchial CA induction appears to be functionally important in both hyper- and hypo-osmotic regulations of hemolymph osmotic concentrations. Abdominal muscle TNPS made up between 19 and 38% of the total intracellular osmotic concentration in shrimp acclimated to 5, 15, and 30 ppt. TNPS levels did not change across this salinity range, over which hemolymph osmotic concentrations were tightly regulated. At 45 ppt, hemolymph osmolality increased, and muscle TNPS also increased, presumably to counteract intracellular water loss and restore cell volume. L. vannamei appears to employ mechanisms of both extracellular osmoregulation and intracellular volume regulation as the basis of its euryhalinity.

Evaluation of pesticides and metals in fish of the Dniester River, Moldova.

The Dniester River is one of the largest rivers in Eastern Europe and receives input from numerous anthropogenic activities. In October 2001, fish samples (Abramis brama, Rutilus rutilus heckeli, Perca fluviatilis, Chondrostoma nasus, Carassius auratus gibelio, and Cyprinus carpio) were collected and analyzed for metals and various pesticides. Maximum total DDT pesticide concentrations were between 27.7 and 34.2 ng/g wet weight in muscles and gonads, respectively. DDE isomers comprised up to 70% of total DDT measurement in fish tissues, indicating historical rather than recent DDT pollution. Chlordane and lindane were also detected in amounts up to 37 and 76 ng/g wet weight in gonads, respectively. Among organophosphorous pesticides, malathion showed extremely high concentrations--3 microg/g wet weight in muscles and 46 microg/g wet weight in gonads, indicating recent exposure. Copper concentrations in muscles (1.8-7.2 microg/g) exceeded Threshold Effect Concentrations for copper in fish. Detection of high concentrations of malathion and copper in fish tissues indicated potential anthropogenic stress for more sensitive aquatic biota, likely from agricultural sources in the Dniester River.

Biochemical effects of petroleum exposure in hornyhead turbot (Pleuronichthys verticalis) exposed to a gradient of sediments collected from a natural petroleum seep in CA, USA.

Concentrations of serum/plasma estradiol, biliary fluorescent aromatic compounds (FACs), levels of hepatic CYP1A expression, and DNA damage were measured in sexually mature hornyhead turbot (Pleuronichthys verticalis) exposed in the laboratory for 7 days to a gradient of sediments collected from a natural petroleum seep in the Santa Barbara Channel. Coal oil point (COP) sediments were homogenized and divided into four treatments containing 0 (sediment from the Orange County Sanitation District's reference location), 33, 66, and 100% (COP) sediments. Sediment concentrations of 20 PAHs ranged from below the detection limit for the 0% COP sediment treatments to 105 microg/g in the 100% treatments with lower molecular weight compounds predominating. Concentrations of biliary FACs were not linear with COP treatment but levels of hepatic DNA damage increased linearly with increasing concentrations of high molecular weight PAHs. Hepatic CYP1A expression was elevated only in the 100% treatments. A reduction of plasma estradiol in male and female fish was observed in all COP exposures. These results demonstrate that acute sediment-only exposure of flatfish to naturally-derived PAHs elicits alterations in biochemical endpoints indicative of PAH bioavailability and adverse effects with different sensitivities.

The relationships of biochemical endpoints to histopathology and population metrics in feral flatfish species collected near the municipal wastewater outfall of Orange County, California, USA.

In July 2000, 330 individuals of three flatfish species were collected from reference locations and nine sites surrounding the outfall of the Orange County (CA, USA) Sanitation District (OCSD) municipal wastewater discharge. Species included hornyhead turbot (Pleuronichthys verticalis), English sole (Pleuronectes vetulus), and bigmouth sole (Hippoglossina stomata). Livers of sampled animals were examined for the expression of vitellogenin (in males), cytochrome P450 1A (CYP1A), and DNA damage (comet assay). Biliary fluorescent aromatic compounds (FACs) were also measured. Comparisons with tissue and sediment contaminant residues, liver histopathology, and population estimates were assessed to determine whether relationships exist between levels of biological organization. The CYP1A results indicated exposure to planar aromatic hydrocarbons at one nearshore site. Regression analysis of all English sole CYP1A to total sediment polychlorinated biphenyls (PCBs) (r2 = 0.97; p < 0.05) indicated a significant correlation. Widespread exposure to estrogens was observed at all sites without correlation to the abundance of the three species examined. Fluorescent aromatic compounds demonstrated no correlation to CYP1A expression. Overall, histopathology and biochemical endpoints did not indicate significant adverse effects in fish at the OCSD outfall.