Effects of Temperature on the Uptake and Depuration of 2-Methylisoborneol (MIB) in Channel Catfish Ictalurus punctatus

The microbial metabolite 2-methylisoborneol (MIB) imparts a muddy off-flavor to channel catfish Ictalurus punctatus . Uptake and depuration of MIB from fish are important considerations in the design and implementation of systems to remove off-flavors from fish prior to processing. The kinetics of MIB uptake by channel catfish were determined by placing fish in 6.5, 14.0, 25.0, and 34.0 C water containing approximately 1.0 μg/L chemically-synthesized MIB. Fish were sacrificed following 0, 2, 4, 8, and 24 h exposure to MIB. Fillet tissue samples were subjected to gas chromatographic and fat content analysis. The model for MIB uptake was:
MIB in fillet tissue (μg/kg) =−0.61 ± 4.2 [log( h ± 1)] ± 0.0076( T ) ( h ) ± 0.089( T ),
where h is the duration of exposure to MIB in hours and T is the water temperature in degrees C. The model accounted for 74% of the total variation observed in the tissue MIB concentrations and indicated that the fillet fat content was not strongly correlated with MIB uptake. To investigate the depuration of off-flavors, exposure to MIB was halted. Tissue samples were obtained 4, 8, 24, 48, and 72 h from fish held at 6.5, 14.0, 25.0, and 34.0 C. These data yielded the model:
MIB in fillet tissue (μg/kg) = 3.6 ± 0.176( T ) – 2.06 [log( h ± 1)] – 0.00296( T ) ( h ) ± 0.197 (% fat),
where h is the duration of exposure to MIB in hours, T is the water temperature in degrees C, and % fat is the % fat in the fillet tissue. The model accounted for 67% of the total observed variation in tissue MIB concentrations. Reducing the fat content of fish and optimizing water temperatures may augment MIB removal from fish tissues prior to processing.     

Phytoplankton Community Structure, Biomass, and Off-flavor: Pond Size Relationships in Louisiana Catfish Ponds

Abstract.— Many aquaculture studies are conducted in relatively small research ponds and the results are then extrapolated to larger commercial ponds. Implicit in this research is the assumption that there is no relationship between pond size and phytoplankton composition. Study objectives were to assess phytoplankton composition and biomass by several methods in 17 channel catfish Ictalurus punctatus ponds at the Aqua‐culture Research Station, Louisiana Agricultural Experiment Station in Baton Rouge, Louisiana, USA. Pond size ranged from 0.04–0.60 ha. Sampling occurred weekly from 10 September – 1 October 1997. Water temperatures coincided with a transition from summer to fall‐winter conditions. Biomass was assessed by cell counts and quantification of photopigments. Concentrations of dissolved off‐flavor compounds (2‐methylisoborneol and geosmin) were assessed by gas chromatography/mass spectroscopy of water column samples. Cell count data showed differences in dominant species, biovolume, and diagnostic pigment signatures among ponds. The smaller ponds had more diverse phytoplankton composition compared to the larger ponds, whereas chlorophyll levels were nearly an order of magnitude lower in the smaller ponds. Ultraplanktonic (2–20 μm) unicellular cyanobacteria dominated the numerical counts on most sampling dates; however, biovolume transformations of cell count data reduced the dominance of this component relative to cryptophytes, diatoms, and filamentous cyanobacteria. Pigment and microscopic analyses were well correlated. Unialgal isolates of dominant taxa from these samples indicated the presence of at least five genera of off‐flavor producers in these ponds; these taxa included Anabaena, Aphanizomenon, Pseudanabaena, as well as two species of Oscillatoria. Care in extrapolating results from smaller‐sized research ponds to larger commercial ponds is warranted, as is the potential for taxa other than Oscillatoria and Anabaena in forming off‐flavor compounds.     

Enhancing the effectiveness of biological control programs of invasive species through a more comprehensive pest management approach

Invasive species are one of the greatest economic and ecological threats to agriculture and natural areas in the US and the world. Among the available management tools, biological control provides one of the most economical and long‐term effective strategies for managing widespread and damaging invasive species populations of nearly all taxa. However, integrating biological control programs in a more complete integrated pest management approach that utilizes increased information and communication, post‐release monitoring, adaptive management practices, long‐term stewardship strategies, and new and innovative ecological and genetic technologies can greatly improve the effectiveness of biological control. In addition, expanding partnerships among relevant national, regional, and local agencies, as well as academic scientists and land managers, offers far greater opportunities for long‐term success in the suppression of established invasive species. In this paper we direct our recommendations to federal agencies that oversee, fund, conduct research, and develop classical biological control programs for invasive species. By incorporating these recommendations into adaptive management strategies, private and public land managers will have far greater opportunities for long‐term success in suppression of established invasive species. © 2016 Society of Chemical Industry     

Assessing Noxious Phytoplankton in Aquaculture Systems Using Bio-Optical Methodologies: A Review

Management practices in aquaculture systems contribute to maximum growth of phytoplankton, often resulting in extensive blooms of noxious cyanobacteria. Because periods of oxygen depletion and “off flavor” events correspond to intense algal growth and metabolic activity, accurate identification of algal dynamics and physiological state is important. Current efforts to assess algal assemblages rely upon microscopic evaluation; however, the incorporation of such evaluation into monitoring programs is limited due to the level of skill and training required, the excessive costs and time required to assess algal heterogeneity within/among aquaculture systems, and the lack of information provided concerning physiological state. The distinct biwptical characteristics of the blooms lend themselves to pigment-based methodologies (pigment and in vivo absorption “signatures”, chlorophyll a fluorescence, multi-spectral remote sensing) which complement microscopic evaluation and can be implemented into large-scale monitoring programs. For example, because the key ingredient for success of such programs is the rapid, reliable, and accurate characterization of algal biomass along variable temporal/spatial scales, remotely-sensed data acquisition most likely will be required. High-performance liquid chromatography (HPLC)-derived pigment and in vivo absorption “signatures” can delineate problematic algal phylogenetic groups and physiological states. Further, measurements of chlorophyll a fluorescence provide estimates of phytoplankton absorption, quantum efficiency, and potentially production potential and growth rate. As such, they can be used to confirm the systematic significance of remotely-sensed data. It would be highly desirable to integrate an evaluation program using bio-optical methodologies into a geographic information system to allow for integrating, modeling, and predicting parameters of management interest over the scales relevant to aquacultural and water resource management.     

Variation in Channel Catfish Ictalurus punctatus Flavor Quality and its Quality Control Implications

Abstract Producers may capture two to three channel catfish Ictalurus punctatus L. for flavor analysis from ponds scheduled for harvest. If off-flavors are not present in several consecutive fish samples, the population may be considered acceptable for harvest. However, instrumental analysis of the muddy/earthy off-flavor metabolites 2-methylisoborneol (1-R-exo-1,2,7,7-tetramethyl-bicyclo-[2,2,1]-heptan-2-ol) (MIB) and geosmin (lα, 10β-dimethyl-9α-decalol) concentrations in approximately 80 catfish from each of three commercial ponds found both acceptable (on-flavor) and unacceptable (off-flavor) individuals within a single pond (i.e., mixed-flavor populations). Ascertaining the frequency of mixed-flavor populations by instrumentally determining the off-flavor metabolite concentration in muscle tissues from a large number of fish sampled from many ponds at several locations over time is not currently feasible. However, analysis of 12,725 commercial processor flavor assessments collected in 1994 and 1995 indicated 120 instances of individual ponds yielding off-flavor fish followed by on-flavor fish in one day or less. Reports indicate that fish require approximately four days to depurate off-flavors fully, suggesting that a proportion of these rapidly changing flavor assessments may reflect the stochastic selection of fish from mixed-flavor populations rather than a complete and rapid conversion of the flavor quality of entire populations. Factors that contribute to the occurrence of mixed-flavor-populations have not been identified fully. However, increased proportion of fat in catfish fillet tissues has been reported to be correlated with a greater retention of MIB by fish. In this investigation, fish fat contents ranged from 4.45% to 30.45%, and were positively correlated (P < 0.0001) with MIB concentrations. Additionally, the spatial distributions of algal populations within certain commercial catfish ponds were not uniform, and the sensory analysis of the flavor intensity of MIB and geosmin in catfish was more variable than the assessment of the intensity of chickeny and nutty flavors. Probability analysis indicated that in certain mixed-flavor populations there was a 10 to 25% probability of a shipment of fish being rejected due to the random collection of only on-flavor fish prior to harvest followed by the post harvest capture of at least one off-flavor fish. In addition, a chance of no off-flavor fish being sampled from a population containing a proportion of unacceptable fish was indicated. At current sample sizes, replacing sensory analysis with instrumental analysis would not completely avoid problems associated with sampling mixed-flavor-populations. Until effective means to reduce/avoid off-flavor metabolite accumulations in fish are widely available, careful attention to proper sensory evaluation protocols, an enhanced attention to pond conditions that affect flavor quality, the production of leaner more uniform populations of fish, and optimizations of sampling strategies offer the most practical near-term augmentations of current practice.     

Agrochemical and nutrient impacts on estuaries and other aquatic systems

This paper summarizes the "Agrochemical and Nutrient Impacts on Estuaries" symposium held at the 220th National Meeting of the American Chemical Society. The focus of the symposium was to highlight ongoing research efforts to understand estuarine function and pollutant fate in these important ecosystems. Expanding urbanization and agricultural activity can result in increased particulate and chemical loads, resulting in decreased light penetration and degraded aquatic habitats. Legislative and regulatory protections, such as the Clean Water Act and Total Maximum Daily Loads (TMDLs), are considered here. Measurement of nutrient and pesticide loads and their ecotoxicological impacts are explored, as well as potential mitigation practices. The complexity and high visibility of estuarine ecosystem health will require continued examination to develop more effective agricultural and land management strategies and sound science-based regulations.