Increased demand has pushed extensive aquaculture towards intensively operated production systems, commonly resulting in eutrophic conditions and cyanobacterial blooms. This review summarizes those ...cyanobacterial secondary metabolites that can cause undesirable tastes and odors (odorous metabolites) or are biochemically active (bioactive metabolites) in marine and freshwater, extensive and intensive aquaculture systems. For the scope of this paper, biochemically active metabolites include (1) toxins that can cause mortality in aquaculture organisms or have the potential to harm consumers via accumulation in the product (hepatotoxins, cytotoxins, neurotoxins, dermatoxins, and brine shrimp/molluskal toxins), (2) metabolites that may degrade the nutritional status of aquaculture species (inhibitors of proteases and grazer deterrents) or (3) metabolites that have the potential to negatively affect the general health of aquaculture species or aquaculture laborers (dermatoxins, irritant toxins, hepatotoxins, cytotoxins). Suggestions are made as to future management practices in intensive and extensive aquaculture and the potential exposure pathways to aquaculture species and human consumers are identified.
Accurate assessment of phytoplankton chlorophyll
a (chl
a) concentration by remote sensing is challenging in turbid hyper-eutrophic waters. This paper assessed methods to resolve this problem. A ...hand-held spectroradiometer was used to measure subsurface spectral reflectance (
R) in the visible and near infrared range of the spectrum. Water samples were collected concurrently and contained variable chlorophyll
a concentration (chl
a from 107 to more than 3000 mg/m
3) and turbidity (from 11 to 423 NTU) levels. The conceptual three-band model
R
−
1
(
λ
1)
−
R
−
1
(
λ
2)
×
R(
λ
3) and its special case, the two-band model
R(
λ
3)/
R(
λ
1), were spectrally tuned in accord with optical properties of the media to optimize spectral bands (
λ
1,
λ
2 and
λ
3) for accurate chlorophyll
a estimation. Strong linear relationships were established between analytically measured chl
a and both the three-band
R
−
1
(650)
−
R
−
1
(710)
×
R(740) and the reflectance ratio model
R(714)/
R(650). The three-band model accounted for 7% more variation of chl
a concentration than the ratio model (78 vs. 71%). Assessment of the model accuracy in dense algal blooms is hampered by the spatial and temporal inhomogeneity of algal distributions—in these waters, non-random algal distributions accounted for more than 20% spatial and up to 8% temporal variation in chlorophyll
a concentration. The findings underlined the rationale behind the conceptual model and demonstrated the robustness of the algorithm for chl
a retrieval in very turbid, hyper-eutrophic waters.
Geosmin (GSM) and 2-methylisoborneol (MIB) are algae metabolites with muddy/musty odors which contaminate water supplies and can be absorbed by aquatic organisms. Humans can perceive them in water ...and aquatic food products at ng/l (parts per trillion) concentrations. A rapid method employing solid phase micro extraction (SPME) has been developed for the analysis of GSM and MIB in water. Routine quantification at
μg/l concentrations can be accomplished using gas chromatography and flame ionization detection (FID) on a 6
ml aqueous sample with a total analysis time of less than 15min. Concentration levels of MIB and GSM at 10
ng/l (parts per trillion) can be detected under optimal conditions employing GC/MS in selected ion monitoring mode. Standard solutions and water samples from MIB producing algae cultures were used to compare SPME against purge and trap (P&T) using both flame ionization and mass spectrometric detection. Results obtained from SPME and P&T were similar in terms of reproducibility and sensitivity. This paper reports a simple, rapid method for monitoring the algal production of MIB and GSM at the
μg/l range which can be extended to the drinking water levels at the ng/l range of concentrations.
▶ TSS, conductivity, DOC contribute to bacterioplankton and phytoplankton dynamics. ▶ Conductivity is related to alkalinity, well known to regulate aquatic production. ▶ Dissolved organic carbon ...serves as a limiting nutrient for bacteria in oxbow lakes. ▶ FDA activity helps predict heterotrophic biochemical activity in oxbow lakes.
The Mississippi Delta Management Systems Evaluation Area (MSEA) project was designed to assess the effects of land management practices on water quality in three small oxbow lake watersheds; Thighman (1338
ha, 16
ha lake); Beasley (915
ha, 25
ha lake); and Deep Hollow (132
ha, 8
ha lake). Monthly water samples were monitored for enzymatic activity (fluorescein diacetate hydrolysis, alkaline phosphatase, and substrate utilization), chemical and physical analysis (suspended solids, dissolved organic carbon, pH, nitrate, ammonium, orthophosphate, and electrical conductivity), phytoplankton and bacterioplankton populations. All of these parameters were influenced by the intrinsic nature of the watersheds, with some parameters shifting as management changes were imposed on the surrounding agricultural fields. Thighman lake water typically maintained the highest suspended solid levels, dissolved organic carbon, algal and bacterial populations, enzyme activities, and heterotrophic metabolic indexes. Introduction of reduced tillage practices and glyphosate-resistant crops in Beasley watershed resulted in lower levels of suspended sediments, but had minimal impact on overall ranking of biochemical or microbiological properties. Likewise, conversion of Deep Hollow watershed from reduced tillage to conventional tillage had little effect on suspended sediment, and most microbial activity parameters remained intermediate. However, canonical analysis indicated dynamic changes in the microbial community, suggesting that biological parameters of lake water quality were affected by changes in crop and soil management practices.
Results from an instrumental method for determining the presence of the earthy, muddy or blue-green off-flavor in catfish were compared with those of four professional flavor checkers. Solid phase ...microextraction and gas chromatography/mass spectrometry were used to detect the off-flavor compounds, 2-methylisoborneol and geosmin. The odor threshold for an average flavor checker was determined to lie between 0.1 and 0.2 μg/kg for 2-methylisoborneol and estimated at 0.25 to 0.5 μg/kg for geosmin. The odor threshold for geosmin in channel catfish appears to be only slightly greater than that of MIB. The lower end of the sensory limits served as the instrumental cutoffs for grading fish off-flavor. Comparison of the instrumental method versus the flavor checkers resulted in a high correlation (
R=0.9).
We evaluated fertilizer effects on phytoplankton and zooplankton concentrations in channel catfish
Ictalurus punctatus nursery ponds. In 2001, three ponds were not fertilized and three ponds were ...fertilized with inorganic (8.4 kg/ha N, 2.0 kg/ha P followed by twice a week applications at half the initial rate) and organic fertilizer (224 kg/ha cottonseed meal followed by once a week applications of 28 kg/ha) for 4 weeks. Total P and soluble reactive P (SRP) were significantly higher in fertilized ponds (
P<0.05), however no differences in algal populations resulted. Of the zooplankton, only copepod nauplii were higher in fertilized ponds. In 2002, 26 ponds were used. Sixteen ponds were newly constructed; 10 ponds were old (>10 years). Within each age group, treatments of no fertilizer (controls), organic fertilizer only, inorganic fertilizer only, or both organic and inorganic fertilizers were used for 3 weeks. In 2002, the same P but higher N rates were used (20.2 kg/ha N followed by twice a week at half rate). Several differences occurred among treatments (
P<0.05). Both total P and total N were significantly higher in ponds fertilized with inorganic fertilizer and both inorganic and organic fertilizers than in control ponds and organically fertilized ponds. Also, total P, total N, SRP, and nitrite were all significantly higher in old ponds than in new ponds. All phytopigment concentrations were also higher in old ponds than in new ponds. Chlorophyll
a (total algal biomass), lutein (green algal biomass), and fucoxanthin (diatom biomass) were significantly higher in ponds fertilized with inorganic fertilizer or both inorganic and organic fertilizers than in control or organically fertilized ponds. Old ponds contained significantly more rotifers, copepod adults, and ostracods than new ponds. Rotifer and ostracod concentrations were not different among fertilizer treatments. Copepods adults and nauplii were significantly increased in ponds fertilized with both organic and inorganic fertilizers than in organically fertilized ponds. Cladocerans were significantly higher in inorganically fertilized ponds than in all others. Results indicated little benefit of organic fertilizer addition at the rates used. Also, ponds appear to be more N limited than P limited. Old ponds are more fertile than new ponds. Applying only inorganic fertilizer at an initial rate of ∼20 kg/ha N and 2 kg/ha P, followed by subsequent applications of half the initial rate for 3–4 weeks increased zooplankton concentrations desirable for fry with larger mouth gapes.
Technological advances have contributed to impressive yield gains and have greatly altered US agriculture. Selective breeding and directed molecular techniques address biological shortcomings of ...plants and animals and overcome environmental limitations. Improvements in mechanization, particularly of power sources and harvest equipment, reduce labor requirements and increase productivity and worker safety. Conservation systems, often designed to overcome problems introduced from other technologies, reduce negative impacts on soil and water and improve the environmental sustainability of production systems. Advances in information systems, largely developed in other disciplines and adapted to agriculture, are only beginning to impact US production practices. This paper is the fourth in the series of manuscripts exploring drivers of US agricultural systems. While development of technology is still largely driven by a need to address a problem, adoption is closely linked with other drivers of agricultural systems, most notably social, political and economic. Here, we explore the processes of innovation and adoption of technologies and how they have shaped agriculture. Technologies have increased yield and net output, and have also resulted in decreased control by producers, increased intensification, specialization and complexity of production, greater dependence on non-renewable resources, increased production inputs and hence decreased return, and an enhanced reliance on future technology. Future technologies will need to address emerging issues in land use, decline in work force and societal support of farming, global competition, changing social values in both taste and convenience of food, and increasing concerns for food safety and the environment. The challenge for farmers and researchers is to address these issues and develop technologies that balance the needs of producers with the expectations of society and create economically and environmentally sustainable production systems.
Unexplained deaths of pond‐grown catfish have occurred for many years. At least some of these mortalities could be from cyanobacteria toxins ingested during feeding on floating diets or passively ...assimilated through gills during breathing. Recently we were able to document algal production and subsequent ingestion of these toxicants by catfish during a mortality event. The causative organism, Microcystis aeruginosa, was the dominant species within the phytoplankton community during the cooler autumn‐winter season. Pond conditions included a drop in water temperature by c. 5 °C during the 10 days preceding the fish mortalities. Microcystin‐LR, a hepatotoxin produced by Microcystis, was detected in water samples and in catfish liver tissue. Fish exposed to pond water containing this toxic bloom were killed within 24 h. Necropsy of fish revealed congested liver and spleen tissues. The combination of clinical signs, detection of microcystin LR in water and in liver, and death of fish exposed to pond water supports the diagnosis of microcystin toxicosis. More research is needed to identify specific environmental conditions initiating toxin production to model and predict occurrence of these toxic algal blooms.
Microcystis aeruginosa is a common form of cyanobacteria (blue-green algae) capable of forming toxic heptapeptides (microcystins) that can cause illness or death. Occasionally, blooms of ...cyanobacteria have caused toxic fish-kills in catfish production ponds. We have developed a PCR test that will detect the presence of microcystin-producing cyanobacteria. Microcystin producers are detected by the presence of the microcystin peptide synthetase B gene (an obligate enzyme in the microcystin pathway), which appears to be present only in toxin-producing cyanobacteria. These PCR amplifications can be performed in multiplex using purified DNA from pond waters or by two-stage amplification from native water samples. A synoptic survey of 476 channel catfish production ponds from four states in the southeastern United States revealed that 31% of the ponds have the genetic potential to produce microcystins by toxic algae.
