Peter W. Perschbacher

Effects of calcium and magnesium hardness on acute copper toxicity to juvenile channel catfish, Ictalurus punctatus

Abstract Two experiments were conducted to evaluate the effects of calcium or magnesium hardness on the acute toxicity of copper sulfate to juvenile channel catfish ( Ictalurus punctatus ) in low alkalinity environments. A preliminary bioassay determined the 48-h LC 50 of copper sulfate to be 1.25 mg l −1 for juvenile catfish placed in water with calcium hardness and total alkalinity set at 20 mg l −1 CaCO 3 . In the first experiment, catfish were exposed to 1.25 mg l −1 copper sulfate in environments where calcium hardness was varied from 10–400 mg l −1 CaCO 3 . Total alkalinity was 20 mg l −1 CaCO 3 . As calcium hardness increased, copper-induced catfish mortalities decreased significantly from 90% at 10 mg l −1 CaCO 3 to 5% at 400 mg l −1 CaCO 3 . In the second experiment, catfish were exposed to 1.25 mg l −1 copper sulfate in environments containing either calcium or magnesium hardness, 20 and 400 mg l −1 CaCO 3 , with total alkalinity set at 20 mg l −1 CaCO 3 . Survival rates in calcium hardness treatments were consistent with those in the first experiment. However, 100% mortality was observed in both treatments containing magnesium-based hardness. These data suggest a calcium-specific mechanism with respect to acute copper toxicity in channel catfish.

Effects of bicarbonate alkalinity and calcium on the acute toxicity of copper to juvenile channel catfish (Ictalurus punctatus)

Abstract Three experiments were conducted to evaluate the relative importance of calcium hardness and bicarbonate alkalinity to the acute response of juvenile channel catfish ( Ictalurus punctatus ) exposed to a toxic concentration of copper sulfate. A preliminary bioassay revealed 28 mg·l −1 copper sulfate caused 50% mortality within 48 h (48-hLC 50 ) in juvenile channel catfish placed in water with calcium hardness and bicarbonate alkalinity, set at 75 mg·l −1 CaCO 3 . Catfish were then exposed to 28 mg·l −1 copper sulfate concentrations in environments where hardness or alkalinity concentrations were varied. Bicarbonate alkalinities above 75 mg·l −1 CaCO 3 , with calcium hardness held at 20 mg·l −1 CaCO 3 , significantly reduced catfish mortalities from 97–100% to 63–70%. Copper-induced mortalities were 100% for all fish placed in calcium hardness treatments (20–250 mg·l −1 CaCO 3 ) in which bicarbonate alkalinity was held at 20 mg·l −1 CaCO 3 . When bicarbonate alkalinity was held constant at 75 mg·l −1 CaCO 3 and calcium hardness was varied from 20 to 250 mg·l −1 CaCO 3 , copper related catfish mortalities displayed high variability and means ranged from 6.7 to 60%. Mortalities decreased as calcium concentrations increased. Although differences in mortalities were not statistically significant, the latter hardness findings appear to suggest a biologically significant calcium effect on copper toxicity in the presence of sufficient alkalinity concentrations.

Microwave mediated distillation with solid-phase microextraction: determination of off-flavors, geosmin and methylisoborneol, in catfish tissue

Abstract Presented is a rapid distillation device for use with solid-phase microextraction (SPME). We apply this device specifically for determining two semivolatile off-flavor compounds, methylisoborneol and geosmin, in channel catfish. The presence of these two compounds in channel catfish filets results in unwelcome tastes. In the presented procedure, a catfish tissue sample is placed within a sample container located inside the microwave device. Microwave radiation is applied and distillates formed migrate through a condenser via a purge gas and are collected in a sample vial. A SPME fiber is placed within the stirred collected distillate and methylisoborneol and geosmin are extracted. Qualitative and quantitative results of these extractions are obtained using a gas chromatograph-ion trap mass spectrometer. This solventless technique results in detection limits far below the human threshold for these off-flavor compounds in channel catfish.

Evaluation of effects of common aerially-applied soybean herbicides and propanil on the plankton communities of aquaculture ponds

Abstract Eight, common, aerially-applied herbicides for soybeans and the rice herbicide propanil were tested for possible adverse impacts on pond phytoplankton productivity, Zooplankton populations and critical water quality variables. Treatments simulated direct spraying of ponds and bracketed amounts of drift judged able to reach the pond at 1 10 and 1 100 direct rates. The study was conducted in 12, 500-1 outdoor pool mesocosms. Pond water was pumped from an adjacent fingerling rearing pond. Water quality measurements were made prior to application and at 24 and 48 h after application. Commercial compounds tested and full rates (kg active ha−1) were fomasefen, aciflourfen and glyphosate (0.43); bentazon (0.57); imazaquin (0.14); fluazifop (0.10); clethodim (0.07); chlorimuron (0.0045); and propanil (0.45 kg). Ten of 1152 soybean herbicide means significantly differed and without pattern. Thus, these herbicides were judged not to affect pond plankton or associated water quality. Propanil at the full rate reduced primary productivity and morning oxygen to critical levels for 3 days.

Determination of methylisoborneol in channel catfish pond water by solid phase extraction followed by gas chromatography-mass spectrometry

Abstract Several compounds exist which are responsible for unwanted taste and odor characteristics that have been found in the edible tissue of the channel catfish (Ictalurus punctatus). Methylisoborneol (MIB), one compound responsible for these off-flavors, is produced through the metabolism of cyanobacteria in aqueous systems such as reservoirs and ponds. The channel catfish accumulates MIB in its tissues from the intake of its culture-pond water. Current methods of analysis for MIB, such as closed- and open-loop stripping, and liquid-liquid extraction, are time-consuming and labor-intensive. A method for the analysis of MIB in catfish culture-pond water is described which, unlike other methods, is rapid, inexpensive, and does not require specialized sample preparation equipment. This method utilizes C18 solid-phase extraction followed by capillary gas chromatography with detection by mass spectrometry. Standard MIB and the internal standard, butylisoborneol (BIB), were prepared from the reaction of d -camphor with methylmagnesium chloride and n-butyllithium, respectively. Extraction efficiencies for MIB in channel catfish pond water averaged 89% at 101 parts per trillion (ppt) and 84% at 202 parts per billion (ppb). The detection limit of the method was calculated to be 11.5 ppt.

Effects of common aerially applied rice herbicides on the plankton communities of aquaculture ponds

Abstract Ten common aerially applied herbicides for rice were tested for possible adverse impacts on pond phytoplankton and zooplankton and critical water quality variables. Treatments simulated direct spraying of ponds and amounts of drift judged able to reach the pond at 1/10 and 1/100 direct rates. The study was conducted in 12, 500-l outdoor pool mesocosms. Pond water from an adjacent baitfish rearing pond was used. Water quality measurements were made prior to application and at 24 and 48 h after application. Commercial compounds tested and direct rates in kg active ingredient ha −1 were clomazone (0.6), thiobencarb (3.4), pendamethalin (1.1), propanil-dry, flowable (4.5), quinclorac (0.6), halosulfuron (0.07), bensulfuron methyl (0.07), triclopyr (0.4), 2,4- d -amine (1.7), and molinate (5.6). In addition, propanil was evaluated in a second application scenario at the same rates and to the same pond water sample as the initial application. Except for propanil, the rice herbicides produced no measurable effect on pond plankton or associated water quality. Following the first application at full rate for propanil, morning oxygen levels were reduced to critical levels (below 3 mg/l) for 2 days. After a second application of propanil at the full and 1/10 rates, oxygen levels were not decreased, although there were significant increases in chlorophyll a and zooplankton concentrations.

Aggressive Biting among Channel Catfish in Pool Studies

Abstract Observations of marks on channel catfish Ictalurus punctatus held for varying lengths of time in experimental ponds and on fish submitted for disease analysis suggested that aggressive biting among channel catfish may sometimes occur at relatively high rates in culture ponds. Studies in experimental pools indicated that larger fish sustained an average of 4 bites per fish while smaller fish sustained less than 1 bite per fish. Unfed catfish sustained an average of 12 bites per fish while fed fish sustained 7 bites per fish. No differences in the level of aggression were observed between genders. Mortality rates, apparently due to biting, ranged from 0% to 40% during the 2–4 week periods. Biting and subsequent infection of the wounds may contribute to the unexplained losses observed by producers.

Ammonia, pH, and Plankton in Sunshine Bass Nursery Ponds: The Effect of Inorganic Fertilizer or Sodium Bicarbonate

Abstract When sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) fingerling production ponds are filled and fertilized according to recommended practices, high pH and high un-ionized ammonia levels often develop at the time recommended for stocking of 5-d-old fry. These levels often exceed those found to be lethal to sunshine bass. We compared the effects of organic fertilizer only, both organic and inorganic fertilizer, and both organic and inorganic fertilizers with sodium bicarbonate on 0.04-ha culture ponds. Rice bran, the organic fertilizer, was applied at 278 kg/ha during the first week and 55.6 kg/ha during the second week. Liquid 9-27-0 NPK (urea and mono-ammonium phosphate), the inorganic fertilizer, was applied at 48 kg/ha during both weeks. Sodium bicarbonate was applied at 56, 112, or 224 kg/ha. Primary productivity, pH, and the concentrations of ammonia, chlorophyll a, phytoplankton, and zooplankton were compared among treatments. We include results from the 12...

Effect of Using Threadfin Shad as Forage for Channel Catfish Fed Daily or Every Third Day

Abstract We evaluated whether stocking threadfin shad Dorosoma petenense as a forage fish in multiple-batch production ponds for channel catfish Ictalurus punctatus could substitute for formulated feed when channel catfish were fed daily or every 3 d. A completely randomized design in a 2 × 2 factorial arrangement was used for the experiment, which was conducted in twelve 0.1-ha earthen ponds. Prespawn adult threadfin shad were stocked at 404 kg/ha in six of the ponds, whereas the remaining ponds received no threadfin shad. Channel catfish stockers (0.35 kg/fish) were stocked at 5,040 kg/ha, and fingerlings (28.2 g/fish) were stocked at 14,820 fish/ha. Channel catfish were fed a floating feed (32% protein) to apparent satiation daily (D; 6 ponds) or every 3 d (3D; 6 ponds). After 144 d, mean channel catfish total net yield was unaffected by the presence of threadfin shad but was significantly greater for fish in the D treatment (7,256 kg/ha) than for fish in the 3D treatment (2,431 kg/ha). Mean fish weigh...

Effects of Structure, Forage, and Stocking Density on Juvenile Production of Alligator Gars in Outdoor Pools

Abstract Populations of alligator gar Atractosteus spatula are greatly reduced, and interest has been shown in developing culture practices for fingerling production for restocking. Unfortunately, little research has been conducted on stocker-sized advanced fingerlings (>250 mm total length). Presence versus absence of physical structure and forage fish were tested against controls (no structure or forage) at two stocking densities (30,000/ha and 15,000/ha) in Arkansas. At 50 d posthatch (dph; July 8), ungraded 2.7-g alligator gars were stocked into 24 outdoor pools (diameter = 2.4 m, depth = 0.6 m). Fish in all pools were fed at 10% body weight/d (assuming 50% survival) with 1.5–2.5-mm steelhead floating pellets (45% protein). No grading was performed, and the study continued until fish grew to 300 mm. Fish were harvested on August 20 (92 dph). At termination, mean survival was significantly different for the high-density forage (72.2%) and the high-density structure treatments (27.8%), but differences i...