Charles C. Mischke

Short-Term Effect of Diuron on Catfish Pond Ecology

Abstract We examined the effects of diuron treatment on catfish pond ecology under commercial culture conditions. Nine weekly treatments of diuron (0.01 mg/L) were applied to eight 0.4-ha experimental ponds; seven ponds served as controls. Water and fish samples were collected from all ponds each week for chemical and biological analysis. Data on mechanical aeration (hours of supplemental aeration required by each pond) were supplied by the pond manager. A compound (2-methylisoborneol) that is known to cause off-flavor was significantly reduced in both water and fish fillets in diuron-treated ponds. Overall, diuron did not strongly affect water quality variables. No differences in supplemental aeration were detected between the pond groups. Diuron altered the phytoplankton composition within the ponds by reducing the biomass of filamentous blue-green algae. However, overall phytoplankton biomass was not different between treatment and control ponds; filamentous blue-green algae were replaced by diatoms. Z...

Zooplankton Size and Taxonomic Selectivity of Channel Catfish Fry

Abstract Zooplankton utilization and their importance to channel catfish Ictalurus punctatus fry during pond culture is not well documented. Current fry stocking decisions are based on total zooplankton densities. We studied the feeding habits (zooplankton size and taxa selection) of channel catfish fry. Catfish fry just completing swim-up were placed into glass aquaria or into cages in ponds and allowed to forage on natural zooplankton assemblages. The zooplankton sizes and taxa consumed by the fry were compared with the available sizes and taxa in the aquarium or pond environments. Rotifers and copepod nauplii were abundant in all environments but were never observed in the fry stomachs. Ostracods, adult copepods, and cladocerans were the only three taxa consumed. The data from both experiments indicated that ostracods were consumed in proportions equal to natural abundances, but in the field experiment larger ostracods were selected. Consumption of adult copepods and cladocerans depended on the relativ...

Pond age-water column trophic relationships in channel catfish Ictalurus punctatus production ponds

Abstract Long-term temporal succession changes in nutrients, phytoplankton and zooplankton have not been previously investigated in aquaculture ponds. This study analyzed relationships of pond age with nutrients, zooplankton and phytoplankton populations, and incidence of off-flavor occurrence. Nutrient levels (iron, silica, total phosphorus, and total nitrogen), phytoplankton community composition, off-flavor compounds, and zooplankton community composition were determined for 10–11 replicate commercial channel catfish Ictalurus punctatus production ponds of ages 1, 2, 3, 4, 9, 10 or 15 years postconstruction. Data were analyzed using canonical discriminant function analysis, multivariate analysis of variance (MANOVA), and multiple regression approaches. Nutrients (N and P) accumulated in ponds during the first 3 years postconstruction; however, concentrations of these nutrients leveled off after this time. The continual addition of nutrients (as feed) makes standard chlorophyll–P relationships reported from natural lakes unable to account for variation in aquaculture data. Algal composition became dominated by filamentous cyanobacteria after year 4; zooplankton composition also was dominated by larger copepods and cladocerans in older ponds. Younger ponds had lower incidence and intensity of off-flavor relative to older pond water. If ponds are drained/reworked every 3–4 years, incidence of off-flavor should decline.

Uniform Application of Copper Sulfate as a Potential Treatment for Controlling Snail Populations in Channel Catfish Production Ponds

Abstract A digenetic trematode identified as Bolbophorus sp. has been implicated as a cause of severe mortality and reduced production in commercially raised channel catfish Ictalurus punctatus in the southeastern United States. Currently, chemical control measures to limit the impact of this disease focus on pond shoreline treatments with hydrated lime or copper sulfate to kill the marsh rams-horn snail Planorbella trivolvis, an intermediate host that inhabits aquatic vegetation around the pond perimeter. Although effective, these treatments have little impact on snails that are not within close proximity to the pond bank. Tests were conducted to determine the feasibility of using elevated levels of copper sulfate pentahydrate (CSP; CuSO4·5H2O), uniformly applied to the surface of the pond water, to eradicate snails from the pond environment. Results demonstrated that uniform application to deliver between 2.5- and 5.0-ppm CSP (0.64–1.27-ppm Cu) was effective in killing snails around the margins of the ...

Pond Fertilization Does Not Affect Nutritional Value of Zooplankton in Channel Catfish Nursery Ponds

Abstract We determined the nutritional value of large zooplankton (500–1,000 μm) from fertilized and nonfertilized channel catfish Ictalurus punctatus nursery ponds. Proximate composition, amino acids, fatty acids, and assimilated algal pigments were statistically compared between pond groups. Analyses of vitamin and mineral composite samples of zooplankton from fertilized and nonfertilized ponds are presented. Treatment and control pond zooplankton were similar in nutritional value. Only two fatty acids (16:0 and 20:4[n-6]) were significantly different (P < 0.05) between fertilized and nonfertilized ponds, but total n-3 and n-6 highly unsaturated fatty acids were not different. The zooplankton in this study met or exceeded all nutritional requirements of channel catfish fry except that zooplankton in nonfertilized ponds appeared to contain less -than the required levels of pantothenic acid and vitamin B6. However, no statistical comparison of vitamins was made between fertilized and nonfertilized ponds. ...

Tolerance of Channel Catfish Fry to Abrupt pH Changes

Abstract Fry survival in the catfish industry is variable, and failure to survive cannot be completely attributable to diseases, fertilization practices, or lack of zooplankton abundance. The variability in fry survival may be related to current handling and stocking methods. When stocked, fry are transferred relatively quickly from hatchery water to pond water. Generally, temperature differences are monitored between hatchery water and pond water, but little attention is paid to pH differences. We conducted studies to determine the tolerance of channel catfish Ictalurus punctatus fry to pH changes. Catfish fry showed a high tolerance for decreasing pH values but a relatively low tolerance for increasing pH values. We estimate that an increase in pH of 0.7 units will cause 10% mortality in 8-d-posthatch catfish fry, and an increase of 1.4 pH units will cause 50% mortality. We recommend that farmers monitor pH before stocking fry and stock ponds that tend to increase in pH throughout the day early in the m...

Evaluation of Two Bio-Stimulants for Improving Water Quality in Channel Catfish, Ictalurus punctatus, Production Ponds

ABSTRACT Two commercial products (LASE and PhytoMax), which are formulations of organic acids, enzymes, vitamins, and micronutrients intended to stimulate microbial activity in fish production ponds, were evaluated. The effects on water quality of twice-monthly applications of PhytoMax and LASE in a replicated field test conducted in commercial channel catfish, Ictalurus punctatus, ponds in northwest Mississippi were studied. Temperature, pH, ammonia, nitrite, nitrate, reactive phosphorus, total phosphorus, chemical oxygen demand, chlorophyll a, and dissolved oxygen were monitored for 7 months and compared among LASE-treated, PhytoMax-treated, and control ponds. Only pH was statistically different (P <0.05) among ponds groups-7.6 in controls vs. 7.7 in LASE and PhytoMax ponds-however, this difference was not biologically significant. The results of this study failed to demonstrate a benefit of adding PhytoMax or LASE to commercial channel catfish ponds. Although adding specific micro-nutrients, vitamins, and enzymes to enhance natural microbial activity is a more ecologically sound strategy than adding bacterial suspensions, PhytoMax and LASE did not improve water quality in ponds at the recommended application rates.

Bacterial Bioaugmentation of Channel Catfish Ponds

Abstract Twelve, 0.1-ha earthen ponds at Stoneville, Mississippi were used in a 2-year, double-blind study of the effects of a Bacillus-based bacterial bioaugmentation product on water quality and production of channel catfish Ictalurus punctatus. Each year, six ponds were treated weekly with the microbial product from late May or early June through October, and six ponds were designated as untreated controls. Mean concentrations of chlorophyll a, nitrite-N, and total ammonia-N did not significantly differ (P > 0.05) between bacteria-treated and untreated ponds in the first year; however, in the second year, mean chlorophyll-a concentrations were higher (P ≤ 0.05) and nitrite-N and total ammonia-N concentrations were lower (P ≤ 0.05) in bacteria-treated ponds than in untreated ponds. Reductions in dissolved inorganic nitrogen concentrations were more likely due to increased phytoplankton growth (i.e., increased algal assimilation) than to a direct effect of bacterial inoculation. The mechanism by which bi...

Evaluation of Zooplankton in Hatchery Diets for Channel Catfish Fry

Abstract The efficacy of zooplankton as a supplemental hatchery diet for fry of channel catfish Ictalurus punctatus was evaluated. When a commercial diet is used as a reference, fry fed exclusively on zooplankton—either live or dried—performed poorly in their growth rate. However, when live or dried zooplankton were fed to fry in conjunction with the commercial diet, fry weight increased 40–50% over the weight of fry fed the commercial diet alone in a 19-d feeding trial. Data from this study indicate that zooplankton may serve as a sustainable and reliable supplement during hatchery production. These data also reaffirm the importance of zooplankton as a feed source in the growth of channel catfish fry. Zooplankton are important in catfish fry culture, and when zooplankton are present with commercial diets, improved growth results. Based on results of this study, supplemental feeding of zooplankton to hatchery fry and managing fry ponds for increased zooplankton densities should increase fry growth during ...

Preliminary Pond Evaluation of a Natural-Based Algicide for Managing Musty Off-Flavor in Channel Catfish Aquaculture

Abstract Environmentally derived “off-flavors” such as “earthy” and “musty” in cultured channel catfish Ictalurus punctatus are attributed to the presence of certain species of cyanobacteria (blue-green algae) in ponds. The musty off-flavor is caused by absorption of the metabolite 2-methylisoborneol (MIB) into channel catfish flesh. Most channel catfish producers manage off-flavor episodes by the application of algicides; however, these algicides have high environmental persistence and broad-spectrum toxicity. Recent research has discovered several natural and natural-based quinones that are effective and selective in reducing the abundance of the MIB-producing cyanobacterium Planktothrix perornata. In this study, efficacy testing of one of these quinones, anthraquinone-59, in a channel catfish pond found that it is effective in reducing the abundance of P. perornata and subsequently lowering the MIB levels in channel catfish.